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Sample records for alpine dwarf shrub

  1. Growth and Phenology of Three Dwarf Shrub Species in a Six-Year Soil Warming Experiment at the Alpine Treeline

    PubMed Central

    Anadon-Rosell, Alba; Rixen, Christian; Cherubini, Paolo; Wipf, Sonja; Hagedorn, Frank; Dawes, Melissa A.

    2014-01-01

    Global warming can have substantial impacts on the phenological and growth patterns of alpine and Arctic species, resulting in shifts in plant community composition and ecosystem dynamics. We evaluated the effects of a six-year experimental soil warming treatment (+4°C, 2007–2012) on the phenology and growth of three co-dominant dwarf shrub species growing in the understory of Larix decidua and Pinus uncinata at treeline in the Swiss Alps. We monitored vegetative and reproductive phenology of Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum throughout the early growing season of 2012 and, following a major harvest at peak season, we measured the biomass of above-ground ramet fractions. For all six years of soil warming we measured annual shoot growth of the three species and analyzed ramet age and xylem ring width of V. myrtillus. Our results show that phenology of the three species was more influenced by snowmelt timing, and also by plot tree species (Larix or Pinus) in the case of V. myrtillus, than by soil warming. However, the warming treatment led to increased V. myrtillus total above-ground ramet biomass (+36% in 2012), especially new shoot biomass (+63% in 2012), as well as increased new shoot increment length and xylem ring width (+22% and +41%, respectively; average for 2007–2012). These results indicate enhanced overall growth of V. myrtillus under soil warming that was sustained over six years and was not caused by an extended growing period in early summer. In contrast, E. hermaphroditum only showed a positive shoot growth response to warming in 2011 (+21%), and V. gaultherioides showed no significant growth response. Our results indicate that V. myrtillus might have a competitive advantage over the less responsive co-occurring dwarf shrub species under future global warming. PMID:24956273

  2. Growth and phenology of three dwarf shrub species in a six-year soil warming experiment at the alpine treeline.

    PubMed

    Anadon-Rosell, Alba; Rixen, Christian; Cherubini, Paolo; Wipf, Sonja; Hagedorn, Frank; Dawes, Melissa A

    2014-01-01

    Global warming can have substantial impacts on the phenological and growth patterns of alpine and Arctic species, resulting in shifts in plant community composition and ecosystem dynamics. We evaluated the effects of a six-year experimental soil warming treatment (+4°C, 2007-2012) on the phenology and growth of three co-dominant dwarf shrub species growing in the understory of Larix decidua and Pinus uncinata at treeline in the Swiss Alps. We monitored vegetative and reproductive phenology of Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum throughout the early growing season of 2012 and, following a major harvest at peak season, we measured the biomass of above-ground ramet fractions. For all six years of soil warming we measured annual shoot growth of the three species and analyzed ramet age and xylem ring width of V. myrtillus. Our results show that phenology of the three species was more influenced by snowmelt timing, and also by plot tree species (Larix or Pinus) in the case of V. myrtillus, than by soil warming. However, the warming treatment led to increased V. myrtillus total above-ground ramet biomass (+36% in 2012), especially new shoot biomass (+63% in 2012), as well as increased new shoot increment length and xylem ring width (+22% and +41%, respectively; average for 2007-2012). These results indicate enhanced overall growth of V. myrtillus under soil warming that was sustained over six years and was not caused by an extended growing period in early summer. In contrast, E. hermaphroditum only showed a positive shoot growth response to warming in 2011 (+21%), and V. gaultherioides showed no significant growth response. Our results indicate that V. myrtillus might have a competitive advantage over the less responsive co-occurring dwarf shrub species under future global warming. PMID:24956273

  3. A novel system for in situ determination of heat tolerance of plants: first results on alpine dwarf shrubs

    PubMed Central

    2013-01-01

    Background Heat stress and heat damage to plants gain globally increasing importance for crop production and plant survival in endangered habitats. Therefore the knowledge of heat tolerance of plants is of great interest. As many heat tolerance measurement procedures require detachment of plants and protocols expose samples to various heat temperatures in darkness, the ecological relevance of such results may be doubted. To overcome these constraints we designed a novel field compatible Heat Tolerance Testing System (HTTS) that opens the opportunity to induce controlled heat stress on plants in situ under full natural solar irradiation. Subsequently, heat tolerance can be evaluated by a variety of standard viability assays like the electrolyte leakage test, chlorophyll fluorescence measurements and visual assessment methods. Furthermore, recuperation can be studied under natural environmental conditions which is impossible when detached plant material is used. First results obtained on three alpine dwarf - shrubs are presented. Results When heat tolerance of Vaccinium gaultherioides Bigelow was tested with the HTTS in situ, the visual assessment of leaves showed 50% heat injury (LT50) at 48.3°C, while on detached leaves where heat exposure took place in small heat chambers this already happened at 45.8°C. Natural solar irradiation being applied during heat exposure in the HTTS had significantly protective effects: In Loiseleuria procumbens L. (Desv.), if heat exposure (in situ) took place in darkness, leaf heat tolerance was 50.6°C. In contrast, when heat exposure was conducted under full natural solar irradiation heat tolerance was increased to 53.1°C. In Rhododendron ferrugineum L. heat tolerance of leaves was 42.5°C if the exposure took place ex situ and in darkness, while it was significantly increased to 45.8°C when this happened in situ under natural solar irradiation. Conclusions The results obtained with the HTTS tested in the field indicate a

  4. Ice barriers promote supercooling and prevent frost injury in reproductive buds, flowers and fruits of alpine dwarf shrubs throughout the summer.

    PubMed

    Kuprian, Edith; Briceño, Verónica F; Wagner, Johanna; Neuner, Gilbert

    2014-10-01

    Over-wintering reproductive buds of many woody plants survive frost by supercooling. The bud tissues are isolated from acropetally advancing ice by the presence of ice barriers that restrict ice growth. Plants living in alpine environments also face the risk of ice formation in summer months. Little knowledge exists, how reproductive structures of woody alpine plants are protected from frost injury during episodic summer frosts. In order to address this question, frost resistance of three common dwarf shrubs, Calluna vulgaris, Empetrum hermaphroditum and Loiseleuria procumbens was measured and ice formation and propagation were monitored in twigs bearing reproductive shoots during various stages of reproductive development (bud, anthesis, and fruit) throughout the alpine summer. Results indicated that, in the investigated species, ice barriers were present at all reproductive stages, isolating the reproductive shoots from ice advancing from the subtending vegetative shoot. Additionally, in the reproductive stems ice nucleating agents that are active at warm, sub-zero temperatures, were absent. The ice barriers were 100% effective, with the exception of L. procumbens, where in 13% of the total observations, the ice barrier failed. The ice barriers were localized at the base of the pedicel, at the anatomical junction of the vegetative and reproductive shoot. There, structural aspects of the tissue impede or prevent ice from advancing from the frozen stem into the pedicel of the reproductive shoot. Under the experimental conditions used in this study, ice nucleation initially occurred in the stem of the vegetative shoot at species-specific mean temperatures in the range of -4.7 to -5.8 °C. Reproductive shoots, however, remained supercooled and ice free down to a range of -7.2 to -18.2 °C or even below -22 °C, the lowest temperature applied in the study. This level of supercooling is sufficient to prevent freezing of reproductive structures at the lowest air

  5. Ice barriers promote supercooling and prevent frost injury in reproductive buds, flowers and fruits of alpine dwarf shrubs throughout the summer☆

    PubMed Central

    Kuprian, Edith; Briceño, Verónica F.; Wagner, Johanna; Neuner, Gilbert

    2014-01-01

    Over-wintering reproductive buds of many woody plants survive frost by supercooling. The bud tissues are isolated from acropetally advancing ice by the presence of ice barriers that restrict ice growth. Plants living in alpine environments also face the risk of ice formation in summer months. Little knowledge exists, how reproductive structures of woody alpine plants are protected from frost injury during episodic summer frosts. In order to address this question, frost resistance of three common dwarf shrubs, Calluna vulgaris, Empetrum hermaphroditum and Loiseleuria procumbens was measured and ice formation and propagation were monitored in twigs bearing reproductive shoots during various stages of reproductive development (bud, anthesis, and fruit) throughout the alpine summer. Results indicated that, in the investigated species, ice barriers were present at all reproductive stages, isolating the reproductive shoots from ice advancing from the subtending vegetative shoot. Additionally, in the reproductive stems ice nucleating agents that are active at warm, sub-zero temperatures, were absent. The ice barriers were 100% effective, with the exception of L. procumbens, where in 13% of the total observations, the ice barrier failed. The ice barriers were localized at the base of the pedicel, at the anatomical junction of the vegetative and reproductive shoot. There, structural aspects of the tissue impede or prevent ice from advancing from the frozen stem into the pedicel of the reproductive shoot. Under the experimental conditions used in this study, ice nucleation initially occurred in the stem of the vegetative shoot at species-specific mean temperatures in the range of −4.7 to −5.8 °C. Reproductive shoots, however, remained supercooled and ice free down to a range of −7.2 to −18.2 °C or even below −22 °C, the lowest temperature applied in the study. This level of supercooling is sufficient to prevent freezing of reproductive structures at the

  6. The Response of the Alpine Dwarf Shrub Salix herbacea to Altered Snowmelt Timing: Lessons from a Multi-Site Transplant Experiment.

    PubMed

    Sedlacek, Janosch; Wheeler, Julia A; Cortés, Andrés J; Bossdorf, Oliver; Hoch, Guenter; Lexer, Christian; Wipf, Sonja; Karrenberg, Sophie; van Kleunen, Mark; Rixen, Christian

    2015-01-01

    Climate change is altering spring snowmelt patterns in alpine and arctic ecosystems, and these changes may alter plant phenology, growth and reproduction. To predict how alpine plants respond to shifts in snowmelt timing, we need to understand trait plasticity, its effects on growth and reproduction, and the degree to which plants experience a home-site advantage. We tested how the common, long-lived dwarf shrub Salix herbacea responded to changing spring snowmelt time by reciprocally transplanting turfs of S. herbacea between early-exposure ridge and late-exposure snowbed microhabitats. After the transplant, we monitored phenological, morphological and fitness traits, as well as leaf damage, during two growing seasons. Salix herbacea leafed out earlier, but had a longer development time and produced smaller leaves on ridges relative to snowbeds. Longer phenological development times and smaller leaves were associated with reduced sexual reproduction on ridges. On snowbeds, larger leaves and intermediate development times were associated with increased clonal reproduction. Clonal and sexual reproduction showed no response to altered snowmelt time. We found no home-site advantage in terms of sexual and clonal reproduction. Leaf damage probability depended on snowmelt and thus exposure period, but had no short-term effect on fitness traits. We conclude that the studied populations of S. herbacea can respond to shifts in snowmelt by plastic changes in phenology and leaf size, while maintaining levels of clonal and sexual reproduction. The lack of a home-site advantage suggests that S. herbacea may not be adapted to different microhabitats. The studied populations are thus unlikely to react to climate change by rapid adaptation, but their responses will also not be constrained by small-scale local adaptation. In the short term, snowbed plants may persist due to high stem densities. However, in the long term, reduction in leaf size and flowering, a longer phenological

  7. Small-scale patterns in snowmelt timing affect gene flow and the distribution of genetic diversity in the alpine dwarf shrub Salix herbacea.

    PubMed

    Cortés, A J; Waeber, S; Lexer, C; Sedlacek, J; Wheeler, J A; van Kleunen, M; Bossdorf, O; Hoch, G; Rixen, C; Wipf, S; Karrenberg, S

    2014-09-01

    Current threats to biodiversity, such as climate change, are thought to alter the within-species genetic diversity among microhabitats in highly heterogeneous alpine environments. Assessing the spatial organization and dynamics of genetic diversity within species can help to predict the responses of organisms to environmental change. In this study, we evaluated whether small-scale heterogeneity in snowmelt timing restricts gene flow between microhabitats in the common long-lived dwarf shrub Salix herbacea L. We surveyed 273 genets across 12 early- and late-snowmelt sites (that is, ridges and snowbeds) in the Swiss Alps for phenological variation over 2 years and for genetic variation using seven SSR markers. Phenological differentiation triggered by differences in snowmelt timing did not correlate with genetic differentiation between microhabitats. On the contrary, extensive gene flow appeared to occur between microhabitats and slightly less extensively among adjacent mountains. However, ridges exhibited significantly lower levels of genetic diversity than snowbeds, and patterns of effective population size (Ne) and migration (Nem) between microhabitats were strongly asymmetric, with ridges acting as sources and snowbeds as sinks. As no recent genetic bottlenecks were detected in the studied sites, this asymmetry is likely to reflect current meta-population dynamics of the species dominated by gene flow via seeds rather than ancient re-colonization after the last glacial period. Overall, our results suggest that seed dispersal prevents snowmelt-driven genetic isolation, and snowbeds act as sinks of genetic diversity. We discuss the consequences of such small-scale variation in gene flow and diversity levels for population responses to climate change. PMID:24619183

  8. Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau

    PubMed Central

    Liang, Eryuan; Eckstein, Dieter

    2009-01-01

    Background and Aims Shrubs and dwarf shrubs are wider spread on the Tibetan Plateau than trees and hence offer a unique opportunity to expand the present dendrochronological network into extreme environments beyond the survival limit of trees. Alpine shrublands on the Tibetan Plateau are characterized by rhododendron species. The dendrochronological potential of one alpine rhododendron species and its growth response to the extreme environment on the south-east Tibetan Plateau were investigated. Methods Twenty stem discs of the alpine snowy rhododendron (Rhododendron nivale) were collected close to the tongue of the Zuoqiupu Glacier in south-east Tibet, China. The skeleton plot technique was used for inter-comparison between samples to detect the growth pattern of each stem section. The ring-width chronology was developed by fitting a negative exponential function or a straight line of any slope. Bootstrapping correlations were calculated between the standard chronology and monthly climate data. Key Results The wood of snowy rhododendron is diffuse-porous with evenly distributed small-diameter vessels. It has well-defined growth rings. Most stem sections can be visually and statistically cross-dated. The resulting 75-year-long standard ring-width chronology is highly correlated with a timberline fir chronology about 200 km apart, providing a high degree of confidence in the cross-dating. The climate/growth association of alpine snowy rhododendron and of this timberline fir is similar, reflecting an impact of monthly mean minimum temperatures in November of the previous year and in July during the year of ring formation. Conclusions The alpine snowy rhododendron offers new research directions to investigate the environmental history of the Tibetan Plateau in those regions where up to now there was no chance of applying dendrochronology. PMID:19556264

  9. [Characteristics of stemflow for typical alpine shrubs in Qilian Mountain].

    PubMed

    Liu, Zhang-wen; Chen, Ren-sheng; Song, Yao-xuan

    2011-08-01

    Taking the typical alpine shrubs Potentilla fruticosa, Salix cupularis, Hippophae rhamnoides, and Caragana jubata in Qilian Mountain as test objects, a field investigation from June 1 to October 31, 2010 was conducted on the variation characteristics of the shrub stemflow, and analyzed the affecting effects of rainfall intensity and canopy structure morphology. The stemflow generated when the rainfall in early period was 2.1 mm, with an average of 3.4%, 3.2%, 8.0%, and 4.2% of the gross rainfall for P. fruticosa, S. cupularis, H. rhamnoides, and C. jubata, respectively. There was a significant positive linear correlation between the stemflow and rainfall intensity. With increasing rainfall, the stemflow percentage showed a trend of increase-decrease-increase. Stemflow played an important role in supplying water to the shrub rhizosphere, and the average funneling ratio was 59, 30, 110, and 49 for P. fruticosa, S. cupularis, H. rhamnoides, and C. jubata, respectively. The stemflow percentage had a significant exponential relationship with the maximum rain intensity in 10 minutes (I10). When the I10 was more than 6.0 mm x h(-1), the stemflow of H. rhamnoides and C. jubata showed a persistently increasing trend, while that of P. fruticosa and S. cupularis tended to be stable. Canopy structure morphology had complicated effects on the stemflow. In the same rainfall intensities, the height and crown projection area of the shrubs were the important factors affecting the generation of stemflow. PMID:22097356

  10. Small-scale drivers: the importance of nutrient availability and snowmelt timing on performance of the alpine shrub Salix herbacea.

    PubMed

    Little, Chelsea J; Wheeler, Julia A; Sedlacek, Janosch; Cortés, Andrés J; Rixen, Christian

    2016-04-01

    Alpine plant communities are predicted to face range shifts and possibly extinctions with climate change. Fine-scale environmental variation such as nutrient availability or snowmelt timing may contribute to the ability of plant species to persist locally; however, variation in nutrient availability in alpine landscapes is largely unmeasured. On three mountains around Davos, Switzerland, we deployed Plant Root Simulator probes around 58 Salix herbacea plants along an elevational and microhabitat gradient to measure nutrient availability during the first 5 weeks of the summer growing season, and used in situ temperature loggers and observational data to determine date of spring snowmelt. We also visited the plants weekly to assess performance, as measured by stem number, fruiting, and herbivory damage. We found a wide snowmelt gradient which determined growing season length, as well as variations of an order of magnitude or more in the accumulation of 12 nutrients between different microhabitats. Higher nutrient availability had negative effects on most shrub performance metrics, for instance decreasing stem number and the proportion of stems producing fruits. High nutrient availability was associated with increased herbivory damage in early-melting microhabitats, but among late-emerging plants this pattern was reversed. We demonstrate that nutrient availability is highly variable in alpine settings, and that it strongly influences performance in an alpine dwarf shrub, sometimes modifying the response of shrubs to snowmelt timing. As the climate warms and human-induced nitrogen deposition continues in the Alps, these factors may contribute to patterns of local plants persistence. PMID:26235963

  11. Phytosociological study of the dwarf shrub heath of Simeonof Wilderness, Shumagin Islands, Southwestern Alaska

    USGS Publications Warehouse

    Daniels, F.J.A.; Talbot, S. S.; Looman, Talbot S.; Schofield, W.B.

    2004-01-01

    The maritime dwarf shrub heath vegetation of the Northern Pacific, Simeonof Island, Shumagin Islands, Southwestern Alaska, was studied according to the Braun-Blanquet approach. Based on 30 releve??s of 16 m2 that include vascular plants, bryophytes, and lichens, two new associations could be described belonging to the class Loiseleurio-Vaccinietea (order Rhododendro-Vaccinietalia): Rubo-Empetretum nigri and Carici-Empetretum nigri. The wind-sheltered Rubo-Empetretum nigri (alliance Phyllodoco-Vaccinion) mainly occurs in the lowlands on level terrain or sloping sites at lower foot slopes of mountains on deeper, mesic soil; this association is the zonal vegetation of the lowlands. Boreal, widespread and amphi-Beringian species are prominent in the distribution-type spectrum of the vascular plants. Two variants of Rubo-Empetretum nigri are described. A Geranium erianthum variant occurs on south-facing slopes and is rich in vascular plants species. A Plagiothecium undulatum variant is restricted to northern exposures and is rich in bryophytes and lichens. A Carici-Empetretum nigri (alliance Loiseleurio-Diapension) occurs on shallow soil on wind exposed sites at higher elevations in the mountains. It is very rich in lichen species of arctic-alpine distribution. Canonical correspondence analysis (CCA) suggests that altitude, nutrient content of the soil and exposition are the most important differential ecological factors. Soil depth, total carbon and nitrogen content, plant available phosphorus and all other measured cation contents are higher in Rubo-Empetretum than in Carici-Empetretum. Literature comparisons confirm the occurrence of both associations in other areas on the Southwest Alaska Peninsula and Aleutian Islands. Presumably both associations have an amphi-Beringian distribution. The syntaxonomy of boreal-montane dwarf shrub heaths and synecological aspects are briefly discussed. ?? 2004 Gebru??der Borntraeger.

  12. Shrub line advance in Arctic and alpine tundra of the Yukon Territory

    NASA Astrophysics Data System (ADS)

    Myers-Smith, I. H.; Hik, D.

    2010-12-01

    a direct response of shrub growth to early summer temperatures suggests that shrub line expansion will continue, possibly at a faster rate, with projected warming in Arctic and alpine ecosystems in the Yukon Territory.

  13. Seasonal Dynamics of Water Use Strategy of Two Salix Shrubs in Alpine Sandy Land, Tibetan Plateau

    PubMed Central

    Zhu, Yajuan; Wang, Guojie; Li, Renqiang

    2016-01-01

    Water is a limiting factor for plant growth and vegetation dynamics in alpine sandy land of the Tibetan Plateau, especially with the increasing frequency of extreme precipitation events and drought caused by climate change. Therefore, a relatively stable water source from either deeper soil profiles or ground water is necessary for plant growth. Understanding the water use strategy of dominant species in the alpine sandy land ecosystem is important for vegetative rehabilitation and ecological restoration. The stable isotope methodology of δD, δ18O, and δ13C was used to determine main water source and long-term water use efficiency of Salix psammophila and S. cheilophila, two dominant shrubs on interdune of alpine sandy land in northeastern Tibetan Plateau. The root systems of two Salix shrubs were investigated to determine their distribution pattern. The results showed that S. psammophila and S. cheilophila absorbed soil water at different soil depths or ground water in different seasons, depending on water availability and water use strategy. Salix psammophila used ground water during the growing season and relied on shallow soil water recharged by rain in summer. Salix cheilophila used ground water in spring and summer, but relied on shallow soil water recharged by rain in spring and deep soil water recharged by ground water in fall. The two shrubs had dimorphic root systems, which is coincident with their water use strategy. Higher biomass of fine roots in S. psammophila and longer fine roots in S. cheilophila facilitated to absorb water in deeper soil layers. The long-term water use efficiency of two Salix shrubs increased during the dry season in spring. The long-term water use efficiency was higher in S. psammophila than in S. cheilophila, as the former species is better adapted to semiarid climate of alpine sandy land. PMID:27243772

  14. Seasonal Dynamics of Water Use Strategy of Two Salix Shrubs in Alpine Sandy Land, Tibetan Plateau.

    PubMed

    Zhu, Yajuan; Wang, Guojie; Li, Renqiang

    2016-01-01

    Water is a limiting factor for plant growth and vegetation dynamics in alpine sandy land of the Tibetan Plateau, especially with the increasing frequency of extreme precipitation events and drought caused by climate change. Therefore, a relatively stable water source from either deeper soil profiles or ground water is necessary for plant growth. Understanding the water use strategy of dominant species in the alpine sandy land ecosystem is important for vegetative rehabilitation and ecological restoration. The stable isotope methodology of δD, δ18O, and δ13C was used to determine main water source and long-term water use efficiency of Salix psammophila and S. cheilophila, two dominant shrubs on interdune of alpine sandy land in northeastern Tibetan Plateau. The root systems of two Salix shrubs were investigated to determine their distribution pattern. The results showed that S. psammophila and S. cheilophila absorbed soil water at different soil depths or ground water in different seasons, depending on water availability and water use strategy. Salix psammophila used ground water during the growing season and relied on shallow soil water recharged by rain in summer. Salix cheilophila used ground water in spring and summer, but relied on shallow soil water recharged by rain in spring and deep soil water recharged by ground water in fall. The two shrubs had dimorphic root systems, which is coincident with their water use strategy. Higher biomass of fine roots in S. psammophila and longer fine roots in S. cheilophila facilitated to absorb water in deeper soil layers. The long-term water use efficiency of two Salix shrubs increased during the dry season in spring. The long-term water use efficiency was higher in S. psammophila than in S. cheilophila, as the former species is better adapted to semiarid climate of alpine sandy land. PMID:27243772

  15. Phenology is plastic: the response of alpine shrub Salix herbacea to earlier snowmelt

    NASA Astrophysics Data System (ADS)

    Wheeler, Julia; Sedlacek, Janosch; van Kleunen, Mark; Bossdorf, Oliver; Hoch, Guenter; Wipf, Sonja; Karrenberg, Sophie; Lexer, Christian; Cortés, Andres; Rixen, Christian

    2014-05-01

    Climate change has been demonstrated to accelerate snowmelt in alpine systems, which can represent a critical ecosystem change for alpine plant communities. Understanding how snowmelt timing affects phenology and the development of alpine plants, and the capacity of these plants to respond, is thus necessary for predicting alpine community response to climate change. We examined the effects of snowmelt timing on the phenological development of the common clonal alpine shrub Salix herbacea over three growing seasons using both a space-for-time substitution along a natural snowmelt gradient and a reciprocal transplant experiment of clonal fragments between early and late snowmelt microhabitats. Leaf, flower and fruit development time was significantly influenced by snowmelt timing along both the natural snow gradient and in the reciprocal transplant, with less time required to develop to each phenophase in shrubs growing naturally in late-lying snowbeds and in S. herbacea clonal fragments transplanted from early-exposure sites into late snowbed microhabitats. This suggests that snowmelt timing, likely through the regulation of seasonal temperature accumulation, controls phenological development. In addition, the transplant experiment indicated that S. herbacea demonstrates a highly plastic phenological response to snowmelt timing, because there was no significant difference in phenology between clones originating either from snowbeds or early exposure sites when exposed to the same climatic conditions. Thus, S. herbacea may be able to profit from accelerated snowmelt due to climate change by developing soon after snowmelt. However, freezing damage during vulnerable early development stages may increase, as phenological development is slowed and the probability of lethal freezing events is increased under early snowmelt conditions.

  16. Gap locations influence the release of carbon, nitrogen and phosphorus in two shrub foliar litter in an alpine fir forest

    PubMed Central

    He, Wei; Wu, Fuzhong; Yang, Wanqin; Zhang, Danju; Xu, Zhenfeng; Tan, Bo; Zhao, Yeyi; Justine, Meta Francis

    2016-01-01

    Gap formation favors the growth of understory plants and affects the decomposition process of plant debris inside and outside of gaps. Little information is available regarding how bioelement release from shrub litter is affected by gap formation during critical periods. The release of carbon (C), nitrogen (N), and phosphorus (P) in the foliar litter of Fargesia nitida and Salix paraplesia in response to gap locations was determined in an alpine forest of the eastern Qinghai-Tibet Plateau via a 2-year litter decomposition experiment. The daily release rates of C, N, and P increased from the closed canopy to the gap centers during the two winters, the two later growing seasons and the entire 2 years, whereas this trend was reversed during the two early growing seasons. The pairwise ratios among C, N, and P converged as the litter decomposition proceeded. Compared with the closed canopy, the gap centers displayed higher C:P and N:P ratio but a lower C:N ratio as the decomposition proceeded. Alpine forest gaps accelerate the release of C, N, and P in decomposing shrub litter, implying that reduced snow cover resulting from vanishing gaps may inhibit the release of these elements in alpine forests. PMID:26906762

  17. Gap locations influence the release of carbon, nitrogen and phosphorus in two shrub foliar litter in an alpine fir forest.

    PubMed

    He, Wei; Wu, Fuzhong; Yang, Wanqin; Zhang, Danju; Xu, Zhenfeng; Tan, Bo; Zhao, Yeyi; Justine, Meta Francis

    2016-01-01

    Gap formation favors the growth of understory plants and affects the decomposition process of plant debris inside and outside of gaps. Little information is available regarding how bioelement release from shrub litter is affected by gap formation during critical periods. The release of carbon (C), nitrogen (N), and phosphorus (P) in the foliar litter of Fargesia nitida and Salix paraplesia in response to gap locations was determined in an alpine forest of the eastern Qinghai-Tibet Plateau via a 2-year litter decomposition experiment. The daily release rates of C, N, and P increased from the closed canopy to the gap centers during the two winters, the two later growing seasons and the entire 2 years, whereas this trend was reversed during the two early growing seasons. The pairwise ratios among C, N, and P converged as the litter decomposition proceeded. Compared with the closed canopy, the gap centers displayed higher C:P and N:P ratio but a lower C:N ratio as the decomposition proceeded. Alpine forest gaps accelerate the release of C, N, and P in decomposing shrub litter, implying that reduced snow cover resulting from vanishing gaps may inhibit the release of these elements in alpine forests. PMID:26906762

  18. Invasion of dwarf bamboo into alpine snow-meadows in northern Japan: pattern of expansion and impact on species diversity.

    PubMed

    Kudo, Gaku; Amagai, Yukihiro; Hoshino, Buho; Kaneko, Masami

    2011-09-01

    Recently, a dwarf bamboo species,Sasa kurilensis; Poaceae, has invaded into alpine snow-meadows in the wilderness area of the Taisetsu Mountains, northern Japan. This dwarf bamboo species has a wide distribution range from lowland to alpine sites of snowy regions. Because of the formation of dense evergreen culms and an extensive rhizome system, other plants are excluded following invasion by this dwarf bamboo, resulting in low species diversity. Dwarf bamboo originally inhabited the leeward slopes of alpine dwarf pine (Pinus pumila) clumps in alpine regions. During the last 32 years, however, dwarf bamboo has expanded its distribution area by up to 47% toward snow-meadows, especially on southeastern facing slopes. This rapid change may be related to the decrease in soil moisture and expansion of the annual growing period caused by the recent acceleration of snowmelt time. A multiyear census revealed that the density of bamboo culms increased 30-150% during 2 years, and the annual expansion of bamboo rhizomes was 39 cm on average. In addition to the expansion of bamboo clumps by vegetative growth, the possibility of migration by seed dispersal was also suggested by a genet analysis. With the increase in culm density, the species richness of snow-meadow vegetation decreased to less than one-quarter of the original level due to intense shading by dwarf bamboo. The rapid vegetation change in these almost pristine alpine environments isolated from the human activity implies that global climate change already influences the alpine ecosystem. PMID:22393485

  19. Invasion of dwarf bamboo into alpine snow-meadows in northern Japan: pattern of expansion and impact on species diversity

    PubMed Central

    Kudo, Gaku; Amagai, Yukihiro; Hoshino, Buho; Kaneko, Masami

    2011-01-01

    Recently, a dwarf bamboo species,Sasa kurilensis; Poaceae, has invaded into alpine snow-meadows in the wilderness area of the Taisetsu Mountains, northern Japan. This dwarf bamboo species has a wide distribution range from lowland to alpine sites of snowy regions. Because of the formation of dense evergreen culms and an extensive rhizome system, other plants are excluded following invasion by this dwarf bamboo, resulting in low species diversity. Dwarf bamboo originally inhabited the leeward slopes of alpine dwarf pine (Pinus pumila) clumps in alpine regions. During the last 32 years, however, dwarf bamboo has expanded its distribution area by up to 47% toward snow-meadows, especially on southeastern facing slopes. This rapid change may be related to the decrease in soil moisture and expansion of the annual growing period caused by the recent acceleration of snowmelt time. A multiyear census revealed that the density of bamboo culms increased 30–150% during 2 years, and the annual expansion of bamboo rhizomes was 39 cm on average. In addition to the expansion of bamboo clumps by vegetative growth, the possibility of migration by seed dispersal was also suggested by a genet analysis. With the increase in culm density, the species richness of snow-meadow vegetation decreased to less than one-quarter of the original level due to intense shading by dwarf bamboo. The rapid vegetation change in these almost pristine alpine environments isolated from the human activity implies that global climate change already influences the alpine ecosystem. PMID:22393485

  20. Matorral and reclamation. The contribution of scrubs and dwarf shrubs to soil and water conservation in Spain

    NASA Astrophysics Data System (ADS)

    Cerdà, A.; González Hidalgo, J. C.

    2009-04-01

    The Mediterranean Matorral (scrubs and dwarf shrubs) was seen by John Thornes as a protective vegetative cover of semiarid lands. His studies on matorral triggered the research, vocations and scientific work of researchers and contributed with a relevant knowledge to the environmental studies in Spain. This research reviews the changes in land use and the use of matorral in Spain. A review of the research done on the effect of matorral on soil and water losses is presented. Books, scientific papers, book chapters and research reports are being reviewed to report how matorral control the soil and water losses under different climatic conditions in Spain. The main conclusion is that scrubs and dwarf shrubs are very efficient in controlling the soil and water losses under semiarid climatic conditions were trees are rare. Nevertheless, scrub has been neglected by the Spanish forestry policy-makers and sometimes the shrubs cover is removed to develop afforestations, mainly with Aleppo pine. Palabras clave: Matorral, Soil, Water, Losses, Spain, Land use, Land management.

  1. Spatial and temporal functional changes in alpine summit vegetation are driven by increases in shrubs and graminoids

    PubMed Central

    Venn, Susanna; Pickering, Catherine; Green, Ken

    2014-01-01

    Classical approaches to investigating temporal and spatial changes in community composition offer only partial insight into the ecology that drives species distribution, community patterns and processes, whereas a functional approach can help to determine many of the underlying mechanisms that drive such patterns. Here, we aim to bring these two approaches together to understand such drivers, using an elevation gradient of sites, a repeat species survey and species functional traits. We used data from a repeat vegetation survey on five alpine summits and measured plant height, leaf area, leaf dry matter content and specific leaf area (SLA) for every species recorded in the surveys. We combined species abundances with trait values to produce a community trait-weighted mean (CTWM) for each trait, and then combined survey results with the CTWMs. Across the gradient of summits, more favourable conditions for plant growth (warmer, longer growing season) occurred at the lower elevations. Vegetation composition changes between 2004 and 2011 (according to non-metric multi-dimensional scaling ordination) were strongly affected by the high and increasing abundance of species with high SLA at high elevations. Species life-form categories strongly affected compositional changes and functional composition, with increasing dominance of tall shrubs and graminoids at the lower-elevation summits, and an overall increase in graminoids across the gradient. The CTWM for plant height and leaf dry matter content significantly decreased with elevation, whereas for leaf area and SLA it significantly increased. The significant relationships between CTWM and elevation may suggest specific ecological processes, namely plant competition and local productivity, influencing vegetation preferentially across the elevation gradient, with the dominance of shrubs and graminoids driving the patterns in the CTWMs. PMID:24790129

  2. Relationship between Shoot-rooting and Root-sprouting Abilities and the Carbohydrate and Nitrogen Reserves of Mediterranean Dwarf Shrubs

    PubMed Central

    Palacio, Sara; Maestro, Melchor; Montserrat-Martí, Gabriel

    2007-01-01

    Background and Aims This study analysed the differences in nitrogen (N), non-structural carbohydrates (NSC) and biomass allocation to the roots and shoots of 18 species of Mediterranean dwarf shrubs with different shoot-rooting and resprouting abilities. Root N and NSC concentrations of strict root-sprouters and species resprouting from the base of the stems were also compared. Methods Soluble sugars (SS), starch and N concentrations were assessed in roots and shoots. The root : shoot ratio of each species was obtained by thorough root excavations. Cross-species analyses were complemented by phylogenetically independent contrasts (PICs). Key Results Shoot-rooting species showed a preferential allocation of starch to shoots rather than roots as compared with non-shoot-rooting species. Resprouters displayed greater starch concentrations than non-sprouters in both shoots and roots. Trends were maintained after PICs analyses, but differences became weak when root-sprouters versus non-root-sprouters were compared. Within resprouters, strict root-sprouters showed greater root concentrations and a preferential allocation of starch to the roots than stem-sprouters. No differences were found in the root : shoot ratio of species with different rooting and resprouting abilities. Conclusions The shoot-rooting ability of Mediterranean dwarf shrubs seems to depend on the preferential allocation of starch and SS to shoots, though alternative C-sources such as current photosynthates may also be involved. In contrast to plants from other mediterranean areas of the world, the resprouting ability of Mediterranean dwarf shrubs is not related to a preferential allocation of N, NSC and biomass to roots. PMID:17728338

  3. Evolutionary potential in the Alpine: trait heritabilities and performance variation of the dwarf willow Salix herbacea from different elevations and microhabitats.

    PubMed

    Sedlacek, Janosch; Cortés, Andrés J; Wheeler, Julia; Bossdorf, Oliver; Hoch, Guenter; Klápště, Jaroslav; Lexer, Christian; Rixen, Christian; Wipf, Sonja; Karrenberg, Sophie; van Kleunen, Mark

    2016-06-01

    Alpine ecosystems are seriously threatened by climate change. One of the key mechanisms by which plants can adapt to changing environmental conditions is through evolutionary change. However, we still know little about the evolutionary potential in wild populations of long-lived alpine plants. Here, we investigated heritabilities of phenological traits, leaf size, and performance traits in natural populations of the long-lived alpine dwarf shrub Salix herbacea using relatedness estimates inferred from SSR (Simple Sequence Repeat) markers. Salix herbacea occurs in early- and late-snowmelt microhabitats (ridges and snowbeds), and we assessed how performance consequences of phenological traits and leaf size differ between these microhabitats in order to infer potential for evolutionary responses. Salix herbacea showed low, but significant, heritabilities of leaf size, clonal and sexual reproduction, and moderate heritabilities of phenological traits. In both microhabitats, we found that larger leaves, longer intervals between snowmelt and leaf expansion, and longer GDD (growing-degree days) until leaf expansion resulted in a stronger increase in the number of stems (clonal reproduction). In snowbeds, clonal reproduction increased with a shorter GDD until flowering, while the opposite was found on ridges. Furthermore, the proportion of flowering stems increased with GDD until flowering in both microhabitats. Our results suggest that the presence of significant heritable variation in morphology and phenology might help S. herbacea to adapt to changing environmental conditions. However, it remains to be seen if the rate of such an evolutionary response can keep pace with the rapid rate of climate change. PMID:27516856

  4. Effect of Shrub Cover on Spruce Seedling Establishment at and Above Alpine Treeline in the Alaska Range

    NASA Astrophysics Data System (ADS)

    Fastie, G.; Lloyd, A. H.

    2014-12-01

    Shrub coverage in the arctic has significantly increased in the past 50 years. Spruce seedling establishment in areas above the upper forest boundary has likewise increased as treeline has advanced. Little is known about the effect of shrubs on spruce seedlings near arctic tree lines, and how shrubs may affect the advance of tree line. In order to determine the effect of these shrubs on seedling establishment, we took measurements of shrub coverage in study plots in the Alaska Range established in the late 1990s at and above the current treeline. At each of ten plots located at and above treeline, ten points were systematically selected, using a grid pattern, and ten were selected at haphazardly chosen seedlings. At each point, a measurement of shrub coverage was taken, indicating the species present at the ground level, under 25 centimeters, between 25cm and a meter, between one and two meters, and between two and four meters, and above four meters above ground level. The data at systematic points indicates almost ubiquitous cover of shrubs in the under 25 cm height class, 43 percent coverage between 25cm and a meter, 14.5 percent coverage between one and two meters, 2 percent coverage between two and four meters, and three percent coverage above four meters. The frequency of each shrub height category at points with seedlings differed significantly from the frequency at the systematic points (χ2 = 26.3, p =.0000337). Points with seedlings had less shrub coverage overall than the systematic points, particularly in the tallest height categories. The frequency of tall shrubs in sites with seedlings was almost half that in the systematic points. Very similar patterns existed in both the tree line and above tree line transects. These results suggest that seedlings preferentially establish in sites without tall shrubs. Shrubs may therefore limit establishment of spruce at tree line, and continued shrub expansion may inhibit or slow tree line expansion.

  5. Pastoral Practices to Reverse Shrub Encroachment of Sub-Alpine Grasslands: Dung Beetles (Coleoptera, Scarabaeoidea) Respond More Quickly Than Vegetation

    PubMed Central

    Tocco, Claudia; Probo, Massimiliano; Lonati, Michele; Lombardi, Giampiero; Negro, Matteo; Nervo, Beatrice; Rolando, Antonio; Palestrini, Claudia

    2013-01-01

    In recent decades, pastoral abandonment has produced profound ecological changes in the Alps. In particular, the reduction in grazing has led to extensive shrub encroachment of semi-natural grasslands, which may represent a threat to open habitat biodiversity. To reverse shrub encroachment, we assessed short-term effects of two different pastoral practices on vegetation and dung beetles (Coleoptera, Scarabaeoidea). Strategic placement of mineral mix supplements (MMS) and arrangement of temporary night camp areas (TNCA) for cattle were carried out during summer 2011 in the Val Troncea Natural Park, north-western Italian Alps. In 2012, one year after treatment, a reduction in shrub cover and an increase in bare ground cover around MMS sites was detected. A more intense effect was detected within TNCA through increases in forage pastoral value, and in the cover and height of the herbaceous layer. Immediately after treatment, changes in dung beetle diversity (total abundance, species richness, Shannon diversity, taxonomic and functional diversity) showed a limited disturbance effect caused by high cattle density. In contrast, dung beetle diversity significantly increased one year later both at MMS and TNCA sites, with a stronger effect within TNCA. Multivariate Regression Trees and associated Indicator Value analyses showed that some ecologically relevant dung beetle species preferred areas deprived of shrub vegetation. Our main conclusions are: i) TNCA are more effective than MMS in terms of changes to vegetation and dung beetles, ii) dung beetles respond more quickly than vegetation to pastoral practices, and iii) the main driver of the rapid response by dung beetles is the removal of shrubs. The resulting increase in dung beetle abundance and diversity, which are largely responsible for grassland ecosystem functioning, may have a positive effect on meso-eutrophic grassland restoration. Shrub encroachment in the Alps may therefore be reversed, and restoration of

  6. Monsoon Season Moisture Deficit Limits Growth in Co-Occurring Alpine Shrub (Cassiope fastigata) and Tree (Abies spectabilis) Species in the Central Himalayas, Nepal

    NASA Astrophysics Data System (ADS)

    Rayback, S. A.; Shrestha, K. B.; Hofgaard, A.

    2015-12-01

    landscape transitions from forest to alpine shrubs and have important implications for future land surface-atmosphere interactions in the region.

  7. Vegetation shift from deciduous to evergreen dwarf shrubs in response to selective herbivory offsets carbon losses: evidence from 19 years of warming and simulated herbivory in the subarctic tundra.

    PubMed

    Ylänne, Henni; Stark, Sari; Tolvanen, Anne

    2015-10-01

    Selective herbivory of palatable plant species provides a competitive advantage for unpalatable plant species, which often have slow growth rates and produce slowly decomposable litter. We hypothesized that through a shift in the vegetation community from palatable, deciduous dwarf shrubs to unpalatable, evergreen dwarf shrubs, selective herbivory may counteract the increased shrub abundance that is otherwise found in tundra ecosystems, in turn interacting with the responses of ecosystem carbon (C) stocks and CO2 balance to climatic warming. We tested this hypothesis in a 19-year field experiment with factorial treatments of warming and simulated herbivory on the dominant deciduous dwarf shrub Vaccinium myrtillus. Warming was associated with a significantly increased vegetation abundance, with the strongest effect on deciduous dwarf shrubs, resulting in greater rates of both gross ecosystem production (GEP) and ecosystem respiration (ER) as well as increased C stocks. Simulated herbivory increased the abundance of evergreen dwarf shrubs, most importantly Empetrum nigrum ssp. hermaphroditum, which led to a recent shift in the dominant vegetation from deciduous to evergreen dwarf shrubs. Simulated herbivory caused no effect on GEP and ER or the total ecosystem C stocks, indicating that the vegetation shift counteracted the herbivore-induced C loss from the system. A larger proportion of the total ecosystem C stock was found aboveground, rather than belowground, in plots treated with simulated herbivory. We conclude that by providing a competitive advantage to unpalatable plant species with slow growth rates and long life spans, selective herbivory may promote aboveground C stocks in a warming tundra ecosystem and, through this mechanism, counteract C losses that result from plant biomass consumption. PMID:25950664

  8. Consequences and feedbacks on CO2 fluxes of climate change impacts on alpine vegetation

    NASA Astrophysics Data System (ADS)

    Cannone, N.; Guglielmin, M.

    2009-04-01

    The vegetation in a high alpine site of the European Alps experienced changes in area between 1953 and 2003 as a result of climate change (Cannone et al. 2007). Shrubs showed rapid expansion rates of 5.6% per decade at altitudes between 2400 m and 2500 m. Above 2500 m, vegetation coverage exhibited unexpected patterns of regression associated with increased precipitation and permafrost degradation. The warming of air temperature induced a cascade effect, with changes in the all ecological series (from the shrubland to the nival snowbed vegetation), with the arrival of the alpine shrubland and upward displacement of the alpine grassland (especially between 2230 and 2500 m). During the growing season 2008 (since the late-spring snowmelt to the start of the continuous snow cover in fall) we analyzed and measured the CO2 fluxes associated to the vegetation types exhibiting the highest changes since 1953 until today. In particular, we monitored two different ecological types of shrubland vegetations (the chionophilous alpine shrubs dominated by Rhododendron ferrugineum and the wind-swept community of dwarf shrubs dominated by Loiseleuria procumbens), the climax alpine grassland (dominated by Carex curvula), the pioneer discontinuous alpine vegetation, the snowbed vegetation (dominated by Salix herbacea) and the barren ground. CO2 fluxes (i.e. net ecosystem exchange, ecosystem photosynthesis and ecosystem respiration), biomass, soil C and N were measured for all these vegetation types. Implications of the changes occurred to the CO2 fluxes above 2200 m a.s.l. in response to the areal changes of spatial distribution of the investigated vegetation types and their potential feedbacks are discussed. Nicoletta Cannone, Sergio Sgorbati, and Mauro Guglielmin 2007. Unexpected impacts of climate change on alpine vegetation. Front Ecol Environ 2007; 5(7): 360-364

  9. Phenological indicators derived with CO2 flux, MODIS image and ground monitor at a temperate mixed forest and an alpine shrub

    NASA Astrophysics Data System (ADS)

    Zhang, Leiming; Cao, Peiyu; Li, Shenggong; Yu, Guirui; Zhang, Junhui; Li, Yingnian

    2016-04-01

    To accurately assess the change of phenology and its relationship with ecosystem gross primary productivity (GPP) is one of the key issues in context of global change study. In this study, an alpine shrubland meadow in Haibei (HBS) of Qinghai-Tibetan plateau and a broad-leaved Korean pine forest in Changbai Mountain (CBM) of Northeastern China were selected. Based on the long-term GPP from eddy flux measurements and the Normalized Difference Vegetation Index (NDVI) from remote sensed vegetation index, phenological indicators including the start of growing season (SOS), the end of growing season (EOS), and the growing season length (GSL) since 2003 were derived via multiple methods, and then the influences of phenology variation on GPP were explored. Compared with ground phenology observations of dominant plant species, both GPP- and NDVI-derived SOS and EOS exhibited a similar interannual trend. GPP-derived SOS was quite close to NDVI-derived SOS, but GPP-derived EOS differed significantly from NDVI-derived EOS, and thus leading to a significant difference between GPP- and NDVI-derived GSL. Relative to SOS, EOS presented larger differences between the extraction methods, indicating large uncertainties to accurately define EOS. In general, among the methods used, the threshold methods produced more satisfactory assessment on phenology change. This study highlights that how to harmonize with the flux measurements, remote sensing and ground monitoring are a big challenge that needs further consideration in phenology study, especially the accurate extraction of EOS. Key words: phenological variation, carbon flux, vegetation index, vegetation grwoth, interannual varibility

  10. Tree and shrub expansion over the past 34 years at the tree-line near Abisko, Sweden.

    PubMed

    Rundqvist, Sara; Hedenås, Henrik; Sandström, Anneli; Emanuelsson, Urban; Eriksson, Håkan; Jonasson, Christer; Callaghan, Terry V

    2011-09-01

    Shrubs and trees are expected to expand in the sub-Arctic due to global warming. Our study was conducted in Abisko, sub-arctic Sweden. We recorded the change in coverage of shrub and tree species over a 32- to 34-year period, in three 50 x 50 m plots; in the alpine-tree-line ecotone. The cover of shrubs and trees (<3.5 cm diameter at breast height) were estimated during 2009-2010 and compared with historical documentation from 1976 to 1977. Similarly, all tree stems (> or =3.5 cm) were noted and positions determined. There has been a substantial increase of cover of shrubs and trees, particularly dwarf birch (Betula nana), and mountain birch (Betula pubescens ssp. czerepanovii), and an establishment of aspen (Populus tremula). The other species willows (Salix spp.), juniper (Juniperus communis), and rowan (Sorbus aucuparia) revealed inconsistent changes among the plots. Although this study was unable to identify the causes for the change in shrubs and small trees, they are consistent with anticipated changes due to climate change and reduced herbivory. PMID:21954730

  11. Shrub tundra snowmelt

    NASA Astrophysics Data System (ADS)

    Pomeroy, J. W.; Bewley, D. S.; Essery, R. L. H.; Hedstrom, N. R.; Link, T.; Granger, R. J.; Sicart, J. E.; Ellis, C. R.; Janowicz, J. R.

    2006-03-01

    Observations of land surface and snowpack energetics and mass fluxes were made over arctic shrub tundra of varying canopy height and density using radiometers, eddy covariance flux measurements, and snow mass changes from snow surveys of depth and density. Over several years, snow accumulation in the shrubs was found to be consistently higher than in sparse tundra due to greater retention of snowfall by all shrubs and wind redistribution of snowfall to tall shrubs. Where snow accumulation was highest due to snow redistribution, shrubs often became buried by the end of winter. Three classes of shrub-snow interactions were observed: tall shrubs that were exposed over snow, tall shrubs that were bent over and buried by snow, and short shrubs buried by snow. Tall shrubs buried by snow underwent spring-up during melt. Though spring-up was episodic for a single shrub, over an area it was a progressive emergence from early to mid melt of vegetation that dramatically altered the radiative and aerodynamic properties of the surface. Short shrubs were exposed more rapidly once snow depth declined below shrub height, usually near the end of melt. Net radiation increased with increasing shrub due to the decreased reflectance of shortwave radiation overwhelming the increased longwave emission from relatively warm and dark shrubs. Net radiation to snow under shrubs was much smaller than that over shrubs, but was greater than that to snow with minimal shrub exposure, in this case the difference was due to downward longwave radiation from the canopy exceeding the effect of attenuated shortwave transmission through the canopy. Because of reduced turbulent transfer under shrub canopies and minimal water vapour contributions from the bare shrub branches, sublimation fluxes declined with increasing shrub exposure. In contrast, sensible heat fluxes to the shrub surface became more negative and those to the underlying snow surface more positive with increasing shrub exposure, because of

  12. Effects of experimentally modified soil temperatures and nutrient availability on growth and mycorrhization of Pinus cembra at the alpine treeline

    NASA Astrophysics Data System (ADS)

    Gruber, Andreas; Peintner, Ursula; Wieser, Gerhard; Oberhuber, Walter

    2015-04-01

    Soil temperature affects litter decomposition, nutrient uptake, root growth and respiration and it is suggested that soil temperature has direct impact on tree growth at the alpine treeline. We have evaluated the impact of experimentally modified soil temperatures and nutrient availability on growth and mycorrhization of Pinus cembra at the treeline in the Central Eastern Alps (c. 2150 m a.s.l., Tyrol, Austria). Soil temperature in the rooting zone of naturally grown c. 25 year old trees (n=6 trees per treatment) was altered by shading and heat-trapping using non-transparent and glasshouse foils mounted c. 20 cm above soil surface. Additional trees were selected for a nitrogen fertilisation treatment and as controls. During the study period, mean soil temperatures at 10 cm depth were reduced by c. 3°C at the cooled vs. warmed plots. Soil moisture was not influenced due to soil water transport along the slope. Results revealed that changed soil temperatures did not significantly affect tree growth, gas exchange, needle nutrient content and specific leaf area. We also found no significant difference in degree of mycorrhization or number of mycorrhized root tips between treatments. On the other hand, nitrogen fertilization and a reduction of interspecific root competition led to significantly raised radial stem growth. Results indicate that tree growth at the selected study area was not limited by soil temperature, while interspecific competition for nutrients among trees and low stature vegetation (dwarf shrubs, grasses) had significant impact. Therefore, we suggest that root competition with alpine grassland and dwarf-shrub communities will hamper temperature driven advance of alpine treeline in the course of climate warming. Acknowledgements This work was funded by the Austrian Science Fund (FWF Project No. P22836-B16, 'Growth response of Pinus cembra to experimentally modified soil temperatures at the treeline').

  13. High diversity of root associated fungi in both alpine and arctic Dryas octopetala

    PubMed Central

    2010-01-01

    Background Dryas octopetala is a widespread dwarf shrub in alpine and arctic regions that forms ectomycorrhizal (ECM) symbiotic relationships with fungi. In this study we investigated the fungal communities associated with roots of D. octopetala in alpine sites in Norway and in the High Arctic on Svalbard, where we aimed to reveal whether the fungal diversity and species composition varied across the Alpine and Arctic regions. The internal transcribed spacer (ITS) region of nuclear ribosomal DNA was used to identify the fungal communities from bulk root samples obtained from 24 plants. Results A total of 137 operational taxonomic units (OTUs) were detected (using 97% similarity cut off during sequence clustering) and well-known ECM genera such as Cenococcum, Cortinarius, Hebeloma, Inocybe and Tomentella occurred frequently. There was no decrease in fungal diversity with increasing latitude. The overall spatial heterogeneity was high, but a weak geographical structuring of the composition of OTUs in the root systems was observed. Calculated species accumulation curves did not level off. Conclusions This study indicates that the diversity of fungi associated with D. octopetala does not decrease in high latitude arctic regions, which contrasts observations made in a wide spectrum of other organism groups. A high degree of patchiness was observed across root systems, but the fungal communities were nevertheless weakly spatially structured. Non-asymptotical species accumulation curves and the occurrence of a high number of singletons indicated that only a small fraction of the fungal diversity was detected. PMID:21070665

  14. Climate sensitivity of shrub growth across the tundra biome

    NASA Astrophysics Data System (ADS)

    Myers-Smith, Isla H.; Elmendorf, Sarah C.; Beck, Pieter S. A.; Wilmking, Martin; Hallinger, Martin; Blok, Daan; Tape, Ken D.; Rayback, Shelly A.; Macias-Fauria, Marc; Forbes, Bruce C.; Speed, James D. M.; Boulanger-Lapointe, Noémie; Rixen, Christian; Lévesque, Esther; Schmidt, Niels Martin; Baittinger, Claudia; Trant, Andrew J.; Hermanutz, Luise; Collier, Laura Siegwart; Dawes, Melissa A.; Lantz, Trevor C.; Weijers, Stef; Jørgensen, Rasmus Halfdan; Buchwal, Agata; Buras, Allan; Naito, Adam T.; Ravolainen, Virve; Schaepman-Strub, Gabriela; Wheeler, Julia A.; Wipf, Sonja; Guay, Kevin C.; Hik, David S.; Vellend, Mark

    2015-09-01

    Rapid climate warming in the tundra biome has been linked to increasing shrub dominance. Shrub expansion can modify climate by altering surface albedo, energy and water balance, and permafrost, yet the drivers of shrub growth remain poorly understood. Dendroecological data consisting of multi-decadal time series of annual shrub growth provide an underused resource to explore climate-growth relationships. Here, we analyse circumpolar data from 37 Arctic and alpine sites in 9 countries, including 25 species, and ~42,000 annual growth records from 1,821 individuals. Our analyses demonstrate that the sensitivity of shrub growth to climate was: (1) heterogeneous, with European sites showing greater summer temperature sensitivity than North American sites, and (2) higher at sites with greater soil moisture and for taller shrubs (for example, alders and willows) growing at their northern or upper elevational range edges. Across latitude, climate sensitivity of growth was greatest at the boundary between the Low and High Arctic, where permafrost is thawing and most of the global permafrost soil carbon pool is stored. The observed variation in climate-shrub growth relationships should be incorporated into Earth system models to improve future projections of climate change impacts across the tundra biome.

  15. Palatability of Selected Alpine Plant Litters for the Decomposer Lumbricus rubellus (Lumbricidae)

    PubMed Central

    Rief, Alexander; Knapp, Brigitte A.; Seeber, Julia

    2012-01-01

    On alpine pastureland the decline in large-bodied earthworm numbers and biomass after abandonment of management might be the result of a shift from highly palatable grass litter to poorly digestible leaf litter of dwarf shrubs. To test this hypothesis, we analysed nitrogen, phosphorous and total phenolic contents of fresh and aged litter of eight commonly occuring alpine plant species and compared consumption rates of these food sources in a controlled feeding experiment with Lumbricus rubellus (Lumbricidae). Furthermore, we analysed the microbial community structure of aged litter materials to check for a relationship between the microbial characteristics of the different plant litter types and the food choice of earthworms. Plant litters differed significantly in their chemical composition, earthworms, however, showed no preference for any litter species, but generally rejected fresh litter material. Microbial community structures of the litter types were significantly different, but we could find no evidence for selective feeding of L. rubellus. We conclude that L. rubellus is a widespread, adaptable ubiquist, which is able to feed on a variety of food sources differing in quality and palatability, as long as they have been exposed to wheathering. PMID:23028949

  16. Frost resistance in alpine woody plants.

    PubMed

    Neuner, Gilbert

    2014-01-01

    This report provides a brief review of key findings related to frost resistance in alpine woody plant species, summarizes data on their frost resistance, highlights the importance of freeze avoidance mechanisms, and indicates areas of future research. Freezing temperatures are possible throughout the whole growing period in the alpine life zone. Frost severity, comprised of both intensity and duration, becomes greater with increasing elevation and, there is also a greater probability, that small statured woody plants, may be insulated by snow cover. Several frost survival mechanisms have evolved in woody alpine plants in response to these environmental conditions. Examples of tolerance to extracellular freezing and freeze dehydration, life cycles that allow species to escape frost, and freeze avoidance mechanisms can all be found. Despite their specific adaption to the alpine environment, frost damage can occur in spring, while all alpine woody plants have a low risk of frost damage in winter. Experimental evidence indicates that premature deacclimation in Pinus cembra in the spring, and a limited ability of many species of alpine woody shrubs to rapidly reacclimate when they lose snow cover, resulting in reduced levels of frost resistance in the spring, may be particularly critical under the projected changes in climate. In this review, frost resistance and specific frost survival mechanisms of different organs (leaves, stems, vegetative and reproductive over-wintering buds, flowers, and fruits) and tissues are compared. The seasonal dynamics of frost resistance of leaves of trees, as opposed to woody shrubs, is also discussed. The ability of some tissues and organs to avoid freezing by supercooling, as visualized by high resolution infrared thermography, are also provided. Collectively, the report provides a review of the complex and diverse ways that woody plants survive in the frost dominated environment of the alpine life zone. PMID:25520725

  17. Frost resistance in alpine woody plants

    PubMed Central

    Neuner, Gilbert

    2014-01-01

    This report provides a brief review of key findings related to frost resistance in alpine woody plant species, summarizes data on their frost resistance, highlights the importance of freeze avoidance mechanisms, and indicates areas of future research. Freezing temperatures are possible throughout the whole growing period in the alpine life zone. Frost severity, comprised of both intensity and duration, becomes greater with increasing elevation and, there is also a greater probability, that small statured woody plants, may be insulated by snow cover. Several frost survival mechanisms have evolved in woody alpine plants in response to these environmental conditions. Examples of tolerance to extracellular freezing and freeze dehydration, life cycles that allow species to escape frost, and freeze avoidance mechanisms can all be found. Despite their specific adaption to the alpine environment, frost damage can occur in spring, while all alpine woody plants have a low risk of frost damage in winter. Experimental evidence indicates that premature deacclimation in Pinus cembra in the spring, and a limited ability of many species of alpine woody shrubs to rapidly reacclimate when they lose snow cover, resulting in reduced levels of frost resistance in the spring, may be particularly critical under the projected changes in climate. In this review, frost resistance and specific frost survival mechanisms of different organs (leaves, stems, vegetative and reproductive over-wintering buds, flowers, and fruits) and tissues are compared. The seasonal dynamics of frost resistance of leaves of trees, as opposed to woody shrubs, is also discussed. The ability of some tissues and organs to avoid freezing by supercooling, as visualized by high resolution infrared thermography, are also provided. Collectively, the report provides a review of the complex and diverse ways that woody plants survive in the frost dominated environment of the alpine life zone. PMID:25520725

  18. Distinct temperature sensitivity among taiga and tundra shrubs in Alaska

    NASA Astrophysics Data System (ADS)

    Andreu-Hayles, L.; Anchukaitis, K. J.; D'Arrigo, R.

    2014-12-01

    Shrub expansion into Arctic and alpine tundra ecosystems is well documented, mostly over the last 50 years, based on remote sensing data, aerial photography, and in-situ observations. Warming temperatures are considered the main driver of the observed change in shrub vegetation patterns. Here, we assess the relationship between temperatures and shrub growth from five populations of Salix spp. (willow) and Alnus spp. (alder) in Alaska growing within the tundra and the boreal forest (~taiga) using dendrochronological techniques. The three tundra shrub sites are located on the Dalton Highway north from Toolik Lake (~69ºN 148ºW), whereas the two taiga shrub sites are located closer to Fairbanks at the Twelve Mile Summit site (~65ºN 146ºW). Because shrub ages vary among the studied populations lead to different time spans for the ring-width chronologies generated, a common period with available satellite data spanning from 1982 to 2010 was selected for this study. All tundra shrub chronologies shared a strong positive response to summer temperatures despite growing in heterogeneous site conditions and belonging to different species. In contrast, in the taiga, summer temperatures enhance willow growth, whereas alder growth appears almost insensitive to temperature over the interval studied. Extending the analyses back in time, a very strong positive relationship was found between alder ring-width and June temperatures prior to 1970. This phenomenon, a weakening of the previously existing relationship between growth and temperatures, was also detected in white spruce (Picea glauca) growing at the same site, and it is known in the literature as the 'divergence problem'. Thus, at this taiga location, alder shrubs and trees seem to have similar growth patterns. Summer temperatures no longer seem to enhance taiga alder growth. Shrubs of different species exposed to the same climatic conditions can exhibit varied growth responses. The distinct temperature sensitivities

  19. Impacts after four years of experimental trampling on alpine/sub-alpine environments in western Tasmania.

    PubMed

    Whinam, Jennie; Chilcott, Nicole M

    2003-04-01

    Experimental trials were undertaken over four years to assess the impact of recreational trampling in undisturbed alpine and sub-alpine vegetation communities in the Western Arthur Range, western Tasmania. Data on 'pad' formation due to human trampling were collected using vegetation cover assessments, biomass estimates and detailed cross-sectional surface profiles. In sub-alpine buttongrass and alpine herbfield, prolonged and sustained damage may occur after 100 passes by walkers. The environmental threshold of the flat alpine herbfield site was breached after 200 passes. Plant morphology was one determinant of resistance and resilience, with upright woody shrubs and tall tussock graminoids most vulnerable to sustained trampling damage. Cushions are susceptible to trampling impacts at 500 passes. Loss of vegetation cover peaks 6-12 months after trampling. Our results show that pads formed with as few as 30-100 passes per annum and tracks form at between 100 and 500 passes per annum. Two years after the cessation of trampling, there is some small recovery in vegetation cover after 30 and 100 passes per annum applied for three years, but no evidence of recovery at the 500 pass treatments. The low trampling threshold and slow recovery rates in western Tasmania suggest that concentrating walkers on a minimal number of sites may be the best management option for these untracked alpine and sub-alpine environments. PMID:12710922

  20. Above- and Belowground Biomass Allocation in Shrub Biomes across the Northeast Tibetan Plateau

    PubMed Central

    Yang, Yuanhe; Yang, Lucun; Zhou, Guoying

    2016-01-01

    Biomass partitioning has been explored across various biomes. However, the strategies of allocation in plants still remain contentious. This study investigated allocation patterns of above- and belowground biomass at the community level, using biomass survey from the Tibetan Plateau. We explored above- and belowground biomass by conducting three consecutive sampling campaigns across shrub biomes on the northeast Tibetan Plateau during 2011–2013. We then documented the above-ground biomass (AGB), below-ground biomass (BGB) and root: shoot ratio (R/S) and the relationships between R/S and environment factors using data from 201 plots surveyed from 67 sites. We further examined relationships between above-ground and below-ground biomass across various shrub types. Our results indicated that the median values of AGB, BGB, and R/S in Tibetan shrub were 1102.55, 874.91 g m-2, and 0.85, respectively. R/S showed significant trend with mean annual precipitation (MAP), while decreased with mean annual temperature (MAT). Reduced major axis analysis indicated that the slope of the log-log relationship between above- and belowground biomass revealed a significant difference from 1.0 over space, supporting the optimal hypothesis. Interestingly, the slopes of the allometric relationship between log AGB and log BGB differed significantly between alpine and desert shrub. Our findings supported the optimal theory of above- and belowground biomass partitioning in Tibetan shrub, while the isometric hypothesis for alpine shrub at the community level. PMID:27119379

  1. Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra

    NASA Astrophysics Data System (ADS)

    Juszak, Inge; Eugster, Werner; Heijmans, Monique M. P. D.; Schaepman-Strub, Gabriela

    2016-07-01

    Vegetation changes, such as shrub encroachment and wetland expansion, have been observed in many Arctic tundra regions. These changes feed back to permafrost and climate. Permafrost can be protected by soil shading through vegetation as it reduces the amount of solar energy available for thawing. Regional climate can be affected by a reduction in surface albedo as more energy is available for atmospheric and soil heating. Here, we compared the shortwave radiation budget of two common Arctic tundra vegetation types dominated by dwarf shrubs (Betula nana) and wet sedges (Eriophorum angustifolium) in North-East Siberia. We measured time series of the shortwave and longwave radiation budget above the canopy and transmitted radiation below the canopy. Additionally, we quantified soil temperature and heat flux as well as active layer thickness. The mean growing season albedo of dwarf shrubs was 0.15 ± 0.01, for sedges it was higher (0.17 ± 0.02). Dwarf shrub transmittance was 0.36 ± 0.07 on average, and sedge transmittance was 0.28 ± 0.08. The standing dead leaves contributed strongly to the soil shading of wet sedges. Despite a lower albedo and less soil shading, the soil below dwarf shrubs conducted less heat resulting in a 17 cm shallower active layer as compared to sedges. This result was supported by additional, spatially distributed measurements of both vegetation types. Clouds were a major influencing factor for albedo and transmittance, particularly in sedge vegetation. Cloud cover reduced the albedo by 0.01 in dwarf shrubs and by 0.03 in sedges, while transmittance was increased by 0.08 and 0.10 in dwarf shrubs and sedges, respectively. Our results suggest that the observed deeper active layer below wet sedges is not primarily a result of the summer canopy radiation budget. Soil properties, such as soil albedo, moisture, and thermal conductivity, may be more influential, at least in our comparison between dwarf shrub vegetation on relatively dry patches and

  2. Drivers of tall shrub proliferation adjacent to the Dempster Highway, Northwest Territories, Canada

    NASA Astrophysics Data System (ADS)

    Cameron, Emily A.; Lantz, Trevor C.

    2016-04-01

    Arctic ecosystems are undergoing rapid changes as a result of climate warming and more frequent disturbances. Disturbances can have particularly large effects on high-latitude ecosystems when ecosystem structure and function is controlled by strong feedbacks between soil conditions, vegetation, and ground thermal regime. In this study we investigated the impact of road construction and maintenance on vegetation structure and biomass along the Dempster Highway where it crosses the Peel Plateau in the Northwest Territories. To explore drivers of tall shrub proliferation and to quantify shrub proliferation in this region of continuous permafrost, greyscale air photos (1975) and Quickbird satellite imagery (2008) were used to map landcover change within two 0.6 km2 belts next to the road and two 0.6 km2 belts 500 m away from the road. Maps showing areas where: 1) tall shrubs expanded, and 2) dwarf shrub tundra resisted invasion were then used to select field sites where a suite of biophysical variables were measured. Rapid tall shrub proliferation and greater biomass adjacent to the road indicate that disturbance can facilitate vegetation change in tundra environments. Our field data also suggests that increased shrub proliferation adjacent to the road was caused by greater soil moisture. Tall shrub proliferation adjacent to the road occurred at lower elevation sites characterized by wetter soils with thicker organic layers. Areas that resisted tall shrub encroachment were located at higher elevations and had drier soils with thin organic layers. Our observations also support previous work illustrating that tall shrub expansion next to the highway promotes strong positive feedbacks to ongoing shrub growth and proliferation.

  3. Coping with shrub secondary metabolites by ruminants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rangelands throughout the world contain varying but often substantial proportions of shrubs. Shrubs are generally heavily chemically defended, and herbivores must either contend with their plant secondary metabolites (PSM) or avoid a significant component of the available forage. Browsing ruminants ...

  4. Alpine plant community trends on the elk summer range of Rocky Mountain National Park, Colorado: An analysis of existing data

    USGS Publications Warehouse

    Zeigenfuss, Linda C.

    2006-01-01

    The majority of the elk (Cervus elaphus) population of Rocky Mountain National Park in Colorado summer in the park’s high-elevation alpine and subalpine meadows and willow krummholz. The park’s population of white-tailed ptarmigan (Lagopus leucurus altipetens) depends on both dwarf and krummholz willows for food and cover. Concern about the effects of elk herbivory on these communities prompted the monitoring of 12 vegetation transects in these regions from 1971 to 1996. Over this 25-year period, data were collected on plant species cover and frequency and shrub heights. These data have not been statistically analyzed for trends in the measured variables over time to determine changes in species abundance. Krummholz willow species (Salix planifolia, S. brachycarpa) declined 17–20 percent in cover and about 25 centimeters in height over the study period. Graminoids (particularly Deschampsia caespitosa, Carex, and Poa) increased slightly from 1971 to 1996. No significant increases of nonnative plant species were observed. An increase in presence of bare ground over the 25-year period warrants continued measurement of these transects. Lack of good data on elk density, distribution, or use levels precludes correlating changes in plant species cover, frequency, or heights with elk population trends. I recommend development of a more rigorously designed monitoring program that includes these transects as well as others chosen on a random or stratified design and consistent measurement protocol and sampling intervals. Some method of quantifying elk use, either through measurement of plant utilization, pellet counts, or census-type surveys, would allow correlation of changes in plant species over time with changes in elk distribution and density on the park’s alpine and subalpine regions.

  5. Canopy storage capacity of xerophytic shrubs in Northwestern China

    NASA Astrophysics Data System (ADS)

    Wang, Xin-ping; Zhang, Ya-feng; Hu, Rui; Pan, Yan-xia; Berndtsson, Ronny

    2012-08-01

    SummaryThe capacity of shrub canopy water storage is a key factor in controlling the rainfall interception. Thus, it affects a variety of hydrological processes in water-limited arid desert ecosystems. Vast areas of revegetated desert ecosystems in Northwestern China are occupied by shrub and dwarf shrub communities. Yet, data are still scarce regarding their rainwater storage capacity. In this study, simulated rainfall tests were conducted in controlled conditions for three dominant xerophytic shrub types in the arid Tengger Desert. Eight rainfall intensities varying from 1.15 to 11.53 mm h-1 were used to determine the canopy water storage capacity. The simulated rainfall intensities were selected according to the long-term rainfall records in the study area. The results indicate that canopy storage capacity (expressed in water storage per leaf area, canopy projection area, biomass, and volume of shrub respectively) increased exponentially with increase in rainfall intensity for the selected shrubs. Linear relationships were found between canopy storage capacity and leaf area (LA) or leaf area index (LAI), although there was a striking difference in correlation between storage capacity and LA or LAI of Artemisia ordosica compared to Caragana korshinskii and Hedysarum scoparium. This is a result of differences in biometric characteristics, especially canopy morphology between the shrub species. Pearson correlation coefficient indicated that LA and dry biomass are better predictors as compared to canopy projection area and volume of samples for precise estimation of canopy water storage capacity. In terms of unit leaf area, mean storage capacity was 0.39 mm (range of 0.24-0.53 mm), 0.43 mm (range of 0.28-0.60 mm), and 0.61 mm (range of 0.29-0.89 mm) for C. korshinskii, H. scoparium, and A. ordosica, respectively. Correspondingly, divided per unit dry biomass, mean storage capacity was 0.51 g g-1 (range of 0.30-0.70 g g-1), 0.41 g g-1 (range of 0.26-0.57 g g-1), and

  6. Why Be a Shrub? A Basic Model and Hypotheses for the Adaptive Values of a Common Growth Form

    PubMed Central

    Götmark, Frank; Götmark, Elin; Jensen, Anna M.

    2016-01-01

    Shrubs are multi-stemmed short woody plants, more widespread than trees, important in many ecosystems, neglected in ecology compared to herbs and trees, but currently in focus due to their global expansion. We present a novel model based on scaling relationships and four hypotheses to explain the adaptive significance of shrubs, including a review of the literature with a test of one hypothesis. Our model describes advantages for a small shrub compared to a small tree with the same above-ground woody volume, based on larger cross-sectional stem area, larger area of photosynthetic tissue in bark and stem, larger vascular cambium area, larger epidermis (bark) area, and larger area for sprouting, and faster production of twigs and canopy. These components form our Hypothesis 1 that predicts higher growth rate for a small shrub than a small tree. This prediction was supported by available relevant empirical studies (14 publications). Further, a shrub will produce seeds faster than a tree (Hypothesis 2), multiple stems in shrubs insure future survival and growth if one or more stems die (Hypothesis 3), and three structural traits of short shrub stems improve survival compared to tall tree stems (Hypothesis 4)—all hypotheses have some empirical support. Multi-stemmed trees may be distinguished from shrubs by more upright stems, reducing bending moment. Improved understanding of shrubs can clarify their recent expansion on savannas, grasslands, and alpine heaths. More experiments and other empirical studies, followed by more elaborate models, are needed to understand why the shrub growth form is successful in many habitats. PMID:27507981

  7. Why Be a Shrub? A Basic Model and Hypotheses for the Adaptive Values of a Common Growth Form.

    PubMed

    Götmark, Frank; Götmark, Elin; Jensen, Anna M

    2016-01-01

    Shrubs are multi-stemmed short woody plants, more widespread than trees, important in many ecosystems, neglected in ecology compared to herbs and trees, but currently in focus due to their global expansion. We present a novel model based on scaling relationships and four hypotheses to explain the adaptive significance of shrubs, including a review of the literature with a test of one hypothesis. Our model describes advantages for a small shrub compared to a small tree with the same above-ground woody volume, based on larger cross-sectional stem area, larger area of photosynthetic tissue in bark and stem, larger vascular cambium area, larger epidermis (bark) area, and larger area for sprouting, and faster production of twigs and canopy. These components form our Hypothesis 1 that predicts higher growth rate for a small shrub than a small tree. This prediction was supported by available relevant empirical studies (14 publications). Further, a shrub will produce seeds faster than a tree (Hypothesis 2), multiple stems in shrubs insure future survival and growth if one or more stems die (Hypothesis 3), and three structural traits of short shrub stems improve survival compared to tall tree stems (Hypothesis 4)-all hypotheses have some empirical support. Multi-stemmed trees may be distinguished from shrubs by more upright stems, reducing bending moment. Improved understanding of shrubs can clarify their recent expansion on savannas, grasslands, and alpine heaths. More experiments and other empirical studies, followed by more elaborate models, are needed to understand why the shrub growth form is successful in many habitats. PMID:27507981

  8. Variations in the Sensitivity of Shrub Growth to Climate Change along Arctic Environmental and Biotic Gradients

    NASA Astrophysics Data System (ADS)

    Beck, P. S. A.; Myers-Smith, I. H.; Elmendorf, S.; Georges, D.

    2015-12-01

    Despite evidence of rapid shrub expansion at many Arctic sites and the profound effects this has on ecosystem structure, biogeochemical cycling, and land-atmosphere feedbacks in the Arctic, the drivers of shrub growth remain poorly understood. The compilation of 41,576 annual shrub growth measurements made around the Arctic, allowed for the first systematic evaluation of the climate sensitivity of Arctic shrub growth, i.e. the strength of the relationship between annual shrub growth and monthly climate variables. The growth measurements were taken on 1821 plants of 25 species at 37 arctic and alpine sites, either as annual ring widths or as stem increments. We evaluated climate sensitivity of shrub growth for each genus-by-site combination in this data set based on the performance and parameters of linear mixed models that used CRU TS3.21 climate data as predictors of shrub growth between 1950 and 2010. 76% of genus-by-site combinations showed climate sensitive growth, but climate-growth relationships varied with soil moisture, species canopy height, and geographic position within the species ranges. Shrubs growing at sites with more soil moisture showed greater climate sensitivity, suggesting that water availability might limit shrub growth if continued warming isn't matched by a steady increase in soil moisture. Tall shrub species growing at their northern range limit were particularly climate sensitive causing climate sensitivity of shrubs to peak at the transition between Low and High Arctic, where carbon storage in permafrost is greatest. Local and regional studies have documented matching spatial and temporal patterns in dendrochronological measurements and satellite observations of vegetation indices both in boreal and Arctic regions. Yet the circumarctic comparison of patterns in dendrochronological and remote sensing data sets yielded poor levels of agreement. In much of the Arctic, steep environmental gradients generate fine spatial patterns of vegetation

  9. Tall shrub and tree expansion in Siberian tundra ecotones since the 1960s.

    PubMed

    Frost, Gerald V; Epstein, Howard E

    2014-04-01

    Circumpolar expansion of tall shrubs and trees into Arctic tundra is widely thought to be occurring as a result of recent climate warming, but little quantitative evidence exists for northern Siberia, which encompasses the world's largest forest-tundra ecotonal belt. We quantified changes in tall shrub and tree canopy cover in 11, widely distributed Siberian ecotonal landscapes by comparing very high-resolution photography from the Cold War-era 'Gambit' and 'Corona' satellite surveillance systems (1965-1969) with modern imagery. We also analyzed within-landscape patterns of vegetation change to evaluate the susceptibility of different landscape components to tall shrub and tree increase. The total cover of tall shrubs and trees increased in nine of 11 ecotones. In northwest Siberia, alder (Alnus) shrubland cover increased 5.3-25.9% in five ecotones. In Taymyr and Yakutia, larch (Larix) cover increased 3.0-6.7% within three ecotones, but declined 16.8% at a fourth ecotone due to thaw of ice-rich permafrost. In Chukotka, the total cover of alder and dwarf pine (Pinus) increased 6.1% within one ecotone and was little changed at a second ecotone. Within most landscapes, shrub and tree increase was linked to specific geomorphic settings, especially those with active disturbance regimes such as permafrost patterned-ground, floodplains, and colluvial hillslopes. Mean summer temperatures increased at most ecotones since the mid-1960s, but rates of shrub and tree canopy cover expansion were not strongly correlated with temperature trends and were better correlated with mean annual precipitation. We conclude that shrub and tree cover is increasing in tundra ecotones across most of northern Siberia, but rates of increase vary widely regionally and at the landscape scale. Our results indicate that extensive changes can occur within decades in moist, shrub-dominated ecotones, as in northwest Siberia, while changes are likely to occur much more slowly in the highly continental

  10. Dwarf novae

    NASA Technical Reports Server (NTRS)

    Ladous, Constanze

    1993-01-01

    Dwarf novae are defined on grounds of their semi-regular brightness variations of some two to five magnitudes on time scales of typically 10 to 100 days. Historically several different classification schemes have been used. Today, dwarf novae are divided into three sub-classes: the U Geminorum stars, the SU Ursae Majoris stars, and the Z Camelopardalis stars. Outbursts of dwarf novae occur at semi-periodic intervals of time, typically every 10 to 100 days; amplitudes range from typically 2 to 5 mag. Within certain limits values are characteristic for each object. Relations between the outburst amplitude, or the total energy released during outburst, and the recurrence time have been found, as well as relations between the orbital period and the outburst decay time, the absolute magnitude during outburst maximum, and the widths of long and short outbursts, respectively. Some dwarf novae are known to have suspended their normal outburst activity altogether for a while. They later resumed it without having undergone any observable changes. The optical colors of dwarf novae all are quite similar during outburst, considerably bluer than during the quiescent state. During the outburst cycle, characteristic loops in the two color diagram are performed. At a time resolution on the order of minutes, strictly periodic photometric changes due to orbital motion become visible in the light curves of dwarf novae. These are characteristic for each system. Remarkably little is known about orbital variations during the course of an outburst. On time-scales of minutes and seconds, further more or less periodic types of variability are seen in dwarf novae. Appreciable flux is emitted by dwarf novae at all wavelengths from the X-rays to the longest IR wavelengths, and in some cases even in the radio. Most dwarf novae exhibit strong emission line spectra in the optical and UV during quiescence, although some have only very weak emissions in the optical and/or weak absorptions at UV

  11. Soil warming and CO2 enrichment induce biomass shifts in alpine tree line vegetation.

    PubMed

    Dawes, Melissa A; Philipson, Christopher D; Fonti, Patrick; Bebi, Peter; Hättenschwiler, Stephan; Hagedorn, Frank; Rixen, Christian

    2015-05-01

    Responses of alpine tree line ecosystems to increasing atmospheric CO2 concentrations and global warming are poorly understood. We used an experiment at the Swiss tree line to investigate changes in vegetation biomass after 9 years of free air CO2 enrichment (+200 ppm; 2001-2009) and 6 years of soil warming (+4 °C; 2007-2012). The study contained two key tree line species, Larix decidua and Pinus uncinata, both approximately 40 years old, growing in heath vegetation dominated by dwarf shrubs. In 2012, we harvested and measured biomass of all trees (including root systems), above-ground understorey vegetation and fine roots. Overall, soil warming had clearer effects on plant biomass than CO2 enrichment, and there were no interactive effects between treatments. Total plant biomass increased in warmed plots containing Pinus but not in those with Larix. This response was driven by changes in tree mass (+50%), which contributed an average of 84% (5.7 kg m(-2) ) of total plant mass. Pinus coarse root mass was especially enhanced by warming (+100%), yielding an increased root mass fraction. Elevated CO2 led to an increased relative growth rate of Larix stem basal area but no change in the final biomass of either tree species. Total understorey above-ground mass was not altered by soil warming or elevated CO2 . However, Vaccinium myrtillus mass increased with both treatments, graminoid mass declined with warming, and forb and nonvascular plant (moss and lichen) mass decreased with both treatments. Fine roots showed a substantial reduction under soil warming (-40% for all roots <2 mm in diameter at 0-20 cm soil depth) but no change with CO2 enrichment. Our findings suggest that enhanced overall productivity and shifts in biomass allocation will occur at the tree line, particularly with global warming. However, individual species and functional groups will respond differently to these environmental changes, with consequences for ecosystem structure and functioning. PMID

  12. Stable carbon isotopic evidence of methane consumption and production in three alpine ecosystems on the Qinghai-Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Kato, Tomomichi; Yamada, Keita; Tang, Yanhong; Yoshida, Naohiro; Wada, Eitaro

    2013-10-01

    To understand the mechanisms of soil CH4 consumption and production in alpine ecosystems, we for the first time examined the stable carbon isotope ratio of CH4 (δ13C-CH4) at three major grassland vegetation types, alpine meadow, alpine shrub, and alpine wetland, on the Qinghai-Tibetan Plateau. The alpine meadow and shrub showed net CH4 absorption in their vertical profiles of CH4 concentration in summer, but a difference in their processes. Whereas the alpine shrub was dominated by CH4 consumption in its soil profile, CH4 production in the alpine meadow could slightly cancel consumed CH4 in shallow soil from -0.3 to -0.1 m. This potential CH4 production can be attributed to the relatively wet soil type of that ecosystem, which might allow methanogenesis to act in moist soil lumps in the shallow layer. The alpine wetland differed in methane production, consumption, and transport pathways between hummock and hollow plots. In summer, both plots were enriched in 13C-CH4 in dissolved CH4 in soil pore water, suggesting that CH4 production was conducted mainly by acetate fermentation. In autumn, CH4 production was shifted toward CO2/H2 reduction. Furthermore, in hummocks, plant-mediated transport of CH4 by vascular plants appeared to perform passive CH4 flow from deep soil to atmosphere, which allowed the produced CH4 to bypass the oxidation zone in shallow soil. In hollows, however, CH4 produced in shallow soil was subject to simultaneous oxidation. The fractional oxidation rate on gross CH4 production in hollows was estimated by simple mass balance model at 7-17% in summer and 35-36% in autumn.

  13. Are low altitude alpine tundra ecosystems under threat? A case study from the Parc National de la Gaspésie, Québec

    NASA Astrophysics Data System (ADS)

    Dumais, Catherine; Ropars, Pascale; Denis, Marie-Pier; Dufour-Tremblay, Geneviève; Boudreau, Stéphane

    2014-09-01

    According to the 2007 IPCC report, the alpine tundra ecosystems found on low mountains of the northern hemisphere are amongst the most threatened by climate change. A treeline advance or a significant erect shrub expansion could result in increased competition for the arctic-alpine species usually found on mountaintops and eventually lead to their local extinction. The objectives of our study were to identify recent changes in the cover and growth of erect woody vegetation in the alpine tundra of Mont de la Passe, in the Parc National de la Gaspésie (Québec, Canada). The comparison of two orthorectified aerial photos revealed no significant shift of the treeline between 1975 and 2004. During the same period however, shrub species cover increased from 20.2% to 30.4% in the lower alpine zone. Dendrochronological analyses conducted on Betula glandulosa Michx. sampled at three different positions along an altitudinal gradient (low, intermediate and high alpine zone) revealed that the climatic determinants of B. glandulosa radial growth become more complex with increasing altitude. In the lower alpine zone, B. glandulosa radial growth is only significantly associated positively to July temperature. In the intermediate alpine zone, radial growth is associated positively to July temperature but negatively to March temperature. In the high alpine zone, radial growth is positively associated to January, July and August temperature but negatively to March temperature. The positive association between summer temperatures and radial growth suggests that B. glandulosa could potentially benefit from warmer temperatures, a phenomenon that could lead to an increase in its cover over the next few decades. Although alpine tundra vegetation is not threatened in the short-term in the Parc National de la Gaspésie, erect shrub cover, especially B. glandulosa, could likely increase in the near future, threatening the local arctic-alpine flora.

  14. Within-population spatial variation in pollinator visitation rates, pollen limitation on seed set, and flower longevity in an alpine species

    NASA Astrophysics Data System (ADS)

    Lundemo, Sverre; Totland, Ørjan

    2007-11-01

    Pollen limitation through insufficient pollen deposition on stigmas caused by too infrequent pollinator visitation may influence the reproductive outcome of plants. In this study we investigated how pollinator visitation rate, the degree of pollen limitation, and flower longevity varied spatially among three sites at different altitudes within a population of the dwarf shrub Dryas octopetala L. in alpine southern Norway. Significant pollen limitation on seed set only occurred at the mid-elevation site, while seed set at the other sites appeared to be mainly resource limited, thus indicating a spatial variation in pollen limitation. There was no association between the spatial variation in the extent of pollen limitation and pollinator visitation rate to flowers. However, pollinator visitation rates were related to flower longevity of Dryas; sites with low visitation rates had long-lived flowers and vice versa. Thus, our results suggest within-population spatial co-variation between pollinator visitation rates, pollen limitation, and a developmental response to these factors, flower longevity.

  15. Automatic monitoring of the effective thermal conductivity of snow in a low Arctic shrub tundra

    NASA Astrophysics Data System (ADS)

    Domine, F.; Barrere, M.; Sarrazin, D.; Morin, S.

    2015-03-01

    The effective thermal conductivity of snow, keff, is a critical variable which determines the temperature gradient in the snowpack and heat exchanges between the ground and the atmosphere through the snow. Its accurate knowledge is therefore required to simulate snow metamorphism, the ground thermal regime, permafrost stability, nutrient recycling and vegetation growth. Yet, few data are available on the seasonal evolution of snow thermal conductivity in the Arctic. We have deployed heated needle probes on low Arctic shrub tundra near Umiujaq, Quebec, (56°34´ N; 76°29´ W) and monitored automatically the evolution of keff for two consecutive winters, 2012-2013 and 2013-2014, at 4 heights in the snowpack. Shrubs are 20 cm high dwarf birch. Here, we develop an algorithm for the automatic determination of keff from the heating curves and obtain 404 keff values. We evaluate possible errors and biases associated with the use of the heated needles. The time-evolution of keff is very different for both winters. This is explained by comparing the meteorological conditions in both winters, which induced different conditions for snow metamorphism. In particular, important melting events the second year increased snow hardness, impeding subsequent densification and increase in thermal conductivity. Shrubs are observed to have very important impacts on snow physical evolution: (1) shrubs absorb light and facilitate snow melt under intense radiation; (2) the dense twig network of dwarf birch prevents snow compaction and therefore keff increase; (3) the low density depth hoar that forms within shrubs collapsed in late winter, leaving a void that was not filled by snow.

  16. Automatic monitoring of the effective thermal conductivity of snow in a low-Arctic shrub tundra

    NASA Astrophysics Data System (ADS)

    Domine, F.; Barrere, M.; Sarrazin, D.; Morin, S.; Arnaud, L.

    2015-06-01

    The effective thermal conductivity of snow, keff, is a critical variable which determines the temperature gradient in the snowpack and heat exchanges between the ground and the atmosphere through the snow. Its accurate knowledge is therefore required to simulate snow metamorphism, the ground thermal regime, permafrost stability, nutrient recycling and vegetation growth. Yet, few data are available on the seasonal evolution of snow thermal conductivity in the Arctic. We have deployed heated needle probes on low-Arctic shrub tundra near Umiujaq, Quebec, (N56°34'; W76°29') and monitored automatically the evolution of keff for two consecutive winters, 2012-2013 and 2013-2014, at four heights in the snowpack. Shrubs are 20 cm high dwarf birch. Here, we develop an algorithm for the automatic determination of keff from the heating curves and obtain 404 keff values. We evaluate possible errors and biases associated with the use of the heated needles. The time evolution of keff is very different for both winters. This is explained by comparing the meteorological conditions in both winters, which induced different conditions for snow metamorphism. In particular, important melting events in the second year increased snow hardness, impeding subsequent densification and increase in thermal conductivity. We conclude that shrubs have very important impacts on snow physical evolution: (1) shrubs absorb light and facilitate snow melt under intense radiation; (2) the dense twig network of dwarf birch prevent snow compaction, and therefore keff increase; (3) the low density depth hoar that forms within shrubs collapsed in late winter, leaving a void that was not filled by snow.

  17. Land use and surface process domains on alpine hillslopes

    NASA Astrophysics Data System (ADS)

    Kuhn, Nikolaus J.; Caviezel, Chatrina; Hunziker, Matthias

    2015-04-01

    Shrubs and trees are generally considered to protect hillslopes from erosion. As a consequence, shrub encroachment on mountain pastures after abandoning grazing is not considered a threat to soils. However, the abandonment of mown or grazed grasslands causes a shift in vegetation composition and thus a change in landscape ecology and geomorphology. On many alpine slopes, current changes in land use and vegetation cover are accompanied by climate change, potentially generating a new geomorphic regime. Most of the debate focuses on the effect of land abandonment on water erosion rates. Generally, an established perennial vegetation cover improves the mechanical anchoring of the soil and the regulation of the soil water budget, including runoff generation and erosion. However, changing vegetation composition affects many other above- and below-ground properties like root density, -diversity and -geometry, soil structure, pore volume and acidity. Each combination of these properties can lead to a distinct scenario of dominating surface processes, often not reflected by common erosion risk assessment procedures. The study of soil properties along a chronosequence of green alder (alnusviridis) encroachment on the Unteralptal in central Switzerland reveals that shrub encroachment changes soil and vegetation properties towards an increase of resistance to run-off related erosion processes, but a decrease of slope stability against shallow landslides. The latter are a particular threat because of the currently increasing frequency of slide-triggering high magnitude rainfalls. The potential change of process domain on alpine pastures highlights the need for a careful use of erosion models when assessing future land use and climate scenarios. In mountains, but also other intensively managed agricultural landscapes, risk assessment without the appropriate reflection on the shifting relevance of surface processes carries the risk of missing future threats to environmental

  18. Changes in alpine plant growth under future climate conditions

    NASA Astrophysics Data System (ADS)

    Rammig, A.; Jonas, T.; Zimmermann, N. E.; Rixen, C.

    2010-06-01

    Alpine shrub- and grasslands are shaped by extreme climatic conditions such as a long-lasting snow cover and a short vegetation period. Such ecosystems are expected to be highly sensitive to global environmental change. Prolonged growing seasons and shifts in temperature and precipitation are likely to affect plant phenology and growth. In a unique experiment, climatology and plant growth was monitored for almost a decade at 17 snow meteorological stations in different alpine regions along the Swiss Alps. Regression analyses revealed highly significant correlations between mean air temperature in May/June and snow melt out, onset of plant growth, and plant height. These correlations were used to project plant growth phenology for future climate conditions based on the gridded output of a set of regional climate models runs. Melt out and onset of growth were projected to occur on average 17 days earlier by the end of the century than in the control period from 1971-2000 under the future climate conditions of the low resolution climate model ensemble. Plant height and biomass production were expected to increase by 77% and 45%, respectively. The earlier melt out and onset of growth will probably cause a considerable shift towards higher growing plants and thus increased biomass. Our results represent the first quantitative and spatially explicit estimates of climate change impacts on future growing season length and the respective productivity of alpine plant communities in the Swiss Alps.

  19. Changes in alpine plant growth under future climate conditions

    NASA Astrophysics Data System (ADS)

    Rammig, A.; Jonas, T.; Zimmermann, N. E.; Rixen, C.

    2009-11-01

    Alpine shrub- and grasslands are shaped by extreme climatic conditions such as a long-lasting snow cover and a short vegetation period. Such ecosystems are expected to be highly sensitive to global environmental change. Prolonged growing seasons and shifts in temperature and precipitation are likely to affect plant phenology and growth. In a unique experiment, climatology and plant growth was monitored for almost a decade at 17 snow meteorological stations in different alpine regions along the Swiss Alps. Regression analyses revealed highly significant correlations between mean air temperature in May/June and snow melt-out, onset of plant growth, and plant height. These correlations were used to project plant growth phenology for future climate conditions based on the gridded output of a set of regional climate models runs. Melt-out and onset of growth were projected to occur on average 17 days earlier by the end of the century than in the control period from 1971-2000 under the future climate conditions of the low resolution climate model ensemble. Plant height and biomass production were expected to increase by 77% and 45%, respectively. The earlier melt-out and onset of growth will probably cause a considerable shift towards higher growing plants and thus increased biomass. Our results represent the first quantitative and spatially explicit estimates of climate change impacts on future growing season length and the respective productivity of alpine plant communities in the Swiss Alps.

  20. 137Cs re-sampling as a method for soil erosion assessment in Alpine grasslands

    NASA Astrophysics Data System (ADS)

    Arata, Laura; Meusburger, Katrin; Bissig, Nicole; Mabit, Lionel; Alewell, Christine

    2014-05-01

    Over the past decades, radioactive fallout 137Cs has been used as a tracer to provide information on soil erosion and sedimentation rates. However, the method may produce relatively large uncertainties in Alpine grasslands. The latter difficulties are caused by a combination of (i) the heterogeneous distribution of atmospheric 137Cs Chernobyl fallout, (ii) the partly snow covered ground in Alpine areas during the fallout event in April 1986, which results in inhomogeneous 137Cs distribution during snow melt and (iii) uncertainties in finding undisturbed references sites in the geomorphological and anthropogenic highly active slopes of the Alps. To overcome these difficulties, our aim is to replace the classical 137Cs approach, where an undisturbed reference site is compared to erosional sites, with a re-sampling approach, where we re-sample sites which have already been measured for 137Cs inventories in the past. Thus, we use temporal instead of spatial reference. The study area is located in the Central Swiss Alps in the Urseren Valley. Potential erosional sites have been sampled in 2007 and re-sampled in 2012. Two different grassland types were investigated: hayfield (2 sites) and pasture without dwarf shrubs (3 sites). For each site, 4 to 9 sampling points have been defined, and at each point two soil samples have been collected. To reduce the random error, the two soil samples were bulked prior to gamma-analysis. 137Cs inventories of the two sampling years were calculated and used to assess recent soil erosion in the experimental sites. Our results show that within the 5 years measurable soil erosion and deposition processes have occurred within the sites, as indicated by the relevant difference between the 137Cs inventories of 2007 and 2012. 64% of the sites exhibit a decrease in 137Cs inventories, 20% of the sites an increase, and the remaining 16% no significant difference. In particular, hayfield sites have been affected by erosion processes, mostly due to

  1. Effects of surface characteristics on infiltration patterns in an arid shrub desert

    NASA Astrophysics Data System (ADS)

    Wang, Xin-Ping; Li, Xin-Rong; Xiao, Hong-Lang; Berndtsson, Ronny; Pan, Yan-Xia

    2007-01-01

    Precipitation is often the sole source of water replenishment in arid and semi-arid areas and, thus, plays a pertinent role in sustaining desert ecosystems. Revegetation over 40 years using mainly Artemisia ordosica and Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou, China, has established a dwarf-shrub and microbiotic soil crust cover on the stabilized sand dunes. The redistribution of infiltrated moisture through percolation, root extraction, and evapotranspiration pathways was investigated. Three sets of time-domain reflectometry (TDR) probes were inserted horizontally at 5, 10, 15, 20, 30 and 40 cm depths below the ground surface in a soil pit. The three sets of TDR probes were installed in dwarf-shrub sites of A. ordosica and C. korshinskii community with and without a microbiotic soil crust cover, and an additional set was placed in a bare sand dune area that had neither vegetation nor a microbiotic soil crust present. Volumetric soil moisture content was recorded at hourly intervals and used in the assessment of infiltration for the different surface covers. Infiltration varied greatly, from 7.5 cm to more than 45 cm, depending upon rainfall quantity and soil surface conditions. In the shrub community area without microbiotic soil crust cover, infiltration increased due to preferential flow associated with root tunnels. The microbiotic soil crust cover had a significant negative influence on the infiltration for small rainfall events (10 mm), restricting the infiltration depth to less than 20 cm and increasing soil moisture content just beneath the soil profile of 10 cm, whereas it was not as strong or clear for larger rainfall events (60 mm). For small rainfall events, the wetting front depth for the three kinds of surface cover was as follows: shrub community without microbiotic soil crust > bare area > shrub community with microbiotic soil crust. In contrast, for large rainfall events, infiltration was similar in shrub

  2. Naming Disney's Dwarfs.

    ERIC Educational Resources Information Center

    Sidwell, Robert T.

    1980-01-01

    Discusses Disney's version of the folkloric dwarfs in his production of "Snow White" and weighs the Disney rendition of the dwarf figure against the corpus of traits and behaviors pertaining to dwarfs in traditional folklore. Concludes that Disney's dwarfs are "anthropologically true." (HOD)

  3. What are the patterns of carbon allocation in Arctic shrub tundra: do species differ?

    NASA Astrophysics Data System (ADS)

    Street, Lorna; Subke, Jens-Arne; Baxter, Robert; Billett, Mike; Dinsmore, Kerry; Lessels, Jason; Wookey, Philip

    2014-05-01

    Arctic "greening" is now a well-accepted phenomenon; multiple lines of evidence suggest that plant productivity has increased, driven by increases in shrub abundance. There is very little understanding, however, of how this "shrubification" will impact biogeochemical cycling, including the allocation and turnover of carbon. Recent research has shown, for example, that greater plant productivity is not necessary associated with greater ecosystem C storage. Proliferation of a number of shrub species has been observed in different regions; for example increased willow growth in Arctic Russia, as opposed to primarily alder expansion in NW Canada, where stem density increased 68 % between 1968 and 2004. The degree to which shrub type will determine the impacts of shrub expansion on the carbon cycle is unknown. We use 13C pulse-labelling to trace the fate of recently photosynthesised carbon in vegetation dominated by two common Arctic shrubs, Betula nana (dwarf birch) and Alnus viridis (green alder) just above the Arctic treeline in NW Canada. We quantify the amount of 13C assimilated, and the proportion of assimilate returned to the atmosphere via respiration versus that allocated to plant tissues. This enables an analysis of the contrasting carbon-use-efficiencies and aboveground versus belowground allocation patterns in the two vegetation types. We use these novel field data to address the hypothesis that belowground C allocation in A. viridis (a symbiotic nitrogen fixing species) is a smaller proportion of total C assimilation, as this species supports less extensive ectomycorrhizal networks compared to B. nana. This is the first tracer study of carbon allocation in N-fixing and non-N-fixing vegetation types in a natural system and provides crucial data for predictive modelling of the Arctic carbon cycle.

  4. Negative impacts of a vertebrate predator on insect pollinator visitation and seed output in Chuquiraga oppositifolia, a high Andean shrub.

    PubMed

    Muñoz, Alejandro A; Arroyo, Mary T K

    2004-01-01

    Studies on plant-pollinator interactions have largely neglected the potential negative effects of the predators of pollinators on seed output, even though anti-predatory behaviour of pollinators may affect visitation patterns, pollen transfer, and therefore potentially, plant reproductive output. We tested the hypothesis that the presence of lizards and insectivorous birds, by reducing pollinator visitation, can have significant negative effects on seed output in the insect-pollinated, genetically self-incompatible lower alpine Andean shrub, Chuquiraga oppositifolia (Asteraceae). The lower alpine belt supports a high density of territorial Liolaemus (Tropiduridae) lizards and low shrubs interspersed among rocks of varying sizes, the latter inhabited by lizards and commonly used by flycatchers Muscisaxicola (Tyrannidae) as perching sites. In a 2x2 factorial predator-exclusion experiment, visitation rates of the most frequent pollinators of C. oppositifolia (the satyrid butterfly Cosmosatyrus chilensis and the syrphid fly Scaeva melanostoma), the duration of pollinator visits, and seed output, were 2-4 times greater when lizards were excluded, while birds had no effect. In a natural experiment, visits by S. melanostoma were 9 times shorter, and pollinator visitation rates of C. chilensis and S. melanostoma, and C. oppositifolia seed output were 2-3 times lower on shrubs growing adjacent to lizard-occupied rocks compared to those growing distant from rocks. Our results, verified for additional Andean sites, suggest that lizard predators can alter the behaviour of pollinators and elicit strong top-down indirect negative effects on seed output. Such effects may be especially important in high alpine plant communities, where pollinator activity can be low and erratic, and pollen limitation has been reported. PMID:14551828

  5. Nye Lecture: Snow Crystals, Shrubs, and the Changing Climate of the Arctic

    NASA Astrophysics Data System (ADS)

    Sturm, M.

    2005-12-01

    At the peak of winter, snow covers more than 45 million km2 of the northern hemisphere. More than 90 percent of this snow will melt before the end of the following summer. In the southern part of this snow-covered area, the seasonal pack is ephemeral, lasting but a few short weeks, but with increasing latitude (or altitude), it lasts much longer. In arctic and alpine locations it can persist for 9 months of the year. In these more extreme locations, the snow is an essential element of the ecosystem, both acting upon, and being acted on, by the biota. For historical reasons, our understanding of snow cover and its interactions has come from two disparate scientific sources: geophysicists working on glaciers and avalanches who were trying to understand snow properties and to develop a physical basis for snow science, and ecologists who were trying to understand the impact of snow on plants, animals, and humans. With the recognition now that snow is both a passive and active agent, we are seeing an increasing number of studies wherein both of these traditional approaches are combined. Geophysicists are learning the Latin names of shrubs while botanist can now identify wind slab. A personal example that illustrates the necessity of this melding process has been our effort to understand the climatic implications of Arctic snow-shrub interactions. We have had to combine traditional snow geophysical studies (i.e., crystal growth, thermal processes, light reflection) with traditional ecological studies (i.e., competition, carbon and nitrogen cycling). Through this process we have discovered that snow-shrub interactions, or more broadly, snow-vegetation interactions, are helping to push the Arctic down a warming trajectory that has global implications. Soil microbes and snow crystals, wind-blown snow and shrubs, are all leading actors in a climate change drama whose outcome is of concern to us all.

  6. Shrub canopies influence soil temperatures but not nutrient dynamics: An experimental test of tundra snow–shrub interactions

    PubMed Central

    Myers-Smith, Isla H; Hik, David S

    2013-01-01

    Shrubs are the largest plant life form in tundra ecosystems; therefore, any changes in the abundance of shrubs will feedback to influence biodiversity, ecosystem function, and climate. The snow–shrub hypothesis asserts that shrub canopies trap snow and insulate soils in winter, increasing the rates of nutrient cycling to create a positive feedback to shrub expansion. However, previous work has not been able to separate the abiotic from the biotic influences of shrub canopies. We conducted a 3-year factorial experiment to determine the influences of canopies on soil temperatures and nutrient cycling parameters by removing ∼0.5 m high willow (Salix spp.) and birch (Betula glandulosa) shrubs, creating artificial shrub canopies and comparing these manipulations to nearby open tundra and shrub patches. Soil temperatures were 4–5°C warmer in January, and 2°C cooler in July under shrub cover. Natural shrub plots had 14–33 cm more snow in January than adjacent open tundra plots. Snow cover and soil temperatures were similar in the manipulated plots when compared with the respective unmanipulated treatments, indicating that shrub canopy cover was a dominant factor influencing the soil thermal regime. Conversely, we found no strong evidence of increased soil decomposition, CO2 fluxes, or nitrate or ammonia adsorbtion under artificial shrub canopy treatments when compared with unmanipulated open tundra. Our results suggest that the abiotic influences of shrub canopy cover alone on nutrient dynamics are weaker than previously asserted. PMID:24198933

  7. SHRUB BATTLE: Understanding the Making of Landscape

    ERIC Educational Resources Information Center

    Depigny, Sylvain; Michelin, Yves

    2007-01-01

    Landscape changes in Europe's rural areas seem to generate a more visible impact. This trend raises new questions on rural management and brings about a conflict between farmers' land-use patterns and public expectations, which are often exclusively based on esthetics. The aim of the SHRUB BATTLE board game is to help tutors make future rural…

  8. Breeding Lyonia and Leucothoe, native evergreen shrubs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Native evergreen shrubs that thrive in shade are typically limited to specific hollies and azaleas. Few evergreen ornamental plants tolerate deep shade and humidity in the south. Several species of Lyonia and Leucothoe thrive in partial to full shade and tolerate a wide variety of soil and environme...

  9. Why trees and shrubs but rarely trubs?

    PubMed

    Scheffer, Marten; Vergnon, Remi; Cornelissen, J Hans C; Hantson, Stijn; Holmgren, Milena; van Nes, Egbert H; Xu, Chi

    2014-08-01

    An analysis of the maximum height of woody plant species across the globe reveals that an intermediate size is remarkably rare. We speculate that this may be due to intrinsic suboptimality or to ecosystem bistability with open landscapes favouring shrubs, and closed canopies propelling trees to excessive tallness. PMID:24951396

  10. Shrub control by browsing: Targeting adult plants

    NASA Astrophysics Data System (ADS)

    da Silveira Pontes, Laíse; Magda, Danièle; Gleizes, Benoît; Agreil, Cyril

    2016-01-01

    Reconciling the well known benefits of shrubs for forage with environmental goals, whilst preventing their dominance, is a major challenge in rangeland management. Browsing may be an economical solution for shrubby rangelands as herbivore browsing has been shown to control juvenile shrub growth. Less convincing results have been obtained for adult plants, and long-term experiments are required to investigate the cumulative effects on adult plants. We therefore assessed the impact of different levels of browsing intensity on key demographic parameters for a major dominant shrub species (broom, Cytisus scoparius), focusing on adult plants. We assigned individual broom plants to one of three age classes: 3-5 years (young adults); 5-7 years (adults); and 7-9 years (mature adults). These plants were then left untouched or had 50% or 90% of their total edible stem biomass removed in simulated low-intensity and high-intensity browsing treatments, respectively. Morphological, survival and fecundity data were collected over a period of four years. Browsing affected the morphology of individual plants, promoting changes in subsequent regrowth, and decreasing seed production. The heavily browsed plants were 17% shorter, 32% narrower, and their twigs were 28% shorter. Light browsing seemed to control the growth of young adult plants more effectively than that of older plants. Reproductive output was considerably lower than for control plants after light browsing, and almost 100% lower after heavy browsing. High-intensity browsing had a major effect on survival causing high levels of plant mortality. We conclude that suitable browsing practices could be used to modify adult shrub demography in the management of shrub dominance and forage value.

  11. Soil erosion rates in rangelands of northeastern Patagonia: A dendrogeomorphological analysis using exposed shrub roots

    NASA Astrophysics Data System (ADS)

    Chartier, Marcelo Pablo; Rostagno, César Mario; Roig, Fidel Alejandro

    2009-05-01

    Soil erosion is an important process of land degradation in many rangelands and a significant driver of desertification in the world's drylands. Dendrogeomorphology is an alternative to traditional methods for determining soil erosion rate. Specifically, the vertical distance between the upper portion of exposed roots and the actual soil surface can be used as a bioindicator of erosion since plant establishment. In this study, we determined (i) the soil erosion rate from exposed roots of the dwarf shrub Margyricarpus pinnatus [Lam.] Kuntze in two ecological sites in the northeastern rangelands of Patagonia and (ii) the relationship between shrub age and upper root diameter. We selected two ecological sites, a pediment-like plateau and a flank pediment, where the dominant soils were Xeric Haplocalcids and Xeric Calciargids, respectively. The soil erosion rates in the pediment-like plateau and in the flank pediment were 2.4 and 3.1 mm yr - 1 , respectively. Data clearly indicate a high rate of soil erosion during the mean 8-year life span of the dwarf shrubs in degraded patches, which represent ~ 10% of surface cover in the study area. Simple linear regression analysis yielded a highly significant predictive model for age estimation of M. pinnatus plants using the upper root diameter as a predictor variable. The measurement of ground lowering against datable exposed roots represents a simple method for the determination of soil erosion rates. In combination with other soil surface features, it was used to infer the episodic nature of soil erosion. This approach could be particularly useful for monitoring the effects of land management practices on recent soil erosion and for the establishment of records in regions where historical data regarding this process are scarce or absent.

  12. Tolerance of an Expanding Subarctic Shrub, Betula glandulosa, to Simulated Caribou Browsing

    PubMed Central

    Champagne, Emilie; Tremblay, Jean-Pierre; Côté, Steeve D.

    2012-01-01

    Densification of the shrub layer has been reported in many subarctic regions, raising questions about the implication for large herbivores and their resources. Shrubs can tolerate browsing and their level of tolerance could be affected by browsing and soils productivity, eventually modifying resource availability for the caribou. Our objective was to assess the compensatory growth potential of a subarctic shrub, Betula glandulosa Michx., in relation with caribou browsing and nutriment availability for the plants. We used a simulated browsing (0, 25 and 75% of available shoots) and nitrogen-fertilisation (0 and 10 g m−2) experiment to test two main hypotheses linking tolerance to resource availability, the Compensatory Continuum Hypothesis and the Growth Rate Hypothesis as well as the predictions from the Limiting Resource Model. We seek to explicitly integrate the relative browsing pressure in our predictions since the amount of tissues removed could affect the capacity of long-lived plants to compensate. Birches fully compensated for moderate browsing with an overall leaf biomass similar to unbrowsed birches but undercompensated under heavy browsing pressure. The main mechanism explaining compensation appears to be the conversion of short shoots into long shoots. The leaf area increased under heavy browsing pressure but only led to undercompensation. Fertilisation for two consecutive years did not influence the response of birch, thus we conclude that our results support the LRM hypothesis of equal tolerance under both high and low nitrogen availability. Our results highlight that the potential for compensatory growth in dwarf birch is surpassed under heavy browsing pressure independently of the fertilisation regime. In the context of the worldwide decline in caribou herds, the reduction in browsing pressure could act synergistically with global climate change to promote the current shrub expansion reported in subarctic regions. PMID:23272191

  13. Chernobyl fallout on Alpine glaciers

    SciTech Connect

    Ambach, W.; Rehwald, W.; Blumthaler, M.; Eisner, H.; Brunner, P.

    1989-01-01

    Measurements of the gross beta activity of snow samples from four Alpine glaciers contaminated by radioactive fallout from the Chernobyl nuclear accident and a gamma-spectrum analysis of selected samples are reported. The results are discussed with respect to possible risks to the population from using meltwater from these glaciers as drinking water.

  14. Alpine Skiing in the Classroom

    ERIC Educational Resources Information Center

    Mendez-Gimenez, Antonio; Fernandez-Rio, Javier

    2012-01-01

    Many students settle indoors in the winter. However, this does not mean that winter should be a period of time with no physical activity. Several snow activities could be practiced during those months, such as ice-skating, ice-hockey, snowshoeing, cross-country skiing, alpine skiing, or snowboarding. In order to counteract the tendency for…

  15. Contrasting water use pattern of introduced and native plants in an alpine desert ecosystem, Northeast Qinghai-Tibet Plateau, China.

    PubMed

    Wu, Huawu; Li, Xiao-Yan; Jiang, Zhiyun; Chen, Huiying; Zhang, Cicheng; Xiao, Xiong

    2016-01-15

    Plant water use patterns reflect the complex interactions between different functional types and environmental conditions in water-limited ecosystems. However, the mechanisms underlying the water use patterns of plants in the alpine desert of the Qinghai-Tibet Plateau remain poorly understood. This study investigated seasonal variations in the water sources of herbs (Carex moorcroftii, Astragalus adsurgens) and shrubs (Artemisia oxycephala, Hippophae rhamnoides) using stable oxygen-18 isotope methods. The results indicated that the native herbs (C. moorcroftii, A. adsurgens) and one of the shrubs (A. oxycephala) mainly relied on water from the shallow layer (0-30 cm) throughout the growing season, while the introduced shrub (H. rhamnoides) showed plasticity in switching between water from shallow and deep soil layers depending on soil water availability. All studied plants primarily depended on water from shallow soil layers early in the season. The differences of water use patterns between the introduced and native plants are closely linked with the range of active root zones when competing for water. Our findings will facilitate the mechanistic understanding of plant-soil-water relations in alpine desert ecosystems and provide information for screening introduced species for sand fixation. PMID:26519579

  16. Meter scale variation in shrub dominance and soil moisture structure Arctic arthropod communities

    PubMed Central

    Hansen, Oskar Liset Pryds; Bowden, Joseph J.; Treier, Urs A.; Normand, Signe; Høye, Toke

    2016-01-01

    The Arctic is warming at twice the rate of the rest of the world. This impacts Arctic species both directly, through increased temperatures, and indirectly, through structural changes in their habitats. Species are expected to exhibit idiosyncratic responses to structural change, which calls for detailed investigations at the species and community level. Here, we investigate how arthropod assemblages of spiders and beetles respond to variation in habitat structure at small spatial scales. We sampled transitions in shrub dominance and soil moisture between three different habitats (fen, dwarf shrub heath, and tall shrub tundra) at three different sites along a fjord gradient in southwest Greenland, using yellow pitfall cups. We identified 2,547 individuals belonging to 47 species. We used species richness estimation, indicator species analysis and latent variable modeling to examine differences in arthropod community structure in response to habitat variation at local (within site) and regional scales (between sites). We estimated species responses to the environment by fitting species-specific generalized linear models with environmental covariates. Species assemblages were segregated at the habitat and site level. Each habitat hosted significant indicator species, and species richness and diversity were significantly lower in fen habitats. Assemblage patterns were significantly linked to changes in soil moisture and vegetation height, as well as geographic location. We show that meter-scale variation among habitats affects arthropod community structure, supporting the notion that the Arctic tundra is a heterogeneous environment. To gain sufficient insight into temporal biodiversity change, we require studies of species distributions detailing species habitat preferences. PMID:27478709

  17. Meter scale variation in shrub dominance and soil moisture structure Arctic arthropod communities.

    PubMed

    Hansen, Rikke Reisner; Hansen, Oskar Liset Pryds; Bowden, Joseph J; Treier, Urs A; Normand, Signe; Høye, Toke

    2016-01-01

    The Arctic is warming at twice the rate of the rest of the world. This impacts Arctic species both directly, through increased temperatures, and indirectly, through structural changes in their habitats. Species are expected to exhibit idiosyncratic responses to structural change, which calls for detailed investigations at the species and community level. Here, we investigate how arthropod assemblages of spiders and beetles respond to variation in habitat structure at small spatial scales. We sampled transitions in shrub dominance and soil moisture between three different habitats (fen, dwarf shrub heath, and tall shrub tundra) at three different sites along a fjord gradient in southwest Greenland, using yellow pitfall cups. We identified 2,547 individuals belonging to 47 species. We used species richness estimation, indicator species analysis and latent variable modeling to examine differences in arthropod community structure in response to habitat variation at local (within site) and regional scales (between sites). We estimated species responses to the environment by fitting species-specific generalized linear models with environmental covariates. Species assemblages were segregated at the habitat and site level. Each habitat hosted significant indicator species, and species richness and diversity were significantly lower in fen habitats. Assemblage patterns were significantly linked to changes in soil moisture and vegetation height, as well as geographic location. We show that meter-scale variation among habitats affects arthropod community structure, supporting the notion that the Arctic tundra is a heterogeneous environment. To gain sufficient insight into temporal biodiversity change, we require studies of species distributions detailing species habitat preferences. PMID:27478709

  18. Shrubs tracing sea surface temperature— Calluna vulgaris on the Faroe Islands

    NASA Astrophysics Data System (ADS)

    Beil, Ilka; Buras, Allan; Hallinger, Martin; Smiljanić, Marko; Wilmking, Martin

    2015-11-01

    The climate of Central and Northern Europe is highly influenced by the North Atlantic Ocean due to heat transfer from lower latitudes. Detailed knowledge about spatio-temporal variability of sea surface temperature (SST) in that region is thus of high interest for climate and environmental research. Because of the close relations between ocean and coastal climate and the climate sensitivity of plant growth, annual rings of woody plants in coastal regions might be used as a proxy for SST. We show here for the first time the proxy potential of the common and widespread evergreen dwarf shrub Calluna vulgaris (heather), using the Faroe Islands as our case study. Despite its small and irregular ring structure, the species seems suitable for dendroecological investigations. Ring width showed high and significant correlations with summer and winter air temperatures and SST. The C. vulgaris chronology from the Faroe Islands, placed directly within the North Atlantic Current, clearly reflects variations in summer SSTs over an area between Iceland and Scotland. Utilising shrubs like C. vulgaris as easy accessible and annually resolved proxies offers an interesting possibility for reconstruction of the coupled climate-ocean system at high latitudes.

  19. Shrubs tracing sea surface temperature--Calluna vulgaris on the Faroe Islands.

    PubMed

    Beil, Ilka; Buras, Allan; Hallinger, Martin; Smiljanić, Marko; Wilmking, Martin

    2015-11-01

    The climate of Central and Northern Europe is highly influenced by the North Atlantic Ocean due to heat transfer from lower latitudes. Detailed knowledge about spatio-temporal variability of sea surface temperature (SST) in that region is thus of high interest for climate and environmental research. Because of the close relations between ocean and coastal climate and the climate sensitivity of plant growth, annual rings of woody plants in coastal regions might be used as a proxy for SST. We show here for the first time the proxy potential of the common and widespread evergreen dwarf shrub Calluna vulgaris (heather), using the Faroe Islands as our case study. Despite its small and irregular ring structure, the species seems suitable for dendroecological investigations. Ring width showed high and significant correlations with summer and winter air temperatures and SST. The C. vulgaris chronology from the Faroe Islands, placed directly within the North Atlantic Current, clearly reflects variations in summer SSTs over an area between Iceland and Scotland. Utilising shrubs like C. vulgaris as easy accessible and annually resolved proxies offers an interesting possibility for reconstruction of the coupled climate-ocean system at high latitudes. PMID:25620645

  20. Consequences for selected high-elevation butterflies and moths from the spread of Pinus mugo into the alpine zone in the High Sudetes Mountains.

    PubMed

    Bílá, Karolína; Šipoš, Jan; Kindlmann, Pavel; Kuras, Tomáš

    2016-01-01

    Due to changes in the global climate, isolated alpine sites have become one of the most vulnerable habitats worldwide. The indigenous fauna in these habitats is threatened by an invasive species, dwarf pine (Pinus mugo), which is highly competitive and could be important in determining the composition of the invertebrate community. In this study, the association of species richness and abundance of butterflies with the extent of Pinus mugo cover at individual alpine sites was determined. Butterflies at alpine sites in the High Sudetes Mountains (Mts.) were sampled using Moericke yellow water traps. The results of a Canonical Correspondence Analysis (CCA) indicated that at a local scale the area of alpine habitats is the main limiting factor for native species of alpine butterflies. Butterfly assemblages are associated with distance to the tree-line with the optimum situated in the lower forest zone. In addition the CCA revealed that biotic factors (i.e. Pinus mugo and alpine tundra vegetation) accounted for a significant amount of the variability in species data. Regionally, the CCA identified that the species composition of butterflies and moths is associated with presence and origin of Pinus mugo. Our study provides evidence that the structure of the Lepidopteran fauna that formed during the postglacial period and also the present composition of species assemblages is associated with the presence of Pinus mugo. With global warming, Pinus mugo has the potential to spread further into alpine areas and negatively affect the local species communities. PMID:27330857

  1. Consequences for selected high-elevation butterflies and moths from the spread of Pinus mugo into the alpine zone in the High Sudetes Mountains

    PubMed Central

    Šipoš, Jan; Kindlmann, Pavel; Kuras, Tomáš

    2016-01-01

    Due to changes in the global climate, isolated alpine sites have become one of the most vulnerable habitats worldwide. The indigenous fauna in these habitats is threatened by an invasive species, dwarf pine (Pinus mugo), which is highly competitive and could be important in determining the composition of the invertebrate community. In this study, the association of species richness and abundance of butterflies with the extent of Pinus mugo cover at individual alpine sites was determined. Butterflies at alpine sites in the High Sudetes Mountains (Mts.) were sampled using Moericke yellow water traps. The results of a Canonical Correspondence Analysis (CCA) indicated that at a local scale the area of alpine habitats is the main limiting factor for native species of alpine butterflies. Butterfly assemblages are associated with distance to the tree-line with the optimum situated in the lower forest zone. In addition the CCA revealed that biotic factors (i.e. Pinus mugo and alpine tundra vegetation) accounted for a significant amount of the variability in species data. Regionally, the CCA identified that the species composition of butterflies and moths is associated with presence and origin of Pinus mugo. Our study provides evidence that the structure of the Lepidopteran fauna that formed during the postglacial period and also the present composition of species assemblages is associated with the presence of Pinus mugo. With global warming, Pinus mugo has the potential to spread further into alpine areas and negatively affect the local species communities. PMID:27330857

  2. WISE and Brown Dwarfs

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, J. Davy; WISE Team

    2009-05-01

    The search for the nearest and coolest brown dwarfs will use WISE's two short-wavelength channels (W1 and W2), which are optimized for brown dwarf detection. W1 samples the methane fundamental absorption band at 3.3 microns, and W2 measures the relatively opacity-free portion of the brown dwarf atmosphere near 4.7 microns. Cool brown dwarfs will thus have very red [W1]-[W2] colors, maximizing our chances of identifying them. Extrapolating preferred mass functions to very low masses and assuming that the star formation rate has been constant over the last 10 Gyr, we can predict the number of brown dwarfs WISE is expected to image. At spectral types later than T7 (Teff > 850K), WISE is expected to find 500 brown dwarfs, which makes WISE uniquely suited among future surveys to measure the low-mass limit of star formation for the first time. This sample will also show whether a new spectral class beyond T, dubbed "Y", is needed at the lowest temperatures. Although the primary six-month WISE mission will cover the entire sky once, WISE should have sufficient cryogen to perform a second, complete pass of the sky. In this case, the identification of nearby brown dwarfs need not rely solely on color selection. Kinematics (proper motion) and geometry (parallax) can also be used to distinguish our closest brown dwarf neighbors, one of which may lie less distant than Proxima Centauri or even fall within our own Oort Cloud.

  3. Astrophysics: Illuminating brown dwarfs

    NASA Astrophysics Data System (ADS)

    Showman, Adam P.

    2016-05-01

    Objects known as brown dwarfs are midway between stars and planets in mass. Observations of a hot brown dwarf irradiated by a nearby star will help to fill a gap in our knowledge of the atmospheres of fluid planetary objects. See Letter p.366

  4. Blue compact dwarfs - Extreme dwarf irregular galaxies

    NASA Technical Reports Server (NTRS)

    Thuan, Trinh X.

    1987-01-01

    Observational data on the most extreme members of the irregular dwarf (dI) galaxy class, the blue compact dwarfs (BCDs), are characterized, reviewing the results of recent investigations. The properties of the young stellar population, the ionized gas, the older star population, and the gas and dust of BCDs are contrasted with those of other dIs; BCD morphology is illustrated with sample images; and the value of BCDs (as nearby 'young' chemically unevolved galaxies) for studies of galaxy formation, galactic evolution, and starburst triggering mechanisms is indicated.

  5. Does browsing reduce shrub survival and vigor following summer fires?

    NASA Astrophysics Data System (ADS)

    Fulbright, Timothy E.; Dacy, Emily C.; Drawe, D. Lynn

    2011-01-01

    Periodic fire is widely hypothesized to limit woody plant encroachment in semiarid grasslands. In southern Texas, however, most of the woody plants that have invaded grasslands during the past two centuries are resistant to fire. We hypothesized that browsing by Odocoileus virginianus increases mortality of palatable shrubs and reduces vigor of shrubs following fire. We randomly selected ten pairs of each of three shrub species -Condalia hookeri, Acacia farnesiana, and Celtis ehrenbergiana - in each of three locations before prescribed burns during summer 2001. Following burns, we used a wire fence to protect one shrub of each pair from browsing. We estimated intensity of O. virginianus browsing and number and height of sprouts 4, 12, 20, 30, 38, and 47 weeks post-fire. We determined shrub height, survival, and biomass one year post-fire. Averaged across species, browsing intensity on unfenced shrubs was greater (LS Means, P < 0.05) than on fenced shrubs on all sampling dates except four and 30 weeks post-fire. Mortality of unfenced (11 ± 9%) (mean ± SE) and fenced (12 ± 7%, n = 9) shrubs was similar (P = 0.674) one year post-fire, averaged across shrub species. Number of sprouts, sprout height, total plant height, and biomass of protected and browsed plants were similar (P > 0.05) one year post-burn. Browsing by O. virginianus at the intensity in our study does not increase mortality or reduce vigor of C. hookeri, A. farnesiana, and Condalia ehrenbergiana producing new growth following destruction of aboveground tissues by a single fire compared to shrubs that are not browsed following fire.

  6. The changing role of shrubs in rangeland-based livestock production systems: Can shrubs increase our forage supply?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Projected global increases in ruminant numbers and loss of native grasslands will present a number of challenges for livestock agriculture. Escalated demand for livestock products may stimulate interest in using shrubs on western rangelands. A paradigm shift is needed to change the role of shrubs in...

  7. Root reinforcement and its implications in shallow landsliding susceptibility on a small alpine catchment

    NASA Astrophysics Data System (ADS)

    Morandi, M. C.; Farabegoli, E.; Onorevoli, G.

    2012-04-01

    Roots shear resistance offers a considerable contribution to hill-slope stability on vegetated terrains. Through the pseudo-cohesion of shrubs, trees and turf's roots, the geomechanical properties of soils can be drastically increased, exerting a positive influence on the hillslope stability. We analysed the shallow landsliding susceptibility of a small alpine catchment (Duron valley, Central Dolomites, Italy) that we consider representative of a wide altitude belt of the Dolomites (1800 - 2400 m a.s.l). The catchment is mostly mantled by grass (Nardetum strictae s.l.), with clustered shrubs (Rhododendron hirsutum and Juniperus nana), and trees (Pinus cembra, Larix decidua and Picea abies). The soil depth, investigated with direct and indirect methods, ranges from 0 to 180 cm, with its peak at the hollow axes. Locally, the bedrock, made of Triassic volcanic rocks, is deeply incised by the Holocene drainage network. Intensive grazing of cows and horses pervades the catchment area and cattle-trails occupy ca 20% of the grass cover. We used laboratory and field tests to characterize the geotechnical properties of these alpine soils; moreover we designed and tested an experimental device that measures, in situ, the shear strengths of the grass mantle. In the study area we mapped 18 shallow landslides, mostly related to road cuts and periodically reactivated as retrogressive landslides. The triggering mechanisms of these shallow landslides were qualitatively analysed at large scale and modelled at smaller scale. We used SHALSTAB to model the shallow landsliding susceptibility of the catchment at the basin scale and SLIDE (RocScience) to compute the Safety Factor at the versant scale. Qualitative management solutions are provided, in order to reduce the shallow landsliding susceptibility risk in this alpine context.

  8. Shrub Expansion Effects on Soil Carbon Dynamics in the Arctic

    NASA Astrophysics Data System (ADS)

    Holden, S. R.; Mortero, G.; Welker, J. M.; Czimczik, C. I.

    2015-12-01

    Shrubs are increasing in abundance in the Arctic in response to climate warming, but the consequences of shrub expansion for the vast soil carbon (C) stocks in the Arctic are poorly understood. Increases in productivity and associated increases in soil C inputs may augment soil C stocks. Alternatively, labile C exudates from shrub roots may stimulate decomposition of existing soil C and decrease C stocks. We used two complementary approaches to characterize the potential impacts of shrub expansion on soil C dynamics in the Arctic. First, in graminoid and shrub tundra near Toolik Lake, AK we surveyed thaw depth, measured depth profiles of %C, %N, δ13C, and Δ14C, and inventoried soil C stocks to 1 m. We found that the thaw depth was 42% shallower under shrubs compared to graminoid tundra. In addition, mineral soils from shrub tundra had a significantly higher C content than graminoid tundra. Similarly, mineral soils from shrub tundra had lower (depleted) δ13C values compared to graminoid tundra, indicating that this soil has undergone less microbial processing. We also found that C under shrub tundra was on average older, and shrub tundra had significantly higher C stocks to 1 m than graminoid tundra. Second, we conducted a priming experiment with graminoid soil from Toolik Lake, AK. We incubated organic soil, the top 10 cm of mineral soil, and the lower 10 cm of active layer mineral soil with supplemental sucrose at 7°C and 22°C. We found that the addition of labile C did not increase microbial decomposition of existing C in mineral soils. Taken together, our findings suggest that shrub expansion may augment soil C storage in the Arctic because a greater proportion of soil C is frozen in permafrost, soil C under shrubs turns over more slowly, and existing C in mineral soil does not appear to be vulnerable to loss via priming. The observed impacts of shrub expansion on soil C stocks should be incorporated into earth system models that predict the carbon

  9. M dwarfs: Theoretical work

    NASA Technical Reports Server (NTRS)

    Mullan, Dermott J.

    1987-01-01

    Theoretical work on the atmospheres of M dwarfs has progressed along lines parallel to those followed in the study of other classes of stars. Such models have become increasingly sophisticated as improvements in opacities, in the equation of state, and in the treatment of convection were incorporated during the last 15 to 20 years. As a result, spectrophotometric data on M dwarfs can now be fitted rather well by current models. The various attempts at modeling M dwarf photospheres in purely thermal terms are summarized. Some extensions of these models to include the effects of microturbulence and magnetic inhomogeneities are presented.

  10. When White Dwarfs Collide

    NASA Astrophysics Data System (ADS)

    Hawley, Wendy Phyllis

    2012-01-01

    3D models of white dwarf collisions are used to assess the likelihood of double-degenerate mergers as progenitors for Type Ia supernovae (henceforth SNIa) and to identify observational signatures of double-degenerate collisions. Observations of individual SNIa, SNIa rates in different galaxy types, and double white dwarf binary systems suggest that mergers or collisions between two white dwarfs play a role in the overall SNIa population. Given the possibility of two progenitor systems (single-degenerate and double-degenerate), the sample of SNIa used in cosmological calcula- tions needs to be carefully examined. To improve calculations of cosmological parameters, the development of calibrated diagnostics for double-degenerate progenitor SNIa is essential. Head-on white dwarf collision simulations are used to provide an upper limit on the 56Ni production in white dwarf collisions. In chapter II, I explore zero impact parameter collisions of white dwarfs using the Eulerian grid code FLASH. The initial 1D white dwarf profiles are created assuming hydrostatic equilibrium and a uniform composition of 50% 12C and 50% 16O. The masses range from 0.64 to 0.81 solar masses and have an isothermal temperature of 107 K. I map these 1D models onto a 3D grid, where the dimensions of the grid are each eight times the white dwarf radius, and the dwarfs are initially placed four white dwarf radii apart (center to center). To provide insight into a larger range of physical possibilities, I also model non-zero impact parameter white dwarf collisions (Chapter III). Although head-on white dwarf collisions provide an upper limit on 56Ni production, non-zero impact parameter collisions provide insight into a wider range of physical scenarios. The initial conditions (box size, initial separation, composition, and initial temperature) are identical to those used for the head-on collisions (Chapter II) for the same range of masses. For each mass pair- ing, collision simulations are carried

  11. Shrub expansion and climate feedbacks in Arctic tundra

    NASA Astrophysics Data System (ADS)

    Loranty, Michael M.; Goetz, Scott J.

    2012-03-01

    Arctic tundra ecosystems stand to play a substantial role in both the magnitude and rate of global climate warming over the coming decades and centuries. The exact nature of this role will be determined by the combined effects of currently amplified rates of climate warming in the Arctic (Serreze et al 2000) and a series of related positive climate feedbacks that include mobilization of permafrost carbon (Schuur et al 2008), decreases in surface albedo (Chapin et al 2005) and evapotranspiration (ET) mediated increases in atmospheric water vapor (Swann et al 2010). Conceptually, these feedback mechanisms are intuitive and readily comprehensible: warming-induced permafrost thaw will make new soil carbon pools accessible for microbial respiration, and increased vegetation productivity, expansion of shrubs in particular, will lower surface reflectance and increase ET. However, our current understanding of these feedback mechanisms relies largely on limited and local field studies and, as such, the quantitative estimates of feedback effects on regional and global climate require spatial upscaling and uncertainty estimates derived from models. Moreover, the feedback mechanisms interact and their combined net effect on climate is highly variable and not well characterized. A recent study by Bonfils et al (2012) is among the first to explicitly examine how shrub expansion in tundra ecosystems will impact regional climate. Using an Earth system model, Bonfils et al find that an idealized 20% increase in shrub cover north of 60°N latitude will lead to annual temperature increases of 0.66 °C and 1.84 °C, respectively, when the shrubs are 0.5 m and 2 m tall. The modeled temperature increases arise from atmospheric heating as a combined consequence of decreased albedo and increased ET. The primary difference between the two cases is associated with the fact that tall shrubs protrude above the snow, thus reducing albedo year round, whereas short shrubs are completely

  12. Experimental icing affects growth, mortality, and flowering in a high Arctic dwarf shrub.

    PubMed

    Milner, Jos M; Varpe, Øystein; van der Wal, René; Hansen, Brage Bremset

    2016-04-01

    Effects of climate change are predicted to be greatest at high latitudes, with more pronounced warming in winter than summer. Extreme mid-winter warm spells and heavy rain-on-snow events are already increasing in frequency in the Arctic, with implications for snow-pack and ground-ice formation. These may in turn affect key components of Arctic ecosystems. However, the fitness consequences of extreme winter weather events for tundra plants are not well understood, especially in the high Arctic. We simulated an extreme mid-winter rain-on-snow event at a field site in high Arctic Svalbard (78°N) by experimentally encasing tundra vegetation in ice. After the subsequent growing season, we measured the effects of icing on growth and fitness indices in the common tundra plant, Arctic bell-heather (Cassiope tetragona). The suitability of this species for retrospective growth analysis enabled us to compare shoot growth in pre and postmanipulation years in icing treatment and control plants, as well as shoot survival and flowering. Plants from icing treatment plots had higher shoot mortality and lower flowering success than controls. At the individual sample level, heavily flowering plants invested less in shoot growth than nonflowering plants, while shoot growth was positively related to the degree of shoot mortality. Therefore, contrary to expectation, undamaged shoots showed enhanced growth in ice treatment plants. This suggests that following damage, aboveground resources were allocated to the few remaining undamaged meristems. The enhanced shoot growth measured in our icing treatment plants has implications for climate studies based on retrospective analyses of Cassiope. As shoot growth in this species responds positively to summer warming, it also highlights a potentially complex interaction between summer and winter conditions. By documenting strong effects of icing on growth and reproduction of a widespread tundra plant, our study contributes to an understanding of Arctic plant responses to projected changes in winter climatic conditions. PMID:27066227

  13. Long-Term Perspectives of Shrub Expansions and Peat Initiation in Arctic Tundra on the North Slope of Alaska

    NASA Astrophysics Data System (ADS)

    Cleary, K.; Yu, Z.

    2014-12-01

    The ongoing climate warming in the Arctic has caused rapid terrestrial ecosystem changes, including shrub expansion and permafrost thaw. Here we used results from a peat-accumulating permafrost tundra in upper Imnavait Creek on the Arctic foothills of Alaska (68° 36' N, 149° 18' W) to investigate ecological responses to recent climate warming in the context of the last millennium. Six peat soil cores were collected from Sphagnum mosaics along an elevational gradient from 906 m to 950 m on a hillslope covered by Eriophorum-dominated tussock tundra. Macrofossil analysis documents a consistent development sequence among all cores from a mineral soil to a minerotrophic sedge peat and finally to an ombrotrophic Sphagnum peat. The 14C dating results show the ages of peat initiation range from about 900 to 140 cal BP, but do not follow the elevation gradient, suggesting the dominant control of local factors. The Sphagnum onset begins at 1820 AD near the ridge top, and subsequently propagates downslope to the floodplain at 2008 AD. This transition (ombrotrophication) was likely in response to Arctic warming, and subsequent permafrost thaw and active layer thickening, leading to drying initiating at the ridge top and facilitating Sphagnum colonization. Pollen analysis of the master core UIC13-3 at 916 m elevation (basal age 700 cal BP) shows that the vegetation was dominated by sedges (up to 84%) during the cool Little Ice Age until 1800 AD, followed by increases in shrubs first from dwarf birch (Betula nana) (up to 57%) and then willows (Salix spp.) up to 62% in the 1960s. These results indicate that shrub expansion of willows, due to accelerated warming in recent decades, was preceded by birch expansion over the last two centuries. Our new results provide a long-term perspective on ecological transformations in the Arctic, in particular the history of recent shrub expansions and the process of peatland initiation and expansion across Arctic tundra.

  14. Dwarfs in ancient Egypt.

    PubMed

    Kozma, Chahira

    2006-02-15

    Ancient Egypt was one of the most advanced and productive civilizations in antiquity, spanning 3000 years before the "Christian" era. Ancient Egyptians built colossal temples and magnificent tombs to honor their gods and religious leaders. Their hieroglyphic language, system of organization, and recording of events give contemporary researchers insights into their daily activities. Based on the record left by their art, the ancient Egyptians documented the presence of dwarfs in almost every facet of life. Due to the hot dry climate and natural and artificial mummification, Egypt is a major source of information on achondroplasia in the old world. The remains of dwarfs are abundant and include complete and partial skeletons. Dwarfs were employed as personal attendants, animal tenders, jewelers, and entertainers. Several high-ranking dwarfs especially from the Old Kingdom (2700-2190 BCE) achieved important status and had lavish burial places close to the pyramids. Their costly tombs in the royal cemeteries and the inscriptions on their statutes indicate their high-ranking position in Egyptian society and their close relation to the king. Some of them were Seneb, Pereniankh, Khnumhotpe, and Djeder. There were at least two dwarf gods, Ptah and Bes. The god Ptah was associated with regeneration and rejuvenation. The god Bes was a protector of sexuality, childbirth, women, and children. He was a favored deity particularly during the Greco-Roman period. His temple was recently excavated in the Baharia oasis in the middle of Egypt. The burial sites and artistic sources provide glimpses of the positions of dwarfs in daily life in ancient Egypt. Dwarfs were accepted in ancient Egypt; their recorded daily activities suggest assimilation into daily life, and their disorder was not shown as a physical handicap. Wisdom writings and moral teachings in ancient Egypt commanded respect for dwarfs and other individuals with disabilities. PMID:16380966

  15. Plant and soil surface responses to a combination of shrub removal and grazing in a shrub-encroached woodland.

    PubMed

    Daryanto, Stefani; Eldridge, David J

    2010-12-01

    Shrub encroachment into open woodland is a widespread phenomenon in semi-arid woodlands worldwide. Encroachment or woody thickening, is thought to result from overgrazing, changes in fire regimes and increased atmospheric carbon dioxide concentrations. Eighteen years after one-off shrub removal by ploughing we assessed the effects of four different land management systems resulting from two levels each of grazing (grazed, ungrazed) with and without ploughing, on the cover of landscape units, soil surface condition, diversity of understorey plants and density of shrubs. We recorded 2-7 times more patches under conventional conservation (unploughed-ungrazed) than the others treatments, and plant cover and diversity were greater on the two conservation (ungrazed) plots, irrespective of ploughing. Soils under shrubs and log mounds had greater indices of infiltration, stability and nutrients. Shrub density under the active pastoral (ploughed-grazed) treatment was two and a half times greater than that in other treatments, but results were not significant. The effects of different treatments on shrubs were largely species-specific. Overall, our results suggest that ploughing does not provide long-term control of encroaching shrubs. PMID:20696514

  16. Alpine 1/Federal: Executive summary final report

    SciTech Connect

    Witcher, J.C.

    1994-04-01

    This summary report overviews a State of Arizona and US Department of Energy funded drilling project to determine if near-term hot dry rock (HDR) geothermal potential exists in the eastern portion of the White Mountains region of Arizona. A 4,505 feet deep slim-hole exploratory well, Alpine1/Federal, was drilled within the Apache-Sitgreaves National Forest at Alpine Divide near the Alpine Divide camp ground about 5 miles north of Alpine, Arizona in Apache County (Figure 1). A comprehensive technical report, in two parts, details the results of the project. Part 1, Alpin1/Federal, Drilling Report discusses the drilling operations, logging program, permitting and site selection for the hole. Part 2, Temperature Gradients, Geothermal Potential, and Geology, summarizes the temperature gradients, heat flow, geothermal potential, and subsurface geology.

  17. Hydraulic properties of leaves from desert shrubs

    SciTech Connect

    Schulte, P.J. )

    1991-05-01

    Changes in certain tissue hydraulic properties such as elasticity, capacitance, and resistance to water flow were considered as a function of leaf water content. It has been suggested in the literature that variation in such properties may be of significance during changes in leaf hydration. In addition, the author was interested in the potential role of changes in these same tissue properties for maintaining leaf water status during drought. Two shrubs occurring in the Mojave desert, mesquite and live-oak, were studied. Measurements suggest that over the range of leaf water potential from zero to turgor loss, the elastic modulus varies 5-fold, capacitance varies 2-fold, and the resistance to flow between the xylem and storage in the leaf parenchyma tissues 2 to 3-fold. A model for water flow was developed based on these and other tissue properties. This modeling approach is being used as a hypothesis-generating tool for future experimentation. Results of the modeling are discussed in the context of published speculations on the functional role of changes in properties such as elasticity for plants under water stress.

  18. AIS spectra of desert shrub canopies

    NASA Technical Reports Server (NTRS)

    Murray, R.; Isaacson, D. L.; Schrumpf, B. J.; Ripple, W. J.; Lewis, A. J.

    1986-01-01

    Airborne Imaging Spectrometer (AIS) data were collected 30 August 1985 from a desert shrub community in central Oregon. Spectra from artificial targets placed on the test site and from bare soil, big sagebrush (Artemesia tridentata wyomingensis), silver sagebrush (Artemesia cana bolander), and exposed volcanic rocks were studied. Spectral data from grating position 3 (tree mode) were selected from 25 ground positions for analysis by Principal Factor Analysis (PFA). In this grating position, as many as six factors were identified as significant in contributing to spectral structure. Channels 74 through 84 (tree mode) best characterized between-class differences. Other channels were identified as nondiscriminating and as associated with such errors as excessive atmospheric absorption and grating positin changes. The test site was relatively simple with the two species (A. tridentata and A. cana) representing nearly 95% of biomass and with only two mineral backgrounds, a montmorillonitic soil and volcanic rocks. If, as in this study, six factors of spectral structure can be extracted from a single grating position from data acquired over a simple vegetation community, then AIS data must be considered rich in information-gathering potential.

  19. Episodic death across species of desert shrubs.

    PubMed

    Miriti, Maria N; Rodríguez-Buriticá, Susana; Wright, S Joseph; Howe, Henry F

    2007-01-01

    Extreme events shape population and community trajectories. We report episodic mortality across common species of thousands of long-lived perennials individually tagged and monitored for 20 years in the Colorado Desert of California following severe regional drought. Demographic records from 1984 to 2004 show 15 years of virtual stasis in populations of adult shrubs and cacti, punctuated by a 55-100% die-off of six of the seven most common perennial species. In this episode, adults that experienced reduced growth in a lesser drought during 1984-1989 failed to survive the drought of 2002. The significance of this event is potentially profound because population dynamics of long-lived plants can be far more strongly affected by deaths of adults, which in deserts potentially live for centuries, than by seedling births or deaths. Differential mortality and rates of recovery during and after extreme climatic events quite likely determine the species composition of plant and associated animal communities for at least decades. The die-off recorded in this closely monitored community provides a unique window into the mechanics of this process of species decline and replacement. PMID:17489450

  20. Pheno-anomalies of sub-alpine Vaccinium heaths in response to climatic variations

    NASA Astrophysics Data System (ADS)

    Puppi, Giovanna; Monti, Alessandra; Bonafede, Fausto; Vignodelli, Michele; Zanotti, Anna Letizia

    2014-05-01

    A phenological survey on Vaccinium heaths was repeated thirty years after the first observations, in the Northern Apennines (Italy). In line with the sampling method adopted in the earliest phases of the study, the phenological monitoring was undertaken in the same sites, located above the tree line between 1600 and 1800 m asl. The phenology of each plant species was recorded in order to single out the flowering patterns of the plant communities and their variations. In the years with average weather conditions, flowerings begin at the end of May, after the melting of the last spring snow, and finish in September, showing a bimodal pattern. The first blooming peak occurs in mid June and the second in mid July, in coincidence with the annual maximum temperatures. The first peak is due to the dwarf shrubs and to other species typical of the Vaccinium heaths, while the second is due to herbs with a wider ecology. Among the years on study, we found that 1984 and 2012 diverged from the aforementioned pattern, in that flowerings showed strong pheno-anomalies and a lower phenological diversity. In 1984, a marked delay of the blooming start (1 month) and of the first peak (3 weeks) were observed, while the second peak and the flowering end were normal: the delay was due to a very cold and snowy spring in 1984. On the contrary, 2012 was characterized by the disappearance of the second flowering peak and by a dramatic advance of the blooming end: it is worth mentioning that summer 2012 was exceptionally dry, with temperatures above the average. In summary, while the very cold spring 1984 led simply to an initial shift and then to a compaction of the blooming rhythms, the xero-thermal stress of the summer 2012 caused a deep variation of the symphenological pattern and a fail of sexual reproduction in several late flowering species. Given that xero-thermal stress occurred often in the last decades, some sensible species, flowering in mid summer, could have undergone a

  1. Experimental soil warming leads to sustained losses of old C from alpine treeline ecosystems

    NASA Astrophysics Data System (ADS)

    Dawes, Melissa; Hagedorn, Frank; Rixen, Christian; Streit, Kathrin

    2013-04-01

    The impact of climatic warming on the soil C balance is uncertain because rising temperature increases both C inputs into soils, but also respiratory C losses. 'Cold' ecosystems such as treeline ecotones will respond particularly sensitive to climatic changes because many processes are limited by temperature and soils store particular large amounts of labile soil organic matter. In our study, we investigate responses of carbon fluxes to 6 years of experimental soil warming by 4°C with heating cables on the soil surface. The warming study was conducted in a 9-year CO2 enrichment experiment, in which the added CO2 carried another ˜13C signature than normal air, which allows the tracing of new carbon through the plant and soil system. This provides new insight into carbon cycling at the treeline and it shows which C flux respond most sensitive to climatic changes. Results showed that soil warming increased soil CO2 effluxes instantaneously and persistent for six vegetation periods (+30-50%; +80 to 120 g C m y-1). Annual C uptake of new shoots was not significantly affected by elevated soil temperatures, with a 10 to 20% increase for larch, pine, and dwarf shrubs, respectively, resulting in an overall increase in net C uptake by plants of 20 to 40 g C m-2y-1. The temperature dependency of soil respiration did not change through six years of experimental soil warming, suggesting little impact of warming-induced lower soil moisture (-15% relative decrease) or a depletion in labile soil C. The fraction of recent plant-derived C in soil respired CO2 from warmed soils was smaller than that from control soils (30 vs. 50% of total C respired), which implies that the warming-induced increase in soil CO2 efflux resulted mainly from mineralization of older SOM rather than from stimulated root respiration. Analysis of phospholipid fatty acids indicated an unchanged microbial community on the group level, but significantly smaller fractions of new plant C in the warmed soils. In

  2. Can shrub cover increase predation risk for a desert rodent?

    USGS Publications Warehouse

    Schooley, R.L.; Sharpe, Peter B.

    1996-01-01

    Previous research indicates that predation risk may influence activity patterns, habitat partitioning, and community structure of nocturnal desert rodents. Shrub microhabitat is typically considered safer than open microhabitat for these small mammals. We investigated predation risk for Townsend's ground squirrels (Spermophilus townsendii), which are diurnal desert rodents that detect predators visually and use burrows for refuge. Our results suggested that shrub cover may increase risk for these squirrels by decreasing their ability to escape from predators. Our field experiment indicated that running speeds of juvenile squirrels were lower in shrub (Ceratoides lanata) habitat than in open areas. Shrub cover was also associated with shorter predator-detection distances (mammalian and avian) and fewer refuges (burrow entrances per hectare) than in open areas in one year but not in another. Our study demonstrated that the visual and locomotive obstruction of vegetative cover may increase predation risk for diurnal desert rodents and that elements of habitat-dependent risk may be temporally dynamic.

  3. IMPACTS ON FLOODPLAINS BY AN INVASIVE SHRUB, BUDDLEJA DAVIDII

    EPA Science Inventory

    Despite its popularity, the ornamental, Buddleja davidii, a woody shrub of Asian origin, is considered problematic because of its ability to rapidly colonize and dominate floodplain and riparian ecosystems. Dominance during early succession may influence community dynamics and ec...

  4. Willow Shrub Expansion Following Tundra Fires in Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Racine, C.

    2010-12-01

    Climate warming in the Arctic is predicted to result in the expansion of woody shrubs and increased frequency and size of tundra fires. How will fire influence this shrub expansion? Over a period of 32 years, following a 1977 tundra fire in the central Seward Peninsula, we sampled seven times the post-fire vegetation at eight permanently marked sites on a long (2 Km) hillslope (Nimrod Hill). We had previously sampled vegetation here in 1973 prior to the fire. By 2001, 24 years post-fire conspicuous willow shrubs (mostly Salix pulchra) had increased in numbers, size and cover over the entire slope in moist tussock-shrub tundra, well-drained heath, and wet meadow. Prior to fire, willow on this slope was largely restricted to small drainages or watertracks. Willows here have originated from both seed and vegetative resprouting - the latter mostly in moist tussock-shrub tundra from willows resprouting within one to three years post-fire. With fire-induced removal of vascular plant competition and Spagnum moss cover and litter in tussock-shrub tundra, both seedling and resprouting willows have grown rapidly to overtop tussocks by 30-40 cm. Similar rapid post-fire resprouting of willows has been observed in tussock-shrub tundra after the 2007 Anaktuvuk River tundra fire and after the 1977 tundra fires in the Noatak River basin. On Nimrod Hill the most striking willow expansion has occurred on the severely burned and well-drained backslope where willow establishment from seed 5-10 years after fire has resulted in up to 40% cover of rapidly growing willows of both upright and spreading growth form. At several sites along the slope there is evidence of continuing willow expansion from seedlings 24 to 32 years post-fire, when we might expect the effects of fire on seedbeds would have ceased. We conclude that tundra fire may promote shrub expansion in the Arctic.

  5. Linking Hydrology, Shrub Habitat, and Novel Wildlife in the Arctic

    NASA Astrophysics Data System (ADS)

    Tape, K. D.; O'Donnell, J. A.; Christie, K.

    2014-12-01

    Warming during the 20th century changed the Arctic landscape, including aspects of vegetation, permafrost, and glaciers, but effects on wildlife have been difficult to detect. We explored linkages between components of the riparian ecosystem in Arctic Alaska since the 1970s, including streamflow timing, temperature, floodplain shrub habitat, and shrub herbivore distributions. Streamflow records showed that the peak spring snowmelt discharge has occurred 3.4 days per decade earlier, and consistent fall temperatures and snow arrival dates over the same period suggest that earlier peak discharge has prolonged the ensuing period of reduced flow in the floodplain. We used empirical correlations between cumulative summer warmth and riparian shrub height to estimate that the longer and warmer growing seasons since the 1970s have stimulated a 63% increase in the height of riparian shrubs. Earlier spring discharge and the estimated increase in riparian shrub height are consistent with the observed riparian shrub expansion in the region. Our measurements showed that snowshoe hares (Lepus americanus) require a mean riparian shrub height of at least 1.05 to 1.35 m, a threshold which our hindcasting indicates was met between 1977 and 2002. This generally coincides with observational evidence we present suggesting that snowshoe hares became established in 1977 or 1978. Similar relationships are shown for moose, which colonized the region in the 1940s. We also show that Canada lynx (Lynx canadensis) inhabited the region in 1998, probably due in part to increasing availability of snowshoe hares. The novel appearance in the Arctic during the 20th century of terrestrial herbivores such as snowshoe hares and moose in response increased shrub habitat is a contrasting terrestrial counterpart to the decline in marine mammals reliant on decreasing sea ice.

  6. Fencing enhances shrub survival and growth for Mojave desert revegetation

    SciTech Connect

    Hunter, R.B.; Romney, E.M.; Wallace, A.

    1980-01-01

    Fourteen species of native shrubs were transplanted to bare areas of the northern Mojave Desert in 1972 and 1973. By 1978 plants surrounded by small fences were larger (0.26 vs 0.11 m/sup 3/ overall average for several species) and survived better (42 percent versus 23 percent) than unfenced plants. These effects are primarily due to reduced grazing of shoots. Loss of shrubs to pocket gophers or other burrowing rodents was not prevented by fencing.

  7. Enhanced precipitation variability decreases grass- and increases shrub-productivity

    PubMed Central

    Gherardi, Laureano A.; Sala, Osvaldo E.

    2015-01-01

    Although projections of precipitation change indicate increases in variability, most studies of impacts of climate change on ecosystems focused on effects of changes in amount of precipitation, overlooking precipitation variability effects, especially at the interannual scale. Here, we present results from a 6-y field experiment, where we applied sequences of wet and dry years, increasing interannual precipitation coefficient of variation while maintaining a precipitation amount constant. Increased precipitation variability significantly reduced ecosystem primary production. Dominant plant-functional types showed opposite responses: perennial-grass productivity decreased by 81%, whereas shrub productivity increased by 67%. This pattern was explained by different nonlinear responses to precipitation. Grass productivity presented a saturating response to precipitation where dry years had a larger negative effect than the positive effects of wet years. In contrast, shrubs showed an increasing response to precipitation that resulted in an increase in average productivity with increasing precipitation variability. In addition, the effects of precipitation variation increased through time. We argue that the differential responses of grasses and shrubs to precipitation variability and the amplification of this phenomenon through time result from contrasting root distributions of grasses and shrubs and competitive interactions among plant types, confirmed by structural equation analysis. Under drought conditions, grasses reduce their abundance and their ability to absorb water that then is transferred to deep soil layers that are exclusively explored by shrubs. Our work addresses an understudied dimension of climate change that might lead to widespread shrub encroachment reducing the provisioning of ecosystem services to society. PMID:26417095

  8. Enhanced precipitation variability decreases grass- and increases shrub-productivity.

    PubMed

    Gherardi, Laureano A; Sala, Osvaldo E

    2015-10-13

    Although projections of precipitation change indicate increases in variability, most studies of impacts of climate change on ecosystems focused on effects of changes in amount of precipitation, overlooking precipitation variability effects, especially at the interannual scale. Here, we present results from a 6-y field experiment, where we applied sequences of wet and dry years, increasing interannual precipitation coefficient of variation while maintaining a precipitation amount constant. Increased precipitation variability significantly reduced ecosystem primary production. Dominant plant-functional types showed opposite responses: perennial-grass productivity decreased by 81%, whereas shrub productivity increased by 67%. This pattern was explained by different nonlinear responses to precipitation. Grass productivity presented a saturating response to precipitation where dry years had a larger negative effect than the positive effects of wet years. In contrast, shrubs showed an increasing response to precipitation that resulted in an increase in average productivity with increasing precipitation variability. In addition, the effects of precipitation variation increased through time. We argue that the differential responses of grasses and shrubs to precipitation variability and the amplification of this phenomenon through time result from contrasting root distributions of grasses and shrubs and competitive interactions among plant types, confirmed by structural equation analysis. Under drought conditions, grasses reduce their abundance and their ability to absorb water that then is transferred to deep soil layers that are exclusively explored by shrubs. Our work addresses an understudied dimension of climate change that might lead to widespread shrub encroachment reducing the provisioning of ecosystem services to society. PMID:26417095

  9. Seed dormancy in alpine species

    PubMed Central

    Schwienbacher, Erich; Navarro-Cano, Jose Antonio; Neuner, Gilbert; Erschbamer, Brigitta

    2011-01-01

    In alpine species the classification of the various mechanisms underlying seed dormancy has been rather questionable and controversial. Thus, we investigated 28 alpine species to evaluate the prevailing types of dormancy. Embryo type and water impermeability of seed coats gave an indication of the potential seed dormancy class. To ascertain the actual dormancy class and level, we performed germination experiments comparing the behavior of seeds without storage, after cold-dry storage, after cold-wet storage, and scarification. We also tested the light requirement for germination in some species. Germination behavior was characterized using the final germination percentage and the mean germination time. Considering the effects of the pretreatments, a refined classification of the prevailing dormancy types was constructed based on the results of our pretreatments. Only two out of the 28 species that we evaluated had predominantly non-dormant seeds. Physiological dormancy was prevalent in 20 species, with deep physiological dormancy being the most abundant, followed by non-deep and intermediate physiological dormancy. Seeds of four species with underdeveloped embryos were assigned to the morphophysiologial dormancy class. An impermeable seed coat was identified in two species, with no additional physiological germination block. We defined these species as having physical dormancy. Light promoted the germination of seeds without storage in all but one species with physiological dormancy. In species with physical dormancy, light responses were of minor importance. We discuss our new classification in the context of former germination studies and draw implications for the timing of germination in the field. PMID:24415831

  10. Asteroseismology of White Dwarf Stars

    NASA Technical Reports Server (NTRS)

    Hansen, Carl J.

    1997-01-01

    The primary purpose of this investigation has been to study various aspects of multimode pulsations in variable white dwarfs. In particular, nonlinear interactions among pulsation modes in white dwarfs (and, to some extent, in other variable stars), analysis of recent observations where such interactions are important, and preliminary work on the effects of crystallization in cool white dwarfs are reported.

  11. The Geomorphic Effectiveness of a Woody Shrub

    NASA Astrophysics Data System (ADS)

    Manners, R.; Schmidt, J. C.; Wheaton, J. M.

    2010-12-01

    Vegetation plays a fundamental role in controlling channel form and influencing channel processes. Experimental work has shown that stem density, stem spacing, relative submergence, and stem flexibility are key indicators of the effectiveness of vegetation in altering the flow field. These parameters are likely to be species dependent and change over time as vegetation grows, dies back and is replaced by late successional species. Thus, the role of vegetation is highly variable in both space and time. Capturing this variability is essential in understanding how vegetation controls channel processes. Here, we investigate the spatial and temporal variability of stand characteristics (i.e. stem density and spacing) for the non-native riparian shrub, Tamarix spp. In the Colorado River basin, Tamarix dominates large portions of the riparian corridor. Tamarix is capable of establishing rapidly and in dense stands and as such been implicated in enhancing channel changes observed during the last century. However, questions relating to Tamarix’s role relative to other pervasive environmental changes necessitate a robust way to capture the effectiveness of Tamarix in altering the flow field and inducing deposition. We focus on the stand structure of aging Tamarix stands in order to relate Tamarix life-history to hydrodynamic roughness. High resolution terrestrial laser scans (TLS) were collected for Tamarix patches (10-15 m2) on different geomorphic surfaces (i.e. gravel bar, disconnected floodplain) and ages (5-60 years). Stem frontal area at varying depths was calculated from the scans over the patch and for the patch as a whole. We used Telemac 2D to evaluate how the stem density and spacing influence flow characteristics, such as drag on the stems and Froude number. To do this, the representative stem density and spacing was translated into cylindrical elements on a flat (i.e no topography) mesh. Elevation above the channel influences stand density. For example, a 20

  12. Erosion by an Alpine glacier.

    PubMed

    Herman, Frédéric; Beyssac, Olivier; Brughelli, Mattia; Lane, Stuart N; Leprince, Sébastien; Adatte, Thierry; Lin, Jiao Y Y; Avouac, Jean-Philippe; Cox, Simon C

    2015-10-01

    Assessing the impact of glaciation on Earth's surface requires understanding glacial erosion processes. Developing erosion theories is challenging because of the complex nature of the erosion processes and the difficulty of examining the ice/bedrock interface of contemporary glaciers. We demonstrate that the glacial erosion rate is proportional to the ice-sliding velocity squared, by quantifying spatial variations in ice-sliding velocity and the erosion rate of a fast-flowing Alpine glacier. The nonlinear behavior implies a high erosion sensitivity to small variations in topographic slope and precipitation. A nonlinear rate law suggests that abrasion may dominate over other erosion processes in fast-flowing glaciers. It may also explain the wide range of observed glacial erosion rates and, in part, the impact of glaciation on mountainous landscapes during the past few million years. PMID:26450208

  13. Deceleration efficiencies of shrub windbreaks in a wind tunnel

    NASA Astrophysics Data System (ADS)

    Wu, Xiaoxu; Zou, Xueyong; Zhou, Na; Zhang, Chunlai; Shi, Sha

    2015-03-01

    Artemisia and Salix are dominant shrub species for windbreaks in arid areas of China, and they show similar features to shrubs in other arid areas of the world. We compared the mean velocity fields and shelter effects of two shrub windbreaks with different layouts. For a single plant of Artemisia, the higher the free airflow velocity is, the more the wind velocity around two sides of the plant increases. The velocity gradient around a single plant of Salix is smaller than that around an Artemisia plant due to the difference in the plant shapes. Seven new velocity zones in the horizontal direction appear when airflow passes through an Artemisia windbreak, including four deceleration zones and three acceleration zones. The mean velocity field that is affected by a Salix windbreak can be divided into a deceleration zone in the front, an acceleration zone above, a vortex zone behind and a restoration zone downwind of the vortex zone. Shelter effects of the shrub windbreaks vary with the wind velocity and are influenced by the construct of the windbreaks. Shrub windbreaks that have a complex construction have better shelter effects than simple ones. The shelter effects of plant windbreaks are also influenced by the growth features of the plants. Considering the plant characteristics and the shelter effects of Salix and Artemisia windbreaks, it is optimal to plant these two windbreaks together in a sand-control system. This research is intended to be useful for sand movement control in arid areas.

  14. Soil Microbial Activity Provides Insight to Carbon Cycling in Shrub Ecotones of Sub-Arctic Sweden

    NASA Astrophysics Data System (ADS)

    Marek, E.; Kashi, N. N.; Chen, J.; Hobbie, E. A.; Schwan, M. R.; Varner, R. K.

    2015-12-01

    Shrubs are expanding in Arctic and sub-Arctic regions due to rising atmospheric temperatures. Microbial activity increases as growing temperatures cause permafrost warming and subsequent thaw, leading to a greater resource of soil nutrients enabling shrub growth. Increased carbon inputs from shrubs is predicted to result in faster carbon turnover by microbial decomposition. Further understanding of microbial activity underneath shrubs could uncover how microbes and soil processes interact to promote shrub expansion and carbon cycling. To address how higher soil carbon input from shrubs influences decomposition, soil samples were taken across a heath, shrub, and forest ecotone gradient at two sites near Abikso, Sweden. Samples were analyzed for soluble carbon and nitrogen, microbial abundance, and microbial activity of chitinase, glucosidase, and phosphatase to reflect organic matter decomposition and availability of nitrogen, carbon, and phosphate respectively. Chitinase activity positively correlated with shrub cover, suggesting microbial demands for nitrogen increase with higher shrub cover. Glucosidase activity negatively correlated with shrub cover and soluble carbon, suggesting decreased microbial demand for carbon as shrub cover and carbon stores increase. Lower glucosidase activity in areas with high carbon input from shrubs implies that microbes are decomposing carbon less readily than carbon is being put into the soil. Increasing soil carbon stores in shrub covered areas can lead to shrubs becoming a net carbon sink and a negative feedback to changing climate.

  15. Barley Yellow Dwarf

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Barley yellow dwarf is the most economically important virus disease affecting most cereal crops world wide. This manuscript summarizes the current knowledge of the disease etiology, epidemiology and management. This information is incorporated into the latest revision of the American Phytopathologi...

  16. Barley Yellow Dwarf Virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Barley yellow dwarf (BYD) is the most widespread and economically important virus disease of cereals. The viruses causing BYD were initially grouped based on common biological properties, including persistent and often strain-specific transmission by aphids and induction of yellowing symptoms. The...

  17. Dwarf Eye Disorder

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    Johns Hopkins researchers at the Wilmer Eye Institute have discovered what appears to be the first human gene mutation that causes extreme farsightedness. The researchers report that nanophthalmos, Greek for "dwarf eye," is a rare, potentially blinding disorder caused by an alteration in a gene called MFRP that helps control eye growth and…

  18. White Dwarf Stars

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.

    2014-10-01

    White dwarfs are the evolutionary endpoint for nearly 95% of all stars born in our Galaxy, the final stages of evolution of all low- and intermediate mass stars, i.e., main sequence stars with masses below (8.5± 1.5) M_{odot}, depending on metallicity of the progenitor, mass loss and core overshoot. Massive white dwarfs are intrinsically rare objects, tand produce a gap in the determination of the initial vs. final mass relation at the high mass end (e.g. Weidemann 2000 A&A, 363, 647; Kalirai et al. 2008, ApJ, 676, 594; Williams, Bolte & Koester 2009, ApJ, 693, 355). Main sequences stars with higher masses will explode as SNII (Smartt S. 2009 ARA&A, 47, 63), but the limit does depend on the metallicity of the progenitor. Massive white dwarfs are probably SNIa progenitors through accretion or merger. They are rare, being the final product of massive stars (less common) and have smaller radius (less luminous). Kepler et al. 2007 (MNRAS, 375, 1315), Kleinman et al. 2013 (ApJS, 204, 5) estimate only 1-2% white dwarfs have masses above 1 M_{odot}. The final stages of evolution after helium burning are a race between core growth and loss of the H-rich envelope in a stellar wind. When the burning shell is exposed, the star rapidly cools and burning ceases, leaving a white dwarf. As they cool down, the magnetic field freezes in, ranging from a few kilogauss to a gigagauss. Peculiar type Ia SN 2006gz, SN 2007if, SN 2009dc, SN 2003fg suggest progenitors in the range 2.4-2.8 M_{odot}, and Das U. & Mukhopadhyay B. (2012, Phys. Rev. D, 86, 042001) estimate that the Chandrasekhar limit increases to 2.3-2.6 M_{odot} for extremely high magnetic field stars, but differential rotation induced by accretion could also increase it, according to Hachisu I. et al. 2012 (ApJ, 744, 69). García-Berro et al. 2012, ApJ, 749, 25, for example, proposes double degenerate mergers are the progenitors of high-field magnetic white dwarfs. We propose magnetic fields enhance the line broadening in

  19. Modeling rates of life form cover change in burned and unburned alpine heathland subject to experimental warming.

    PubMed

    Camac, James S; Williams, Richard J; Wahren, Carl-Henrik; Jarrad, Frith; Hoffmann, Ary A; Vesk, Peter A

    2015-06-01

    Elevated global temperatures are expected to alter vegetation dynamics by interacting with physiological processes, biotic relationships and disturbance regimes. However, few studies have explicitly modeled the effects of these interactions on rates of vegetation change, despite such information being critical to forecasting temporal patterns in vegetation dynamics. In this study, we build and parameterize rate-change models for three dominant alpine life forms using data from a 7-year warming experiment. These models allowed us to examine how the interactions between experimental warming, the abundance of bare ground (a measure of past disturbance) and neighboring life forms (a measure of life form interaction) affect rates of cover change in alpine shrubs, graminoids and forbs. We show that experimental warming altered rates of life form cover change by reducing the negative effects of neighboring life forms and positive effects of bare ground. Furthermore, we show that our models can predict the observed direction and rate of life form cover change at burned and unburned long-term monitoring sites. Model simulations revealed that warming in unburned vegetation is expected to result in increased forb and shrub cover and decreased graminoid cover. In contrast, in burned vegetation, warming is predicted to slow post-fire regeneration in both graminoids and forbs and facilitate rapid expansion in shrub cover. These findings illustrate the applicability of modeling rates of vegetation change using experimental data. Our results also highlight the need to account for both disturbance and the abundance of other life forms when examining and forecasting vegetation dynamics under climatic change. PMID:25694042

  20. Environmental Limits of Tall Shrubs in Alaska's Arctic National Parks.

    PubMed

    Swanson, David K

    2015-01-01

    We sampled shrub canopy volume (height times area) and environmental factors (soil wetness, soil depth of thaw, soil pH, mean July air temperature, and typical date of spring snow loss) on 471 plots across five National Park Service units in northern Alaska. Our goal was to determine the environments where tall shrubs thrive and use this information to predict the location of future shrub expansion. The study area covers over 80,000 km2 and has mostly tundra vegetation. Large canopy volumes were uncommon, with volumes over 0.5 m3/m2 present on just 8% of plots. Shrub canopy volumes were highest where mean July temperatures were above 10.5°C and on weakly acid to neutral soils (pH of 6 to 7) with deep summer thaw (>80 cm) and good drainage. On many sites, flooding helped maintain favorable soil conditions for shrub growth. Canopy volumes were highest where the typical snow loss date was near 20 May; these represent sites that are neither strongly wind-scoured in the winter nor late to melt from deep snowdrifts. Individual species varied widely in the canopy volumes they attained and their response to the environmental factors. Betula sp. shrubs were the most common and quite tolerant of soil acidity, cold July temperatures, and shallow thaw depths, but they did not form high-volume canopies under these conditions. Alnus viridis formed the largest canopies and was tolerant of soil acidity down to about pH 5, but required more summer warmth (over 12°C) than the other species. The Salix species varied widely from S. pulchra, tolerant of wet and moderately acid soils, to S. alaxensis, requiring well-drained soils with near neutral pH. Nearly half of the land area in ARCN has mean July temperatures of 10.5 to 12.5°C, where 2°C of warming would bring temperatures into the range needed for all of the potential tall shrub species to form large canopies. However, limitations in the other environmental factors would probably prevent the formation of large shrub canopies

  1. A contribution of groundwater to Mojave Desert shrub transpiration

    SciTech Connect

    Hunter, R.B.

    1988-12-31

    Soil moisture was measured to 1-m depths in the northern Mojave Desert on two plots, one of which was denuded of shrubs. The pattern of wetting-drying near the surface and below the depth wet by rainfall suggested roughly 2 mm per month of transpired water was supplied by percolation upward from below the root zone. This deep moisture built up during fall and winter and depleted in spring and summer, which correlates well with local shrub phenology. 10 refs., 3 figs.

  2. Rooting Dynamics and Soil Water Variation of Native Shrubs

    NASA Astrophysics Data System (ADS)

    Kizito, A.; Dragila, M. I.; Sene, M.; Dick, R.

    2003-12-01

    Understanding the relationships that exist in the soil-plant-atmosphere continuum in semi-arid areas presents particular challenges, requiring accurate quantification of soil water with depth, a highly variable and limiting parameter in these vulnerable ecosystems. Two sites in the Peanut Basin of Senegal were selected to study rooting patterns of native shrubs and the corresponding variation of water distribution within the soil profile in both the dry and wet season. During dry periods or dry spells in the wet season, soil moisture content (θ v) surrounding the shrub's shallow roots is substantially moister than the adjacent soil matrix. It is therefore hypothesized, that nearing a condition of water stress, shrubs may participate in redistribution of soil water, effectively changing their own environment and enhancing their survival as well as that of neighboring annual crops. A possible region of water redistribution is interpreted to be between 15-75 cm depth, with the upper 0-15 cm remaining typically dry (θ v < 1 m3m-3) and forming a self mulching mechanism protecting lower horizons from the intense evaporation, and the lower 75 to 105 cm depth acting as a "moist reservoir" (θ v ˜ 6 m3m-3). We investigated shrub root depths, distribution, size, density and gravimetric soil water variation at 15 cm depth increments to 110 cm, and at 10 cm lateral spread increments to 200 cm from each shrub trunk. Shrubs exhibited a complex heterogeneous rooting system with approximately 50% of the root biomass occurring in the upper 30 cm and 95% in the upper 110 cm. Root study and soil moisture results are used to select optimal sensor placement in relation to shrub root depth and lateral spread extent. Monitoring is continuing for soil water and tension variation with sensors concentrated between 15 and 75 cm. Accurate quantitative data on the vertical and horizontal distribution of roots permits us to estimate how shrubs may alter water use by annual crops and modify

  3. Positive effects of native shrubs on Bromus tectorum demography.

    PubMed

    Griffith, Alden B

    2010-01-01

    There is increasing recognition that overall interactions among plant species are often the net result of both positive and negative effects. However, the positive influence of other plants has rarely been examined using detailed demographic methods, which are useful for partitioning net effects at the population level into positive and/or negative effects on individual vital rates. This study examines the influence of microhabitats created by the native shrubs Artemisia tridentata and Purshia tridentata on the demography of the invasive annual grass Bromus tectorum in the Great Basin Desert, California, USA. Shrub understory environments differed significantly from intershrub space and were characterized by higher soil fertility and less extreme microclimates. There existed a strong spatial association between B. tectorum and the shrubs across four years, with more than double the density of B. tectorum in shrub microhabitats compared to intershrub space. Periodic matrix models were used to calculate population growth (lamda) and reproductive potential (RP, expected lifetime fecundity of seedlings) of B. tectorum in different microhabitats over two years. Modeled population growth was significantly increased in shrub microhabitats in the first of two years. This was primarily due to increased seedling establishment in Artemisia microhabitats, rather than effects during the growing season. In the following year, B. tectorum individuals in shrub microhabitats had a significantly greater reproductive potential than those in intershrub microhabitats, indicating shrub facilitation during the growing season. Loop analysis revealed an interacting effect of year and microhabitat on B. tectorum life history pathway elasticity values, demonstrating a fundamental influence of spatiotemporal factors on which life history pathways are important and/or possible. Life table response experiment (LTRE) analysis showed that increased survival and growth rates positively contributed

  4. Alpine radar conversion for LAWR

    NASA Astrophysics Data System (ADS)

    Savina, M.; Burlando, P.

    2012-04-01

    The Local Area Weather Radar (LAWR) is a ship-born weather radar system operating in X-band developed by the DHI Group to detect precipitation in urban areas. To date more than thirty units are installed in different settings around the world. A LAWR was also deployed in the Alps, at 3883 m a.s.l. on the Kl. Matterhorn (Valais, Switzerland). This was the highest LAWR of the world and it led to the development of an Alpine LAWR system that, besides featuring important technological improvements needed to withstand the severe Alpine conditions, required the development of a new Alpine Radar COnversion Model (ARCOM), which is the main focus of this contribution. The LAWR system is equipped with the original FURUNO fan-beam slotted antenna and the original logarithmic receiver, which limits the radar observations to the video signal (L) withour providing the reflectivity (Z). The beam is 0.95 deg wide and 20 deg high. It can detect precipitation to a max range of 60 km. In order to account for the limited availability of raw signal and information and the specific mountain set-up, the conversion model had to be developed differently from the state-of-the-art radar conversion technique used for this class of radars. In particular, the ARCOM is based on a model used to simulate a spatial dependent factor, hereafter called ACF, which is in turn function of parameters that take in account climatological conditions, also used in other conversion methods, but additionally accounting for local radar beam features and for orographic forcings such as the effective sampling power (sP), which is modelled by means of antenna pattern, geometric ground clutter and their interaction. The result is a conversion factor formulated to account for a range correction that is based on the increase of the sampling volume, partial beam blocking and local climatological conditions. The importance of the latter in this study is double with respect to the standard conversion technique for this

  5. Vascular plant abundance and diversity in an alpine heath under observed and simulated global change

    PubMed Central

    Alatalo, Juha M.; Little, Chelsea J.; Jägerbrand, Annika K.; Molau, Ulf

    2015-01-01

    Global change is predicted to cause shifts in species distributions and biodiversity in arctic tundra. We applied factorial warming and nutrient manipulation to a nutrient and species poor alpine/arctic heath community for seven years. Vascular plant abundance in control plots increased by 31%. There were also notable changes in cover in the nutrient and combined nutrient and warming treatments, with deciduous and evergreen shrubs declining, grasses overgrowing these plots. Sedge abundance initially increased significantly with nutrient amendment and then declined, going below initial values in the combined nutrient and warming treatment. Nutrient addition resulted in a change in dominance hierarchy from deciduous shrubs to grasses. We found significant declines in vascular plant diversity and evenness in the warming treatment and a decline in diversity in the combined warming and nutrient addition treatment, while nutrient addition caused a decline in species richness. The results give some experimental support that species poor plant communities with low diversity may be more vulnerable to loss of species diversity than communities with higher initial diversity. The projected increase in nutrient deposition and warming may therefore have negative impacts on ecosystem processes, functioning and services due to loss of species diversity in an already impoverished environment. PMID:25950370

  6. Alpine Groundwater - Pristine Aquifers Under Threat?

    NASA Astrophysics Data System (ADS)

    Schneider, P.; Lange, A.

    2014-12-01

    Glacier and permafrost retreat are prominent climate change indicators. However, the characteristics of climate and hydrology in mountain areas remain poorly understood relative to lowland areas. Specifically, not much is known about alpine groundwater, its recharge and water quality variations, as these remote reservoirs are rarely monitored. As global temperatures rise, glaciers and permafrost will continue to retreat forming new sediment deposits and changing infiltration conditions in high alpine terrain. Climate change impacts the hydro-chemical composition of alpine waters, accelerates weathering processes, and potentially triggers mobilization of pollutants. Accordingly, we monitored groundwater quantity and quality parameters of an alpine porous aquifer near the Tiefenbach glacier in the Gotthard Massif in Switzerland. The goal of this research was to assess quality and seasonal storage dynamics of groundwater above the timberline (2000 m). To translate hydrological science into an ecosystem service context, we focused on four attributes: Water quantity: observations of groundwater level fluctuations combined with analysis of contributing water sources based on stable isotope analysis to give a quantitative understanding of origin and amount of water, Water quality: groundwater level, groundwater temperature and electrical conductivity were used as proxies for sampling of hydro-chemical parameters with automated water samplers during primary groundwater recharge periods (snowmelt and rainfall events), Location: Alpine terrain above the timberline, especially recharge into/out of an alpine porous aquifer at a pro-glacial floodplain and Date of annual melt (albedo effect) and timing of flow (snow- and icemelt from May to September) and groundwater recharge during the growing season. The study found that the summer groundwater temperatures depend on the date of annual melt and are more sensitive to climate forcing than lowland groundwater temperatures

  7. Calibrating brown dwarf ages using white dwarfs in wide binaries

    NASA Astrophysics Data System (ADS)

    Catalán, S.

    Even though age is a critical parameter for all objects, it can also be one of the most difficult to measure, in particular for low-mass stars and brown dwarfs. Brown dwarf models suffer from degeneracy and are not useful to infer ages without well constrained atmospheric parameters \\citep{pin06}. However, there is a way to overcome this problem by studying brown dwarfs for which some external constraints are available, for example brown dwarfs in wide binary systems. Wide binary members share proper motion and are supposed to have been born simultaneously and with the same chemical composition. Since they are well separated (⪆ 1000 AU) we can assume that no interaction has occurred between them in the past and they have evolved as isolated objects. If the companion of the brown dwarfs is a white dwarf, we can use it to calibrate the age of the system. White dwarf evolution can be described as a cooling process which is relatively well understood \\citep[e.g.][]{sal00}. Thus, they yield robust age constraints from the use of cooling sequences \\citep{gar11}. White dwarf cooling ages will uniformally give age lower limits (despite some uncertainty on progenitor life-time), and in some cases yield ages to better than 10% accuracy. Hence, wide binary systems containing a white dwarf can have system age constraints inferred from the white dwarf component. There are not many white dwarf-brown dwarf systems known so far, but with the combination of optical and IR surveys, SDSS+UKIDSS and Gaia + UKIDSS/VHS, new systems will be detected.

  8. Holocene Asian monsoon evolution revealed by a pollen record from an alpine lake on the southeastern margin of the Qinghai-Tibetan Plateau, China

    NASA Astrophysics Data System (ADS)

    Zhang, Enlou; Wang, Yongbo; Sun, Weiwei; Shen, Ji

    2016-02-01

    We present the results of pollen analyses from a 1105 cm long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed humid period in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño-Southern Oscillation strength in the tropical Pacific.

  9. Holocene Asian monsoon evolution revealed by a pollen record from an alpine lake on the southeastern margin of the Qinghai-Tibetan Plateau, China

    NASA Astrophysics Data System (ADS)

    Zhang, E.; Wang, Y.; Sun, W.; Shen, J.

    2015-10-01

    We present the results of pollen analyses from a 1105-cm-long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed strengthening of the ISM in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño Southern Oscillation strength in the tropical Pacific.

  10. Ductile extension in alpine Corsica

    NASA Astrophysics Data System (ADS)

    Jolivet, Laurent; Dubois, Roland; Fournier, Marc; Goffé, Bruno; Michard, André; Jourdan, Claudie

    1990-10-01

    Ductile deformation in high-pressure (P)-low temperature (T) conditions due to the westward thrusting of oceanic material onto a continental basement in alpine Corsica is overprinted by a late deformation event with a reverse shear sense (eastward) that took place in less severe P-T conditions. We show that the late deformation can be linked to extension during rifting and spreading of the Liguro Provençal basin from late Oligocene to late-middle Miocene time. Major compressive thrust contacts were reactivated as ductile normal faults and, in some units, only a penetrative eastward shear can be observed. This extension following the thickening of the crust brought tectonic units which underwent very different P- T conditions during the earlier stage into close contact. The Balagne nappe, which shows neither significant ductile deformation nor metamorphism, directly overlies the high-P units. The extensional deformation is distributed through the entire thickness of the nappe stack but is more important along the major thrust contacts, which localize the strain. The geometry of the crustal extension is controlled by that of the early compressive thrusts. The latest structures are east-dipping brittle normal faults which bound the early to middle Miocene Saint Florent half graben.

  11. Alpine Corsica Metamorphic Core Complex

    NASA Astrophysics Data System (ADS)

    Fournier, Marc; Jolivet, Laurent; Goffé, Bruno; Dubois, Roland

    1991-12-01

    Alpine Corsica is an example where superficial nonmetamorphic allochtonous units rest upon a highly strained metamorphic complex. Early ductile deformation under high pressure-low temperature (HP-LT) conditions is due to the westward thrusting of oceanic material onto a continental basement as shown by previous studies. New thermobarometric estimates yield minimal peak HP-LT metamorphism conditions of 11 kbar at 400°C. The early deformation is overprinted by a ductile deformation with an eastward sense of shear postdating or contemporaneous with mineral recrystallizations in the greenschist facies conditions. Early compressive thrust contacts are reworked as east dipping ductile normal faults and the less competent units display only eastward shear criteria. The upper units are affected by an extensional brittle deformation, and east dipping brittle normal faults bound to the west the early to middle Miocene Saint-Florent half-graben. The greenschist metamorphic event lasted until 33 Ma, which is contemporaneous with the beginning of the extension in the Liguro-Provençal basin. We interpret the second deformation stage as the result of a ductile extension following the overthickening of the crust due to the westward thrusting. Extension reduces the thickness of the crust so that upper units free from early P-T conditions are brought into close contact with a HP-LT metamorphic core complex. The geometry of the late extension is controlled by that of the early compressive thrust.

  12. Modelling photochemistry in alpine valleys

    NASA Astrophysics Data System (ADS)

    Brulfert, G.; Chemel, C.; Chaxel, E.; Chollet, J. P.

    2005-03-01

    Road traffic is a serious problem in the Chamonix Valley, France: traffic, noise and above all air pollution worry the inhabitants. The big fire in the Mont-Blanc tunnel made it possible, in the framework of the POVA project (POllution in Alpine Valleys), to undertake measurement campaigns with and without heavy-vehicle traffic through the valley, towards Italy (before and after the tunnel re-opening). Modelling in POVA should make it possible to explain the processes leading to episodes of atmospheric pollution, both in summer and in winter. Atmospheric prediction model ARPS 4.5.2 (Advanced Regional Prediction System), developed at the CAPS (Center for Analysis and Prediction of Storms) of the University of Oklahoma, enables to resolve the dynamics above a complex terrain. This model is coupled to the TAPOM 1.5.2 atmospheric chemistry (Transport and Air POllution Model) code developed at the Air and Soil Pollution Laboratory of the Ecole Polytechnique Fédérale de Lausanne. The numerical codes MM5 and CHIMERE are used to compute large scale boundary forcing. Using 300-m grid cells to calculate the dynamics and the reactive chemistry makes possible to accurately represent the dynamics in the valley (slope and valley winds) and to process chemistry at fine scale. Validation of campaign days allows to study chemistry indicators in the valley. NOy according to O3 reduction demonstrates a VOC controlled regime, different from the NOx controlled regime expected and observed in the nearby city of Grenoble.

  13. Catchment-mediated atmospheric nitrogen deposition drives ecological change in two alpine lakes in SE Tibet.

    PubMed

    Hu, Zhujun; Anderson, Nicholas John; Yang, Xiangdong; McGowan, Suzanne

    2014-05-01

    The south-east margin of Tibet is highly sensitive to global environmental change pressures, in particular, high contemporary reactive nitrogen (Nr) deposition rates (ca. 40 kg ha(-1)  yr(-1) ), but the extent and timescale of recent ecological change is not well prescribed. Multiproxy analyses (diatoms, pigments and geochemistry) of (210) Pb-dated sediment cores from two alpine lakes in Sichuan were used to assess whether they have undergone ecological change comparable to those in Europe and North America over the last two centuries. The study lakes have contrasting catchment-to-lake ratios and vegetation cover: Shade Co has a relatively larger catchment and denser alpine shrub than Moon Lake. Both lakes exhibited unambiguous increasing production since the late 19th to early 20th. Principle component analysis was used to summarize the trends of diatom and pigment data after the little ice age (LIA). There was strong linear change in biological proxies at both lakes, which were not consistent with regional temperature, suggesting that climate is not the primary driver of ecological change. The multiproxy analysis indicated an indirect ecological response to Nr deposition at Shade Co mediated through catchment processes since ca. 1930, while ecological change at Moon Lake started earlier (ca. 1880) and was more directly related to Nr deposition (depleted δ(15) N). The only pronounced climate effect was evidenced by changes during the LIA when photoautotrophic groups shifted dramatically at Shade Co (a 4-fold increase in lutein concentration) and planktonic diatom abundance declined at both sites because of longer ice cover. The substantial increases in aquatic production over the last ca. 100 years required a substantial nutrient subsidy and the geochemical data point to a major role for Nr deposition although dust cannot be excluded. The study also highlights the importance of lake and catchment morphology for determining the response of alpine lakes to

  14. How do snow and winter changes influence alpine plant growth, vegetation patterns and phenology?

    NASA Astrophysics Data System (ADS)

    Rixen, C.

    2012-12-01

    Alpine shrub- and grasslands are shaped by extreme climatic conditions such as a long-lasting snow cover and a short vegetation period. Such ecosystems are expected to be highly sensitive to global environmental change. Prolonged growing seasons and shifts in temperature and precipitation are likely to affect plant phenology and growth. In this talk I will report on long-term and large-scale experiments in the Swiss Alps on alpine plants, treelines and snow cover. In one study, we used data from a network of snow and climate measuring stations in Switzerland to analyse relationships between snow cover, plant phenology and productivity. Regression analyses revealed highly significant correlations between mean air temperature in May/June and snow melt out, onset of plant growth, and plant height. These correlations were used to project plant growth phenology for future climate conditions based on the gridded output of a set of regional climate models runs. Melt out and onset of growth were projected to occur on average 17 days earlier by the end of the century than in the control period from 1971-2000 under the future climate conditions of the low resolution climate model ensemble. Plant height and biomass production were expected to increase by 77% and 45%, respectively. The earlier melt out and onset of growth will probably cause a considerable shift towards higher growing plants and thus increased biomass production. Our results represent the first quantitative and spatially explicit estimates of climate change impacts on future growing season length and the respective productivity of alpine plant communities in the Swiss Alps.

  15. Shrub spatial aggregation and consequences for reproductive success.

    PubMed

    Tirado, Reyes; Pugnaire, Francisco I

    2003-07-01

    To link spatial patterns and ecological processes, we analysed the distribution of two shrub species (one large and dominant, the other smaller) and estimated the reproductive consequences of their distribution for the smaller species. We tested the significance of the spatial distribution pattern of the two shrubs by second-order bivariate point pattern analysis (Ripley's K function). Performance of Asparagus albus, the smaller shrub, was measured as (1) survival of transplanted seedlings in two contrasting habitats: patches of the dominant shrub (Ziziphus lotus), and open interspaces; and (2) reproductive output of plants naturally occurring in both habitats. The two species were significantly aggregated. Transplanted Asparagus albus seedlings had higher survival rates in patches than in the open. Plants produced more flowers, fruits, and showed a higher mass of seeds when living in aggregates than when isolated. The mechanisms responsible for this facilitative effect seem to be related to soil enrichment in patches. These results suggest that the spatial aggregation of species can be indicative of a positive interaction among them, directly affecting fitness of at least one of the species. Facilitation, by inducing variations in the reproductive performance may play a major role in the demography and dynamics of plant populations. PMID:12695906

  16. The Invasive Shrub, Buddleja davidii (Butterfl y Bush)

    EPA Science Inventory

    Buddleja davidii Franchet (Synonym. Buddleia davidii; common name Butterfly bush) is a perennial, semi-deciduous shrub or small multi-stemmed tree that is resident in gardens and disturbed areas in temperate locations worldwide. Since its introduction to the United Kingdom from c...

  17. Siliceous Shrubs in Yellowstone's Hot Springs: Implications for Exobiological Investigations

    NASA Technical Reports Server (NTRS)

    Guidry, S. A.; Chafetz, H. S.

    2003-01-01

    Potential relict hot springs have been identified on Mars and, using the Earth as an analog, Martian hot springs are postulated to be an optimal locality for recognizing preserved evidence of extraterrestrial life. Distinctive organic and inorganic biomarkers are necessary to recognize preserved evidence of life in terrestrial and extraterrestrial hot spring accumulations. Hot springs in Yellowstone National Park, Wyoming, U.S.A., contain a wealth of information about primitive microbial life and associated biosignatures that may be useful for future exobiological investigations. Numerous siliceous hot springs in Yellowstone contain abundant, centimeter-scale, spinose precipitates of opaline silica (opal-A). Although areally extensive in siliceous hot spring discharge channel facies, these spinose forms have largely escaped attention. These precipitates referred to as shrubs, consist of porous aggregates of spinose opaline silica that superficially resemble miniature woody plants, i.e., the term shrubs. Shrubs in carbonate precipitating systems have received considerable attention, and represent naturally occurring biotically induced precipitates. As such, shrubs have great potential as hot spring environmental indicators and, more importantly, proxies for pre-existing microbial life.

  18. Plant Identification Characteristics for Deciduous Trees & Shrubs. Lesson Plans.

    ERIC Educational Resources Information Center

    Burkholder, Kathy

    This manual contains a group of lesson plans designed for use with a slide series (not included here). Its purpose is to introduce students to the basic concepts and terminology used in the identification of deciduous trees and shrubs. The manual is composed of 12 lesson plans. The first lesson is an introduction to plant identification. The…

  19. LIGNIN DEGRADATION IN GRASSLAND, FOREST, AND SHRUB-STEPPE SOILS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Lignin decomposition was studied in soils from research plots in 5 locations in the US: restored tallgrass prairie, farmland (grain), semiarid shrub-steppe, and loblolly pine and Douglas fir forests. Soils were amended with 14C- lignocellulose and incubated for 6 months during which total- and 14C-C...

  20. Solidification of carbon-oxygen white dwarfs

    NASA Technical Reports Server (NTRS)

    Schatzman, E.

    1982-01-01

    The internal structure of white dwarfs is discussed. Highly correlated plasmas are reviewed. Implications for phase separation in the core of cooling white dwarfs are considered. The consequences for evolution of white dwarfs are addressed.

  1. Local Universe Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Carignan, Claude

    2015-08-01

    One of the outstanding problems in cosmology is addressing the "small-scale crisis" and understanding structure formation at the smallest scales. Standard Lambda Cold Dark Matter cosmological simulations of Milky Way-size DM halos predict many more DM sub-halos than the number of dwarf galaxies observed. This is the so-called Missing Satellites Problem. The most popular interpretation of the Missing Satellites Problem is that the smallest dark matter halos in the universe are extremely inefficient at forming stars. The virialized extent of the Milky Way's halo should contain ~500 satellites, while only ˜100 satellites and dwarfs are observed in the whole Local Group. Despite the large amount of theoretical work and new optical observations, the discrepancy, even if reduced, still persists between observations and hierarchical models, regardless of the model parameters. It may be possible to find those isolated ultra-faint missing dwarf galaxies via their neutral gas component, which is one of the goals we are pursuing with the SKA precursor KAT-7 in South Africa, and soon with the SKA pathfinder MeerKAT.

  2. Distances to WISE Y dwarfs

    NASA Astrophysics Data System (ADS)

    Beichman; A., C.; Gelino; R., C.; Kirkpatrick, J. Davy

    The WISE satellite has detected some of the coldest, lowest mass objects in the solar neighborhood. These late T and early Y dwarfs have effective temperatures in the range 250-800 K and inferred masses in the range 5-25 MJup. A critical piece of information for determining the physical properties of a brown dwarf is its distance, which greatly improves the comparison with evolutionary models. We discuss the importance of Y dwarfs in the context of star and planet formation. We also update our recent paper on Y dwarf parallaxes with improved values for four objects based on recent observations.

  3. Climate change and its impacts on vegetation distribution and net primary productivity of the alpine ecosystem in the Qinghai-Tibetan Plateau.

    PubMed

    Gao, Qingzhu; Guo, Yaqi; Xu, Hongmei; Ganjurjav, Hasbagen; Li, Yue; Wan, Yunfan; Qin, Xiaobo; Ma, Xin; Liu, Shuo

    2016-06-01

    Changes in climate have caused impacts on ecosystems on all continents scale, and climate change is also projected to be a stressor on most ecosystems even at the rate of low- to medium-range warming scenarios. Alpine ecosystem in the Qinghai-Tibetan Plateau is vulnerable to climate change. To quantify the climate change impacts on alpine ecosystems, we simulated the vegetation distribution and net primary production in the Qinghai-Tibetan Plateau for three future periods (2020s, 2050s and 2080s) using climate projection for RCPs (Representative Concentration Pathways) RCP4.5 and RCP8.5 scenarios. The modified Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ model) was parameter and test to make it applicable to the Qinghai-Tibetan Plateau. Climate projections that were applied to LPJ model in the Qinghai-Tibetan Plateau showed trends toward warmer and wetter conditions. Results based on climate projections indicated changes from 1.3°C to 4.2°C in annual temperature and changes from 2% to 5% in annual precipitation. The main impacts on vegetation distribution was increase in the area of forests and shrubs, decrease in alpine meadows which mainly replaced by shrubs which dominated the eastern plateau, and expanding in alpine steppes to the northwest dominated the western and northern plateau. The NPP was projected to increase by 79% and 134% under the RCP4.5 and RCP8.5. The projected NPP generally increased about 200gC·m(-2)·yr(-1) in most parts of the plateau with a gradual increase from the eastern to the western region of the Qinghai-Tibetan Plateau at the end of this century. PMID:26950617

  4. Spatial patterns of grasses and shrubs in an arid grassland environment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In the Chihuahuan Desert of Mexico and New Mexico, shrub invasion is a common problem, and once-abundant grassland ecosystems are being replaced by shrub-dominated habitat. The spatial arrangement of grasses and shrubs in these arid grasslands can provide better insight into community dynamics and c...

  5. Modelling photochemistry in alpine valleys

    NASA Astrophysics Data System (ADS)

    Brulfert, G.; Chemel, C.; Chaxel, E.; Chollet, J. P.

    2005-09-01

    Road traffic is a serious problem in the Chamonix Valley, France: traffic, noise and above all air pollution worry the inhabitants. The big fire in the Mont-Blanc tunnel made it possible, in the framework of the POVA project (POllution in Alpine Valleys), to undertake measurement campaigns with and without heavy-vehicle traffic through the Chamonix and Maurienne valleys, towards Italy (before and after the tunnel re-opening). Modelling is one of the aspects of POVA and should make it possible to explain the processes leading to episodes of atmospheric pollution, both in summer and in winter. Atmospheric prediction model ARPS 4.5.2 (Advanced Regional Prediction System), developed at the CAPS (Center for Analysis and Prediction of Storms) of the University of Oklahoma, enables to resolve the dynamics above a complex terrain. This model is coupled to the TAPOM 1.5.2 atmospheric chemistry (Transport and Air POllution Model) code developed at the Air and Soil Pollution Laboratory of the Ecole Polytechnique Fédérale de Lausanne. The numerical codes MM5 and CHIMERE are used to compute large scale boundary forcing.

    This paper focuses on modelling Chamonix valley using 300-m grid cells to calculate the dynamics and the reactive chemistry which makes possible to accurately represent the dynamics in the Chamonix valley (slope and valley winds) and to process chemistry at fine scale. The summer 2003 intensive campaign was used to validate the model and to study chemistry. NOy according to O3 reduction demonstrates a VOC controlled regime, different from the NOx controlled regime expected and observed in the nearby city of Grenoble.

  6. Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

    SciTech Connect

    Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea

    2014-10-20

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M {sub star} > 10{sup 6} M {sub ☉} that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

  7. The Evolution of Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Dunn, Jacqueline M.

    2016-01-01

    Dwarf galaxies are the most numerous galaxies in the Universe, yet the driving forces in their evolution remain elusive. The proposed evolutionary link between dwarf irregular and dwarf elliptical/spheroidal galaxies is investigated using broad-band UBVR photometry obtained for a sample of 29 dwarf galaxies. The galaxies span a range of absolute B-band magnitude from -13.67 to -19.86 mag. Broad-band colors and Sérsic surface brightness profile fits are compared for the two morphological types. All optical parameters are statistically different between the two subsamples, as evidenced by the significance level of the Kolmogorov-Smirnov statistic.Others have noted that dwarf ellipticals might have looked much like the currently observed dwarf irregulars in the past based on optical colors. An overlap between in the range of colors observed is noted for these targets, implying the possibility of an evolutionary link. A difference is noted between the two samples in the value of n (the power-law exponent determined from the Sérsic profile fitting), suggesting that the two main types of dwarf galaxy are structurally distinct. The differences in the structure of the stellar components would imply that dwarf irregulars do not evolve to become dwarf ellipticals in isolation, meaning that some sort of external interaction is required if the transformation is to occur. However, when the brightest dwarf elliptical targets are eliminated from the comparison, the two dwarf samples are much more similar in their values and range for the power-law exponent, which again suggests a possible evolutionary link. The environments of the galaxies are initially classified as either field or group/cluster, though no definitive environmental comparison is presented here.

  8. Catchment nitrogen saturation drives ecological change in an alpine lake in SW China (eastern margin of Tibet)

    NASA Astrophysics Data System (ADS)

    Anderson, N. J.; Hu, Z.; Yang, X.; Zhang, E.

    2011-12-01

    There is substantial evidence for recent (last ca. 120 years) ecological change in remote arctic and alpine lakes (increased productivity, altered biological structure). Initially, these changes were attributed to global warming which has altered the heat budgets of these lakes (stronger stratification, longer ice free periods). The emphasis on temperature, however, ignores that global environmental change is driven by a range of multiple stressors (e.g. altered biogeochemical cycles, land cover change). One of the characteristics of the observed change in remote lakes is the expansion of small species of the planktonic diatom genus Cyclotella. It is increasingly obvious that the recent success of this diatom genus is driven by other factors (nutrients, light, mixing depth) as much as temperature. SE Asia is a major hotspot for the emission of reactive nitrogen as a result of intensive agriculture and fossil fuel combustion. In this study we report recent ecological change in a small, oligotrophic alpine lake (ShadeCo; altitude 4423 m) located in Sichuan Province (SW China), one of many relatively unstudied alpine lakes on the eastern margin of Tibet. The lake is located above the tree-line and there is no cultural land-use; the catchment vegetation is dominated by alpine shrub (predominantly Rhododendron). We used a multi-proxy palaeolimnological approach (diatom, geochemical and stable isotope analyses of a 210-Pb dated core) coupled with regional long-term climate data to understand the pronounced 20th century changes in the diatom record, notably an expansion of Cyclotella spp from around 1920. This initial increase is coincident with warming in SW China but the maximum Cyclotella abundance occurs in in the 1970s and 1980s, a period of regional cooling and major changes in catchment-lake biogeochemistry as indicated by geochemical analyses. The possible drivers of the observed changes (nitrogen deposition, temperature) at this site are discussed in the context

  9. Kinematics of faint white dwarfs.

    PubMed

    Luyten, W J

    1978-10-01

    An analysis has been made for solar motion for 128 very faint white dwarfs of color class b or a. While about 40% of these stars may be high-velocity objects, it seems definitely indicated that the luminosity of all of them is considerably lower than that for the "normal" white dwarf of the same color. PMID:16592566

  10. Testing gravity using dwarf stars

    NASA Astrophysics Data System (ADS)

    Sakstein, Jeremy

    2015-12-01

    Generic scalar-tensor theories of gravity predict deviations from Newtonian physics inside astrophysical bodies. In this paper, we point out that low mass stellar objects, red and brown dwarf stars, are excellent probes of these theories. We calculate two important and potentially observable quantities: the radius of brown dwarfs and the minimum mass for hydrogen burning in red dwarfs. The brown dwarf radius can differ significantly from the general relativity prediction, and upcoming surveys that probe the mass-radius relation for stars with masses dwarf stars. This places a new and extremely stringent constraint on the parameters that appear in the effective field theory of dark energy and rules out several well-studied dark energy models.

  11. Dwarfs in Coma Cluster

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Click on image for larger poster version

    This false-color mosaic of the central region of the Coma cluster combines infrared and visible-light images to reveal thousands of faint objects (green). Follow-up observations showed that many of these objects, which appear here as faint green smudges, are dwarf galaxies belonging to the cluster. Two large elliptical galaxies, NGC 4889 and NGC 4874, dominate the cluster's center. The mosaic combines visible-light data from the Sloan Digital Sky Survey (color coded blue) with long- and short-wavelength infrared views (red and green, respectively) from NASA's Spitzer Space Telescope.

  12. Seeing Baby Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    2009-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Visible/DSS Click on image for larger version Ultraviolet/GALEX Click on image for larger version Poster Version Click on image for larger version

    The unique ultraviolet vision of NASA's Galaxy Evolution Explorer reveals, for the first time, dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe. Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way.

    The forming dwarf galaxies shine in the far ultraviolet spectrum, rendered as blue in the call-out on the right hand side of this image. Near ultraviolet light, also obtained by the Galaxy Evolution Explorer, is displayed in green, and visible light from the blue part of the spectrum here is represented by red. The clumps (in circles) are distinctively blue, indicating they are primarily detected in far ultraviolet light.

    The faint blue overlay traces the outline of the Leo Ring, a huge cloud of hydrogen and helium that orbits around two massive galaxies in the constellation Leo (left panel). The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe. Identified about 25 years ago by radio waves, the ring cannot be seen in visible light.

    Only a portion of the Leo Ring has been imaged in the ultraviolet, but this section contains the telltale ultraviolet signature of recent massive star formation within this ring of pristine gas. Astronomers have previously only seen dwarf galaxies form out of gas that has already been cycled through a galaxy and enriched with metals elements heavier than helium produced as stars evolve.

    The visible data come from the Digitized Sky Survey of the Space Telescope Science Institute in Baltimore, Md. The

  13. Barley yellow dwarf viruses.

    PubMed

    Miller, W A; Rasochová, L

    1997-01-01

    Barley yellow dwarf viruses represent one of the most economically important and ubiquitous groups of plant viruses. This review focuses primarily on four research areas in which progress has been most rapid. These include (a) evidence supporting reclassification of BYDVs into two genera; (b) elucidation of gene function and novel mechanisms controlling gene expression; (c) initial forays into understanding the complex interactions between BYDV virions and their aphid vectors; and (d) replication of a BYDV satellite RNA. Economic losses, symptomatology, and means of control of BYD are also discussed. PMID:15012520

  14. [Effect of degradation succession process on the temperature sensitivity of ecosystem respiration in alpine Potentilla fruticosa scrub meadow].

    PubMed

    Li, Dong; Luo, Xu-Peng; Cao, Guang-Min; Wu, Qin; Hu, Qi-Wu; Zhuo, Ma-Cuo; Li, Hui-Mei

    2015-03-01

    Grazing is one of the main artificial driving forces for the degradation succession process of alpine meadow. In order to quantitatively study the temperature sensitivity of alpine meadow ecosystem respiration in different degradation stages, we conducted the research in Haibei Alpine Meadow Ecosystem Research Station, CAS from July 2003 to July 2004. The static chamber-chromatography methodology was used to observe the seasonal changes of alpine scrub ecosystem respiration flux during different degradation stages. The results showed that: (1) The seasonal changes of ecosystem respiration flux in different degradation stages of alpine shrub presented a unimodal curve. The maximum appeared in August and the minimum appeared during the period from October to next April. The degradation succession process significantly decreased the ecosystem respiratory CO2 release rate. The respiratory rate ranges of alpine Potentilla fruticosa scrub (GG), Kobresia capillifolia meadow (GC) and bare land (GL) were 34.21-1 168.23, 2.30-1 112.38 and 20.40-509.72 mg (m2 x h)(-1), respectively. The average respiration rate of GG was 1.29 and 2.56 times of that of GC and GL, respectively; (2) Temperature was the main factor that affected the ecosystem respiration rate, and contributed 25% - 79% of the variation of the ecosystem respiration. The degradation succession process significantly changed the correlation between ecosystem respiration rate and temperature. The correlation (R2) between ecosystem respiration rate and each temperature indicator (T(s), T(d) and T(a)) was reduced by 47.23%, 46.95% and 55.28%, respectively when the ground vegetation disappeared and the scrub was degraded into secondary bare land; (3) The difference of Q10 between warm and cool seasons was significant (P < 0.05), and the value of cold season was larger than that of warm season. Degradation succession process apparently changed the temperature sensitivity of ecosystem respiration. The Q10 values of GG, GC

  15. Educational and Demographic Profile: Alpine County.

    ERIC Educational Resources Information Center

    California Postsecondary Education Commission, 2004

    2004-01-01

    This profile uniquely presents a variety of educational and socioeconomic information for Alpine County, nearby counties, and the state. The profile highlights the relationship between various factors that affect the economic well-being of individuals and communities. This presentation of information provides a framework for enhanced…

  16. Shrub Abundance Mapping in Arctic Tundra with Misr

    NASA Astrophysics Data System (ADS)

    Duchesne, R.; Chopping, M. J.; Wang, Z.; Schaaf, C.; Tape, K. D.

    2013-12-01

    Over the last 60 years an increase in shrub abundance has been observed in the Arctic tundra in connection with a rapid surface warming trend. Rapid shrub expansion may have consequences in terms of ecosystem structure and function, albedo, and feedbacks to climate; however, its rate is not yet known. The goal of this research effort is thus to map large scale changes in Arctic tundra vegetation by exploiting the structural signal in moderate resolution satellite remote sensing images from NASA's Multiangle Imaging SpectroRadiometer (MISR), mapped onto a 250m Albers Conic Equal Area grid. We present here large area shrub mapping supported by reference data collated using extensive field inventory data and high resolution panchromatic imagery. MISR Level 1B2 Terrain radiance scenes from the Terra satellite from 15 June-31 July, 2000 - 2010 were converted to surface bidirectional reflectance factors (BRF) using MISR Toolkit routines and the MISR 1 km LAND product BRFs. The red band data in all available cameras were used to invert the RossThick-LiSparse-Reciprocal BRDF model to retrieve kernel weights, model-fitting RMSE, and Weights of Determination. The reference database was constructed using aerial survey, three field campaigns (field inventory for shrub count, cover, mean radius and height), and high resolution imagery. Tall shrub number, mean crown radius, cover, and mean height estimates were obtained from QuickBird and GeoEye panchromatic image chips using the CANAPI algorithm, and calibrated using field-based estimates, thus extending the database to over eight hundred locations. Tall shrub fractional cover maps for the North Slope of Alaska were constructed using the bootstrap forest machine learning algorithm that exploits the surface information provided by MISR. The reference database was divided into two datasets for training and validation. The model derived used a set of 19 independent variables(the three kernel weights, ratios and interaction terms

  17. Shrub communities as inhibitors of plant succession in southern Quebec

    NASA Astrophysics Data System (ADS)

    Meilleur, Alain; Véronneau, Hélène; Bouchard, André

    1994-11-01

    The purpose of our research was to identify shrub species growing in southern Quebec that inhibit ecological succession in power-line corridors. Results are presented in three parts. First, clonal characteristics that allowed the establishment of stable communities were identified. Second, successional vector analysis identified those species that have the potential to inhibit succession. In poorly drained sites those species were Cornus stolonifera, C. obliqua, Salix petiolaris, and Spiraea alba. In well-drained sites, those species were Zanthoxylum americanum, Rubus idaeus, Spiraea alba, Rhus typhina, and Thuja occidentalis. Third, analysis of variance showed that there is a significantly larger number of tree seedlings found in adjacent herbaceous communities than found under the dense cover of Cornus stolonifera, C. obliqua, Salix petiolaris, Spiraea alba, Rhus typhina, Rubus idaeus, Thuya occidentalis, and Zanthoxylum americanum. These results indicate that the planting of selected shrub species could, through biological control, delay reforestation.

  18. Shrub encroachment control by browsing: Targeting the right demographic process

    NASA Astrophysics Data System (ADS)

    da Silveira Pontes, Laíse; Magda, Danièle; Jarry, Marc; Gleizes, Benoît; Agreil, Cyril

    2012-11-01

    Exploring key demographic parameters for establishment and growth of shrub populations enables us to identify the life stages or plant organs that browsers need to consume to effectively influence shrub population dynamics. However, there is a lack of concrete knowledge on how browsing can efficiently meet this goal. We therefore tested the impact of different levels of browsing intensity on a key demographic parameter (survival of juveniles) of a major colonizing shrub species (broom, Cytisus scoparius) in order to control population growth, and designed a browsing management strategy focused on this target stage. Three browsing intensities, representing pertinent management practices, were simulated on juveniles (2 years old) in a broom population. Juvenile broom plants were either left untouched (control treatment; n = 126) or had 50% or 90% of their total edible stem biomass removed for "light-intensity browsing" (n = 127) and "high-intensity browsing" (n = 77) treatments, respectively. Survival and fecundity data were collected over 6 years. Standard matrix modeling was used to analyze the impact of browsing on changes in population growth rate (λ), and the results were 6.34 (control), 2.26 (light browsing) and 0.85 (heavy browsing). Therefore, the natural expansion of broom populations may be slowed by light browsing or even reversed by heavy browsing (λ < 1). This multi-year survey confirms that focusing browsing on juveniles is an efficient strategy for controlling broom dominance. Shrub control strategies should therefore target early-growth-stage populations and repeat the browsing strategy at the same intensity over several years to achieve cumulative effects.

  19. Multi-scale investigation of shrub encroachment in southern Africa

    NASA Astrophysics Data System (ADS)

    Aplin, Paul; Marston, Christopher; Wilkinson, David; Field, Richard; O'Regan, Hannah

    2016-04-01

    There is growing speculation that savannah environments throughout Africa have been subject to shrub encroachment in recent years, whereby grassland is lost to woody vegetation cover. Changes in the relative proportions of grassland and woodland are important in the context of conservation of savannah systems, with implications for faunal distributions, environmental management and tourism. Here, we focus on southern Kruger National Park, South Africa, and investigate whether or not shrub encroachment has occurred over the last decade and a half. We use a multi-scale approach, examining the complementarity of medium (e.g. Landsat TM and OLI) and fine (e.g. QuickBird and WorldView-2) spatial resolution satellite sensor imagery, supported by intensive field survey in 2002 and 2014. We employ semi-automated land cover classification, involving a hybrid unsupervised clustering approach with manual class grouping and checking, followed by change detection post-classification comparison analysis. The results show that shrub encroachment is indeed occurring, a finding evidenced through three fine resolution replicate images plus medium resolution imagery. The results also demonstrate the complementarity of medium and fine resolution imagery, though some thematic information must be sacrificed to maintain high medium resolution classification accuracy. Finally, the findings have broader implications for issues such as vegetation seasonality, spatial transferability and management practices.

  20. Fire tolerance of a resprouting Artemisia (Asteraceae) shrub

    USGS Publications Warehouse

    Winter, S.L.; Fuhlendorf, S.D.; Goad, C.L.; Davis, C.A.; Hickman, K.R.; Leslie, David M., Jr.

    2011-01-01

    In North America, most Artemisia (Asteraceae) shrub species lack the ability to resprout after disturbances that remove aboveground biomass. We studied the response of one of the few resprouting Artemisia shrubs, Artemisia filifolia (sand sagebrush), to the effects of prescribed fires. We collected data on A. filifolia density and structural characteristics (height, canopy area, and canopy volume) in an A. filifolia shrubland in the southern Great Plains of North America. Our study sites included areas that had not been treated with prescribed fire, areas that had been treated with only one prescribed fire within the previous 5 years, and areas that had been treated with two prescribed fires within the previous 10 years. Our data were collected at time periods ranging from 1/2 to 5 years after the prescribed fires. Density of A. filifolia was not affected by one or two fires. Structural characteristics, although initially altered by prescribed fire, recovered to levels characteristic of unburned areas in 3-4 years after those fires. In contrast to most non-sprouting North American Artemisia shrub species, our research suggested that the resprouting A. filifolia is highly tolerant to the effects of fire. ?? 2011 Springer Science+Business Media B.V.

  1. White Dwarf Stars

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy, giving astronomers a fresh reading on the age of the universe.

    Located in the globular cluster M4, these small, burned-out stars -- called white dwarfs -- are about 12 to 13 billion years old. By adding the one billion years it took the cluster to form after the Big Bang, astronomers found that the age of the white dwarfs agrees with previous estimates that the universe is 13 to 14 billion years old.

    The images, including some taken by Hubble's Wide Field and Planetary Camera 2, are available online at

    http://oposite.stsci.edu/pubinfo/pr/2002/10/ or

    http://www.jpl.nasa.gov/images/wfpc .

    The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

    In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's .9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope.

    The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles indicate the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars.

    Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the

  2. PROPERTIES OF THE COOLEST DWARFS

    SciTech Connect

    SAUMON, DIDIER; LEGGETT, SANDY K.; FREEDMAN, RICHARD S.; GEBALLE, THOMAS R.; GOLIMOWSKI, DAVID A.; LODIEU, NICOLAS; MARLEY, MARK S.; STEPHENS, DENISE; PINFIELD, DAVID J.; WARREN, STEPHEN J.

    2007-01-18

    Eleven years after the discovery of the first T dwarf, we have a population of ultracool L and T dwarfs that is large enough to show a range of atmospheric properties, as well as model atmospheres advanced enough to study these properties in detail. Since the last Cool Stars meeting, there have been observational developments which aid in these studies. they present recent mid-infrared photometry and spectroscopy from the Spitzer Space Telescope which confirms the prevalence of vertical mixing in the atmospheres of L and T dwarfs. Hence, the 700 K to 2200 K L and t dwarf photspheres require a large number of parameters for successful modeling: effective temperature, gravity, metallicity, grain sedimentation and vertical mixing efficiency. They also describe initial results of a search for ultracool dwarfs in the UKIRT Infrared Deep Sky Survey, and present the latest T dwarf found to date. They conclude with a discussion of the definition of the later-than-T spectral type, the Y dwarf.

  3. The Influence of an Invasive Shrub, Buddleja Davidii on a Native Shrub, Griselinia Littoralis Transplanted into a New Zealand Floodplain Chronosequence

    EPA Science Inventory

    Griselinia littoralis, a native New Zealand shrub, was planted into a chronosequence (0 to 8 yrs since flooding) dominated by the non-indigenous shrub, Buddleja davidii in three New Zealand floodplains to determine to what extent facilitation and competitive inhibition may influe...

  4. The potential for retreating alpine glaciers to alter alpine ecosystems in the Colorado Front Range

    NASA Astrophysics Data System (ADS)

    Hall, E.; Baron, J.

    2013-12-01

    Glaciers are retreating at an unprecedented rate. In mid-latitude alpine ecosystems the presence of glaciers and rock glaciers govern rates and ecology of alpine and sub-alpine ecosystems. Changes in the thermal environment due to the loss of isothermal habitat and inputs from glacier melt chemistry are altering alpine ecosystems in unpredictable ways. In particular, glacier may be a source of nitrogen that is altering alpine ecosystem dynamics. Loch Vale Watershed (LVWS) located within Rocky Mountain National Park. LVWS contains a surface glacier (Andrew's glacier) and a rock glacier (Taylor's glacier) at the headwater of each of the two drainages within the watershed. We collected precipitation from a National Atmospheric Deposition Site and surface water from multiple alpine lakes and streams during a particularly high and low snow year in the Colorado Front Range. We also sampled stream and lake sediments at each site to analyze the associated microbial community. Concentrations of nitrate and ammonium, relative abundance of amoA (the gene responsible for a key step in the microbial nitrification pathway), and the dual isotope signal to nitrate all point to snow melt as a key deliverer of nitrogen to ecosystems along the Colorado Front Range. However, late summer surface water chemistry is isotopically similar to the chemistry of glacial ice. This suggests that retreating glacier may be an additional source of N to alpine ecosystems and have the potential to alter microbial community composition, biogeochemical rate processes, and ecosystem function. These dynamics are most likely not unique to the Colorado Front Range and should be globally distributed as glaciers continue to retreat in high altitude ecosystems around the world.

  5. Magnetic Field of Strange Dwarfs

    NASA Astrophysics Data System (ADS)

    Baghdasaryan, D. S.

    2016-03-01

    The generation of a magnetic field in a strange quark star owing to differential rotation of the superfluid and superconducting quark core relative to the normal electron-nuclear crust of the star is examined. The maximum possible magnetic field on the surface is estimated for various models of strange dwarfs. Depending on the configuration parameters, i.e., the mass M and radius R of the star, a range of 103-105 G is found. These values of the magnetic field may be an additional condition for identification of strange dwarfs among the extensive class of observed white dwarfs.

  6. Shifts in Aboveground Biomass Allocation Patterns of Dominant Shrub Species across a Strong Environmental Gradient

    PubMed Central

    Kumordzi, Bright B.; Gundale, Michael J.; Nilsson, Marie-Charlotte; Wardle, David A.

    2016-01-01

    Most plant biomass allocation studies have focused on allocation to shoots versus roots, and little is known about drivers of allocation for aboveground plant organs. We explored the drivers of within-and between-species variation of aboveground biomass allocation across a strong environmental resource gradient, i.e., a long-term chronosequence of 30 forested islands in northern Sweden across which soil fertility and plant productivity declines while light availability increases. For each of the three coexisting dominant understory dwarf shrub species on each island, we estimated the fraction of the total aboveground biomass produced year of sampling that was allocated to sexual reproduction (i.e., fruits), leaves and stems for each of two growing seasons, to determine how biomass allocation responded to the chronosequence at both the within-species and whole community levels. Against expectations, within-species allocation to fruits was least on less fertile islands, and allocation to leaves at the whole community level was greatest on intermediate islands. Consistent with expectations, different coexisting species showed contrasting allocation patterns, with the species that was best adapted for more fertile conditions allocating the most to vegetative organs, and with its allocation pattern showing the strongest response to the gradient. Our study suggests that co-existing dominant plant species can display highly contrasting biomass allocations to different aboveground organs within and across species in response to limiting environmental resources within the same plant community. Such knowledge is important for understanding how community assembly, trait spectra, and ecological processes driven by the plant community vary across environmental gradients and among contrasting ecosystems. PMID:27270445

  7. Shifts in Aboveground Biomass Allocation Patterns of Dominant Shrub Species across a Strong Environmental Gradient.

    PubMed

    Kumordzi, Bright B; Gundale, Michael J; Nilsson, Marie-Charlotte; Wardle, David A

    2016-01-01

    Most plant biomass allocation studies have focused on allocation to shoots versus roots, and little is known about drivers of allocation for aboveground plant organs. We explored the drivers of within-and between-species variation of aboveground biomass allocation across a strong environmental resource gradient, i.e., a long-term chronosequence of 30 forested islands in northern Sweden across which soil fertility and plant productivity declines while light availability increases. For each of the three coexisting dominant understory dwarf shrub species on each island, we estimated the fraction of the total aboveground biomass produced year of sampling that was allocated to sexual reproduction (i.e., fruits), leaves and stems for each of two growing seasons, to determine how biomass allocation responded to the chronosequence at both the within-species and whole community levels. Against expectations, within-species allocation to fruits was least on less fertile islands, and allocation to leaves at the whole community level was greatest on intermediate islands. Consistent with expectations, different coexisting species showed contrasting allocation patterns, with the species that was best adapted for more fertile conditions allocating the most to vegetative organs, and with its allocation pattern showing the strongest response to the gradient. Our study suggests that co-existing dominant plant species can display highly contrasting biomass allocations to different aboveground organs within and across species in response to limiting environmental resources within the same plant community. Such knowledge is important for understanding how community assembly, trait spectra, and ecological processes driven by the plant community vary across environmental gradients and among contrasting ecosystems. PMID:27270445

  8. Do shrubs reduce the adverse effects of grazing on soil properties?

    USGS Publications Warehouse

    Eldridge, David J.; Beecham, Genevieve; Grace, James B.

    2015-01-01

    Increases in the density of woody plants are a global phenomenon in drylands, and large aggregations of shrubs, in particular, are regarded as being indicative of dysfunctional ecosystems. There is increasing evidence that overgrazing by livestock reduces ecosystem functions in shrublands, but that shrubs may buffer the negative effects of increasing grazing. We examined changes in water infiltration and nutrient concentrations in soils under shrubs and in their interspaces in shrublands in eastern Australia that varied in the intensity of livestock grazing. We used structural equation modelling to test whether shrubs might reduce the negative effects of overgrazing on infiltration and soil carbon and nitrogen (henceforth ‘soil nutrients’). Soils under shrubs and subject to low levels of grazing were more stable and had greater levels of soil nutrients. Shrubs had a direct positive effect on soil nutrients; but, grazing negatively affected nutrients by increasing soil bulk density. Structural equation modelling showed that shrubs had a direct positive effect on water flow under ponded conditions but also enhanced water flow, indirectly, through increased litter cover. Any positive effects of shrubs on water flow under low levels of grazing waned at high levels of grazing. Our results indicate that shrubs may reduce the adverse effects of grazing on soil properties. Specifically, shrubs could restrict access to livestock and therefore protect soils and plants beneath their canopies. Low levels of grazing are likely to ensure the retention of soil water and soil carbon and nitrogen in shrubland soils.

  9. Measuring M Dwarf Winds with DAZ White Dwarfs

    NASA Astrophysics Data System (ADS)

    Debes, John H.

    2006-11-01

    Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, show evidence for ongoing accretion of material onto their surfaces. Some DAZs are known to have unresolved M dwarf companions, which could account for the observed accretion through a stellar wind. I combine observed Ca abundances of the DAZs with information on the orbital separation of their M dwarf companions to infer the mass-loss rate of the M dwarfs. I find that for three of the six known DAZs with M dwarf companions, a stellar wind can plausibly explain the observed accretion on the white dwarfs assuming Bondi-Hoyle accretion of solar abundance stellar winds on the order of 10-14 to 10-16 Msolar yr-1. The rest of the sample have companions with orbits >~1 AU and require companion mass-loss rates of >10-11 Msolar yr-1. I conclude that there must be an alternative explanation for accretion of material onto DAZs with widely separated companions. The inferred winds for two of the close binaries are orders of magnitude smaller than typically assumed for the angular momentum loss of red dwarf-white dwarf pairs due to magnetic braking from a stellar wind and may seriously affect predictions for the formation rate of CVs with low-mass companions. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 10255.

  10. FIRST DIRECT EVIDENCE THAT BARIUM DWARFS HAVE WHITE DWARF COMPANIONS

    SciTech Connect

    Gray, R. O.; McGahee, C. E.; Griffin, R. E. M.; Corbally, C. J. E-mail: cmcgahe@g.clemson.edu E-mail: corbally@as.arizona.edu

    2011-05-15

    Barium II (Ba) stars are chemically peculiar F-, G-, and K-type objects that show enhanced abundances of s-process elements. Since s-process nucleosynthesis is unlikely to take place in stars prior to the advanced asymptotic giant branch (AGB) stage, the prevailing hypothesis is that each present Ba star was contaminated by an AGB companion which is now a white dwarf (WD). Unless the initial mass ratio of such a binary was fairly close to unity, the receiving star is thus at least as likely to be a dwarf as a giant. So although most known Ba stars appear to be giants, the hypothesis requires that Ba dwarfs be comparably plentiful and moreover that they should all have WD companions. However, despite dedicated searches with the IUE satellite, no WD companions have been directly detected to date among the classical Ba dwarfs, even though some 90% of those stars are spectroscopic binaries, so the contamination hypothesis is therefore presently in some jeopardy. In this paper, we analyze recent deep, near-UV and far-UV Galaxy Evolution Explorer (GALEX) exposures of four of the brightest of the class (HD 2454, 15360, 26367, and 221531), together with archived GALEX data for two newly recognized Ba dwarfs: HD 34654 and HD 114520 (which also prove to be spectroscopic binaries). The GALEX observations of the Ba dwarfs as a group show a significant far-UV excess compared to a control sample of normal F-type dwarfs. We suggest that this ensemble far-UV excess constitutes the first direct evidence that Ba dwarfs have WD companions.

  11. [Quality level assessment of lowly efficient Tamarix chinensis secondary shrubs in Laizhou Bay of Yellow River Delta].

    PubMed

    Xia, Jiang-Bao; Liu, Yu-Ting; Zhu, Jin-Fang; Xu, Jing-Wei; Lu, Zhao-Hua; Liu, Jing-Tao; Liu, Qing

    2013-06-01

    Taking the Tamarix chinensis secondary shrubs in Laizhou Bay of Yellow River Delta as test objects, and by using synthetic factor method, this paper studied the main factors causing the lowly efficiency of T. chinensis secondary shrubs as well as the main parameters for the classification of lowly efficient T. chinensis secondary shrubs. A total of 24 indices including shrubs growth and soil physical and chemical properties were selected to determine the main affecting factors and parameters in evaluating and classifying the lowly efficient shrubs. There were no obvious correlations between the indices reflecting the shrubs growth and soil quality, and thus, only using shrub growth index to reflect the lowly efficiency level of T. chinensis was not enough, and it would be necessary to combine with soil quality factors to make a comprehensive evaluation. The principal factors reflecting the quality level of lowly efficient T. chinensis shrubs included soil salt content and moisture content, stand age, single tree's aboveground stem, leaf biomass, and basal diameter, followed by soil density, porosity, and soil nutrient status. The lowly efficient T. chinensis shrubs in the Bay could be classified into five types, namely, shrub with growth potential, slightly low quality shrub, moderately lowly efficient shrub, moderately low quality and lowly efficient shrub, and seriously low quality and lowly efficient shrub. The main features, low efficiency causes, and management measures of these shrubs were discussed based on the mean cluster value. PMID:24066539

  12. Secondary Airflow Structure around Clustered Shrubs and Its Significance for Vegetated Dune Evolution

    NASA Astrophysics Data System (ADS)

    Luo, Wanyin; Dong, Zhibao; Qian, Guangqiang; Lu, Junfeng

    2016-04-01

    Shrubs have an important significance in aeolian processes due to their disturbance of the local airflow. In the formation of vegetated dunes, there is an iterative interaction between shrub geometry, the structure of the secondary airflow, and the interaction between neighboring shrubs. Understanding the dynamics of vegetated dunes thus requires an insight into the airflow fields around shrubs. Based on aerodynamic and aeolian sand physics theory, this project measured the complex secondary flow field and aeolian sand deposition pattern around single and cluster shrubs with varied densities (i.e., 0.05, 0.08, 0.15, 0.20) and gap ratios (the ratio of the gap spacing between the shrub models to the center-to-center distance for the shrub models, ranged from 1.1 to 1.8 with side-by-side arrangement and 1.2 to 4.3 with tandem arrangement) using the particle image velocimetry system through wind tunnle simulation. The relationship between the secondary airflow structure and the shrub's porosity and arrangement was analyzed quantitatively. Research results revealed that porosity (density) is the key parameter to affect the flow patterns around single shrub. Compared to solid obstacles, bleed flow through the shrubs has great influence on the secondary airflow patterns around itself. Under cluster modes, the distance between two adjacent shrubs has great influence on flow field structures around them. The flow patterns around two side-by-side arranged shrubs can be classified into three kinds of modes, that is: single-bluff-body, biased flow pattern and parallel vortex streets. The flow patterns around two tandem arranged shrubs can be classified into three regimes, that is: the extended body regime, reattachment regime and co-shedding regime. The "shadow zone" with low velocity in the lee of shrubs is the optimal position for sand deposition, but its form, size and orientation would varied with the shrub porosity and gap ratio between them. With the increase of the gap

  13. Contexts for change in alpine tundra

    USGS Publications Warehouse

    Malanson, George P.; Rose, Jonathan P.; Schroeder, P. Jason; Fagre, Daniel B.

    2011-01-01

    Because alpine tundra is responding to climate change, a need exists to understand the meaning of observed changes. To provide context for such interpretation, the relevance of niche and neutral theories of biogeography and the continuum and classification approaches to biogeographic description are assessed. Two extensive studies of alpine tundra, from the Indian Peaks area, Colorado and Glacier National Park, Montana, are combined. The data are ordinated to describe relations. The pattern that emerges is one of a continuum of vegetation, but with the distinctions one might expect from distant sites. The relationships of the similarity of vegetation on all possible pairs of sites to the environmental differences and geographic distances are analyzed using Mantel correlations. Because distance and environmental differences in climate between the two sites are correlated, partial correlations are weak but still significant. More advanced analyses are suggested for this environment prior to interpretation of monitoring efforts such as GLORIA.

  14. Mediterranean shrub vegetation: soil protection vs. water availability

    NASA Astrophysics Data System (ADS)

    García Estringana, Pablo; Nieves Alonso-Blázquez, M.; Alegre, Alegre; Cerdà, Artemi

    2014-05-01

    Soil Erosion and Land Degradation are closely related to the changes in the vegetation cover (Zhao et al., 2013). Although other factors such as rainfall intensiy or slope (Ziadat and Taimeh, 2013) the plant covers is the main factor that controls the soil erosion (Haregeweyn, 2013). Plant cover is the main factor of soil erosion processes as the vegetation control the infiltration and runoff generation (Cerdà, 1998a; Kargar Chigani et al., 2012). Vegetation cover acts in a complex way in influencing on the one hand on runoff and soil loss and on the other hand on the amount and the way that rainfall reaches the soil surface. In arid and semiarid regions, where erosion is one of the main degradation processes and water is a scant resource, a minimum percentage of vegetation coverage is necessary to protect the soil from erosion, but without compromising the availability of water (Belmonte Serrato and Romero Diaz, 1998). This is mainly controlled by the vegetation distribution (Cerdà, 1997a; Cammeraat et al., 2010; Kakembo et al., 2012). Land abandonment is common in Mediterranean region under extensive land use (Cerdà, 1997b; García-Ruiz, 2010). Abandoned lands typically have a rolling landscape with steep slopes, and are dominated by herbaceous communities that grow on pasture land interspersed by shrubs. Land abandonment use to trigger an increase in soil erosion, but the vegetation recovery reduces the impact of the vegetation. The goal of this work is to assess the effects of different Mediterranean shrub species (Dorycnium pentaphyllum Scop., Medicago strasseri, Colutea arborescens L., Retama sphaerocarpa, L., Pistacia Lentiscus L. and Quercus coccifera L.) on soil protection (runoff and soil losses) and on rainfall reaching soil surface (rainfall partitioning fluxes). To characterize the effects of shrub vegetation and to evaluate their effects on soil protection, two field experiments were carried out. The presence of shrub vegetation reduced runoff by

  15. ALPINE LAKES WILDERNESS STUDY AREA, WASHINGTON.

    USGS Publications Warehouse

    Gualtieri, J.L.; Thurber, H.K.

    1984-01-01

    The Alpine Lakes Wilderness study area, located in the central part of the Cascade Mountains of Washington was examined for its mineral-resource potential. On the basis of that study the area was found to contain deposits of copper, other base metals, and gold and silver. Probable or substantiated mineral-resource potential exists for these commodities in the southwest-central, northwest, and southeast-central parts of the area. The geologic terrane precludes the occurrence of fossil fuel resources.

  16. Alpine Microbial Community Responses to Summer Warming

    NASA Astrophysics Data System (ADS)

    Osborne, B. B.; Baron, J.; Wallenstein, M. D.

    2011-12-01

    Remote alpine ecosystems of the western US are vulnerable to anthropogenic drivers of change. Atmospheric nitrogen (N) deposition and a changing climate introduce nutrients, alter hydrological processes, and expose soils to novel temperature regimes. We asked whether terrestrial microbes, specifically nitrifiers that may contribute to already high lake and stream NO3- concentrations, may be responding to changes in important controls of community development and activity associated with a changing climate, namely temperature and moisture. In August 2010 we sampled three soils from the Loch Vale Watershed in Rocky Mountain National Park which fell along a gradient of succession commonly represented in deglaciated alpine catchments. These included well-developed meadow soils, poorly vegetated talus substrate, and newly-exposed glacial outwash. Outwash, talus, and meadow samples were all N-rich and contained NH4-N concentrations ~7 times higher than NO3-N. Soils were incubated for 45 days at 2.5, 10, and 25oC and three moisture levels based on initial field conditions. Nitrifier concentrations were greatest in outwash, intermediate in talus, and lowest in meadow samples. Bacterial nitrifier abundance greatly surpassed archaeal nitrifier levels. Net nitrification was also greatest in outwash, followed by meadow and talus respectively. Moisture, rather than temperature, was a dominant control over both nitrifier abundance and activity. Linking the influence of temperature and moisture on alpine microbial communities will provide insight into control thresholds, optima, and synergistic interactions. This research is part of a larger study of controls on headwater stream and lake NO3-. Characterizing microbial NO3- production in the alpine will help us evaluate the importance of biological, as opposed to physical, sources of stream NO3-. It will also inform our ability to forecast and mitigate consequences of anthropogenic drivers of change on these systems.

  17. Differential physiological responses to environmental change promote woody shrub expansion.

    PubMed

    Heskel, Mary; Greaves, Heather; Kornfeld, Ari; Gough, Laura; Atkin, Owen K; Turnbull, Matthew H; Shaver, Gaius; Griffin, Kevin L

    2013-05-01

    Direct and indirect effects of warming are increasingly modifying the carbon-rich vegetation and soils of the Arctic tundra, with important implications for the terrestrial carbon cycle. Understanding the biological and environmental influences on the processes that regulate foliar carbon cycling in tundra species is essential for predicting the future terrestrial carbon balance in this region. To determine the effect of climate change impacts on gas exchange in tundra, we quantified foliar photosynthesis (A net), respiration in the dark and light (R D and R L, determined using the Kok method), photorespiration (PR), carbon gain efficiency (CGE, the ratio of photosynthetic CO2 uptake to total CO2 exchange of photosynthesis, PR, and respiration), and leaf traits of three dominant species - Betula nana, a woody shrub; Eriophorum vaginatum, a graminoid; and Rubus chamaemorus, a forb - grown under long-term warming and fertilization treatments since 1989 at Toolik Lake, Alaska. Under warming, B. nana exhibited the highest rates of A net and strongest light inhibition of respiration, increasing CGE nearly 50% compared with leaves grown in ambient conditions, which corresponded to a 52% increase in relative abundance. Gas exchange did not shift under fertilization in B. nana despite increases in leaf N and P and near-complete dominance at the community scale, suggesting a morphological rather than physiological response. Rubus chamaemorus, exhibited minimal shifts in foliar gas exchange, and responded similarly to B. nana under treatment conditions. By contrast, E. vaginatum, did not significantly alter its gas exchange physiology under treatments and exhibited dramatic decreases in relative cover (warming: -19.7%; fertilization: -79.7%; warming with fertilization: -91.1%). Our findings suggest a foliar physiological advantage in the woody shrub B. nana that is further mediated by warming and increased soil nutrient availability, which may facilitate shrub expansion and

  18. Differential physiological responses to environmental change promote woody shrub expansion

    PubMed Central

    Heskel, Mary; Greaves, Heather; Kornfeld, Ari; Gough, Laura; Atkin, Owen K; Turnbull, Matthew H; Shaver, Gaius; Griffin, Kevin L

    2013-01-01

    Direct and indirect effects of warming are increasingly modifying the carbon-rich vegetation and soils of the Arctic tundra, with important implications for the terrestrial carbon cycle. Understanding the biological and environmental influences on the processes that regulate foliar carbon cycling in tundra species is essential for predicting the future terrestrial carbon balance in this region. To determine the effect of climate change impacts on gas exchange in tundra, we quantified foliar photosynthesis (Anet), respiration in the dark and light (RD and RL, determined using the Kok method), photorespiration (PR), carbon gain efficiency (CGE, the ratio of photosynthetic CO2 uptake to total CO2 exchange of photosynthesis, PR, and respiration), and leaf traits of three dominant species – Betula nana, a woody shrub; Eriophorum vaginatum, a graminoid; and Rubus chamaemorus, a forb – grown under long-term warming and fertilization treatments since 1989 at Toolik Lake, Alaska. Under warming, B. nana exhibited the highest rates of Anet and strongest light inhibition of respiration, increasing CGE nearly 50% compared with leaves grown in ambient conditions, which corresponded to a 52% increase in relative abundance. Gas exchange did not shift under fertilization in B. nana despite increases in leaf N and P and near-complete dominance at the community scale, suggesting a morphological rather than physiological response. Rubus chamaemorus, exhibited minimal shifts in foliar gas exchange, and responded similarly to B. nana under treatment conditions. By contrast, E. vaginatum, did not significantly alter its gas exchange physiology under treatments and exhibited dramatic decreases in relative cover (warming: −19.7%; fertilization: −79.7%; warming with fertilization: −91.1%). Our findings suggest a foliar physiological advantage in the woody shrub B. nana that is further mediated by warming and increased soil nutrient availability, which may facilitate shrub

  19. Chemical Signatures in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Venn, Kim A.; Hill, Vanessa M.

    2008-12-01

    Chemical signatures in dwarf galaxies describe the examination of specific elemental abundance ratios to investigate the formation and evolution of dwarf galaxies, particularly when compared with the variety of stellar populations in the Galaxy. Abundance ratios can come from HII region emission lines, planetary nebulae, or supernova remnants, but mostly they come from stars. Since stars can live a very long time, for example, a 0.8 MSun star born at the time of the Big Bang would only now be ascending the red giant branch, and, if, for the most part, its quiescent main sequence lifetime had been uneventful, then it is possible that the surface chemistry of stars actually still resembles their natal chemistry. Detailed abundances of stars in dwarf galaxies can be used to reconstruct their chemical evolution, which we now find to be distinct from any other component of the Galaxy, questioning the assertion that dwarf galaxies like these built up the Galaxy. Potential solutions to reconciling dwarf galaxy abundances and Galaxy formation models include the timescale for significant merging and the possibility for uncovering different stellar populations in the new ultra-faint dwarfs.

  20. Alpine Soils as long-term Bioindicators

    NASA Astrophysics Data System (ADS)

    Nestroy, O.

    2009-04-01

    Alpine soils as long-term bioindicators The introductory words concern the definitions and peculiarities of alpine soils and their position in the Austrian Soil Classification 2000 in comparison with the World Reference Base for Soil Resources 2006. The important parameters for genesis and threats for these soils in steep and high positions are discussed. It must be emphasized that the main threats are the very different kinds of erosion e.g. by water, wind and snow, and also by skiing (end of season) as well as and mountain-biking (mainly summer-sport). Due the very slow regeneration and - in this connection - due to the very slow changes of the soil entities, these soils give an utmost importance as a long-time bioindicator. With regard to the climate change one can assume an increase in the content of organic matter on site, but also an increase of erosion and mass movement on the other site, e. g. in kind of "plaiken" (soil slide) as result of an increasing intensity of rainfall. It lies partly in our hands to diminish the number and the intensity of the threats, we can influence the soil development, but the result to reach a new ecological equilibrium is very long - in case of alpine soil more than two generations.

  1. Trees, more than shrubs, protect against soil erosion

    NASA Astrophysics Data System (ADS)

    Wendel, JoAnna

    2014-05-01

    Soil erosion and saltation—the transport of ground particles by wind—are significant producers of dust and can damage crops or lead to nutrient-poor soil in semiarid regions. These regions are particularly vulnerable to climate warming and increased human activity, which can exacerbate erosion and induce dust bowl-like conditions. Previous research and observations have shown that vegetation such as shrubs and trees can reduce soil erosion, but existing models do not account for variations in wind direction or strength.

  2. Atmospheric water uptake by an atacama desert shrub.

    PubMed

    Mooney, H A; Gulmon, S L; Ehleringer, J; Rundel, P W

    1980-08-01

    Nolana mollis, a succulent-leaved shrub of the extreme coastal desert of Chile, has the capacity to condense water on its leaves out of unsaturated atmospheres, Metabolic energy would have to be expended to move this water either from the leaf surface directly to the mesophyll or, when dripped to the soil, from there into the roots. Because of the unusual aridity of its habitat and of the utilization of water-use-efficient metabolism by Nolana, at least during certain periods, such an energy expenditure could be effective. PMID:17821192

  3. Working toward integrated models of alpine plant distribution

    PubMed Central

    Carlson, Bradley Z.; Randin, Christophe F.; Boulangeat, Isabelle; Lavergne, Sébastien; Thuiller, Wilfried; Choler, Philippe

    2014-01-01

    Species distribution models (SDMs) have been frequently employed to forecast the response of alpine plants to global changes. Efforts to model alpine plant distribution have thus far been primarily based on a correlative approach, in which ecological processes are implicitly addressed through a statistical relationship between observed species occurrences and environmental predictors. Recent evidence, however, highlights the shortcomings of correlative SDMs, especially in alpine landscapes where plant species tend to be decoupled from atmospheric conditions in micro-topographic habitats and are particularly exposed to geomorphic disturbances. While alpine plants respond to the same limiting factors as plants found at lower elevations, alpine environments impose a particular set of scale-dependent and hierarchical drivers that shape the realized niche of species and that require explicit consideration in a modelling context. Several recent studies in the European Alps have successfully integrated both correlative and process-based elements into distribution models of alpine plants, but for the time being a single integrative modelling framework that includes all key drivers remains elusive. As a first step in working toward a comprehensive integrated model applicable to alpine plant communities, we propose a conceptual framework that structures the primary mechanisms affecting alpine plant distributions. We group processes into four categories, including multi-scalar abiotic drivers, gradient dependent species interactions, dispersal and spatial–temporal plant responses to disturbance. Finally, we propose a methodological framework aimed at developing an integrated model to better predict alpine plant distribution. PMID:24790594

  4. Working toward integrated models of alpine plant distribution.

    PubMed

    Carlson, Bradley Z; Randin, Christophe F; Boulangeat, Isabelle; Lavergne, Sébastien; Thuiller, Wilfried; Choler, Philippe

    2013-10-01

    Species distribution models (SDMs) have been frequently employed to forecast the response of alpine plants to global changes. Efforts to model alpine plant distribution have thus far been primarily based on a correlative approach, in which ecological processes are implicitly addressed through a statistical relationship between observed species occurrences and environmental predictors. Recent evidence, however, highlights the shortcomings of correlative SDMs, especially in alpine landscapes where plant species tend to be decoupled from atmospheric conditions in micro-topographic habitats and are particularly exposed to geomorphic disturbances. While alpine plants respond to the same limiting factors as plants found at lower elevations, alpine environments impose a particular set of scale-dependent and hierarchical drivers that shape the realized niche of species and that require explicit consideration in a modelling context. Several recent studies in the European Alps have successfully integrated both correlative and process-based elements into distribution models of alpine plants, but for the time being a single integrative modelling framework that includes all key drivers remains elusive. As a first step in working toward a comprehensive integrated model applicable to alpine plant communities, we propose a conceptual framework that structures the primary mechanisms affecting alpine plant distributions. We group processes into four categories, including multi-scalar abiotic drivers, gradient dependent species interactions, dispersal and spatial-temporal plant responses to disturbance. Finally, we propose a methodological framework aimed at developing an integrated model to better predict alpine plant distribution. PMID:24790594

  5. Plant community responses to 5 years of simulated climate change in meadow and heath ecosystems at a subarctic-alpine site.

    PubMed

    Jägerbrand, Annika K; Alatalo, Juha M; Chrimes, Dillon; Molau, Ulf

    2009-09-01

    Climate change was simulated by increasing temperature and nutrient availability in an alpine landscape. We conducted a field experiment of BACI-design (before/after control/impact) running for five seasons in two alpine communities (heath and meadow) with the factors temperature (increase of ca. 1.5-3.0 degrees C) and nutrients (5 g N, 5 g P per m(2)) in a fully factorial design in northern Swedish Lapland. The response variables were abundances of plant species and functional types. Plant community responses to the experimental perturbations were investigated, and the responses of plant functional types were examined in comparison to responses at the species level. Nutrient addition, exclusively and in combination with enhanced temperature increase, exerted the most pronounced responses at the species-specific and community levels. The main responses to nutrient addition were increases in graminoids and forbs, whereas deciduous shrubs, evergreen shrubs, bryophytes, and lichens decreased. The two plant communities of heath or meadow showed different vegetation responses to the environmental treatments despite the fact that both communities were located on the same subarctic-alpine site. Furthermore, we showed that the abundance of forbs increased in response to the combined treatment of temperature and nutrient addition in the meadow plant community. Within a single-plant functional type, most species responded similarly to the enhanced treatments although there were exceptions, particularly in the moss and lichen functional types. Plant community structure showed BACI responses in that vegetation dominance relationships in the existing plant functional types changed to varying degrees in all plots, including control plots. Betula nana and lichens increased in the temperature-increased enhancements and in control plots in the heath plant community during the treatment period. The increases in control plots were probably a response to the observed warming during

  6. Soil Fauna Affects Dissolved Carbon and Nitrogen in Foliar Litter in Alpine Forest and Alpine Meadow.

    PubMed

    Liao, Shu; Yang, Wanqin; Tan, Yu; Peng, Yan; Li, Jun; Tan, Bo; Wu, Fuzhong

    2015-01-01

    Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) are generally considered important active biogeochemical pools of total carbon and nitrogen. Many studies have documented the contributions of soil fauna to litter decomposition, but the effects of the soil fauna on labile substances (i.e., DOC and TDN) in litter during early decomposition are not completely clear. Therefore, a field litterbag experiment was carried out from 13th November 2013 to 23rd October 2014 in an alpine forest and an alpine meadow located on the eastern Tibetan Plateau. Litterbags with different mesh sizes were used to provide access to or prohibit the access of the soil fauna, and the concentrations of DOC and TDN in the foliar litter were measured during the winter (the onset of freezing, deep freezing and thawing stage) and the growing season (early and late). After one year of field incubation, the concentration of DOC in the litter significantly decreased, whereas the TDN concentration in the litter increased. Similar dynamic patterns were detected under the effects of the soil fauna on both DOC and TDN in the litter between the alpine forest and the alpine meadow. The soil fauna showed greater positive effects on decreasing DOC concentration in the litter in the winter than in the growing season. In contrast, the dynamics of TND in the litter were related to seasonal changes in environmental factors, rather than the soil fauna. In addition, the soil fauna promoted a decrease in litter DOC/TDN ratio in both the alpine forest and the alpine meadow throughout the first year of decomposition, except for in the late growing season. These results suggest that the soil fauna can promote decreases in DOC and TDN concentrations in litter, contributing to early litter decomposition in these cold biomes. PMID:26406249

  7. Soil Fauna Affects Dissolved Carbon and Nitrogen in Foliar Litter in Alpine Forest and Alpine Meadow

    PubMed Central

    Liao, Shu; Yang, Wanqin; Tan, Yu; Peng, Yan; Li, Jun; Tan, Bo; Wu, Fuzhong

    2015-01-01

    Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) are generally considered important active biogeochemical pools of total carbon and nitrogen. Many studies have documented the contributions of soil fauna to litter decomposition, but the effects of the soil fauna on labile substances (i.e., DOC and TDN) in litter during early decomposition are not completely clear. Therefore, a field litterbag experiment was carried out from 13th November 2013 to 23rd October 2014 in an alpine forest and an alpine meadow located on the eastern Tibetan Plateau. Litterbags with different mesh sizes were used to provide access to or prohibit the access of the soil fauna, and the concentrations of DOC and TDN in the foliar litter were measured during the winter (the onset of freezing, deep freezing and thawing stage) and the growing season (early and late). After one year of field incubation, the concentration of DOC in the litter significantly decreased, whereas the TDN concentration in the litter increased. Similar dynamic patterns were detected under the effects of the soil fauna on both DOC and TDN in the litter between the alpine forest and the alpine meadow. The soil fauna showed greater positive effects on decreasing DOC concentration in the litter in the winter than in the growing season. In contrast, the dynamics of TND in the litter were related to seasonal changes in environmental factors, rather than the soil fauna. In addition, the soil fauna promoted a decrease in litter DOC/TDN ratio in both the alpine forest and the alpine meadow throughout the first year of decomposition, except for in the late growing season. These results suggest that the soil fauna can promote decreases in DOC and TDN concentrations in litter, contributing to early litter decomposition in these cold biomes. PMID:26406249

  8. Range Expansion of Moose in Arctic Alaska Linked to Warming and Increased Shrub Habitat

    PubMed Central

    Tape, Ken D.

    2016-01-01

    Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators. PMID:27074023

  9. Shrub encroachment affects mammalian carnivore abundance and species richness in semiarid rangelands

    NASA Astrophysics Data System (ADS)

    Blaum, Niels; Rossmanith, Eva; Popp, Alexander; Jeltsch, Florian

    2007-01-01

    Shrub encroachment due to overgrazing has led to dramatic changes of savanna landscapes and is considered to be one of the most threatening forms of rangeland degradation e.g. via habitat fragmentation. Mammalian carnivores are particularly vulnerable to local extinction in fragmented landscapes. However, our understanding of how shrub encroachment affects mammalian carnivores is poor. Here we investigated the relative sensitivities of ten native carnivores to different levels of shrub cover ranging from low (<5%) to high shrub cover (>25%) in 20 southern Kalahari rangeland sites. Relative abundance of carnivores was monitored along 40 sand transects (5 m × 250 m) for each site. Our results show that increasing shrub cover affects carnivore species differently. African wild cats, striped polecats, cape foxes and suricates were negatively affected, whereas we found hump-shaped responses for yellow mongooses, bat-eared foxes and small-spotted genets with maximum abundance at shrub covers between 10 and 18%. In contrast, black-backed jackals, slender mongooses and small spotted cats were not significantly affected by increasing shrub cover. However, a negative impact of high shrub cover above 18% was congruent for all species. We conclude that intermediate shrub cover (10-18%) in savanna landscapes sustain viable populations of small carnivores.

  10. Seed and vegetative production of shrubs and growth of understory conifer regeneration

    USGS Publications Warehouse

    Wender, B.; Harrington, C.; Tappeiner, J.C.

    2004-01-01

    We observed flower and fruit production for nine understory shrub species in western Washington and Oregon and examined the relationships between shrub reproductive output and plant size, plant age, site factors, and overstory density to determine the factors that control flowering or fruiting in understory shrubs. In Washington, 50 or more shrubs or microplots (for rhizomatous species) were sampled for each of eight species. The variables examined were more useful for explaining abundance of flowers or fruit on shrubs than they were for explaining the probability that a shrub would produce flowers or fruit. Plant size was consistently the most useful predictor of flower/fruit abundance in all species; plant age was also a good predictor of abundance and was strongly correlated with plant size. Site variables (e.g., slope) and overstory competition variables (e.g., presence/absence of a canopy gap) also helped explain flower/fruit abundance for some species. At two Oregon sites, the responses of five species to four levels of thinning were observed for 2-4 yr (15 shrubs or microplots per treatment per year). Thinning increased the probability and abundance of flowering/fruiting for two species, had no effect on one species, and responses for two other species were positive but inconsistent between sites or from year to year. We believe reducing overstory density or creating canopy gaps may be useful tools for enhancing shrub size and vigor, thus, increasing the probability and abundance of fruiting in some understory shrub species.

  11. Disentangling the effects of shrubs and herbivores on tree regeneration in a dry Chaco forest (Argentina).

    PubMed

    Tálamo, Andrés; Barchuk, Alicia H; Garibaldi, Lucas A; Trucco, Carlos E; Cardozo, Silvana; Mohr, Federico

    2015-07-01

    Successful persistence of dry forests depends on tree regeneration, which depends on a balance of complex biotic interactions. In particular, the relative importance and interactive effects of shrubs and herbivores on tree regeneration are unclear. In a manipulative study, we investigated if thornless shrubs have a direct net effect, an indirect positive effect mediated by livestock, and/or an indirect negative effect mediated by small vertebrates on tree regeneration of two key species of Chaco forest (Argentina). In a spatial association study, we also explored the existence of net positive interactions from thorny and thornless shrubs. The number of Schinopsis lorentzii seedlings was highest under artificial shade with native herbivores and livestock excluded. Even excluding livestock, no seedlings were found with natural conditions (native herbivores present with natural shade or direct sunlight) at the end of the experiment. Surprisingly, seedling recruitment was not enhanced under thornless shrubs, because there was a complementary positive effect of shade and interference. Moreover, thornless shrubs had neither positive nor negative effects on regeneration of S. lorentzii. Regeneration of Aspidosperma quebracho-blanco was minimal in all treatments. In agreement with the experiment, spatial distributions of saplings of both tree species were independent of thornless shrubs, but positively associated with thorny shrubs. Our results suggest that in general thornless shrubs may have a negligible effect and thorny shrubs a net positive effect on tree regeneration in dry forests. These findings provide a conceptual framework for testing the impact of biotic interactions on seedling recruitment in other dry forests. PMID:25707777

  12. Range Expansion of Moose in Arctic Alaska Linked to Warming and Increased Shrub Habitat.

    PubMed

    Tape, Ken D; Gustine, David D; Ruess, Roger W; Adams, Layne G; Clark, Jason A

    2016-01-01

    Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators. PMID:27074023

  13. Mammalian herbivores confer resilience of Arctic shrub-dominated ecosystems to changing climate.

    PubMed

    Kaarlejärvi, Elina; Hoset, Katrine S; Olofsson, Johan

    2015-09-01

    Climate change is resulting in a rapid expansion of shrubs in the Arctic. This expansion has been shown to be reinforced by positive feedbacks, and it could thus set the ecosystem on a trajectory toward an alternate, more productive regime. Herbivores, on the other hand, are known to counteract the effects of simultaneous climate warming on shrub biomass. However, little is known about the impact of herbivores on resilience of these ecosystems, that is, the capacity of a system to absorb disturbance and still remain in the same regime, retaining the same function, structure, and feedbacks. Here, we investigated how herbivores affect resilience of shrub-dominated systems to warming by studying the change of shrub biomass after a cessation of long-term experimental warming in a forest-tundra ecotone. As predicted, warming increased the biomass of shrubs, and in the absence of herbivores, shrub biomass in tundra continued to increase 4 years after cessation of the artificial warming, indicating that positive effects of warming on plant growth may persist even over a subsequent colder period. Herbivores contributed to the resilience of these systems by returning them back to the original low-biomass regime in both forest and tundra habitats. These results support the prediction that higher shrub biomass triggers positive feedbacks on soil processes and microclimate, which enable maintaining the rapid shrub growth even in colder climates. Furthermore, the results show that in our system, herbivores facilitate the resilience of shrub-dominated ecosystems to climate warming. PMID:25967156

  14. Flower and fruit production of understory shrubs in western Washington and Oregon

    USGS Publications Warehouse

    Wender, B.; Harrington, C.; Tappeiner, J. C., II

    2004-01-01

    We observed flower and fruit production for nine understory shrub species in western Washington and Oregon and examined the relationships between shrub reproductive output and plant size, plant age, site factors, and overstory density to determine the factors that control flowering or fruiting in understory shrubs. In Washington, 50 or more shrubs or microplots (for rhizomatous species) were sampled for each of eight species. The variables examined were more useful for explaining abundance of flowers or fruit on shrubs than they were for explaining the probability that a shrub would produce flowers or fruit. Plant size was consistently the most useful predictor of flower/fruit abundance in all species; plant age was also a good predictor of abundance and was strongly correlated with plant size. Site variables (e.g., slope) and overstory competition variables (e.g., presence/absence of a canopy gap) also helped explain flower/fruit abundance for some species. At two Oregon sites, the responses of five species to four levels of thinning were observed for 2-4 yr (15 shrubs or microplots per treatment per year). Thinning increased the probability and abundance of flowering/fruiting for two species, had no effect on one species, and responses for two other species were positive but inconsistent between sites or from year to year. We believe reducing overstory density or creating canopy gaps may be useful tools for enhancing shrub size and vigor, thus, increasing the probability and abundance of fruiting in some understory shrub species.

  15. Soil water dynamics and evapotranspiration in alpine ecosystems in the NE of Qinghai-Tibet Plateau, China

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Yan; Zhang, Si-Yi; Ma, Yu-Jun

    2015-04-01

    Interactions between surface energy flux, evapotranspiration and soil water were poorly understood in the alpine ecosystems in the Qinghai-Tibet Plateau, which is a sensitive and vulnerable region to global climate change. For the first time, we continuously measured surface energy flux and soil water content (SWC) and estimated ET using bowen ratio energy balance method in the Qinghai Lake watershed, located in the northeast of Qinghai-Tibet Plateau between 2012 and 2013. The three ecosystems were Kobresia meadow (KMd.), Potentilla fruticosa shrub (PFSh.) and Achnatherum splendens steppe (ASSt.). Results indicated that there was a good negative correlation between ecosystem Bowen ratios and SWC in the growing season for the three ecosystems. Annual ET at KMd. and PFSh. was 16% and 3% less than local annual precipitation, while that at ASSt. was 26% larger than annual precipitation. Average annual ET was 507.9, 493.2 and 413.7 mm at PFSh., KMd. and ASSt., respectively. Fluctuations of daily ET at alpine ecosystems were primarily controlled by solar radiation, especially in the growing season, whereas, at ASSt. where precipitation and SWC was limited, ET was also controlled by water supply.

  16. Effects of harvesting flowers from shrubs on the persistence and abundance of wild shrub populations at multiple spatial extents.

    PubMed

    Cabral, Juliano Sarmento; Bond, William J; Midgley, Guy F; Rebelo, Anthony G; Thuiller, Wilfried; Schurr, Frank M

    2011-02-01

    Wildflower harvesting is an economically important activity of which the ecological effects are poorly understood. We assessed how harvesting of flowers affects shrub persistence and abundance at multiple spatial extents. To this end, we built a process-based model to examine the mean persistence and abundance of wild shrubs whose flowers are subject to harvest (serotinous Proteaceae in the South African Cape Floristic Region). First, we conducted a general sensitivity analysis of how harvesting affects persistence and abundance at nested spatial extents. For most spatial extents and combinations of demographic parameters, persistence and abundance of flowering shrubs decreased abruptly once harvesting rate exceeded a certain threshold. At larger extents, metapopulations supported higher harvesting rates before their persistence and abundance decreased, but persistence and abundance also decreased more abruptly due to harvesting than at smaller extents. This threshold rate of harvest varied with species' dispersal ability, maximum reproductive rate, adult mortality, probability of extirpation or local extinction, strength of Allee effects, and carrying capacity. Moreover, spatial extent interacted with Allee effects and probability of extirpation because both these demographic properties affected the response of local populations to harvesting more strongly than they affected the response of metapopulations. Subsequently, we simulated the effects of harvesting on three Cape Floristic Region Proteaceae species and found that these species reacted differently to harvesting, but their persistence and abundance decreased at low rates of harvest. Our estimates of harvesting rates at maximum sustainable yield differed from those of previous investigations, perhaps because researchers used different estimates of demographic parameters, models of population dynamics, and spatial extent than we did. Good demographic knowledge and careful identification of the spatial extent

  17. Evidence and Implications of Frequent Fires in Ancient Shrub Tundra

    SciTech Connect

    Higuera, P E; Brubaker, L B; Anderson, P M; Brown, T A; Kennedy, A T; Hu, F S

    2008-03-06

    Understanding feedbacks between terrestrial and atmospheric systems is vital for predicting the consequences of global change, particularly in the rapidly changing Arctic. Fire is a key process in this context, but the consequences of altered fire regimes in tundra ecosystems are rarely considered, largely because tundra fires occur infrequently on the modern landscape. We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago. Charcoal and pollen from lake sediments reveal that ancient birchdominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/- 90 s.d.; n = 44). Although paleoclimate interpretations and data from modern tundra fires suggest that increased burning was aided by low effective moisture, vegetation cover clearly played a critical role in facilitating the paleo-fires by creating an abundance of fine fuels. These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21st century and beyond. Increased tundra burning will have broad impacts on physical and biological systems as well as land-atmosphere interactions in the Arctic, including the potential to release stored organic carbon to the atmosphere.

  18. Nitrogen addition increases fecundity in the desert shrub Sarcobatus vermiculatus.

    PubMed

    Drenovsky, R E; Richards, J H

    2005-04-01

    Nutrients, in addition to water, limit desert primary productivity, but nutrient limitations to fecundity and seed quality in desert ecosystems have received little attention. Reduced seed production and quality may affect recruitment, population, and community processes. At the Mono Basin, CA, USA where the alkaline, sandy soil has very low availability of N, P, and most other nutrients, seed production, recruitment, and dominance of the desert shrub Sarcobatus vermiculatus decrease over a dune successional sequence. Concurrently, Sarcobatus leaf N, P, and Ca/Mg ratio decline from early to later successional dunes. At two later successional dune sites, we fertilized adult Sarcobatus shrubs for 2 years and determined which nutrient(s) limited growth, seed production, and seed quality. We also tested whether nutrient addition at these older sites made these fitness-related variables equivalent to a younger, high-fecundity site. Nitrogen addition, alone, increased Sarcobatus leaf N, growth, and seed production per shoot module. Any treatment including P, Ca, Mg, or micronutrients but not N had an insignificant effect on growth and fecundity. Nitrogen addition also increased filled seed weight, a predictor of potential seedling survival, at one of the sites. Nitrogen-limited seed production and seed mass may reduce Sarcobatus fitness and contribute to the observed successional changes in plant community composition in this alkaline desert ecosystem. PMID:15690179

  19. Ecosystem Carbon Storage in Alpine Grassland on the Qinghai Plateau.

    PubMed

    Liu, Shuli; Zhang, Fawei; Du, Yangong; Guo, Xiaowei; Lin, Li; Li, Yikang; Li, Qian; Cao, Guangmin

    2016-01-01

    The alpine grassland ecosystem can sequester a large quantity of carbon, yet its significance remains controversial owing to large uncertainties in the relative contributions of climate factors and grazing intensity. In this study we surveyed 115 sites to measure ecosystem carbon storage (both biomass and soil) in alpine grassland over the Qinghai Plateau during the peak growing season in 2011 and 2012. Our results revealed three key findings. (1) Total biomass carbon density ranged from 0.04 for alpine steppe to 2.80 kg C m-2 for alpine meadow. Median soil organic carbon (SOC) density was estimated to be 16.43 kg C m-2 in alpine grassland. Total ecosystem carbon density varied across sites and grassland types, from 1.95 to 28.56 kg C m-2. (2) Based on the median estimate, the total carbon storage of alpine grassland on the Qinghai Plateau was 5.14 Pg, of which 94% (4.85 Pg) was soil organic carbon. (3) Overall, we found that ecosystem carbon density was affected by both climate and grazing, but to different extents. Temperature and precipitation interaction significantly affected AGB carbon density in winter pasture, BGB carbon density in alpine meadow, and SOC density in alpine steppe. On the other hand, grazing intensity affected AGB carbon density in summer pasture, SOC density in alpine meadow and ecosystem carbon density in alpine grassland. Our results indicate that grazing intensity was the primary contributing factor controlling carbon storage at the sites tested and should be the primary consideration when accurately estimating the carbon storage in alpine grassland. PMID:27494253

  20. Ecosystem Carbon Storage in Alpine Grassland on the Qinghai Plateau

    PubMed Central

    Liu, Shuli; Zhang, Fawei; Du, Yangong; Guo, Xiaowei; Lin, Li; Li, Yikang; Li, Qian; Cao, Guangmin

    2016-01-01

    The alpine grassland ecosystem can sequester a large quantity of carbon, yet its significance remains controversial owing to large uncertainties in the relative contributions of climate factors and grazing intensity. In this study we surveyed 115 sites to measure ecosystem carbon storage (both biomass and soil) in alpine grassland over the Qinghai Plateau during the peak growing season in 2011 and 2012. Our results revealed three key findings. (1) Total biomass carbon density ranged from 0.04 for alpine steppe to 2.80 kg C m-2 for alpine meadow. Median soil organic carbon (SOC) density was estimated to be 16.43 kg C m-2 in alpine grassland. Total ecosystem carbon density varied across sites and grassland types, from 1.95 to 28.56 kg C m-2. (2) Based on the median estimate, the total carbon storage of alpine grassland on the Qinghai Plateau was 5.14 Pg, of which 94% (4.85 Pg) was soil organic carbon. (3) Overall, we found that ecosystem carbon density was affected by both climate and grazing, but to different extents. Temperature and precipitation interaction significantly affected AGB carbon density in winter pasture, BGB carbon density in alpine meadow, and SOC density in alpine steppe. On the other hand, grazing intensity affected AGB carbon density in summer pasture, SOC density in alpine meadow and ecosystem carbon density in alpine grassland. Our results indicate that grazing intensity was the primary contributing factor controlling carbon storage at the sites tested and should be the primary consideration when accurately estimating the carbon storage in alpine grassland. PMID:27494253

  1. Effects of human trampling on abundance and diversity of vascular plants, bryophytes and lichens in alpine heath vegetation, Northern Sweden.

    PubMed

    Jägerbrand, Annika K; Alatalo, Juha M

    2015-01-01

    This study investigated the effects of human trampling on cover, diversity and species richness in an alpine heath ecosystem in northern Sweden. We tested the hypothesis that proximity to trails decreases plant cover, diversity and species richness of the canopy and the understory. We found a significant decrease in plant cover with proximity to the trail for the understory, but not for the canopy level, and significant decreases in the abundance of deciduous shrubs in the canopy layer and lichens in the understory. Proximity also had a significant negative impact on species richness of lichens. However, there were no significant changes in species richness, diversity or evenness of distribution in the canopy or understory with proximity to the trail. While not significant, liverworts, acrocarpous and pleurocarpous bryophytes tended to have contrasting abundance patterns with differing proximity to the trail, indicating that trampling may cause shifts in dominance hierarchies of different groups of bryophytes. Due to the decrease in understory cover, the abundance of litter, rock and soil increased with proximity to the trail. These results demonstrate that low-frequency human trampling in alpine heaths over long periods can have major negative impacts on lichen abundance and species richness. To our knowledge, this is the first study to demonstrate that trampling can decrease species richness of lichens. It emphasises the importance of including species-level data on non-vascular plants when conducting studies in alpine or tundra ecosystems, since they often make up the majority of species and play a significant role in ecosystem functioning and response in many of these extreme environments. PMID:25774335

  2. White Dwarf Pulsars

    NASA Technical Reports Server (NTRS)

    Patterson, Joseph

    1999-01-01

    This proposal was designed to study pulse and orbital modulations in candidate DQ Herculis stars. Data on 5 stars were obtained. The best results were obtained on YY Draconis, which exhibited a strongly pulsed hard X-ray flux, and even suggested a transition between one-pole and two-pole emission during the course of the observation. This result is being readied for inclusion in a comprehensive study of YY Draconis. A strong pulsation appeared to be present also in H0857-242, but with a period of about 50 minutes, confusion with the first harmonic of the satellite's orbital frequency is possible. So that result is uncertain. A negative result was obtained on 4UO608-49 (V347 Pup), suggesting either that the X-ray identification is incorrect, or that the source is very transient. Finally, data was obtained on V1432 Aql and WZ Sge, respectively the slowest and fastest of these stars. Combined with the Advanced Satellite for Cosmology and Astrophysics (ASCA) data, the high-energy data demonstrates the latter to contain a white dwarf rotating with P = 27.87 s. Optical photometry contemporaneous with the X-ray data was obtained of V1432 Aql, in order to study the variations in the eclipse waveform. As anticipated, the width and centroid of the eclipse appeared to vary with the 50-day "supercycle". A paper reporting this study is now in preparation.

  3. Brown dwarfs as close companions to white dwarfs

    SciTech Connect

    Stringfellow, G.S.; Bodenheimer, P.; Black, D.C. Lunar and Planetary Institute, Houston, TX )

    1990-02-01

    The influence of the radiation flux emitted by a white dwarf primary on the evolution of a closely orbiting brown dwarf (BD) companion is investigated. Full stellar evolutionary calculations are presented for both isolated and thermal bath cases, including effects of large variations in the atmospheric grain opacities. High grain opacities significantly increase the radii of the BDs, but the thermal bath does not. The major influence of the thermal bath is to increase substantially the surface temperature and luminosity of the BD at a given age. These results are compared with the observational properties of the possible BD companion of the white dwarf G29-38. Inclusion of both physical effects, high grain opacities and thermal bath, increases the mass range (0.034-0.063 solar masses) of viable models significantly, yet the final determination of whether the object is indeed a BD requires improvements in the observations of the system's properties. 37 refs.

  4. Brown dwarfs as close companions to white dwarfs

    NASA Technical Reports Server (NTRS)

    Stringfellow, Guy S.; Bodenheimer, Peter; Black, David C.

    1990-01-01

    The influence of the radiation flux emitted by a white dwarf primary on the evolution of a closely orbiting brown dwarf (BD) companion is investigated. Full stellar evolutionary calculations are presented for both isolated and thermal bath cases, including effects of large variations in the atmospheric grain opacities. High grain opacities significantly increase the radii of the BDs, but the thermal bath does not. The major influence of the thermal bath is to increase substantially the surface temperature and luminosity of the BD at a given age. These results are compared with the observational properties of the possible BD companion of the white dwarf G29-38. Inclusion of both physical effects, high grain opacities and thermal bath, increases the mass range (0.034-0.063 solar masses) of viable models significantly, yet the final determination of whether the object is indeed a BD requires improvements in the observations of the system's properties.

  5. Dwarf busting in Abell 868

    NASA Astrophysics Data System (ADS)

    Driver, Simon

    1999-07-01

    We request 24 orbits to obtain a deep mosaic {6 * 4-orbit pointings} of the central region of A868, a rich Abell cluster which we have imaged comprehensively from the ground. The objective is to identify and characterise the morphological nature of the dwarf galaxy population{s} responsible for the steep upturn seen in this cluster's luminosity function. While similar upturns have been reported in many clusters, the specifics of the dwarf population remain unknown as these objects cannot be resolved from the ground. What type of dwarf galaxies are they ? Is there more than one population contributing ? How are they clustered ? By obtaining deep high-resolution HST WFPC2 imaging over a central field roughly 7.5' * 3.75' we will be able to measure morphologies, light- profiles and the clustering properties of the dwarf population{s} down to M_I = -16 mags {H_o=75kms^-1Mpc^-1}. Although we shall primarily concentrate on the dwarf galaxies, we will also recover the cluster's morphological luminosity distributions for elliptical, spirals and irregulars over a broad absolute magnitude range {-24 < M_I < -16 mags} as well as the more quantitative bivariate brightness distribution {- 24 < M_I < -16 mags, 17.0 < mu_e^I < 25 mags per sq arcsec}. Comparing these results to those recently derived for the general field will provide an insight into the environmental influences on morphology and surface brightness.

  6. Alpine and pre-Alpine magmatism in the root-zone of the western Central Alps

    NASA Astrophysics Data System (ADS)

    Romer, R. L.; Schärer, U.; Steck, Albrecht

    1996-03-01

    The highest grade of metamorphism and associated structural elements in orogenic belts may be inherited from earlier orogenic events. We illustrate this point using magmatic and metamorphic rocks from the southern steep belt of the Lepontine Gneiss Dome (Central Alps). The U-Pb zircon ages from an anatectic granite at Verampio and migmatites at Corcapolo and Lavertezzo yield 280 290 Ma, i.e., Hercynian ages. These ages indicate that the highest grade of metamorphism in several crystalline nappes of the Lepontine Gneiss Dome is pre-Alpine. Alpine metamorphism reached sufficiently high grade to reset the Rb-Sr and K-Ar systematics of mica and amphibole, but generally did not result in crustal melting, except in the steep belt to the north of the Insubric Line, where numerous 29 to 26 Ma old pegmatites and aplites had intruded syn- and post-kinematically into gneisses of the ductile Simplon Shear Zone. The emplacement age of these pegmatites gives a minimum estimate for the age of the Alpine metamorphic peak in the Monte Rosa nappe. The U-Pb titanite ages of 33 to 31 Ma from felsic porphyritic veins represent a minimum-age estimate for Alpine metamorphism in the Sesia Zone. A porphyric vein emplaced at 448±5 Ma (U-Pb monazite) demonstrates that there existed a consolidated Caledonian basement in the Sesia Zone.

  7. Water resources: Research network to track alpine water

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The water cycle in alpine environments worldwide supplies fresh water to vast downstream areas inhabited by more than half of humanity. The International Network for Alpine Research Catchment Hydrology (INARCH) was launched this year by the Global Energy and Water Exchanges project of the World Clim...

  8. Seasonal Snow Cold Content Dynamics in the Alpine and Sub-Alpine, Niwot Ridge, Colorado, USA

    NASA Astrophysics Data System (ADS)

    Jennings, K. S.; Molotch, N. P.

    2015-12-01

    Cold content represents the energy required to warm a sub-freezing snowpack to an isothermal 0°C. Across daily and seasonal time scales it is a dynamic interplay between the forces of snowpack accumulation/cooling and warming. Cold content determines snowmelt timing and is an important component of the annual energy budget of mountain sites with seasonal snowpacks. However, little is understood about seasonal snowpack cold content dynamics as calculating cold content requires depth-weighted snowpack temperature and snow water equivalent (SWE) measurements, which are scarce. A spatially distributed network of snow pits has been sampled since 1993 at the Niwot Ridge Long Term Ecological Research site on the eastern slope of the Continental Divide in Colorado's Front Range mountains. This study uses data from 3 pit sites that have at least 8 years of observations and represent alpine and sub-alpine environments. For these pits, cold content is strongly related to SWE during the cold content accumulation phase, here defined as December, January, and February. Average peak cold content ranges between -2.5 MJ m-2 and -9.2 MJ m-2 for the three sites and is strongly related to peak SWE. On average, cold content reaches its maximum on February 26, which is 61 days before the average date of peak SWE (i.e., the snowpack's cold content is satisfied over an average of 61 days). At the alpine site, later peak cold content and SWE was observed relative to the lower elevation sub-alpine sites. Interestingly, the alpine site had a smaller gap between peak cold content and SWE (55 days versus 67 days for the alpine and sub-alpine sites, respectively). The gap between peak cold content and peak SWE is primarily a function of the increase in SWE between the two dates. Hence, persistent snowfall after the date of peak cold content can delay the onset of snowmelt even if peak cold content was relatively low. Improving our understanding of seasonal cold content dynamics in mountain

  9. Carbon sequestration in two alpine soils on the Tibetan Plateau.

    PubMed

    Tian, Yu-Qiang; Xu, Xing-Liang; Song, Ming-Hua; Zhou, Cai-Ping; Gao, Qiong; Ouyang, Hua

    2009-09-01

    Soil carbon sequestration was estimated in a conifer forest and an alpine meadow on the Tibetan Plateau using a carbon-14 radioactive label provided by thermonuclear weapon tests (known as bomb-(14)C). Soil organic matter was physically separated into light and heavy fractions. The concentration spike of bomb-(14)C occurred at a soil depth of 4 cm in both the forest soil and the alpine meadow soil. Based on the depth of the bomb-(14)C spike, the carbon sequestration rate was determined to be 38.5 g C/m(2) per year for the forest soil and 27.1 g C/m(2) per year for the alpine meadow soil. Considering that more than 60% of soil organic carbon (SOC) is stored in the heavy fraction and the large area of alpine forests and meadows on the Tibetan Plateau, these alpine ecosystems might partially contribute to "the missing carbon sink". PMID:19723249

  10. Characterizing streamflow generation in Alpine catchments

    NASA Astrophysics Data System (ADS)

    Chiogna, Gabriele; Cano Paoli, Karina; Bellin, Alberto

    2016-04-01

    Developing effective hydrological models for streamflow generation in Alpine catchments is challenging due to the inherent complexity of the intertwined processes controlling water transfer from hillslopes to streams and along the river network. With water discharge as the sole observational variable it is impossible to differentiate between different streamflow sources, and modelling activity is often limited to simplified phenomenological rainfall-runoff models. This study focuses on quantifying streamflow sources at different temporal scales and the associated uncertainty by using natural tracer data (electrical conductivity, oxygen and hydrogen stable isotopes ratios) as observational variables supplementing streamflow measurements. We determine the spatial and temporal hydrological behavior and the mean residence time of water in the Vermigliana catchment, North-Eastern Italy and we separate contributions to streamflow originating from Presena and Presanella glaciers, both exerting a strong control on the hydrologic budget of the study site. Furthermore, we identify a seasonal control on the effect of storm events. The catchment responded rapidly to precipitation events in early autumn, it was unaffected by precipitation events in early spring, while runoff generation was enhanced by snow melting in late autumn. Air temperature is identified as the main controlling parameter, in addition to precipitation. Two-component mixing analysis showed that the relative contribution of new water, which can contribute up to 75% of total streamflow, is very rapid. Only two hours time-lag was observed between the beginning of the precipitation event and the emergence of a significant contribution of new water. These results evidence the relevance of mixing between pre-event and event water in the Vermigliana catchment, and in similar high elevation Alpine catchments. This study provides new insights on the dynamics of streamflow generation in Alpine catchments and a

  11. 3D cartography of the Alpine Arc

    NASA Astrophysics Data System (ADS)

    Vouillamoz, N.; Sue, C.; Champagnac, J. D.; Calcagno, P.

    2012-04-01

    We present a 3D cartography of the alpine arc, a highly non-cylindrical mountain belt, built using the 3D GeoModeller of the BRGM (French geological survey). The model allows to handle the large-scale 3D structure of seventeen major crustal units of the belt (from the lower crust to the sedimentary cover nappes), and two main discontinuities (the Insubric line and the Crustal Penninic Front). It provides a unique document to better understand their structural relationships and to produce new sections. The study area comprises the western alpine arc, from the Jura to the Northwest, up to the Bergell granite intrusion and the Lepontine Dome to the East, and is limited to the South by the Ligurian basin. The model is limited vertically 10 km above sea level at the top, and the moho interface at the bottom. We discarded the structural relationships between the Alps sensus stricto and the surrounding geodynamic systems such as the Rhine graben or the connection with the Apennines. The 3D-model is based on the global integration of various data such as the DEM of the Alps, the moho isobaths, the simplified geological and tectonic maps of the belt, the crustal cross-sections ECORS-CROP and NFP-20, and complementary cross-sections specifically built to precise local complexities. The database has first been integrated in a GIS-project to prepare their implementation in the GeoModeller, by homogenizing the different spatial referencing systems. The global model is finally interpolated from all these data, using the potential field method. The final document is a new tri-dimentional cartography that would be used as input for further alpine studies.

  12. Branes constrictions with White Dwarfs

    NASA Astrophysics Data System (ADS)

    García-Aspeitia, Miguel A.

    2015-11-01

    We consider here a robust study of stellar dynamics for white dwarf stars with polytropic matter in the weak-field approximation using the Lane-Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze stability and compactness, in order to show whether it is possible to agree with the conventional wisdom of white dwarfs dynamics. Our results predict an average value of the brane tension of < λ rangle ≳ 84.818MeV^4, with a standard deviation σ ˜eq 82.021MeV^4, which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining higher than cosmological results provided by nucleosynthesis among others.

  13. Role of native shrubs of the Sahel in mitigating water and nutrient stresses of agricultural crops

    NASA Astrophysics Data System (ADS)

    Bayala, R.; Ghezzehei, T. A.; Bogie, N. A.; Diedhiou, I.; Dick, R.

    2015-12-01

    In the semi arid zone of the Sahel native woody shrubs are present in many farmers' fields. The native density of these shrubs is fairly low at around 200 to 300 individuals per hectare. An ongoing study in the Peanut Basin, Senegal has shown a vast improvement in crop yields when annual food crops are planted with the shrub Guiera senegalensis, especially in years of low or irregular precipitation. Shrubs in field plots established in 2003 where a rotation of peanuts and millet are grown are planted at a much higher density of 1500-1830 individuals per hectare. In order to increase the density of shrubs on the landscape, the shrubs must be cultivated. We monitored soil moisture, soil temperature, and growth of recently transplanted individuals at a field station in Thies, Senegal.This study seeks to determine the growth characteristics and water use of young shrubs in order to inform possible future plantations of the shrubs in a more intensely managed agroecosystem. If this technique of intercropping is to be expanded we must not exceed the carrying capacity of the landscape. In vulnerable ecosystems where natural resources are scarce and farming inputs are low, we must work to determine ways of exploiting the adaptation of local agroecosystems to increase the sustainability of agriculture in the region.

  14. Atlas of United States Trees, Volume 2: Alaska Trees and Common Shrubs.

    ERIC Educational Resources Information Center

    Viereck, Leslie A.; Little, Elbert L., Jr.

    This volume is the second in a series of atlases describing the natural distribution or range of native tree species in the United States. The 82 species maps include 32 of trees in Alaska, 6 of shrubs rarely reaching tree size, and 44 more of common shrubs. More than 20 additional maps summarize environmental factors and furnish general…

  15. SIMULATING SMALL MAMMAL EFFECTS ON GRASS-SHRUB ECOTONES IN ARID ECOSYSTEMS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Several processes leading to shrub encroachment within semiarid and arid grasslands have been identified. However, the role of small animals in shifting dominance between grasses and shrubs at their ecotones has not been well studied, especially in combination with other factors, such as drought, c...

  16. HIGH FOLIAR NITROGEN IN DESERT SHRUBS: AN IMPORTANT ECOSYSTEM TRAIT OR DEFECTIVE DESERT DOCTRINE?

    EPA Science Inventory

    Nitrogen concentrations in green and senesced leaves of perennial desert shrubs were compiled from a worldwide literature search to test the validity of the doctrine that desert shrubs produce foliage and leaf litter much richer in nitrogen than that in the foliage of plants from...

  17. Numerical modeling evapotranspiration flux components in shrub-encroached grassland in Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Wang, Pei; Li, Xiao-Yan; Huang, Jie-Yu; Yang, Wen-Xin; Wang, Qi-Dan; Xu, Kun; Zheng, Xiao-Ran

    2016-04-01

    Shrub encroachment into arid grasslands occurs around the world. However, few works on shrub encroachment has been conducted in China. Moreover, its hydrological implications remain poorly investigated in arid and semiarid regions. This study combined a two-source energy balanced model and Newton-Raphson iteration scheme to simulate the evapotranspiration (ET) and their components of shrub-encroached(with 15.4% shrub coverage) grassland in Inner Mongolia. Good agreements of ET flux between modelled and measured by Bowen ratio method with relatively insensitive to uncertainties/errors in the assigned models parameters or in measured input variables for its components illustrated that our model was feasible for simulating evapotranspiration flux components in shrub-encroached grassland. The transpiration fraction(T /ET)account for 58±17%during the growing season. With the designed shrub encroachment extreme scenarios (maximum and minimum coverage),the contribution of shrub to local plant transpiration (Tshrub/T) was 20.06±7%during the growing season. Canopy conductance was the main controlling factor of T /ET. In diurnal scale short wave solar radiation was the direct influential factor while in seasonal scale leaf area index (LAI) and soil water content were the direct influential factors. We find that the seasonal variation of Tshrub/T has a good relationship with ratio of LAIshrub/LAI, and rainfall characteristics widened the difference of contribution of shrub and herbs to ecosystem evapotranspiration.

  18. Errors in LiDAR-derived shrub height and crown area on sloped terrain

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study developed and tested four methodologies for determining shrub height measurements with LiDAR data in a semiarid shrub-steppe in southwestern Idaho, USA. Unique to this study was the focus of sagebrush height measurements on sloped terrain. The study also developed one of the first metho...

  19. Shrub expansion in northern Chihuahuan Desert grasslands: Spatial patterns and biophysical constraints

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Conserving and restoring grasslands and shrub-steppe has important ecological and socioeconomic implications in arid rangelands of the world. Among the greatest contemporary threats to the structure, function and biological diversity of desert grassland and shrub savanna ecosystems of the southweste...

  20. Arctic Shrub Growth Response to Climate Variation and Infrastructure Development on the North Slope of Alaska

    NASA Astrophysics Data System (ADS)

    Ackerman, D.; Finlay, J. C.; Griffin, D.

    2015-12-01

    Woody shrub growth in the arctic tundra is increasing on a circumpolar scale. Shrub expansion alters land-atmosphere carbon fluxes, nutrient cycling, and habitat structure. Despite these ecosystem effects, the drivers of shrub expansion have not been precisely established at the landscape scale. This project examined two proposed anthropogenic drivers: global climate change and local infrastructure development, a press disturbance that generates high levels of dust deposition. Effects of global change were studied using dendrochronology to establish a relationship between climate and annual growth in Betula and Salix shrubs growing in the Alaskan low Arctic. To understand the spatial heterogeneity of shrub expansion, this analysis was replicated in shrub populations across levels of landscape properties including soil moisture and substrate age. Effects of dust deposition on normalized difference vegetation index (NDVI) and photosynthetic rate were measured on transects up to 625 meters from the Dalton Highway. Dust deposition rates decreased exponentially with distance from road, matching previous models of road dust deposition. NDVI tracked deposition rates closely, but photosynthetic rates were not strongly affected by deposition. These results suggest that dust deposition may locally bias remote sensing measurements such as NDVI, without altering internal physiological processes such as photosynthesis in arctic shrubs. Distinguishing between the effects of landscape properties, climate, and disturbance will improve our predictions of the biogeochemical feedbacks of arctic shrub expansion, with potential application in climate change modeling.

  1. Effects of grass and shrub cover on the critical unit stream power in overland flow

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Improved knowledge of the effect of grass and shrub cover in overland flow can provide valuable information for soil and water conservation programs. Laboratory simulated rainfall studies were conducted to determine the effect of grasses and shrubs on runoff and soil loss and to ascertain the relati...

  2. Shrub encroachment alters sensitivity of soil respiration to temperature and moisture 2115

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Shrub encroachment into grasslands creates a mosaic of different soil microsites ranging from open spaces to well-developed shrub canopies, and it is unclear how this affects the spatial variability in soil respiration characteristics, such as the sensitivity to soil temperature and moisture. This i...

  3. Pluto: Dwarf planet 134340

    NASA Astrophysics Data System (ADS)

    Ksanfomality, L. V.

    2016-01-01

    In recent decades, investigations of Pluto with up-to-date astronomical instruments yielded results that have been generally confirmed by the New Horizons mission. In 2006, in Prague, the General Assembly of the International Astronomical Union (IAU) reclassified Pluto as a member of the dwarf planet category according to the criteria defined by the IAU for the term "planet". At the same time, interest in studies of Pluto was increasing, while the space investigations of Pluto were delayed. In 2006, the New Horizons Pluto spacecraft started its journey to Pluto. On July 14, 2015, the spacecraft, being in fly-by mode, made its closest approach to Pluto. The heterogeneities and properties of the surface and rarified atmosphere were investigated thoroughly. Due to the extreme remoteness of the spacecraft and the energy limitations, it will take 18 months to transmit the whole data volume. Along with the preliminary results of the New Horizons Pluto mission, this paper reviews the basics on Pluto and its moons acquired from the ground-based observations and with the Hubble Space Telescope (HST). There are only a few meteorite craters on the surfaces of Pluto and Charon, which distinctly marks them apart from such satellites of the giant planets as Ganymede and Callisto. The explanation is that the surface of Pluto is young: its age is estimated at less than 100 Myr. Ice glaciers of apparently a nitrogen nature were found. Nitrogen is also the main component of the atmosphere of Pluto. The planet demonstrates the signs of strong geologic activity, though the energy sources of these processes are unknown.

  4. Is leg compression beneficial for alpine skiers?

    PubMed Central

    2013-01-01

    Background This study examined the effects of different levels of compression (0, 20 and 40 mmHg) produced by leg garments on selected psycho-physiological measures of performance while exposed to passive vibration (60 Hz, amplitude 4-6 mm) and performing 3-min of alpine skiing tuck position. Methods Prior to, during and following the experiment the electromygraphic (EMG) activity of different muscles, cardio-respiratory data, changes in total hemoglobin, tissue oxygenation and oscillatory movement of m. vastus lateralis, blood lactate and perceptual data of 12 highly trained alpine skiers were recorded. Maximal isometric knee extension and flexion strength, balance, and jumping performance were assessed before and after the experiment. Results The knee angle (−10°) and oscillatory movement (−20-25.5%) were lower with compression (P < 0.05 in all cases). The EMG activities of the tibialis anterior (20.2-28.9%), gastrocnemius medialis (4.9-15.1%), rectus femoris (9.6-23.5%), and vastus medialis (13.1-13.7%) muscles were all elevated by compression (P < 0.05 in all cases). Total hemoglobin was maintained during the 3-min period of simulated skiing with 20 or 40 mmHg compression, but the tissue saturation index was lower (P < 0.05) than with no compression. No differences in respiratory parameters, heart rate or blood lactate concentration were observed with or maximal isometric knee extension and flexion strength, balance, and jumping performance following simulated skiing for 3 min in the downhill tuck position were the same as in the absence of compression. Conclusions These findings demonstrate that with leg compression, alpine skiers could maintain a deeper tuck position with less perceived exertion and greater deoxygenation of the vastus lateralis muscle, with no differences in whole-body oxygen consumption or blood lactate concentration. These changes occurred without compromising maximal leg strength, jumping performance or balance

  5. Modelling vegetation dynamics for Alpine meadows

    NASA Astrophysics Data System (ADS)

    Della Chiesa, Stefano; Bertoldi, Giacomo; Wohlfahrt, Georg; Rist, Armin; Niedrist, Georg; Albertson, John D.; Tappeiner, Ulrike

    2010-05-01

    Regional climate scenarios predict a temperature increase and a summer precipitation decrease for the European Alps. This is expected to lead to longer vegetation periods, but also to drought stress in Alpine meadows ecosystems. It is therefore uncertain if the predicted climatic changes will lead to an increase or decrease of biomass production in these grassland ecosystems. Understanding plant growth requires to consider the complex interactions between soil, atmosphere and climate via its physiological properties, in particular LAI, stomatal resistance, rooting depth, albedo, surface roughness and effects on soil moisture. Vegetation Dynamic Models (VDM) coupled with hydrological models take into account these interactions in order to study and estimate biomass production quantitatively. In this contribution, the VDM previously developed by Montaldo et al. (2005) for semi-arid environments is extended to Alpine meadows in the Stubai Valley (Eastern Austria) which are typically not subjected to water and nutrient stresses, but undergoing low temperature limitations. The aim is to assess the model robustness. Moreover, the effects of mowing practice during the season were taken into consideration. The VDM has then been implemented in the distributed hydrological model GEOtop (Rigon et al., 2006). The VDM performed well in the considered case study. The validation and calibration of the model is presented and then the effects of increased temperature and decreased precipitation are investigated numerically. In order to evaluate in the field the effects of climatic change on Alpine grassland biomass production, the inner Alpine continental Mazia Valley (South Tyrol, Italy) has been chosen in 2009 for Long-Term Ecological Research. These climatic changes will be simulated by manipulations along an altitudinal gradient comprising measuring stations at about 1000 m, 1500 m and 2000 m a.s.l.. Meadow monoliths will be transplanted downslope to simulate temperature

  6. High precipitation and seeded species competition reduce seeded shrub establishment during dryland restoration.

    PubMed

    Rinella, Matthew J; Hammond, Darcy H; Bryant, Ana-Elisa M; Kozar, Brian J

    2015-06-01

    Drylands comprise 40% of Earth's land mass and are critical to food security, carbon sequestration, and threatened and endangered wildlife. Exotic weed invasions, overgrazing, energy extraction, and other factors have degraded many drylands, and this has placed an increased emphasis on dryland restoration. The increased restoration focus has generated a wealth of experience, innovations and empirical data, yet the goal of restoring diverse, native, dryland plant assemblages composed of grasses, forbs, and shrubs has generally proven beyond reach. Of particular concern are shrubs, which often fail to establish or establish at trivially low densities. We used data from two Great Plains, USA coal mines to explore factors regulating shrub establishment. Our predictor data related to weather and restoration (e.g., seed rates, rock cover) variables, and our response data described shrub abundances on fields of the mines. We found that seeded non-shrubs, especially grasses, formed an important competitive barrier to shrub establishment: With every one standard deviation increase in non-shrub seed rate, the probability shrubs were present decreased ~0.1 and shrub cover decreased ~35%. Since new fields were seeded almost every year for > 20 years, the data also provided a unique opportunity to explore effects of stochastic drivers (i.e., precipitation, year effects). With every one standard deviation increase in precipitation the first growing season following seeding, the probability shrubs were present decreased ~0.07 and shrub cover decreased ~47%. High precipitation appeared to harm shrubs by increasing grass growth/competition. Also, weak evidence suggested shrub establishment was better in rockier fields where grass abundance/competition was lower. Multiple lines of evidence suggest reducing grass seed rates below levels typically used in Great Plains restoration would benefit shrubs without substantially impacting grass stand development over the long term. We used

  7. Deciduous shrubs for ozone bioindication: Hibiscus syriacus as an example.

    PubMed

    Paoletti, Elena; Ferrara, Anna Maria; Calatayud, Vicent; Cerveró, Júlia; Giannetti, Fabio; Sanz, María José; Manning, William J

    2009-03-01

    Ozone-like visible injury was detected on Hibiscus syriacus plants used as ornamental hedges. Weekly spray of the antiozonant ethylenediurea (EDU, 300ppm) confirmed that the injury was induced by ambient ozone. EDU induced a 75% reduction in visible injury. Injury was more severe on the western than on the eastern exposure of the hedge. This factor of variability should be considered in ozone biomonitoring programmes. Seeds were collected and seedlings were artificially exposed to ozone in filtered vs. not-filtered (+30ppb) Open-Top Chambers. The level of exposure inducing visible injury in the OTC seedlings was lower than that in the ambient-grown hedge. The occurrence of visible injury in the OTC confirmed that the ozone sensitivity was heritable and suggested that symptomatic plants of this deciduous shrub population can be successfully used as ozone bioindicators. EDU is recommended as a simple tool for diagnosing ambient ozone visible injury on field vegetation. PMID:19081168

  8. Assessing the Relationship Between Spectral Vegetation Indices and Shrub Cover in the Jornada Basin, New Mexico

    NASA Technical Reports Server (NTRS)

    Duncan, Jeff; Stow, D.; Franklin, J.; Hope, A.

    1993-01-01

    We assessed the statistical relations between Spectral Vegetation Indices (SVI's) derived from SPOT multi-spectral data and semi-arid shrub cover at the Jornada LTER site in New Mexico. Despite a limited range of shrub cover in the sample the analyses resulted in r(sup 2) values as high as 0 central dot 77. Greenness SVI's (e.g., Simple Ratio, NDVI, SAVI, PVI and an orthogonal Greenness index) were shown to be more sensitive to shrub type and phenology than brightness SVis (e.g., green, red and near-infrared reflectances and a Brightness index). The results varied substantially with small-scale changes in plot size (60m by 60m to 100m by 100m) as a consequence of landscape heterogeneity. The results also indicated the potential for the spectral differentiation of shrub types, and shrubs from grass, using multi-temporal, multi-spectral analysis.

  9. Age determination for Ultracool Dwarfs .

    NASA Astrophysics Data System (ADS)

    Faherty, Jacqueline K.

    Brown dwarfs are notoriously difficult to age date as they lack stable hydrogen burning hence main-sequence star age-dating techniques are inapplicable for their masses. However precise and accurate ages for individual sources are required to determine masses and disentangle how secondary parameters such as differing metallicity, cloud structure and gravity impact observables. In this contribution, I review age-dating techniques for brown dwarfs as well as ``piggy-back" techniques that rely on co-moving, higher mass, main-sequence stars for which Gaia may substantially increase the sample.

  10. Does fire severity influence shrub resprouting after spring prescribed burning?

    NASA Astrophysics Data System (ADS)

    Fernández, Cristina; Vega, José A.; Fonturbel, Teresa

    2013-04-01

    Prescribed burning is commonly used to reduce the risk of severe wildfire. However, further information about the associated environmental effects is required to help forest managers select the most appropriate treatment. To address this question, we evaluated if fire severity during spring prescribed burning significantly affects the resprouting ability of two common shrub species in shrubland under a Mediterranean climate in NW Spain. Fire behaviour and temperatures were recorded in tagged individuals of Erica australis and Pterospartum tridentatum during prescribed burning. The number and length of resprouted shoots were measured three times (6, 12 and 18 months) after the prescribed burning. The influence of a series of fire severity indicators on some plant resprouting vigour parameters was tested by canonical correlation analysis. Six months and one year after prescribed burning, soil burn severity (measured by the absolute reduction in depth of the organic soil layer, maximum temperatures in the organic soil layer and the mineral soil surface during burning and the post-fire depth of the organic soil layer) reduced the resprouting vigour of E. australis and P. tridentatum. In contrast, direct measurements of fire effects on plants (minimum branch diameter, duration of temperatures above 300 °C in the shrub crown and fireline intensity) did not affect the post-fire plant vigour. Soil burn severity during spring prescribed burning significantly affected the short-term resprouting vigour in a mixed heathland in Galicia. The lack of effects eighteen months after prescribed burning indicates the high resilience of these species and illustrates the need to conciliate fire prevention and conservation goals.

  11. Effects of arctic shrub expansion on biophysical vs. biogeochemical drivers of litter decomposition.

    PubMed

    DeMarco, Jennie; Mack, Michelle C; Bret-Harte, M Syndonia

    2014-07-01

    Climate warming in arctic tundra may shift dominant vegetation from graminoids to deciduous shrubs, whose functional traits could, in turn, alter biotic and abiotic controls over biogeochemical cycling of carbon (C) and nitrogen (N). We investigated whether shrub-induced changes in microclimate have stronger effects on litter decomposition and nutrient release than changes in litter quality and quantity. In arctic tundra near Toolik Lake, Alaska, USA, we incubated a common substrate in a snow-addition experiment to test whether snow accumulation around arctic deciduous shrubs altered the environment enough to increase litter decomposition rates. We compared the influence of litter quality on the rate of litter and N loss by decomposing litter from four different plant functional types in a common site. We used aboveground net primary production values and estimated decay constant (k) values from our decomposition experiments to calculate community-weighted mass loss for each site. Snow addition had no effect on decomposition of the common substrate, and the site with the highest abundance of shrubs had the lowest decomposition rates. Species varied in their decomposition rates, with species from the same functional type not always following similar patterns. Community-weighted mass loss was 1.5 times greater in the high shrub site, and only slightly decreased when adjusted for soil environment, suggesting that litter quality and quantity are the primary drivers of community decomposition. Our findings suggest that on a short time scale, the changes in soil environment associated with snow trapping by shrubs are unlikely to influence litter nutrient turnover enough to drive positive snow-shrub feedbacks. The mechanisms driving shrub expansion are more likely to do with shrub-litter feedbacks, where the higher growth rates and N uptake by shrubs allows them to produce more leaves, resulting in a larger litter N pool and faster internal cycling of nutrients. PMID

  12. Throughfall and its spatial variability beneath xerophytic shrub canopies within water-limited arid desert ecosystems

    NASA Astrophysics Data System (ADS)

    Zhang, Ya-feng; Wang, Xin-ping; Hu, Rui; Pan, Yan-xia

    2016-08-01

    Throughfall is known to be a critical component of the hydrological and biogeochemical cycles of forested ecosystems with inherently temporal and spatial variability. Yet little is understood concerning the throughfall variability of shrubs and the associated controlling factors in arid desert ecosystems. Here we systematically investigated the variability of throughfall of two morphological distinct xerophytic shrubs (Caragana korshinskii and Artemisia ordosica) within a re-vegetated arid desert ecosystem, and evaluated the effects of shrub structure and rainfall characteristics on throughfall based on heavily gauged throughfall measurements at the event scale. We found that morphological differences were not sufficient to generate significant difference (P < 0.05) in throughfall between two studied shrub species under the same rainfall and meteorological conditions in our study area, with a throughfall percentage of 69.7% for C. korshinskii and 64.3% for A. ordosica. We also observed a highly variable patchy pattern of throughfall beneath individual shrub canopies, but the spatial patterns appeared to be stable among rainfall events based on time stability analysis. Throughfall linearly increased with the increasing distance from the shrub base for both shrubs, and radial direction beneath shrub canopies had a pronounced impact on throughfall. Throughfall variability, expressed as the coefficient of variation (CV) of throughfall, tended to decline with the increase in rainfall amount, intensity and duration, and stabilized passing a certain threshold. Our findings highlight the great variability of throughfall beneath the canopies of xerophytic shrubs and the time stability of throughfall pattern among rainfall events. The spatially heterogeneous and temporally stable throughfall is expected to generate a dynamic patchy distribution of soil moisture beneath shrub canopies within arid desert ecosystems.

  13. Metabolic Profiling of Alpine and Ecuadorian Lichens.

    PubMed

    Mittermeier, Verena K; Schmitt, Nicola; Volk, Lukas P M; Suárez, Juan Pablo; Beck, Andreas; Eisenreich, Wolfgang

    2015-01-01

    Non-targeted ¹H-NMR methods were used to determine metabolite profiles from crude extracts of Alpine and Ecuadorian lichens collected from their natural habitats. In control experiments, the robustness of metabolite detection and quantification was estimated using replicate measurements of Stereocaulon alpinum extracts. The deviations in the overall metabolite fingerprints were low when analyzing S. alpinum collections from different locations or during different annual and seasonal periods. In contrast, metabolite profiles observed from extracts of different Alpine and Ecuadorian lichens clearly revealed genus- and species-specific profiles. The discriminating functions determining cluster formation in principle component analysis (PCA) were due to differences in the amounts of genus-specific compounds such as sticticin from the Sticta species, but also in the amounts of ubiquitous metabolites, such as sugar alcohols or trehalose. However, varying concentrations of these metabolites from the same lichen species e.g., due to different environmental conditions appeared of minor relevance for the overall cluster formation in PCA. The metabolic clusters matched phylogenetic analyses using nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences of lichen mycobionts, as exemplified for the genus Sticta. It can be concluded that NMR-based non-targeted metabolic profiling is a useful tool in the chemo-taxonomy of lichens. The same approach could also facilitate the discovery of novel lichen metabolites on a rapid and systematical basis. PMID:26437395

  14. FORMATION OF DWARF SPHEROIDAL GALAXIES VIA MERGERS OF DISKY DWARFS

    SciTech Connect

    Kazantzidis, Stelios; Lokas, Ewa L.; Klimentowski, Jaroslaw; Mayer, Lucio; Knebe, Alexander

    2011-10-10

    We perform collisionless N-body simulations to investigate whether binary mergers between rotationally supported dwarfs can lead to the formation of dwarf spheroidal galaxies (dSphs). Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. We select merger events from a Constrained Local Universe simulation of the Local Group (LG) and record the properties of the interacting dwarf-sized halos. This information is subsequently used to seed controlled experiments of binary encounters between dwarf galaxies consisting of exponential stellar disks embedded in cosmologically motivated dark matter halos. These simulations are designed to reproduce eight cosmological merger events, with initial masses of the interacting systems in the range {approx}(5-60) x 10{sup 7} M{sub sun}, occurring quite early in the history of the LG, more than 10 Gyr ago. We compute the properties of the merger remnants as a distant observer would and demonstrate that at least three of the simulated encounters produce systems with kinematic and structural properties akin to those of the classic dSphs in the LG. Tracing the history of the remnants in the cosmological simulation to z = 0, we find that two dSph-like objects remain isolated at distances {approx}> 800 kpc from either the Milky Way or M31. These systems constitute plausible counterparts of the remote dSphs Cetus and Tucana which reside in the LG outskirts, far from the tidal influence of the primary galaxies. We conclude that merging of rotationally supported dwarfs represents a viable mechanism for the formation of dSphs in the LG and similar environments.

  15. New light on dark stars. Red dwarfs, low-mass stars, brown dwarfs.

    NASA Astrophysics Data System (ADS)

    Reid, I. N.; Hawley, S. L.

    This book presents a comprehensive discussion of both the astrophysical structure of individual M dwarf and brown dwarf star, and their collective statistical properties as a Galactic stellar population. The first section of the book discusses M dwarfs and brown dwarfs as individual objects - their observational properties, formation, internal structure and atmospheres. The second section deals with M dwarfs from the Galactic perspective - the number of stars, their possible contribution to dark matter and the missing mass and their use as probes of the stellar populations that make up our Galaxy. Contents: (1) Astronomical concepts. (2) Basic observational properties of low-mass dwarfs. (3) The structure, formation and evolution of low-mass stars and brown dwarfs. (4) The photosphere. (5) Stellar activity. (6) A Galactic structure primer. (7) The stellar luminosity function. (8) The mass function. (9) Brown dwarfs: new light on dark stars. (10) Extrasolar planets. (11) M dwarfs in the Galactic halo. Appendix: The 8 parsec sample.

  16. Mediterranean shrub vegetation: soil protection vs. water availability

    NASA Astrophysics Data System (ADS)

    García Estringana, Pablo; Nieves Alonso-Blázquez, M.; Alegre, Alegre; Cerdà, Artemi

    2014-05-01

    Soil Erosion and Land Degradation are closely related to the changes in the vegetation cover (Zhao et al., 2013). Although other factors such as rainfall intensiy or slope (Ziadat and Taimeh, 2013) the plant covers is the main factor that controls the soil erosion (Haregeweyn, 2013). Plant cover is the main factor of soil erosion processes as the vegetation control the infiltration and runoff generation (Cerdà, 1998a; Kargar Chigani et al., 2012). Vegetation cover acts in a complex way in influencing on the one hand on runoff and soil loss and on the other hand on the amount and the way that rainfall reaches the soil surface. In arid and semiarid regions, where erosion is one of the main degradation processes and water is a scant resource, a minimum percentage of vegetation coverage is necessary to protect the soil from erosion, but without compromising the availability of water (Belmonte Serrato and Romero Diaz, 1998). This is mainly controlled by the vegetation distribution (Cerdà, 1997a; Cammeraat et al., 2010; Kakembo et al., 2012). Land abandonment is common in Mediterranean region under extensive land use (Cerdà, 1997b; García-Ruiz, 2010). Abandoned lands typically have a rolling landscape with steep slopes, and are dominated by herbaceous communities that grow on pasture land interspersed by shrubs. Land abandonment use to trigger an increase in soil erosion, but the vegetation recovery reduces the impact of the vegetation. The goal of this work is to assess the effects of different Mediterranean shrub species (Dorycnium pentaphyllum Scop., Medicago strasseri, Colutea arborescens L., Retama sphaerocarpa, L., Pistacia Lentiscus L. and Quercus coccifera L.) on soil protection (runoff and soil losses) and on rainfall reaching soil surface (rainfall partitioning fluxes). To characterize the effects of shrub vegetation and to evaluate their effects on soil protection, two field experiments were carried out. The presence of shrub vegetation reduced runoff by

  17. Shrubs as landscape modulators in semiarid shrubland - long-term studies in Park Shaked LTER, Israel

    NASA Astrophysics Data System (ADS)

    Boeken, Bertrand; Shachak, Moshe; Zaady, Eli; Brand, Sol

    2010-05-01

    Small shrubs (Atractylis serratuloides and Noaea mucronata) in semiarid shrublands of the northern Negev of Israel (at 150 to 200 mm of rainfall per year) form shrub patches in the soil crust matrix by multiple changes in their immediate environment. The changes include structural modification by creation of a soil mound and water flow redistribution, which produce enriched soil moisture patches. These changes have far-reaching effects on water regime, soil erosion and biological productivity and diversity in watersheds. Landscape modulation by the shrub patches results from: 1) interactions of the growing shrubs with flows of water, sediment and organic matter by wind and runoff, 2) accumulation of material deposited under the shrub canopy, 3) changes in the topography and structure of the surface and substrate near and under the shrubs, 4) successional replacement of shrub species, and 5) colonization by a herbaceous understory. The patch formation processes are linked, resulting in positive feedback relationships between the growing shrub, the properties of the mound underneath, the interception of resource flows, and the density of the herbaceous understory vegetation. Since the shrub patches intercept resource flows, and form patterns of patches on the slopes, they have larger-scale effects on the functioning of the ecosystem by controlling the retention and leakage of resources in the watershed. At the slope scale this gives rise to positive and negative feedbacks. Accumulation of material causes mound expansion, increasing deposition (positive feedback 1), while increased resource retention enhances shrub and herbaceous growth, also causing more accumulation and retention (positive feedback 2). On the other hand, when mounds increase, soil crust cover that generates runoff decreases, halting the process of shrub patch expansion (negative feedback). We present a conceptual model of a growing shrub patch with its direct and large-scale effects on the

  18. Andromeda and the Seven Dwarfs

    NASA Astrophysics Data System (ADS)

    Brasseur, C.; Rix, H.-W.; Martin, N.

    2011-07-01

    With the new generation of wide-field surveys, our understanding of the Andromeda satellite system has dramatically improved in recent years. Since 2004, 12 new dwarf galaxies have been discovered around Andromeda, doubling the number of previously known companions. What are the properties of these newly discovered dwarfs and what do they tell us about galaxy formation? Are these systems bound? Do they show evidence of multiple star formation epochs? To better understand the stellar populations of the faintest dwarfs around M 31, we have used the Large Binocular Camera (LBT) and Suprime-Cam (Subaru) to obtain photometric observations of And X, And XVII, And XVIII, And XIX, And XX, And XXI and And XXII. Reaching below the horizontal branch, these observations have allowed for accurate distance determinations to be made, together with metallicity estimates based on the red giant branch stars. Our analysis shows our 7 dwarfs to be metal poor and with large spreads in [Fe/H], it strongly suggests multiple generations of stars are present in And X, And XVII, And XVIII, and And XIX, And XXI.

  19. The Physics of White Dwarfs.

    ERIC Educational Resources Information Center

    Van Horn, Hugh M.

    1979-01-01

    Describes the current understanding of the structure and evolution of the white dwarf stars that was gained as a result of the increasingly sensitive and detailed astronomical observations coupled with calculations of the properties of matter under extreme conditions. (Author/GA)

  20. Irregular Dwarf Galaxy IC 1613

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Ultraviolet image (left) and visual image (right) of the irregular dwarf galaxy IC 1613. Low surface brightness galaxies, such as IC 1613, are more easily detected in the ultraviolet because of the low background levels compared to visual wavelengths.

  1. Pulsating Helium Atmosphere White Dwarfs

    NASA Astrophysics Data System (ADS)

    Provencal, Judith; Montgomery, Michael H.; Bischoff-Kim, Agnes; Shipman, Harry; Nitta, Atsuko; Whole Earth Telescope Collaboration

    2015-08-01

    The overwhelming majority of all stars currently on the main sequence as well as those from earlier generations will or have ended their stellar lives as white dwarf stars. White dwarfs are rich forensic laboratories linking the history and future evolution of our Galaxy. Their structure and atmospheric composition provide evidence of how the progenitors lived, how they evolved, and how they died. This information reveals details of processes governing the behavior of contemporary main sequence stars. Combined with their distribution in luminosity/temperature, white dwarfs strongly constrain models of galactic and cosmological evolution.GD358 is among the brightest (mv =13.7) and best studied of the pulsating white dwarfs. This helium atmoshere pulsator (DBV) has an extensive photometric database spanning 30 years, including nine multisite Whole Earth Telescope campaigns. GD358 exhibits a range of behaviors, from drastic changes in excited pulsation modes to variable multiplet splittings. We use GD358 as a template for an examination of the DBV class, combining photometric results with recent COS spectroscopy. The results present new questions concerning DB formation and evolution.

  2. White Dwarfs in Intermediate Polars

    NASA Astrophysics Data System (ADS)

    Belle, Kunegunda E.; Sion, E. M.

    2009-01-01

    Intermediate polars (IPs), magnetic cataclysmic variables (CVs) in which the white dwarf (WD) has an intermediate strength magnetic field (B< 5 MG), present an interesting laboratory for the study of the evolution of CVs as they contain elements of both non-magnetic and magnetic systems. Do magnetic CVs and IPs evolve in the same manner as non-magnetic systems? One answer in this puzzle may come from understanding the nature of the white dwarf in a magnetic CV. Standard CV evolution theory predicts a white dwarf temperature for a given CV orbital period and accretion rate. By investigating the temperature of white dwarfs in IPs and comparing the temperatures to those predicted from theory, we can learn where IPs fit into the model of CV evolution. Here we present the results of our continued study of the nature of WDs in IPs. We compare temperatures derived from model fits to UV spectra with temperatures calculated based on the accretion rate and binary orbital period. Our preliminary results indicate that IPs follow the general trend of magnetic CVs containing cooler WDs than non-magnetic CVs.

  3. Arid oil-field restoration: native perennial grasses suppress weeds and erosion, but also suppress native shrubs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    1. Long-lived, drought-tolerant shrubs are dominant components of many arid ecosystems, and shrubs provide multiple ecosystem services (e.g., soil stabilization, herbaceous plant facilitation, carbon storage and wildlife habitat). On denuded sites, shrub restoration is hindered by abiotic (erosion ...

  4. Protection from livestock fails to deter shrub proliferation in a desert landscape with a history of heavy grazing

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Desertification is often characterized by the replacement of mesophytic grasses with xerophytic shrubs. Livestock grazing is considered a key driver of shrub encroachment, although most evidence is anecdotal or confounded by other factors. Mapping of velvet mesquite (Prosopis velutina) shrubs in and...

  5. Pleistocene origin and population history of a neoendemic alpine butterfly.

    PubMed

    Schoville, Sean D; Stuckey, Matthew; Roderick, George K

    2011-03-01

    Alpine environments underwent dramatic transformation during glacial-interglacial cycles, with the consequence that geographical, ecological and demographic changes of alpine populations provided the opportunity for formation of neoendemic species. Several biogeographical models have been proposed to account for the unique history of alpine populations, with different expectations of genetic divergence and speciation. The expanding alpine archipelago model proposes that alpine populations expand spatially and demographically during glacial events, dispersing between mountain ranges. Under this model, alpine populations are unlikely to diverge in isolation due to substantial interpopulation gene flow. In contrast, the alpine archipelago refuge model proposes that gene flow during glacial phases is limited and populations expand demographically during interglacial phases, increasing genetic isolation and the likelihood of speciation. We assess these models by reconstructing the evolutionary history of Colias behrii, a morphologically and ecologically distinct alpine butterfly restricted to the California Sierra Nevada. C. behrii exhibits very low genetic diversity at mitochondrial and nuclear loci, limited population structure and evidence of population expansion. C. behrii and Rocky Mountain C. meadii share identical mitochondrial haplotypes, while in contrast, nuclear data indicate common ancestry between C. behrii and Cascades Range Colias pelidne. The conflict in gene genealogies may be a result of recent expansion in North American Colias, but an isolation with migration analysis indicates that genetic patterns in C. behrii might result from differential introgression following hybridization. Based on the timing of population expansion and gene flow between mountain ranges, the expanding alpine archipelago model is supported in C. behrii. PMID:21244539

  6. THREE NEW ECLIPSING WHITE-DWARF-M-DWARF BINARIES DISCOVERED IN A SEARCH FOR TRANSITING PLANETS AROUND M-DWARFS

    SciTech Connect

    Law, Nicholas M.; Kraus, Adam L.; Street, Rachel; Fulton, Benjamin J.; Shporer, Avi; Lister, Tim; Hillenbrand, Lynne A.; Baranec, Christoph; Bui, Khanh; Davis, Jack T. C.; Dekany, Richard G.; Kulkarni, S. R.; Ofek, Eran O.; Bloom, Joshua S.; Cenko, S. Bradley; Filippenko, Alexei V.; Burse, Mahesh P.; Das, H. K.; Kasliwal, Mansi M.; Nugent, Peter; and others

    2012-10-01

    We present three new eclipsing white-dwarf/M-dwarf binary systems discovered during a search for transiting planets around M-dwarfs. Unlike most known eclipsing systems of this type, the optical and infrared emission is dominated by the M-dwarf components, and the systems have optical colors and discovery light curves consistent with being Jupiter-radius transiting planets around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part of the Palomar Transient Factory (PTF). We present a graphics processing unit (GPU)-based box-least-squares search for transits that runs approximately 8 Multiplication-Sign faster than similar algorithms implemented on general purpose systems. For the discovered systems, we decompose low-resolution spectra of the systems into white-dwarf and M-dwarf components, and use radial velocity measurements and cooling models to estimate masses and radii for the white dwarfs. The systems are compact, with periods between 0.35 and 0.45 days and semimajor axes of approximately 2 R{sub Sun} (0.01 AU). The M-dwarfs have masses of approximately 0.35 M{sub Sun }, and the white dwarfs have hydrogen-rich atmospheres with temperatures of around 8000 K and have masses of approximately 0.5 M{sub Sun }. We use the Robo-AO laser guide star adaptive optics system to tentatively identify one of the objects as a triple system. We also use high-cadence photometry to put an upper limit on the white-dwarf radius of 0.025 R{sub Sun} (95% confidence) in one of the systems. Accounting for our detection efficiency and geometric factors, we estimate that 0.08%{sub -0.05%}{sup +0.10%} (90% confidence) of M-dwarfs are in these short-period, post-common-envelope white-dwarf/M-dwarf binaries where the optical light is dominated by the M-dwarf. The lack of detections at shorter periods, despite near-100% detection efficiency for such systems, suggests that binaries including these relatively low-temperature white dwarfs are preferentially found at

  7. Faint dwarfs in nearby groups

    SciTech Connect

    Speller, Ryan; Taylor, James E. E-mail: taylor@uwaterloo.ca

    2014-06-20

    The number and distribution of dwarf satellite galaxies remain a critical test of cold dark matter-dominated structure formation on small scales. Until recently, observational information about galaxy formation on these scales has been limited mainly to the Local Group. We have searched for faint analogues of Local Group dwarfs around nearby bright galaxies, using a spatial clustering analysis of the photometric catalog of the Sloan Digital Sky Survey (SDSS) Data Release 8. Several other recent searches of SDSS have detected clustered satellite populations down to Δm{sub r} ≡ (m{sub r,} {sub sat} – m{sub r,} {sub main}) ∼ 6-8, using photometric redshifts to reduce background contamination. SDSS photometric redshifts are relatively imprecise, however, for faint and nearby galaxies. Instead, we use angular size to select potential nearby dwarfs and consider only the nearest isolated bright galaxies as primaries. As a result, we are able to detect an excess clustering signal from companions down to Δm{sub r} = 12, 4 mag fainter than most recent studies. We detect an overdensity of objects at separations <400 kpc, corresponding to about 4.6 ± 0.5 satellites per central galaxy, consistent with the satellite abundance expected from the Local Group, given our selection function. Although the sample of satellites detected is incomplete by construction, since it excludes the least and most compact dwarfs, this detection provides a lower bound on the average satellite luminosity function, down to luminosities corresponding to the faintest ''classical'' dwarfs of the Local Group.

  8. AIRSAR studies of woody shrub density in semiarid rangeland: Jornada del Muerto, New Mexico

    USGS Publications Warehouse

    Musick, H.B.; Schaber, G.S.; Breed, C.S.

    1998-01-01

    This study evaluates the use of polarimetric Airborne Synthetic Aperture Radar (AIRSAR) data to assess woody shrub density in a semiarid site where the vegetation consists primarily of varied mixtures of herbaceous vegetation and shrubs. AIRSAR data and field observations of vegetation cover and growth form-composition were obtained for 59 sites in the Jornada del Muerto plain in southern New Mexico. Radar signature measures examined were C-, L- and P-band backscattering coefficients (??0) for HH, HV and W polarizations, ratios of ??0HH and ??0HV to ??0VV, and the HH-VV polarization phase difference and correlation coefficient. The most effective measure for estimation of shrub density was L-band ??0HV, which distinguished among shrub density classes with no misclassification. Sensitivity of this measure to small amounts of shrub cover was indicated by successful separation of sites with <1% shrub cover from sites with 1-5% cover. Separability of shrub density classes was generally least for C-band signature measures. A distinctive radar signature was exhibited by dense stands of Yucca elata, a semitreelike plant with uniformly thick ???10 cm diameter) fibrous stems. Yucca sites were distinguished from others by their high P-band ??0HV relative to L-band ??0HV. The results are largely explained by the greater sensitivity of lounger wavelengths to larger canopy structural elements. L-band ??0HV and other measures responsive to canopy volume scattering were more strongly related to shrub than to herbaceous plant cover because woody shrub canopies have numerous stems of the intermediate size to which L-band is most sensitive, whereas stems of this size are mostly lacking in herbaceous canopies. The uniform-diameter stems of yucca have larger dimensions to which P-band is more sensitive than L-band.This study evaluates the use of polarimetric Airborne Synthetic Aperture Radar (AIRSAR) data to assess woody shrub density in a semiarid site where the vegetation consists

  9. [Spatial distribution of aboveground biomass of shrubs in Tianlaochi catchment of the Qilian Mountains].

    PubMed

    Liang, Bei; Di, Li; Zhao, Chuan-Yan; Peng, Shou-Zhang; Peng, Huan-Hua; Wang, Chao

    2014-02-01

    This study estimated the spatial distribution of the aboveground biomass of shrubs in the Tianlaochi catchment of Qilian Mountains based on the field survey and remote sensing data. A relationship model of the aboveground biomass and its feasibly measured factors (i. e. , canopy perimeter and plant height) was built. The land use was classified by object-oriented technique with the high resolution image (GeoEye-1) of the study area, and the distribution of shrub coverage was extracted. Then the total aboveground biomass of shrubs in the study area was estimated by the relationship model with the distribution of shrub coverage. The results showed that the aboveground biomass of shrubs in the study area was 1.8 x 10(3) t and the aboveground biomass per unit area was 1598.45 kg x m(-2). The distribution of shrubs mainly was at altitudes of 3000-3700 m, and the aboveground biomass of shrubs on the sunny slope (1.15 x 10(3) t) was higher than that on the shady slope (0.65 x 10(3) t). PMID:24830234

  10. Stemflow and its significant to the fertilizer islands in desert shrub area

    NASA Astrophysics Data System (ADS)

    Wang, Xinping; Wang, Zhengning; Pan, Yanxia; Zhang, Yafeng

    2010-05-01

    Stemflow is a spatially localized point input of precipitation and fine particles of airborne dust from vegetation canopy at the plant stem and is of hydrological and ecological significance in desert shrub ecosystems, where precipitation is the sole source of water replenishment to sustaining the desert ecosystem. In the present study, stemflow production and the fine particles associated with the stemflow of the two main xerophytic shrubs was quantified by aluminum foil collar method at the desert shrub area of Shapotou Desert Experimental Research Station, Chinese Academy of Sciences. The results indicated that stemflow yield and the thresholds for stemflow occurrence varied within shrub species. The relationship between funnelling ratios and gross precipitation indicated that a certain value of precipitation was required for the shrubs. There was a large variability of funnelling ratio for the rainfall events with intensity of less than 4 mm h-1, and the variability tended to decease when rainfall intensity was greater than 4 mm h-1. Significant positive linear relationships were found between stemflow production and precipitation for the shrubs, statistical analysis showed that stemflow and fine particle yield varies as a function of meteorological conditions, canopy size and structure. An accurate modeling of stemflow water and nutrient inputs into desert soils may result in the understanding of the formation mechanism of fertilizer islands. Keywords: Desert ecosystem; Hydrology; Stemflow; Xerophytic shrub

  11. Mapping the ecological dimensions and potential distributions of endangered relic shrubs in western Ordos biodiversity center

    PubMed Central

    Zhu, Geng-Ping; Li, Hui-Qi; Zhao, Li; Man, Liang; Liu, Qiang

    2016-01-01

    Potential distributions of endemic relic shrubs in western Ordos were poorly mapped, which hindered our implementation of proper conservation. Here we investigated the applicability of ecological niche modeling for endangered relic shrubs to detect areas of priority for biodiversity conservation and analyze differences in ecological niche spaces used by relic shrubs. We applied ordination and niche modeling techniques to assess main environmental drivers of five endemic relic shrubs in western Ordos, namely, Ammopiptanthus mongolicus, Amygdalus mongolica, Helianthemum songaricum, Potaninia mongolica, and Tetraena mongolica. We calculated niche overlap metrics in gridded environmental spaces and compared geographical projections of ecological niches to determine similarities and differences of niches occupied by relic shrubs. All studied taxa presented different responses to environmental factors, which resulted in a unique combination of niche conditions. Precipitation availability and soil quality characteristics play important roles in the distributions of most shrubs. Each relic shrub is constrained by a unique set of environmental conditions, the distribution of one species cannot be implied by the distribution of another, highlighting the inadequacy of one-fits-all type of conservation measure. Our stacked habitat suitability maps revealed regions around Yellow River, which are highly suitable for most species, thereby providing high conservation value. PMID:27199260

  12. Season and light affect constitutive defenses of understory shrub species against folivorous insects

    NASA Astrophysics Data System (ADS)

    Karolewski, Piotr; Giertych, Marian J.; Żmuda, Michał; Jagodziński, Andrzej M.; Oleksyn, Jacek

    2013-11-01

    Understory shrubs contribute to overall species diversity, providing habitat and forage for animals, influence soil chemistry and forest microclimate. However, very little is known about the chemical defense of various shrub species against folivorous insects. Using six shrub species, we tested how seasonal changes and light conditions affect their constitutive defense to insect damage. We monitored leaf perforation, concentrations of total phenols, condensed tannins, nitrogen (N), and total nonstructural carbohydrates (TNC). Leaf damage caused by insects was low in Sambucus nigra, Cornus sanguinea, and Frangula alnus, intermediate in Corylus avellana and Prunus serotina, and high in Prunus padus. Leaves of all the species, when growing in high light conditions, had high concentrations of defense metabolites. Except for C. avellana, leaves of the other shrub species growing in full sun were less injured than those in shade. This may be due to higher concentrations of defense metabolites and lower concentrations of nitrogen. Similar patterns of the effects of light on metabolites studied and N were observed for leaves with varying location within the crown of individual shrubs (from the top of the south direction to the bottom of the north), as for leaves from shrubs growing in full sun and shrubs in the shade of canopy trees. A probable cause of the greater damage of more sunlit leaves of C. avellana was the fact that they were herbivorized mostly by Altica brevicollis, a specialist insect that prefers plant tissues with a high TNC level and is not very sensitive to a high level of phenolic compounds.

  13. Mapping the ecological dimensions and potential distributions of endangered relic shrubs in western Ordos biodiversity center.

    PubMed

    Zhu, Geng-Ping; Li, Hui-Qi; Zhao, Li; Man, Liang; Liu, Qiang

    2016-01-01

    Potential distributions of endemic relic shrubs in western Ordos were poorly mapped, which hindered our implementation of proper conservation. Here we investigated the applicability of ecological niche modeling for endangered relic shrubs to detect areas of priority for biodiversity conservation and analyze differences in ecological niche spaces used by relic shrubs. We applied ordination and niche modeling techniques to assess main environmental drivers of five endemic relic shrubs in western Ordos, namely, Ammopiptanthus mongolicus, Amygdalus mongolica, Helianthemum songaricum, Potaninia mongolica, and Tetraena mongolica. We calculated niche overlap metrics in gridded environmental spaces and compared geographical projections of ecological niches to determine similarities and differences of niches occupied by relic shrubs. All studied taxa presented different responses to environmental factors, which resulted in a unique combination of niche conditions. Precipitation availability and soil quality characteristics play important roles in the distributions of most shrubs. Each relic shrub is constrained by a unique set of environmental conditions, the distribution of one species cannot be implied by the distribution of another, highlighting the inadequacy of one-fits-all type of conservation measure. Our stacked habitat suitability maps revealed regions around Yellow River, which are highly suitable for most species, thereby providing high conservation value. PMID:27199260

  14. The Eastern Alpine Seismic Investigation (EASI) project

    NASA Astrophysics Data System (ADS)

    Plomerova, Jaroslava; Bianchi, Irene; Hetényi, György; Munzarova, Helena; Bokelmann, Götz; Kissling, Edi; AlpArray-EASI Working Group; AlpArray-EASI Field Team

    2015-04-01

    AlpArray (http://www.seismo.ethz.ch/research/groups/alrt/projects/alparray/) is a large European initiative to study the entire Alpine orogen at high resolution and in 3D with a large variety of methods. The core element of the initiative is an extensive and dense broadband seismological network. In addition, a number of Complementary Experiments will be conducted to focus on targeted problems. The first implemented AlpArray Complementary Experiment is called Eastern Alpine Seismic Investigation (EASI). The Eastern, "straight" part of the Alps is home to a number of open questions, e.g., the origin of the hanging lithospheric slab (Adriatic or European?), the nature of the Moho "hole" between the two plates, the anisotropic nature of the lower crust, and the relationship of the Alpine orogen to the adjacent foreland basin and the lithospheric blocks of the Bohemian Massif. Our research methods include tomography, ambient noise analysis and receiver functions, with anisotropy included in all three types of investigations as well as in shear-wave splitting analyses. The depth range of investigations encompasses the crust and the mantle lithosphere, down to the LAB. In this presentation we detail the design of the experiment. EASI is composed of 55 broadband seismic stations, deployed in a zig-zag pattern on either side of the central longitude line of 13.35°E. The planned north-south distance between stations was 10 km, the distance of each station to either side of the central line was 6 km. We aimed to keep the stations within 1.5 km of the target location, as much as topographic, field and infrastructure condition allowed. The result: with respect to the original deployment plans the closest match is 164m, 10 stations are within 500m, 31 stations are within 1.5km which is also the average match, and the farthest is 4.4km. The overall result remained a very linear and regularly spaced array, spanning 540 km from the Czech-German border to the Adriatic Sea. The

  15. Seed distribution of four co-occurring grasses around Artemisia halodendron shrubs in a sandy habitat

    NASA Astrophysics Data System (ADS)

    Li, Feng-Rui; Zhao, Wen-Zhi; Kang, Ling-Fen; Liu, Ji-Liang; Huang, Zhi-Gang; Wang, Qi

    2009-05-01

    In a natural population of the perennial semi-shrub Artemisia halodendron in a shifting sandy habitat in the Horqin Desert of eastern Inner Mongolia, six isolated adult A. halodendron individuals of similar canopy size were chosen as target plants. The density of seeds in the top 5 cm soil depth around shrubs was measured using transects aligned to the four main wind directions and at different distances from the shrub base on both the windward and leeward sides. The effects of shrub presence on seed distribution of four co-occurring grasses were examined by linking seed distribution to seed traits. Of the four species, Setaris viridis and Eragrostis pilosa had small but similar seed mass, while Chloris virgata and Aristida adscensionis had large but similar seed mass. The species were grouped into two cohorts: small-seeded vs. large-seeded cohorts, and shrub presence effects on seed distribution of both cohorts were examined. We found marked difference in the seed distribution pattern among species, especially between the small-seeded and large-seeded cohorts. The small-seeded cohort had significantly higher seed accumulation on the windward than the leeward sides in the most and least prevailing wind directions and much higher seed accumulation on the leeward than the windward sides in the second and third most prevailing wind directions, while opposite patterns occurred in the large-seeded cohort. Four species also showed marked variation in the seed distribution pattern among transects and between windward and leeward sides of each transect. This study provided further evidence that shrubs embedded in a matrix of herbaceous plants is a key cause of spatial heterogeneity in seed availability of herbaceous species. However, seed distribution responses to the presence of shrubs will vary with species as well as with wind direction, sampling position (windward vs. leeward sides of the shrub) and distance from the shrub.

  16. Range expansion of moose in arctic Alaska linked to warming and increased shrub habitat

    USGS Publications Warehouse

    Tape, Ken D.; Gustine, David D.; Reuss, Roger W.; Adams, Layne G.; Clark, Jason A.

    2016-01-01

    Twentieth century warming has increased vegetation productivity and shrub cover across northern tundra and treeline regions, but effects on terrestrial wildlife have not been demonstrated on a comparable scale. During this period, Alaskan moose (Alces alces gigas) extended their range from the boreal forest into tundra riparian shrub habitat; similar extensions have been observed in Canada (A. a. andersoni) and Eurasia (A. a. alces). Northern moose distribution is thought to be limited by forage availability above the snow in late winter, so the observed increase in shrub habitat could be causing the northward moose establishment, but a previous hypothesis suggested that hunting cessation triggered moose establishment. Here, we use recent changes in shrub cover and empirical relationships between shrub height and growing season temperature to estimate available moose habitat in Arctic Alaska c. 1860. We estimate that riparian shrubs were approximately 1.1 m tall c. 1860, greatly reducing the available forage above the snowpack, compared to 2 m tall in 2009. We believe that increases in riparian shrub habitat after 1860 allowed moose to colonize tundra regions of Alaska hundreds of kilometers north and west of previous distribution limits. The northern shift in the distribution of moose, like that of snowshoe hares, has been in response to the spread of their shrub habitat in the Arctic, but at the same time, herbivores have likely had pronounced impacts on the structure and function of these shrub communities. These northward range shifts are a bellwether for other boreal species and their associated predators.

  17. Greater deciduous shrub abundance extends tundra peak season and increases modeled net CO2 uptake.

    PubMed

    Sweet, Shannan K; Griffin, Kevin L; Steltzer, Heidi; Gough, Laura; Boelman, Natalie T

    2015-06-01

    Satellite studies of the terrestrial Arctic report increased summer greening and longer overall growing and peak seasons since the 1980s, which increases productivity and the period of carbon uptake. These trends are attributed to increasing air temperatures and reduced snow cover duration in spring and fall. Concurrently, deciduous shrubs are becoming increasingly abundant in tundra landscapes, which may also impact canopy phenology and productivity. Our aim was to determine the influence of greater deciduous shrub abundance on tundra canopy phenology and subsequent impacts on net ecosystem carbon exchange (NEE) during the growing and peak seasons in the arctic foothills region of Alaska. We compared deciduous shrub-dominated and evergreen/graminoid-dominated community-level canopy phenology throughout the growing season using the normalized difference vegetation index (NDVI). We used a tundra plant-community-specific leaf area index (LAI) model to estimate LAI throughout the green season and a tundra-specific NEE model to estimate the impact of greater deciduous shrub abundance and associated shifts in both leaf area and canopy phenology on tundra carbon flux. We found that deciduous shrub canopies reached the onset of peak greenness 13 days earlier and the onset of senescence 3 days earlier compared to evergreen/graminoid canopies, resulting in a 10-day extension of the peak season. The combined effect of the longer peak season and greater leaf area of deciduous shrub canopies almost tripled the modeled net carbon uptake of deciduous shrub communities compared to evergreen/graminoid communities, while the longer peak season alone resulted in 84% greater carbon uptake in deciduous shrub communities. These results suggest that greater deciduous shrub abundance increases carbon uptake not only due to greater leaf area, but also due to an extension of the period of peak greenness, which extends the period of maximum carbon uptake. PMID:25556338

  18. RESOLVED SPECTROSCOPY OF A BROWN DWARF BINARY AT THE T DWARF/Y DWARF TRANSITION

    SciTech Connect

    Burgasser, Adam J.; Gelino, Christopher R.; Kirkpatrick, J. Davy; Cushing, Michael C.

    2012-01-20

    We report resolved near-infrared imaging and spectroscopic observations of the T8.5 binary WISEP J045853.90+643452.6AB obtained with Keck/NIRC2, Keck/OSIRIS, and the Keck Laser Guide Star Adaptive Optics system. These data confirm common proper and radial motion for the two components, and we see the first indications of orbital motion (mostly radial) for this system. H-band spectroscopy identifies both components as very late type brown dwarfs with strong H{sub 2}O and CH{sub 4} absorption. The spectrum of WISE J0458+6434B also exhibits a compelling signature of NH{sub 3} absorption over 1.52-1.54 {mu}m when compared to the T9 dwarf UGPS J072227.51-054031.2. Comparison to T8-Y0 spectral standards and H-band spectral indices indicate classifications of T8.5 and T9.5 for these two components, approaching the boundary between the T dwarf and Y dwarf spectral classes.

  19. Browse evaluation of tall shrubs based on direct measurement of a management objective

    USGS Publications Warehouse

    Keigley, R.B.; Frisina, M.R.

    2008-01-01

    The monitoring of Geyer willow was based on the following management objective: Browsing will prevent fewer than 50 percent of Geyer willow shrubs from growing taller than 3 m . Three questions were addressed: (1) Is browsing a potential factor? (2) If so, can young plants grow taller than 3 meters? (3) If not, is browsing the dominant factor? All shrubs were intensely browsed. With a post-browsing growth rate of 5.0 cm per yr, no shrub could grow 3 m tall. Analyses of stem growth rate excluded dominant roles for climate and plant vigor. Browsing and stem age were the dominant factors that limited growth to 3 m tall.

  20. Sustainable use of alpine and pre-alpine grassland soils in a changing climate (SUSALPS)

    NASA Astrophysics Data System (ADS)

    Zistl-Schlingmann, Marcus; Beck, Robert; Brandhuber, Robert; Butterbach-Bahl, Klaus; Garcia Franco, Noelia; von Gillhaußen, Phillip; Jentsch, Anke; Kiese, Ralf; Krämer, Alexander; Kögel-Knabner, Ingrid; Köllner, Thomas; Poppenborg, Patrick; Schloter, Michael; Schulz, Stefanie; Wiesmeier, Martin; Wolf, Benjamin; Dannenmann, Michael

    2016-04-01

    The development of ecologically as well as economically sustainable management options for the carbon- and nitrogen rich alpine and pre-alpine grassland soils in a changing climate poses a grand scientific and socio- economical challenge. The transdisciplinary SUSALPS project starting in 2016 aims to essentially improve the knowledge on the functionality of alpine and pre-alpine grassland soils using both natural-scientific/ technical and socio economical approaches. The project is building on existing infrastructure of German grassland-ecosystem-research like the pre-alpine TERENO (Terrestrial ecosystem observation network observatory) observatory sites, the EVENT and SIGNAL sites as well as long term LfL (Bayerische Landesanstalt für Landwirtschaft) sites, plus a new additional high elevation (1400m a.s.l) site in the Bavarian Alps. The site setup along the elevational gradient on the edge of the Alps (1400 m to 300 m) is used for space-for-time climate change experiments which are combined with extensive and intensive management treatments. A key focus of SUSALPS will be the characterization of combined climate change/management effects on carbon and nitrogen biogeochemistry. Hence, we will evaluate the influence of different management options and current and future climate changes on the soil microbiome and associated biogeochemical processes in the plant-soil-system, on nitrogen use efficiency, on biosphere-atmosphere exchange of greenhouse gases as well as on leaching of environmentally relevant compounds. For this purpose, we simulate the predicted climate change in the region by translocation of large lysimeters (1m2, 1.4m depth; TERENO lysimeters, translocated in 2011) for measurements of biosphere-atmosphere hydrosphere exchange of environmentally relevant C and N compounds as well as by newly transferred smaller plant-soil-mesocosms used for destructive biogeochemical process studies. By closely linking this experimental work with biogeochemical and

  1. Seismic monitoring of an Alpine mountain river

    NASA Astrophysics Data System (ADS)

    Díaz, J.; Ruíz, M.; Crescentini, L.; Amoruso, A.; Gallart, J.

    2014-04-01

    The Canfranc underground laboratory (LSC), excavated under the Central Pyrenees, is mainly devoted to the study of phenomena which needs "cosmic silence." It also hosts a geodynamical facility, named Geodyn, which holds an accelerometer, a broadband seismometer, and two high-resolution laser strainmeters. During the routine processing of the seismic data, we detected an unusual spectral signature in the 2-10 Hz frequency band, which does not correspond to the typical sources of seismic noise and which can also be recognized in the strain records. After checking against meteorological and hydrological data, we can relate those signals to variations in the discharge by the Aragon River, an Alpine-style river in the southern Pyrenees, located about 400 m from the LSC Geodyn facility. Four main episodes have been identified since early 2011, each lasting 1-2 to 6-8 days. Additionally, a limited number of shorter episodes have also been detected. Three types of river-generated seismic events have been identified, related respectively to moderate rainfall, snowmelt, and flooding events associated to severe storms. Each of those types has distinctive characteristics which allow monitoring the hydrological events from the analysis of seismic and deformation data. A few previous studies have already described the seismic noise close to rivers with larger discharge or in small-scale experimental settings, and we are showing here that the so-called "fluvial seismology" can be useful to study the hydrological evolution of Alpine style streams and may have a potential interest for the civil authorities in charge of the management of hydrological basins.

  2. The Pulsating White Dwarf Stars

    NASA Astrophysics Data System (ADS)

    Fontaine, G.; Brassard, P.

    2008-10-01

    We present a summary of what is currently known about the three distinct families of isolated pulsating white dwarfs. These are the GW Vir stars (He/C/O-atmosphere stars with Teff sime 120,000 K), the V777 Her stars (He-atmosphere, Teff sime 25,000 K), and the ZZ Ceti stars (H-atmosphere, Teff sime 12,000 K), all showing multiperiodic luminosity variations caused by low-order and low-degree g-mode instabilities. We also provide, in an Appendix, a very brief overview of the newly found evidence in favor of the existence of a fourth category of oscillating white dwarfs bearing strong similarities with these families of pulsators. We begin our survey with a short historical introduction, followed by a general discussion of pulsating white dwarfs as compact pulsators. We then discuss the class properties of these objects, including an updated census. We next focus on the instability domains for each family of pulsators in the log g - Teff diagram, and present their time-averaged properties in more detail. This is followed by a section on excitation physics, i.e., the causes of the pulsational instabilities, with emphasis on the common properties of the different types of pulsator. We then discuss the time-dependent properties of the pulsating white dwarfs featuring, among other things, a brief "picture tour" across the ZZ Ceti instability strip. We next review the methods used to infer or constrain the angular geometry of a pulsation mode in a white dwarf. These include multicolor photometry and time-resolved spectroscopy, the exploitation of the nonlinear features in the observed light curves, and rotational splitting. We also consider basic adiabatic asteroseismology starting with a discussion of the reaction of the period spectrum to variations of model parameters. We next review the various asteroseismological inferences that have so far been claimed for white dwarfs. We also discuss the potential of exploiting the rates of period change. We finally provide some

  3. A Search for Close Red Dwarf-White Dwarf Binaries

    NASA Astrophysics Data System (ADS)

    Boyd, Mark R.; Henry, Todd J.; Subasavage, John P.

    2011-08-01

    We propose to observe 59 objects suspected to be red dwarf-white dwarf (RD-WD) binaries with separations < 3 arcsec using the CTIO 1.0m. Our goals are to use images of these objects to both resolve the systems and to obtain accurate BVRI photometry. The systems have been selected based on positions in three different color-color plots using SuperCOSMOS BRI plate photometry and 2MASS JHK photometry in accordance with the positions of known RD-WD binaries. This effort will identify candidates for detailed observations as part of the RECONS astrometric program on the CTIO 0.9m to yield accurate parallaxes and photocentric orbits. The parallaxes will then be used to determine the ages of the systems from WD cooling curves, and the orbits will eventually be used to measure dynamical masses. Ultimately, we aim to increase significantly the number of dynamical masses for white dwarfs because currently only three have been determined to 5% accuracy. The first observational step outlined here will allow us to identify appropriate systems for long-term work. This 1.0m project is likely to become the undergraduate senior thesis work of the PI.

  4. Dust mediated transfer of phosphorus to alpine lake ecosystems

    NASA Astrophysics Data System (ADS)

    Brahney, J.; Ballantyne, A. P.; Kociolek, P.; Neff, J. C.

    2013-05-01

    Alpine lakes receive a large fraction of their nutrients from atmospheric sources; thus they are potentially sensitive to variations in atmospheric dust loading. Dust generation in western USA is thought to be increasing due to climate and land-use practices; however, the dust-mediated transfer of nutrients to alpine lakes and the potential for ecological consequences has not been extensively investigated in this region. Here, we explore the spatial changes in lake water chemistry and biology across a gradient of dust deposition in the Wind River Range, Wyoming, USA. Areas that receive more dust have altered lake and sediment water chemistries as well as altered planktonic communities. In particular, we found that phosphorus concentrations and primary productivity in dust-impacted alpine lakes were significantly greater than non-dust impacted lakes. The data illustrate the degree to which dust deposition may influence lake water chemistry and planktonic species composition, and the potential influence of human activities on remote alpine ecosystems.

  5. Arctic and Alpine Vegetations: Similarities, Differences, and Susceptibility to Disturbance

    ERIC Educational Resources Information Center

    Billings, W. D.

    1973-01-01

    Discusses environmental and biological aspects of arctic and alpine vegetations in the New World between the equator and the Arctic Ocean, considering their similarities, differences, and susceptibility to disturbance by man. (JR)

  6. Firewood crops: shrub and tree species for energy production

    SciTech Connect

    Not Available

    1980-01-01

    In the face of global concern over the dwindling supply of fuelwood, the rate of forest decimation to provide basic human necessities in developing countries is alarming. We must look upon woody plants as renewable resources that, if effectively managed, could alleviate the problem not only for the present,but for posterity. This report suggests potential significant fuelwood species for introduction to suitable environments, although it does not suggest a solution for the fuelwood crisis. The emphasis is on species suitable for individual crops, but species suited to plantation cultivation for fueling small industrial factories, electric generators, and crop driers are also considered. Most of the plants are little known in traditional forest production. Some are woody shrubs rather than trees, but all are aggressive and quick growing. They should be introduced with care in areas where the climate and soil conditions are not harsh. The substitution of well-designed stoves, kilns, or boilers could improve fuel efficiency. Each species is illustrated with photographs and diagrams. (Refs. 420).

  7. Mutual positive effects between shrubs in an arid ecosystem

    PubMed Central

    Tirado, Reyes; Bråthen, Kari Anne; Pugnaire, Francisco I.

    2015-01-01

    One-way facilitation in plants has been found in many harsh environments and their role as structural forces governing species composition in plant communities is now well established. However, reciprocal positive effects benefiting two interacting species have seldom been reported and, in recent reviews, conceptually considered merely as facilitation when in fact there is room for adaptive strategies and evolutionary responses. We tested the existence of such reciprocal positive effects in an arid environment in SE Spain using spatial pattern analysis, a species removal experiment, and a natural experiment. We found that the spatial association between Maytenus senegalensis and Whitania frutescens, two shrub species of roughly similar size intimately interacting in our community, resulted in mutual benefit for both species. Benefits included improved water relations and nutritional status and protection against browsing, and did occur despite simultaneous competition for resources. Our data suggest two-way facilitation or, rather, a facultative mutualism among higher plant species, a process often overlooked which could be a main driver of plant community dynamics allowing for evolutionary processes. PMID:26419958

  8. Vegetation trends in a 31-year-old ponderosa pine plantation: Effect of different shrub densities. Forest Service research paper

    SciTech Connect

    McDonald, P.M.; Abbott, C.S.

    1997-04-01

    On a poor site in northern California, a brushfield community was treated in various ways which left initial densities of no shrubs, light, medium, and heavy shrubs. Density and development (height, foliar cover, crown volume) for three shrub species (alone and combined), one grass, and planted ponderosa pine in these categories were quantified from 1966 to 1992. Successional trends (ascendance and decline) are presented for these species and for forbs from 1962 (the date pines were planted) through 1992. Regression equations that model density and development are presented for the shrubs and pine. In general, greenleaf manzanita prospered during the study; snowbrush initially developed well, but then declined; Sierra plum endured, but was relegated to the understory; needlegrass invaded rapdily, peaked early, and was mostly gone by the end of the study. Only a trace of forb species remained by study end. Needlegrass displayed strong environmental preference, becoming dense and developing well in shrub-free areas, but was scarcely present in heavy shrubs. Ponderosa pine grew well in no-shrub plots, farily well in light-shrub plots, and poorly in medium- and heavy-shrub plots. Extensive testing showed that shrub foliar cover and crown volume per acre explained more variation in several pine parameters than shrub height or density.

  9. The onset of alpine pastoral systems in the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Oeggl, Klaus; Festi, Daniela; Putzer, Andreas

    2015-04-01

    Since the discovery of the Neolithic glacier mummy "Ötzi" in the nival belt of the main Alpine ridge, the onset of alpine pasture is matter of a highly controversial debate both in archaeology and in palaeo-ecology of the Eastern Alps. The implication is that his sojourn in the high-altitudes of the Alps is considered to be connected with pastoral nomadism. Regrettably any archaeological evidence for the existence of such Neolithic alpine pastoral systems is missing up to now and the assumption is based on palynological data only. However, also the palynological record is ambiguous, because pasture indicators in the alpine regions react positive on grazing as well as on fertilization induced by a higher runoff of precipitation. Thus alpine pasture indicators reflect both grazing pressure and climatic change. Anyhow, alpine pastoral systems are a common practice in Alpine animal husbandry, but from an economic point of view such a seasonal vertical transhumance is costly. There are three main reasons for its practice: i) climatic, ii) economic (mainly in connection with population pressure or mining activities), and iii) cultural ideology. In this study we tested the above mentioned reasons in an interdisciplinary study on the beginning of pastoral activities in high altitudes in the central part of the Eastern Alps. This is conducted by palynological analyses of peat deposits situated in the vicinity of the timberline (1600 - 2400 m a.s.l.) combined with archaeological surveys. The investigated sites are located in traditional Alpine transhumance regions and aligned on a transect through the central part of the Eastern Alps. The studies reveal that grazing pressure is reflected since the Bronze Age, which is corroborated by archaeological findings in the vicinity of the investigated sites.

  10. Sensitivity of Alpine Snow and Streamflow Regimes to Climate Changes

    NASA Astrophysics Data System (ADS)

    Rasouli, K.; Pomeroy, J. W.; Marks, D. G.; Bernhardt, M.

    2014-12-01

    Understanding the sensitivity of hydrological processes to climate change in alpine areas with snow dominated regimes is of paramount importance as alpine basins show both high runoff efficiency associated with the melt of the seasonal snowpack and great sensitivity of snow processes to temperature change. In this study, meteorological data measured in a selection of alpine headwaters basins including Reynolds Mountain East, Idaho, USA, Wolf Creek, Yukon in Canada, and Zugspitze Mountain, Germany with climates ranging from arctic to continental temperate were used to study the snow and streamflow sensitivity to climate change. All research sites have detailed multi-decadal meteorological and snow measurements. The Cold Regions Hydrological Modelling platform (CRHM) was used to create a model representing a typical alpine headwater basin discretized into hydrological response units with physically based representations of snow redistribution by wind, complex terrain snowmelt energetics and runoff processes in alpine tundra. The sensitivity of snow hydrology to climate change was investigated by changing air temperature and precipitation using weather generating methods based on the change factors obtained from different climate model projections for future and current periods. The basin mean and spatial variability of peak snow water equivalent, sublimation loss, duration of snow season, snowmelt rates, streamflow peak, and basin discharge were assessed under varying climate scenarios and the most sensitive hydrological mechanisms to the changes in the different alpine climates were detected. The results show that snow hydrology in colder alpine climates is more resilient to warming than that in warmer climates, but that compensatory factors to warming such as reduced blowing snow sublimation loss and reduced melt rate should also be assessed when considering climate change impacts on alpine hydrology.

  11. Mass Modelling of dwarf Spheroidal Galaxies

    NASA Astrophysics Data System (ADS)

    Klimentowski, Jarosław; Łokas, Ewa L.; Kazantzidis, Stelios; Prada, Francisco; Mayer, Lucio; Mamon, Gary A.

    2008-05-01

    We study the origin and properties of unbound stars in the kinematic samples of dwarf spheroidal galaxies. For this purpose we have run a high resolution N-body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. We create mock kinematic data sets by observing the dwarf in different directions. When the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails. However, most of the unbound stars can be removed by the method of interloper rejection proposed by den Hartog & Katgert. We model the velocity dispersion profiles of the cleaned-up kinematic samples using solutions of the Jeans equation. We show that even for such a strongly stripped dwarf the Jeans analysis, when applied to cleaned samples, allows us to reproduce the mass and mass-to-light ratio of the dwarf with accuracy typically better than 25%.

  12. [The study of M dwarf spectral classification].

    PubMed

    Yi, Zhen-Ping; Pan, Jing-Chang; Luo, A-Li

    2013-08-01

    As the most common stars in the galaxy, M dwarfs can be used to trace the structure and evolution of the Milky Way. Besides, investigating M dwarfs is important for searching for habitability of extrasolar planets orbiting M dwarfs. Spectral classification of M dwarfs is a fundamental work. The authors used DR7 M dwarf sample of SLOAN to extract important features from the range of 600-900 nm by random forest method. Compared to the features used in Hammer Code, the authors added three new indices. Our test showed that the improved Hammer with new indices is more accurate. Our method has been applied to classify M dwarf spectra of LAMOST. PMID:24159887

  13. The physics of white dwarfs

    NASA Astrophysics Data System (ADS)

    Isern, Jordi; García-Berro, Enrique; Hernanz, Margarida; Mochkovitch, Robert

    1998-12-01

    White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for 0953-8984/10/49/015/img6 and allows one to obtain information about the age of the Galaxy as well as about the past stellar formation rate in the solar neighbourhood. Therefore, it is important to identify all of the relevant sources of energy as well as the mechanisms that control its flow to the space. We show in this paper that the inclusion of a detailed treatment of phase transitions in Coulomb plasmas made up of a mixture of different chemical species is crucial, since their redistribution can keep the white dwarf warm for 0.5 to 9 Ga depending on the chemical composition and physical assumptions adopted.

  14. Hydraulic integration and shrub growth form linked across continental aridity gradients

    PubMed Central

    Schenk, H. Jochen; Espino, Susana; Goedhart, Christine M.; Nordenstahl, Marisa; Cabrera, Hugo I. Martinez; Jones, Cynthia S.

    2008-01-01

    Both engineered hydraulic systems and plant hydraulic systems are protected against failure by resistance, reparability, and redundancy. A basic rule of reliability engineering is that the level of independent redundancy should increase with increasing risk of fatal system failure. Here we show that hydraulic systems of plants function as predicted by this engineering rule. Hydraulic systems of shrubs sampled along two transcontinental aridity gradients changed with increasing aridity from highly integrated to independently redundant modular designs. Shrubs in humid environments tend to be hydraulically integrated, with single, round basal stems, whereas dryland shrubs typically have modular hydraulic systems and multiple, segmented basal stems. Modularity is achieved anatomically at the vessel-network scale or developmentally at the whole-plant scale through asymmetric secondary growth, which results in a semiclonal or clonal shrub growth form that appears to be ubiquitous in global deserts. PMID:18678893

  15. Hydraulic integration and shrub growth form linked across continental aridity gradients.

    PubMed

    Schenk, H Jochen; Espino, Susana; Goedhart, Christine M; Nordenstahl, Marisa; Cabrera, Hugo I Martinez; Jones, Cynthia S

    2008-08-12

    Both engineered hydraulic systems and plant hydraulic systems are protected against failure by resistance, reparability, and redundancy. A basic rule of reliability engineering is that the level of independent redundancy should increase with increasing risk of fatal system failure. Here we show that hydraulic systems of plants function as predicted by this engineering rule. Hydraulic systems of shrubs sampled along two transcontinental aridity gradients changed with increasing aridity from highly integrated to independently redundant modular designs. Shrubs in humid environments tend to be hydraulically integrated, with single, round basal stems, whereas dryland shrubs typically have modular hydraulic systems and multiple, segmented basal stems. Modularity is achieved anatomically at the vessel-network scale or developmentally at the whole-plant scale through asymmetric secondary growth, which results in a semiclonal or clonal shrub growth form that appears to be ubiquitous in global deserts. PMID:18678893

  16. Abundances in dwarf irregular galaxies

    NASA Technical Reports Server (NTRS)

    Dufour, Reginald J.

    1986-01-01

    The results of abundance studies of dwarf irregular galaxies and similar objects are reviewed with special attention to variations in the CNO element group. Observations of the forbidden N II and semiforbidden C III lines in the most metal-poor galaxy known, IZw 18, are presented for the first time and CNO abundances are derived via a photoionization model and discussed in the context of the abundances found in other metal-poor H II regions and galaxies.

  17. AST3: dwarf nova outbursts

    NASA Astrophysics Data System (ADS)

    Ma, Bin; Hu, Yi; Shang, Zhaohui; Wang, Lifan

    2016-05-01

    AST3#2 OT J024453.11-580940.1 discovery - new dwarf nova outburst with ampl > 5.8 The 2nd Antarctic Survey Telescope (AST3#2) discovered OT source at (RA, Dec) = 02:44:53.11 -58:09:40.1 on 2016-05-06.071 UT with Sloan-g magnitude of 15.5m (limit 18.6m).

  18. Dwarf spheroidal galaxies and resonant orbital coupling

    NASA Technical Reports Server (NTRS)

    Kuhn, J. R.; Miller, R. H.

    1989-01-01

    The structural properties of the dwarf spheroidal satellite galaxies of the Milky Way may be strongly affected by their time-dependent interactions with the 'tidal' field of the Milky Way. A low Q resonance of the tidal driving force with collective oscillation modes of the dwarf system can produce many of the observed properties of the Local Group dwarf spheroidal galaxies, including large velocity dispersions that would normally be interpreted as indicating large dynamical masses.

  19. Characterizing Accreting White Dwarf Pulsators

    NASA Astrophysics Data System (ADS)

    Szkody, Paula; Mukadam, Anjum

    2014-02-01

    Understanding the population, mass distribution, and evolution of accreting white dwarfs impacts the entire realm of binary interaction, including the creation of Type Ia supernovae. We are concentrating on accreting white dwarf pulsators, as the pulsation properties allow us a view of how the accretion affects the interior of the star. Our ground- based photometry on 11 accreting pulsators with corresponding temperatures from HST UV spectra suggest a broad instability strip in the range of 10500 to 16000K. Additionally, tracking a post-outburst heated white dwarf as it cools and crosses the blue edge and resumes pulsation provides an independent method to locate the empirical instability strip. Determining a post-outburst cooling curve yields an estimate of the amount of heating and the accreted mass during the outburst. We request additional photometry of 2 objects that present unique properties: GW Lib which has not yet returned to its pre-outburst pulsation spectrum after 6 yrs, and EQ Lyn which returned to its pre- outburst pulsation after 3 yrs but is now turning on and off without ongoing outbursts. Following the pulsation spectrum changes over stretches of several nights in a row will provide specific knowledge of the stability of the observed modes.

  20. Uncovering Blue Diffuse Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    James, Bethan; Koposov, Sergey; Stark, Daniel; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.

    2015-01-01

    Extremely metal-poor galaxies (XMPs) and the star-formation within their chemically pristine environments are fundamental to our understanding of the galaxy formation process at early times. However, traditional emission-line surveys detect only the brightest metal-poor galaxies where star-formation occurs in compact, starbursting environments, and thereby give us only a partial view of the dwarf galaxy population. To avoid such biases, we have developed a new search algorithm based on the morphological, rather then spectral, properties of XMPs and have applied to the Sloan Digital Sky Survey database of images. Using this novel approach, we have discovered ~100 previously undetected, faint blue galaxies, each with isolated HII regions embedded in a diffuse continuum. In this talk I will present the first results from follow-up optical spectroscopy of this sample, which reveals these blue diffuse dwarfs (BDDs) to be young, very metal-poor and actively forming stars despite their intrinsically low luminosities. I will present evidence showing that BDDs appear to bridge the gap between quiescent dwarf irregular (dIrr) galaxies and blue compact galaxies (BCDs) and as such offer an ideal opportunity to assess how star-formation occurs in more `normal' metal-poor systems.

  1. Greater shrub dominance alters breeding habitat and food resources for migratory songbirds in Alaskan arctic tundra.

    PubMed

    Boelman, Natalie T; Gough, Laura; Wingfield, John; Goetz, Scott; Asmus, Ashley; Chmura, Helen E; Krause, Jesse S; Perez, Jonathan H; Sweet, Shannan K; Guay, Kevin C

    2015-04-01

    Climate warming is affecting the Arctic in multiple ways, including via increased dominance of deciduous shrubs. Although many studies have focused on how this vegetation shift is altering nutrient cycling and energy balance, few have explicitly considered effects on tundra fauna, such as the millions of migratory songbirds that breed in northern regions every year. To understand how increasing deciduous shrub dominance may alter breeding songbird habitat, we quantified vegetation and arthropod community characteristics in both graminoid and shrub dominated tundra. We combined measurements of preferred nest site characteristics for Lapland longspurs (Calcarius lapponicus) and Gambel's White-crowned sparrows (Zonotrichia leucophrys gambelii) with modeled predictions for the distribution of plant community types in the Alaskan arctic foothills region for the year 2050. Lapland longspur nests were found in sedge-dominated tussock tundra where shrub height does not exceed 20 cm, whereas White-crowned sparrows nested only under shrubs between 20 cm and 1 m in height, with no preference for shrub species. Shrub canopies had higher canopy-dwelling arthropod availability (i.e. small flies and spiders) but lower ground-dwelling arthropod availability (i.e. large spiders and beetles). Since flies are the birds' preferred prey, increasing shrubs may result in a net enhancement in preferred prey availability. Acknowledging the coarse resolution of existing tundra vegetation models, we predict that by 2050 there will be a northward shift in current White-crowned sparrow habitat range and a 20-60% increase in their preferred habitat extent, while Lapland longspur habitat extent will be equivalently reduced. Our findings can be used to make first approximations of future habitat change for species with similar nesting requirements. However, we contend that as exemplified by this study's findings, existing tundra modeling tools cannot yet simulate the fine-scale habitat

  2. Native shrub reestablishment in exotic annual grasslands: do ecosystem processes recover?

    PubMed

    Yelenik, S G; Levine, J M

    2010-04-01

    The impacts of exotic plant species on ecosystem processes are well established, motivating numerous efforts to facilitate native-species recovery. Nonetheless, how the return of native species influences ecosystem processes and how these changes feed back to influence the recovery process are poorly understood. We examined these questions in exotic annual grasslands on Santa Cruz Island, California, USA, where the removal of nonnative herbivores has led to the recovery of the native shrubs Artemisia californica and Eriogonum arborescens. To examine the influence of shrub colonization on nutrient cycling, and the mechanisms by which these changes arise, we measured available nitrogen and phosphorus, and quantified nitrogen mineralization and litterfall rates under shrubs and grasses in the field and in experimental monoculture plots. Both native shrubs altered nitrogen cycling as they colonized the grassland, but they did so in opposite directions. Eriogonum depressed nitrogen pools and mineralization rates via large inputs of nitrogen-poor litter. In contrast Artemisia increased nitrogen and phosphorus pools and nitrogen mineralization rates. Last, to determine if shrub effects on soils favor shrubs or grasses, we conducted a nitrogen and phosphorus fertilization experiment in the field. Only the exotic grass was significantly limited by nitrogen. Thus the depressed nitrogen availability associated with Eriogonum colonization is more harmful to exotic grasses than to the native shrub. By contrast, the elevated nitrogen associated with recovering Artemisia favors grasses over the shrub, possibly hindering recovery of the native. Mechanistic studies of the ecosystem ,impacts of native-plant recovery are useful for managers wishing to predict which native species return ecosystem function, and whether such changes feed back to influence native recovery. PMID:20437958

  3. How Spatial Heterogeneity of Cover Affects Patterns of Shrub Encroachment into Mesic Grasslands

    PubMed Central

    Montané, Francesc; Casals, Pere; Dale, Mark R. T.

    2011-01-01

    We used a multi-method approach to analyze the spatial patterns of shrubs and cover types (plant species, litter or bare soil) in grassland-shrubland ecotones. This approach allows us to assess how fine-scale spatial heterogeneity of cover types affects the patterns of Cytisus balansae shrub encroachment into mesic mountain grasslands (Catalan Pyrenees, Spain). Spatial patterns and the spatial associations between juvenile shrubs and different cover types were assessed in mesic grasslands dominated by species with different palatabilities (palatable grass Festuca nigrescens and unpalatable grass Festuca eskia). A new index, called RISES (“Relative Index of Shrub Encroachment Susceptibility”), was proposed to calculate the chances of shrub encroachment into a given grassland, combining the magnitude of the spatial associations and the surface area for each cover type. Overall, juveniles showed positive associations with palatable F. nigrescens and negative associations with unpalatable F. eskia, although these associations shifted with shrub development stage. In F. eskia grasslands, bare soil showed a low scale of pattern and positive associations with juveniles. Although the highest RISES values were found in F. nigrescens plots, the number of juvenile Cytisus was similar in both types of grasslands. However, F. nigrescens grasslands showed the greatest number of juveniles in early development stage (i.e. height<10 cm) whereas F. eskia grasslands showed the greatest number of juveniles in late development stages (i.e. height>30 cm). We concluded that in F. eskia grasslands, where establishment may be constrained by the dominant cover type, the low scale of pattern on bare soil may result in higher chances of shrub establishment and survival. In contrast, although grasslands dominated by the palatable F. nigrescens may be more susceptible to shrub establishment; current grazing rates may reduce juvenile survival. PMID:22174858

  4. AmeriFlux US-Whs Walnut Gulch Lucky Hills Shrub

    SciTech Connect

    Scott, Russ

    2016-01-01

    This is the AmeriFlux version of the carbon flux data for the site US-Whs Walnut Gulch Lucky Hills Shrub. Site Description - A semiarid Chihuahuan Desert shrubland located in the USDA-ARS Walnut Gulch Experimental Watershed (WGEW) surrounding the town of Tombstone, AZ. The site vegetation is comprised of a diverse stand of mainly Chihuahuan desert shrub species like acacia constricta, larrea tridentata, and florensia cernua.

  5. Scrub-shrub bird habitat associations at multiple spatial scales in beaver meadows in Massachusetts

    USGS Publications Warehouse

    Chandler, R.B.; King, D.I.; DeStefano, S.

    2009-01-01

    Most scrub-shrub bird species are declining in the northeastern United States, and these declines are largely attributed to regional declines in habitat availability. American Beaver (Castor canadensis; hereafter "beaver") populations have been increasing in the Northeast in recent decades, and beavers create scrub-shrub habitat through their dam-building and foraging activities. Few systematic studies have been conducted on the value of beaver-modified habitats for scrub-shrub birds, and these data are important for understanding habitat selection of scrub-shrub birds as well as for assessing regional habitat availability for these species. We conducted surveys in 37 beaver meadows in a 2,800-km2 study area in western Massachusetts during 2005 and 2006 to determine the extent to which these beaver-modified habitats are used by scrub-shrub birds, as well as the characteristics of beaver meadows most closely related to bird use. We modeled bird abundance in relation to microhabitat-, patch-, and landscape-context variables while adjusting for survey-specific covariates affecting detectability using N-mixture models. We found that scrub-shrub birds of regional conservation concern occupied these sites and that birds responded differently to microhabitat, patch, and landscape characteristics of beaver meadows. Generally, scrub-shrub birds increased in abundance along a gradient of increasing vegetation complexity, and three species were positively related to patch size. We conclude that these habitats can potentially play an important role in regional conservation of scrub-shrub birds and recommend that conservation priority be given to larger beaver meadows with diverse vegetation structure and composition. ?? 2009 by The American Ornithologists' Union. All rights reserved.

  6. Auroral Phenomena in Brown Dwarf Atmospheres

    NASA Astrophysics Data System (ADS)

    Pineda, J. Sebastian; Hallinan, Gregg

    2016-01-01

    Since the unexpected discovery of radio emission from brown dwarfs some 15 years ago, investigations into the nature of this emission have revealed that, despite their cool and neutral atmospheres, brown dwarfs harbor strong kG magnetic fields, but unlike the warmer stellar objects, they generate highly circularly polarized auroral radio emission, like the giant planets of the Solar System. Our recent results from Keck LRIS monitoring of the brown dwarf LSR1835+32 definitively confirm this picture by connecting the auroral radio emission to spectroscopic variability at optical wavelengths as coherent manifestations of strong large-scale magnetospheric auroral current systems. I present some of the results of my dissertation work to understand the nature brown dwarf auroral phenomena. My efforts include a survey of Late L dwarfs and T dwarfs, looking for auroral Hα emission and a concurrent survey looking for the auroral emission of H3+ from brown dwarfs with radio pulse detections. I discuss the potential connection of this auroral activity to brown dwarf weather phenomena and how brown dwarf aurorae may differ from the analogous emission of the magnetized giant planets in the Solar System.

  7. Stellar Rotation Curves of Starbursting Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    van Zee, Liese; Skillman, Evan D.; Salzer, John J.

    2001-02-01

    A year ago, we successfully completed a pilot project to obtain stellar rotation curves of starbursting dwarf galaxies. These observations provided the first spatially resolved stellar rotation curves of gas-rich dwarf galaxies. We now propose to expand our sample (by a factor of 2) by observing 4 additional dwarf galaxies with the CTIO 4m. The fundamental question to be addressed is whether the gas and stars are kinematically coupled in these small galaxies. These observations will place the first kinematic constraints on evolutionary models for dwarf galaxies.

  8. White Dwarf Critical Tests for Modified Gravity.

    PubMed

    Jain, Rajeev Kumar; Kouvaris, Chris; Nielsen, Niklas Grønlund

    2016-04-15

    Scalar-tensor theories of gravity can lead to modifications of the gravitational force inside astrophysical objects. We exhibit that compact stars such as white dwarfs provide a unique setup to test beyond Horndeski theories of G^{3} type. We obtain stringent and independent constraints on the parameter ϒ characterizing the deviations from Newtonian gravity using the mass-radius relation, the Chandrasekhar mass limit, and the maximal rotational frequency of white dwarfs. We find that white dwarfs impose stronger constraints on ϒ than red and brown dwarfs. PMID:27127952

  9. White Dwarf Critical Tests for Modified Gravity

    NASA Astrophysics Data System (ADS)

    Jain, Rajeev Kumar; Kouvaris, Chris; Nielsen, Niklas Grønlund

    2016-04-01

    Scalar-tensor theories of gravity can lead to modifications of the gravitational force inside astrophysical objects. We exhibit that compact stars such as white dwarfs provide a unique setup to test beyond Horndeski theories of G3 type. We obtain stringent and independent constraints on the parameter ϒ characterizing the deviations from Newtonian gravity using the mass-radius relation, the Chandrasekhar mass limit, and the maximal rotational frequency of white dwarfs. We find that white dwarfs impose stronger constraints on ϒ than red and brown dwarfs.

  10. Abscission Is Regulated by the ESCRT-III Protein Shrub in Drosophila Germline Stem Cells

    PubMed Central

    Matias, Neuza Reis; Mathieu, Juliette; Huynh, Jean-René

    2015-01-01

    Abscission is the final event of cytokinesis that leads to the physical separation of the two daughter cells. Recent technical advances have allowed a better understanding of the cellular and molecular events leading to abscission in isolated yeast or mammalian cells. However, how abscission is regulated in different cell types or in a developing organism remains poorly understood. Here, we characterized the function of the ESCRT-III protein Shrub during cytokinesis in germ cells undergoing a series of complete and incomplete divisions. We found that Shrub is required for complete abscission, and that levels of Shrub are critical for proper timing of abscission. Loss or gain of Shrub delays abscission in germline stem cells (GSCs), and leads to the formation of stem-cysts, where daughter cells share the same cytoplasm as the mother stem cell and cannot differentiate. In addition, our results indicate a negative regulation of Shrub by the Aurora B kinase during GSC abscission. Finally, we found that Lethal giant discs (lgd), known to be required for Shrub function in the endosomal pathway, also regulates the duration of abscission in GSCs. PMID:25647097

  11. Warming-Induced Shrub Expansion and Lichen Decline Across the Tuktoyaktuk Coastal Plain

    NASA Astrophysics Data System (ADS)

    Fraser, R.; Lantz, T. C.; Olthof, I.; Kokelj, S. V.; Sims, R. A.

    2014-12-01

    Recent field and remote sensing studies show that shrub expansion has been widespread in low-Arctic ecosystems. However, there are still uncertainties regarding the extent of these changes, the plant functional groups involved, and the relative importance of climate and disturbance as causes of observed changes. Some authors have suggested that shrub expansion may have caused declines in lichens important for caribou forage, but these changes have not been examined at regional scales. Our research on the Tuktoyaktuk Coastal Plain using 30m resolution Landsat satellite imagery from 1985-2011 and high resolution (1:2000) vertical aerial photographs from 1980 and 2013 shows that shrub expansion has been associated with widespread lichen decline . Our analysis shows that the most likely driver of shrub expansion is a 4°C winter temperature increase over the past 30 years, leading to warmer soils and enhanced supply of growth-limiting nutrients. Natural and human-caused disturbances also stimulated increases in shrub cover, but these effects were limited spatially. Our observations are consistent with plot-scale warming experiments showing reductions in lichen cover from shrub growth, and modeling studies predicting large-scale vegetation shifts in the low-Arctic from climate change. These vegetation changes have implications for caribou forage, wildfire regimes, and permafrost conditions.

  12. Male-biased hermaphrodites in a gynodioecious shrub, Daphne jezoensis.

    PubMed

    Sinclair, J P; Kameyama, Y; Shibata, A; Kudo, G

    2016-09-01

    Gynodioecy, a state where female and hermaphrodite plants coexist in populations, has been widely proposed an intermediate stage in the evolutionary pathway from hermaphroditism to dioecy. In the gynodioecy-dioecy pathway, hermaphrodites may gain most of their fitness through male function once females invade populations. To test this prediction, comprehensive studies on sex ratio variation across populations and reproductive characteristics of hermaphrodite and female phenotypes are necessary. This study examined the variation in sex ratio, sex expression, flower and fruit production and sexual dimorphism of morphological traits in a gynodioecious shrub, Daphne jezoensis, over multiple populations and years. Population sex ratio (hermaphrodite:female) was close to 1:1 or slightly hermaphrodite-biased. Sex type of individual plants was largely fixed, but 15% of plants changed their sex during a 6-year census. Hermaphrodite plants produced larger flowers and invested 2.5 times more resources in flower production than female plants, but they exhibited remarkably low fruit set (proportion of flowers setting fruits). Female plants produced six times more fruits than hermaphrodite plants. Low fruiting ability of hermaphrodite plants was retained even when hand-pollination was performed. Fruit production of female plants was restricted by pollen limitation under natural conditions, irrespective of high potential fecundity, and this minimised the difference in resources allocated to reproduction between the sexes. Negative effects of previous flower and fruit production on current reproduction were not apparent in both sexes. This study suggests that gynodioecy in this species is functionally close to a dioecious mating system: smaller flower production with larger fruiting ability in female plants, and larger flower production with little fruiting ability in hermaphrodite plants. PMID:27090773

  13. Phenological observations on shrubs to predict weed emergence in turf

    NASA Astrophysics Data System (ADS)

    Masin, Roberta; Zuin, Maria Clara; Zanin, Giuseppe

    2005-09-01

    Phenology is the study of periodic biological events. If we can find easily recognizable events in common plants that precede or coincide with weed emergences, these plants could be used as indicators. Weed seedlings are usually difficult to detect in turf, so the use of phenological indicators may provide an alternative approach to predict the time when a weed appears and consequently guide management decisions. A study was undertaken to determine whether the phenological phases of some plants could serve as reliable indicators of time of weed emergence in turf. The phenology of six shrubs (Crataegus monogyna Jacq., Forsythia viridissima Lindl., Sambucus nigra L., Syringa vulgaris L., Rosa multiflora Thunb., Ziziphus jujuba Miller) and a perennial herbaceous plant [Cynodon dactylon (L.) Pers.] was observed and the emergence dynamics of four annual weed species [Digitaria sanguinalis (L.) Scop., Eleusine indica (L.) Gaertner, Setaria glauca (L.) Beauv., Setaria viridis (L.) Beauv.] were studied from 1999 to 2004 in northern Italy. A correlation between certain events and weed emergence was verified. S. vulgaris and F. viridissima appear to be the best indicators: there is a quite close correspondence between the appearance of D. sanguinalis and lilac flowering and between the beginning of emergence of E. indica and the end of lilac flowering; emergences of S. glauca and S. viridis were predicted well in relation to the end of forsythia flowering. Base temperatures and starting dates required to calculate the heat unit sums to reach and complete the flowering phase of the indicators were calculated using two different methods and the resultant cumulative growing degree days were compared.

  14. Late Pleistocene climate change and landscape dynamics in the Eastern Alps: the inner-alpine Unterangerberg record (Austria)

    PubMed Central

    Starnberger, Reinhard; Drescher-Schneider, Ruth; Reitner, Jürgen M.; Rodnight, Helena; Reimer, Paula J.; Spötl, Christoph

    2013-01-01

    Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ∼120–110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ∼70–60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ∼55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ∼45 ka and/or was truncated by ice during the Last Glacial Maximum. PMID:23805019

  15. Late Pleistocene climate change and landscape dynamics in the Eastern Alps: the inner-alpine Unterangerberg record (Austria)

    NASA Astrophysics Data System (ADS)

    Starnberger, Reinhard; Drescher-Schneider, Ruth; Reitner, Jürgen M.; Rodnight, Helena; Reimer, Paula J.; Spötl, Christoph

    2013-05-01

    Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ˜120-110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ˜70-60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ˜55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ˜45 ka and/or was truncated by ice during the Last Glacial Maximum.

  16. An unsuccessful search for brown dwarf companions to white dwarf stars

    NASA Technical Reports Server (NTRS)

    Shipman, Harry L.

    1986-01-01

    The results of a survey to detect excess infrared emission from white dwarf stars which would be attributable to a low mass companion are reviewed. Neither a simple comparison of spectroscopically identified white dwarf stars with the IRAS Point Source Catalog nor the coadding of IRAS survey data resulted in a detection of a brown dwarf. The seven nearest stars where the most stringent limits to the presence of a brown dwarf were obtained are listed, and an effort to detect brown dwarfs in the solar neighborhood is discussed.

  17. THE FORNAX DWARF GALAXY AS A REMNANT OF RECENT DWARF-DWARF MERGING IN THE LOCAL GROUP

    SciTech Connect

    Yozin, C.; Bekki, K.

    2012-09-01

    We present results from the first numerical analysis to support the hypothesis, first proposed in Coleman et al., that the Fornax dwarf galaxy was formed from the minor merging of two dwarfs about 2 Gyr ago. Using orbits for the Fornax dwarf that are consistent with the latest proper motion measurements, our dynamical evolution models show that the observed asymmetric shell-like substructures can be formed from the remnant of a smaller dwarf during minor merging. These models also predict the formation of diffuse stellar streams. We discuss how these stellar substructures depend on model parameters of dwarf-dwarf merging, and how the intermediate-age subpopulations found in the vicinity of these substructures may be formed from gas accretion in past merger events. We also suggest that one of Fornax's globular clusters originates from a merged dwarf companion, and demonstrate where as yet undetected tidal streams or H I gas formed from the dwarf merging may be found in the outer halo of the Galaxy.

  18. Response of dominant grass and shrub species to water manipulation: an ecophysiological basis for shrub invasion in a Chihuahuan Desert grassland

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Increases in woody vegetation and declines in grasses in arid and semi-arid ecosystems have occurred globally since the 1800s, but the mechanisms driving this major land-cover change remain uncertain and controversial. Working in a shrub-encroached grassland in the northern Chihuahuan Desert where ...

  19. Quantifying instantaneous performance in alpine ski racing.

    PubMed

    Federolf, Peter Andreas

    2012-01-01

    Alpine ski racing is a popular sport in many countries and a lot of research has gone into optimising athlete performance. Two factors influence athlete performance in a ski race: speed and the chosen path between the gates. However, to date there is no objective, quantitative method to determine instantaneous skiing performance that takes both of these factors into account. The purpose of this short communication was to define a variable quantifying instantaneous skiing performance and to study how this variable depended on the skiers' speed and on their chosen path. Instantaneous skiing performance was defined as time loss per elevation difference dt/dz, which depends on the skier's speed v(z), and the distance travelled per elevation difference ds/dz. Using kinematic data collected in an earlier study, it was evaluated how these variables can be used to assess the individual performance of six ski racers in two slalom turns. The performance analysis conducted in this study might be a useful tool not only for athletes and coaches preparing for competition, but also for sports scientists investigating skiing techniques or engineers developing and testing skiing equipment. PMID:22620279

  20. Geophysical imaging of alpine rock glaciers

    NASA Astrophysics Data System (ADS)

    Maurer, Hansruedi; Hauck, Christian

    Slope instabilities caused by the disappearance of ice within alpine rock glaciers are an issue of increasing concern. Design of suitable counter-measures requires detailed knowledge of the internal structures of rock glaciers, which can be obtained using geophysical methods. We examine benefits and limitations of diffusive electromagnetics, geoelectrics, seismics and ground-penetrating radar (georadar) for determining the depth and lateral variability of the active layer, the distributions of ice and water, the occurrence of shear horizons and the bedrock topography. In particular, we highlight new developments in data acquisition and data analysis that allow 2-D or even 3-D structures within rock glaciers to be imaged. After describing peculiarities associated with acquiring appropriate geophysical datasets across rock glaciers and emphasizing the importance of state-of-the-art tomographic inversion algorithms, we demonstrate the applicability of 2-D imaging techniques using two case studies of rock glaciers in the eastern Swiss Alps. We present joint interpretations of geoelectric, seismic and georadar data, appropriately constrained by information extracted from boreholes. A key conclusion of our study is that the different geophysical images are largely complementary, with each image resolving a different suite of subsurface features. Based on our results, we propose a general template for the cost-effective and reliable geophysical characterization of mountain permafrost.

  1. Annual variability of ozone along alpine hillsides

    NASA Technical Reports Server (NTRS)

    Putz, Erich; Kosmus, Walter

    1994-01-01

    Over a period of more than two years (March 1989 till June 1991) ozone and nitrogen dioxide have been monitored along twelve alpine hillsides in the Austrian alps. The profiles had a height-resolution of 100 m and cover a range between 400 m and 1800 m asl, that is 100 m to 1100 m above the bottom of the valleys. They were situated in remote rural areas as well as in the vicinity of polluted urban and industrial areas. Both trace gases were monitored by means of integral chemical (SAM-surface active monitor) methods with a measuring cycle of two weeks. The concentration of ozone exhibits a substantial annual variation over the entire height range. In summer, highest ozone levels are observed near the ground and at the top of the mountains, whereas in winter the maxima are found mainly in the crest regions. The overall ozone burden shows a relative maximum near the temperature inversion layer in the valleys and an absolute maximum at the crest.

  2. Aortic Dissection Type A in Alpine Skiers

    PubMed Central

    Schachner, Thomas; Fischler, Nikolaus; Dumfarth, Julia; Bonaros, Nikolaos; Krapf, Christoph; Schobersberger, Wolfgang; Grimm, Michael

    2013-01-01

    Patients and Methods. 140 patients with aortic dissection type A were admitted for cardiac surgery. Seventy-seven patients experienced their dissection in the winter season (from November to April). We analyzed cases of ascending aortic dissection associated with alpine skiing. Results. In 17 patients we found skiing-related aortic dissections. Skiers were taller (180 (172–200) cm versus 175 (157–191) cm, P = 0.008) and heavier (90 (68–125) kg versus 80 (45–110) kg, P = 0.002) than nonskiers. An extension of aortic dissection into the aortic arch, the descending thoracic aorta, and the abdominal aorta was found in 91%, 74%, and 69%, respectively, with no significant difference between skiers and nonskiers. Skiers experienced RCA ostium dissection requiring CABG in 17.6% while this was true for 5% of nonskiers (P = 0.086). Hospital mortality of skiers was 6% versus 13% in nonskiers (P = 0.399). The skiers live at an altitude of 170 (0–853) m.a.s.l. and experience their dissection at 1602 (1185–3105; P < 0.001) m.a.s.l. In 82% symptom start was during recreational skiing without any trauma. Conclusion. Skiing associated aortic dissection type A is usually nontraumatic. The persons affected live at low altitudes and practice an outdoor sport at unusual high altitude at cold temperatures. Postoperative outcome is good. PMID:23971024

  3. Environmental controls on alpine cirque size

    NASA Astrophysics Data System (ADS)

    Delmas, Magali; Gunnell, Yanni; Calvet, Marc

    2014-02-01

    Pleistocene alpine cirques are emblematic landforms of mountain scenery, yet their deceptively simple template conceals complex controlling variables. This comparative study presents a new database of 1071 cirques, the largest of its kind, located in the French eastern Pyrenees. It is embedded in a review of previous work on cirque morphometry and thus provides a perspective on a global scale. First-order cirque attributes of length, width, and amplitude were measured; and their power as predictors of climatic and lithological variables and as proxies for the duration of glacier activity was tested using ANOVA, simple and multiple linear regression, and their various post-hoc tests. Conventional variables such as cirque aspect, floor elevation, and exposure with respect to regional precipitation-bearing weather systems are shown to present some consistency in spatial patterns determined by solar radiation, the morning-afternoon effect, and wind-blown snow accumulation in the lee of ridgetops. This confirms in greater detail the previously encountered links between landforms and climate. A special focus on the influence of bedrock lithology, a previously neglected nonclimatic variable, highlights the potential for spurious relations in the use of cirque size as a proxy of past environmental conditions. Cirques are showcased as complex landforms resulting from the combination of many climatic and nonclimatic variables that remain difficult to rank by order of importance. Apart from a few statistically weak trends, several combinations of different factors in different proportions are shown to produce similar morphometric outcomes, suggesting a case of equifinality in landform development.

  4. Local Group dwarf galaxies: nature and nurture

    NASA Astrophysics Data System (ADS)

    Sawala, Till; Scannapieco, Cecilia; White, Simon

    2012-02-01

    We investigate the formation and evolution of dwarf galaxies in a high-resolution, hydrodynamical cosmological simulation of a Milky Way sized halo and its environment. Our simulation includes gas cooling, star formation, supernova feedback, metal enrichment and ultraviolet heating. In total, 90 satellites and more than 400 isolated dwarf galaxies are formed in the simulation, allowing a systematic study of the internal and environmental processes that determine their evolution. We find that 95 per cent of satellite galaxies are gas free at z= 0, and identify three mechanisms for gas loss: supernova feedback, tidal stripping and photoevaporation due to re-ionization. Gas-rich satellite galaxies are only found with total masses above ˜5 × 109 M⊙. In contrast, for isolated dwarf galaxies, a total mass of ˜109 M⊙ constitutes a sharp transition; less massive galaxies are predominantly gas free at z= 0, more massive, isolated dwarf galaxies are often able to retain their gas. In general, we find that the total mass of a dwarf galaxy is the main factor which determines its star formation, metal enrichment and its gas content, but that stripping may explain the observed difference in gas content between field dwarf galaxies and satellites with total masses close to 109 M⊙. We also find that a morphological transformation via tidal stripping of infalling, luminous dwarf galaxies whose dark matter is less concentrated than their stars cannot explain the high total mass-to-light ratios of the faint dwarf spheroidal galaxies.

  5. Gaia --- A White Dwarf Discovery Machine

    NASA Astrophysics Data System (ADS)

    Jordan, S.

    2007-09-01

    Gaia is a satellite mission of the ESA, aiming at absolute astrometric measurements of about one billion stars (V<20) with unprecedented accuracy. Additionally, magnitudes and colors will be obtained for all these stars, while radial-velocities will be determined only for bright objects (V<17.5). However, the wavelength range for the radial-velocity instrument is rather unsuitable for most white dwarfs. Gaia will probably discover about 400,000 white dwarfs; up to 100 pc the detection probability for white dwarfs is almost 100 %. This survey of white dwarfs will have very clear, easy to understand selection criteria, and will therefore be very suitable for statistical investigations. The Gaia data will help to improve the construction of a luminosity function for the disk and the halo and will provide a more accurate determination of the age of our solar neighborhood. Moreover, reliable stellar dynamical investigations of the disk and halo components will be possible. For the first time it will be possible to test the mass-radius relation of white dwarfs in great detail. Moreover, more accurate masses of magnetic and cool white dwarfs can be expected. Gaia is also expected to discover many new pulsating white dwarfs. The Gaia measurements can also complement the measurements of gravitational waves from close white dwarf binaries with Lisa.

  6. Mechanisms of shrub encroachment into Northern Chihuahuan Desert grasslands and impacts of climate change investigated using a cellular automata model

    NASA Astrophysics Data System (ADS)

    Caracciolo, Domenico; Istanbulluoglu, Erkan; Noto, Leonardo Valerio; Collins, Scott L.

    2016-05-01

    Arid and semiarid grasslands of southwestern North America have changed dramatically over the last 150 years as a result of woody plant encroachment. Overgrazing, reduced fire frequency, and climate change are known drivers of woody plant encroachment into grasslands. In this study, relatively simple algorithms for encroachment factors (i.e., grazing, grassland fires, and seed dispersal by grazers) are proposed and implemented in the ecohydrological Cellular-Automata Tree Grass Shrub Simulator (CATGraSS). CATGraSS is used in a 7.3 km2 rectangular domain located in central New Mexico along a zone of grassland to shrubland transition, where shrub encroachment is currently active. CATGraSS is calibrated and used to investigate the relative contributions of grazing, fire frequency, seed dispersal by herbivores and climate change on shrub abundance over a 150-year period of historical shrub encroachment. The impact of future climate change is examined using a model output that realistically represents current vegetation cover as initial condition, in a series of stochastic CATGraSS future climate simulations. Model simulations are found to be highly sensitive to the initial distribution of shrub cover. Encroachment factors more actively lead to shrub propagation within the domain when the model starts with randomly distributed individual shrubs. However, when shrubs are naturally evolved into clusters, the model response to encroachment factors is muted unless the effect of seed dispersal by herbivores is amplified. The relative contribution of different drivers on modeled shrub encroachment varied based on the initial shrub cover condition used in the model. When historical weather data is used, CATGraSS predicted loss of shrub and grass cover during the 1950 s drought. While future climate change is found to amplify shrub encroachment (∼13% more shrub cover by 2100), grazing remains the dominant factor promoting shrub encroachment. When we modeled future climate

  7. Patterns of shrub expansion in Alaskan arctic river corridors suggest phase transition

    PubMed Central

    Naito, Adam T; Cairns, David M

    2015-01-01

    Recent increases in deciduous shrub cover are a primary focus of terrestrial Arctic research. This study examined the historic spatial patterns of shrub expansion on the North Slope of Alaska to determine the potential for a phase transition from tundra to shrubland. We examined the historic variability of landscape-scale tall shrub expansion patterns on nine sites within river valleys in the Brooks Range and North Slope uplands (BRNS) between the 1950s and circa 2010 by calculating percent cover (PCTCOV), patch density (PADENS), patch size variability (CVSIZE), mean nearest neighbor distance (MEDIST) and the multi-scale information fractal dimension (dI) to assess spatial homogeneity for shrub cover. We also devised conceptual models for trends in these metrics before, during, and after a phase transition, and compared these to our results. By developing a regression equation between PCTCOV and dI and using universal critical dI values, we derived the PCTCOV required for a phase transition to occur. All nine sites exhibited increases in PCTCOV. Five of the nine sites exhibited an increase in PADENS, seven exhibited an increase in CVSIZE, and five exhibited a decrease in MEDIST. The dI values for each site exceeded the requirements necessary for a phase transition. Although fine-scale heterogeneity is still present, landscape-scale patterns suggest our study areas are either currently in a state of phase transition from tundra to shrubland or are progressing towards spatial homogeneity for shrubland. Our results indicate that the shrub tundra in the river valleys of the north slope of Alaska has reached a tipping point. If climate trends observed in recent decades continue, the shrub tundra will continue towards homogeneity with regard to the cover of tall shrubs. PMID:25628866

  8. Activity cycles of M dwarfs

    NASA Astrophysics Data System (ADS)

    Savanov, I. S.

    2012-09-01

    We have determined activity cycles for coolest M dwarfs using photometry from the ASAS survey. The time scales of brightness variations were determined for the program stars using calculated amplitude power spectra and wavelet spectra. Most of ther program stars display periodicities in their light-curve variations, with periods from hundreds of days to years. Analysis of diagrams plotting P cyc/ P rot versus 1/ P rot in logarithmic coordinates shows that the data for all our program objects fit the general relation quite well. No differences in the activity cycles are found for our sample stars, which have different masses and thus internal structures, some having convective envelopes and others being totally convective. Our analysis indicates that the slope i of this relation is close to unity, regardless of whether it is determined from all data, from data for the shortest cycles, or from data for the longest cycles. This value of i differs from values in the literature for stars of other spectral types. Our analysis of the P cyc- P rot relation indicates that the activity cycles for the studied sample of M dwarfs do not depend on the rotation periods of these objects. The data for the studied objects do not agree with any of the relations for relatively young (active) stars or older (less active) stars. The studied M dwarfs probably form another branch of low-mass stars that display more random, irregular magnetic activity on their surfaces, which is generated and supported by the distributed dynamo mechanism or a small-scale dynamo mechanism.

  9. A white dwarf with an oxygen atmosphere.

    PubMed

    Kepler, S O; Koester, Detlev; Ourique, Gustavo

    2016-04-01

    Stars born with masses below around 10 solar masses end their lives as white dwarf stars. Their atmospheres are dominated by the lightest elements because gravitational diffusion brings the lightest element to the surface. We report the discovery of a white dwarf with an atmosphere completely dominated by oxygen, SDSS J124043.01+671034.68. After oxygen, the next most abundant elements in its atmosphere are neon and magnesium, but these are lower by a factor of ≥25 by number. The fact that no hydrogen or helium are observed is surprising. Oxygen, neon, and magnesium are the products of carbon burning, which occurs in stars at the high-mass end of pre-white dwarf formation. This star, a possible oxygen-neon white dwarf, will provide a rare observational test of the evolutionary paths toward white dwarfs. PMID:27034367

  10. A white dwarf with an oxygen atmosphere

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Koester, Detlev; Ourique, Gustavo

    2016-04-01

    Stars born with masses below around 10 solar masses end their lives as white dwarf stars. Their atmospheres are dominated by the lightest elements because gravitational diffusion brings the lightest element to the surface. We report the discovery of a white dwarf with an atmosphere completely dominated by oxygen, SDSS J124043.01+671034.68. After oxygen, the next most abundant elements in its atmosphere are neon and magnesium, but these are lower by a factor of ≥25 by number. The fact that no hydrogen or helium are observed is surprising. Oxygen, neon, and magnesium are the products of carbon burning, which occurs in stars at the high-mass end of pre-white dwarf formation. This star, a possible oxygen-neon white dwarf, will provide a rare observational test of the evolutionary paths toward white dwarfs.

  11. Minimal erosion of Arctic alpine topography during late Quaternary glaciation

    NASA Astrophysics Data System (ADS)

    Gjermundsen, Endre F.; Briner, Jason P.; Akçar, Naki; Foros, Jørn; Kubik, Peter W.; Salvigsen, Otto; Hormes, Anne

    2015-10-01

    The alpine topography observed in many mountainous regions is thought to have formed during repeated glaciations of the Quaternary period. Before this time, landscapes had much less relief. However, the spatial patterns and rates of Quaternary exhumation at high latitudes--where cold-based glaciers may protect rather than erode landscapes--are not fully quantified. Here we determine the exposure and burial histories of rock samples from eight summits of steep alpine peaks in northwestern Svalbard (79.5° N) using analyses of 10Be and 26Al concentrations. We find that the summits have been preserved for at least the past one million years. The antiquity of Svalbard’s alpine landscape is supported by the preservation of sediments older than one million years along a fjord valley, which suggests that both mountain summits and low-elevation landscapes experienced very low erosion rates over the past million years. Our findings support the establishment of northwestern Svalbard’s alpine topography during the early Quaternary. We suggest that, as the Quaternary ice age progressed, glacial erosion in the Arctic became inefficient and confined to ice streams, and high-relief alpine landscapes were preserved by minimally erosive glacier armour.

  12. [Impacts of Ochotona pallasi disturbance on alpine grassland community characteristics].

    PubMed

    Zhao, Guo-qin; Li, Guang-yong; Ma, Wen-hu; Zhao, Dian-zhi; Li, Xiao-yan

    2013-08-01

    Plateau pika is the main fossorial mammal in the alpine grassland in Qinghai Lake Watershed of Northwest China. Based on the field investigation data from 18 alpine grassland quadrats in the Watershed, and by using redundancy analysis (RDA) and the surface fitting offered by 'R-Vegan' , the disturbance intensity of plateau pika (Ochotona pallasi) was classified as four levels. In order to explore the impacts of plateau pika disturbance on the alpine grassland ecosystem and its grazing quality, the community characteristics under different disturbance intensities by plateau pika were analyzed, and a conceptual model about the alpine grassland community succession was proposed. The results showed that with the increase of the disturbance intensity, the dominant species changed from Juncus roemerianus to Poa pratensis and Laux maritima. When the disturbance was small, the community had high quantitative values of coverage, aboveground biomass, biodiversity, and species richness, but the proportion of weeds was also high. When the disturbance was large, the quantitative values were the lowest, while the proportion of weeds was the highest. When the disturbance was moderate, the community had relatively high quantitative values, and the proportion of grasses and sedges was the highest. It was concluded that the community' s characteristic values under low plateau pika disturbance intensity were high but the grazing quality was low, while high disturbance intensity resulted in the grassland degradation. Therefore, the disturbance intensity in the threshold could maintain the stability of alpine grassland ecosystem and improve its grazing quality. PMID:24380328

  13. Theories of white dwarf oscillations

    NASA Technical Reports Server (NTRS)

    Vanhorn, H. M.

    1980-01-01

    The current status of theoretical understanding of the oscillations observed in the ZZ Ceti stars and cataclysmic variables is briefly reviewed. Nonradial g-mode oscillations appear to provide a satisfactory explanation for the low amplitude variables such as R548, with periods in the range of approximately 200 to 300 seconds, but for the longer period (800 to 1000 seconds) oscillators, the situation is still unclear. Rotation may play an important role in this problem, and the effects of both slow and fast rotation upon the mode structure are discussed. In the cataclysmic variables, both accretion and thermonuclear burning may act to excite oscillations of the white dwarf.

  14. Double White Dwarf Merger Rates

    NASA Astrophysics Data System (ADS)

    Toonen, Silvia; Nelemans, Gijs; Portegies Zwart, Simon

    2013-01-01

    Type Ia supernovae (SNe Ia) are very successfully used as standard candles on cosmological distance scales, but so far the nature of the progenitor(s) is unclear. A possible scenario for SNe Ia are merging carbon/oxygen white dwarfs with a combined mass exceeding the Chandrasekhar mass. We determine the theoretical rates and delay time distribution of these mergers for two different common envelope prescriptions and metallicities. The shape of the delay time distributions is rather insensitive to the assumptions. The normalization is a factor ~3-13 too low compared to observations.

  15. The Luminosities of the Coldest Brown Dwarfs

    NASA Astrophysics Data System (ADS)

    Tinney, C. G.; Faherty, Jacqueline K.; Kirkpatrick, J. Davy; Cushing, Mike; Morley, Caroline V.; Wright, Edward L.

    2014-11-01

    In recent years, brown dwarfs have been extended to a new Y-dwarf class with effective temperatures colder than 500 K and masses in the range of 5-30 Jupiter masses. They fill a crucial gap in observable atmospheric properties between the much colder gas-giant planets of our own solar system (at around 130 K) and both hotter T-type brown dwarfs and the hotter planets that can be imaged orbiting young nearby stars (both with effective temperatures in the range of 1500-1000 K). Distance measurements for these objects deliver absolute magnitudes that make critical tests of our understanding of very cool atmospheres. Here we report new distances for nine Y dwarfs and seven very late T dwarfs. These reveal that Y dwarfs do indeed represent a continuation of the T-dwarf sequence to both fainter luminosities and cooler temperatures. They also show that the coolest objects display a large range in absolute magnitude for a given photometric color. The latest atmospheric models show good agreement with the majority of these Y-dwarf absolute magnitudes. This is also the case for WISE0855-0714, the coldest and closest brown dwarf to the Sun, which shows evidence for water ice clouds. However, there are also some outstanding exceptions, which suggest either binarity or the presence of condensate clouds. The former is readily testable with current adaptive optics facilities. The latter would mean that the range of cloudiness in Y dwarfs is substantial with most hosting almost no clouds—while others have dense clouds, making them prime targets for future variability observations to study cloud dynamics. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  16. The luminosities of the coldest brown dwarfs

    SciTech Connect

    Tinney, C. G.; Faherty, Jacqueline K.; Kirkpatrick, J. Davy; Cushing, Mike; Morley, Caroline V.; Wright, Edward L.

    2014-11-20

    In recent years, brown dwarfs have been extended to a new Y-dwarf class with effective temperatures colder than 500 K and masses in the range of 5-30 Jupiter masses. They fill a crucial gap in observable atmospheric properties between the much colder gas-giant planets of our own solar system (at around 130 K) and both hotter T-type brown dwarfs and the hotter planets that can be imaged orbiting young nearby stars (both with effective temperatures in the range of 1500-1000 K). Distance measurements for these objects deliver absolute magnitudes that make critical tests of our understanding of very cool atmospheres. Here we report new distances for nine Y dwarfs and seven very late T dwarfs. These reveal that Y dwarfs do indeed represent a continuation of the T-dwarf sequence to both fainter luminosities and cooler temperatures. They also show that the coolest objects display a large range in absolute magnitude for a given photometric color. The latest atmospheric models show good agreement with the majority of these Y-dwarf absolute magnitudes. This is also the case for WISE0855-0714, the coldest and closest brown dwarf to the Sun, which shows evidence for water ice clouds. However, there are also some outstanding exceptions, which suggest either binarity or the presence of condensate clouds. The former is readily testable with current adaptive optics facilities. The latter would mean that the range of cloudiness in Y dwarfs is substantial with most hosting almost no clouds—while others have dense clouds, making them prime targets for future variability observations to study cloud dynamics.

  17. Relative roles of different-sized herbivores and plant-plant interactions in tall shrub tundra vegetation

    NASA Astrophysics Data System (ADS)

    Ravolainen, Virve; Ims, Rolf; Bårdsen, Bård-Jørgen; Stien, Audun; Kollstrøm, Julie; Lægreid, Eiliv; Bråthen, Kari Anne

    2013-04-01

    Tall shrubs play important roles in the ecology of Arctic tundra ecosystems, including support of high shrub-associated biodiversity and regulation of a range of ecosystem processes. Tall shrub patches and herbaceous vegetation surrounding them often form a two-state vegetation mosaic. Such tall shrub tundra vegetation is an important locus for current vegetation changes in the Arctic. Both abiotic and biotic drivers are known to influence the shrub component. However, although expansion of the shrub state has received much focus lately, relative strengths of the multiple drivers of vegetation state are currently not fully understood. We investigated the role of herbivory relative to temperature and relative to plant-plant interactions, conducting a field survey and experimental studies at large spatial scales in riparian tall shrub tundra in Norway. We found both summer temperatures and summer grazing by reindeer (Rangifer tarandus) to affect tall shrub distribution and expansion potential. Furthermore, we found strong and rapid shrub growth change in response to abundance of key arctic herbivores; small rodents. Finally, we quantified the relative importance of neighboring plants and both herbivore types to recruiting tall shrubs. The previously unforeseen rate at which tall shrub tundra responded to altered herbivore pressures further exemplifies its central role in the tundra ecosystems, promoting tall shrub tundra as a bell-whether of change with respect to both abiotic and biotic drivers. While many of the results clearly relate to herbivory, neighboring plants or climate as drivers, some variation remains unexplained warranting future research focus on this highly dynamic part of the tundra ecosystem. Our results suggest that spatially variable biotic interactions are likely to modify forcing by climate, calling for an ecosystem approach when studying change in tundra ecosystems.

  18. Using deuterium excess to determine the sources of high-altitude precipitation: Implications in hydrological relations between sub-alpine forests and alpine meadows

    NASA Astrophysics Data System (ADS)

    Cui, Jun; An, Shuqing; Wang, Zhongsheng; Fang, Changming; Liu, Yuhong; Yang, Haibo; Xu, Zhen; Liu, Shirong

    2009-06-01

    SummaryAlpine meadows in the upper catchments of the Yangtze River, China provide critical amounts of water to maintain regional water resources, but little is known about the hydrological processes in these alpine ecosystems. In this paper, we analyzed the sources of precipitation in an alpine meadow using the deuterium excess in rain, fog, soil water, shallow groundwater and stream water. Rain and fog in the alpine meadow had high deuterium excess, 35‰ and 38‰ compared to 10‰ of precipitation brought by monsoon at lower elevation. These high values suggested that a large part of rain at the alpine meadow derived from secondarily evaporated water and that fog derived from the evaporated water produced shortly after rain events. However, averaged evaporation rate calculated by an isotopic mass balance model of soil water was only 0.26 mm/d, about 3.6% of the rainfall and 7.57‰ of the average deuterium excess value of rain. The contribution from evaporated water to precipitation in the alpine meadow therefore had to be mainly from sub-alpine vegetations in the region. This eco-hydrological relation between sub-alpine and alpine ecosystems can partly explain the high water yield of the alpine meadow and should be considered for regional resource management.

  19. Beneficial Hydrologic Relations Between Evergreen Woody Shrubs and Food Crops In the Peanut Basin, Senegal

    NASA Astrophysics Data System (ADS)

    Bogie, N. A.; Bayala, R.; McCants, T.; Bethel, D.; Diedhiou, I.; Dick, R.; Ghezzehei, T. A.

    2012-12-01

    The soils of the Sahel and surrounding regions are threatened by soil degradation and desertification that can lead to significant reduction in food supply. In Senegal, millet and peanut crops are grown in rotation in fields, where to varying degrees, two native shrubs Piliostigma reticulatum, and Guiera senegalensis are allowed to exist. Previous work established that the presence of shrubs increased moisture content, organic matter, crop yield, and ground water recharge beneath shrub canopies. However, relatively little is known about the mechanism controlling nutrient and water relations between the rhizospheres of the crops and shrubs. Therefore, the objective of this ongoing research is to provide mechanistic explanation for why and how the shrubs aid the crop productivity. This research involves field measurements of: crop yield and physiological responses to water stress, water balance, and meteorological data at two sites in the Peanut Basin of Senegal -- a northern site in Kuer Matar (with annual rainfall of 400-500 mm) for G. senegalensis and a southern site in Nioro du Rip (with 600-800 mm annual rainfall) for P. reticulatum. Although a water balance was performed once in the past, it is important to track water dynamics due to large fluctuations in precipitation and rainfall intensity. Interpretation of current observations is aided by numerical simulations using the HYDRUS 1D model calibrated against field data. Preliminary observations from Nioro du Rip show no significant difference between treatments in leaf area index or leaf water potential throughout the daily cycle (predawn, mid-morning, mid-afternoon, and evening) 30 days after sowing (DAS) and during a period of ample rainfall for crop establishment. There were, however, increases of 12.4mm and 13.0mm in profile moisture storage between sole crop and crop and shrub treatments from 20cm to 250cm depth at Keur Matar and Nioro du Rip, respectively. These profile moisture values come from the

  20. Deciduous shrub growth and the greening of the Arctic in West Siberia

    NASA Astrophysics Data System (ADS)

    Forbes, B. C.; Macias Fauria, M.; Zetterberg, P.; Kumpula, T.

    2010-12-01

    Salix lanata and Alnus fruticosa are common and widespread shrub species in the low arctic tundra zone of West Siberia. They often occur in similar local habitats with the live portions of genets up to 100 years old. We have recently established that growth rings of S. lanata provide an excellent proxy for summer temperature. In that study our data were derived from shrubs growing on organic soils near the arctic coast of the Nenets Autonomous Okrug (NAO), west of the Ural Mountains. East of the Urals, in the Yamal-Nenets Autonomous Okrug (YNAO), climate is more continental and sandy soils provide a relatively nutrient-poor substrate for plant growth. By sampling two different species side by side on the Yamal Peninsula, we shed light on the relationship between deciduous shrubs and growing season temperatures in the last half century or so, a period of pronounced regional warming. We discern differences in the climate signal within a single species (S. lanata) as well as between it and a neighboring species with a strongly overlapping ecological amplitude (A. fruticosa). July is the main month for temperature correlation in Alnus, whereas Salix responds to June-July-August temperatures in both regions. The high correlations of shrub growth with summer temperature (r > 0.7 over the period 1956-2004) strongly suggest a link between increased shrub growth and recent decadal warming in both regions (~2°C). Both species showed significant correlation with the regional Normalized Difference Vegetation Index (NDVI), although it was somewhat lower in YNAO compared to NAO, probably due to the relative land cover (10% vs. 20%, respectively) of erect shrubs in both areas, which affects their overall contribution to the NDVI. In both regions Salix lanata biomass peaks in the second half of July. Hand-held leaf area index data from Yamal indicate a significant difference between loamy/clayey and sandy sites. We hypothesized that this same variation would be evident at the

  1. Nitrogen niches revealed through species and functional group removal in a boreal shrub community.

    PubMed

    Gundale, Michael J; Hyodo, Fujio; Nilsson, Marie-Charlotte; Wardle, David A

    2012-07-01

    Most theories attempting to explain the coexistence of species in local communities make fundamental assumptions regarding whether neighbors exhibit competitive, neutral, or positive resource-use interactions; however, few long-term data from naturally assembled plant communities exist to test these assumptions. We utilized a 13-year experiment consisting of factorial removal of three shrub species (Vaccinium myrtillus, V. vitis-idaea, and Empetrum hermaphroditum) and factorial removal of two functional groups (tree roots and feather mosses) to assess how neighbors affect N acquisition and growth of each of the three shrub species. The removal plots were established on each of 30 lake islands in northern Sweden that form a natural gradient of resource availability. We tested the hypotheses that: (1) the presence of functionally similar neighbors would reduce shrub N acquisition through competition for a shared N resource; (2) the removal of functional groups would affect shrub N acquisition by altering the breadth of their niches; and (3) soil fertility would influence the effects of neighbor removals. We found that the removal of functionally similar neighbors (i.e., other shrub species) usually resulted in higher biomass and biomass N, with the strength of these effects varying strongly with site fertility. Shrub species removals never resulted in altered stable N isotope ratios (delta(15)N), suggesting that the niche breadth of the three shrubs was unaffected by the presence of neighboring shrub species. In the functional group removal experiment, we found positive effects of feather moss removal on V. myrtillus biomass and biomass N, and negative effects on E. hermaphrotium N concentration and V. vitis-idaea biomass and biomass N. Tree root removal also caused a significant shift in foliar delta(15)N of V. myrtillus and altered the delta(15)N, biomass, and biomass N of E. hermaphroditum. Collectively, these results show that the resource acquisition and niche

  2. PREFACE: 16th European White Dwarfs Workshop

    NASA Astrophysics Data System (ADS)

    Garcia-Berro, Enrique; Hernanz, Margarita; Isern, Jordi; Torres, Santiago

    2009-07-01

    The 16th European Workshop on White Dwarfs was held in Barcelona, Spain, from 30 June to 4 July 2008 at the premises of the UPC. Almost 120 participants from Europe (France, Germany, United Kingdom, Italy, and several others), America (USA, Canada, Argentina, Brazil, and Chile), and other continents (Australia, South Africa, . . . ) attended the workshop. Among these participants were the most relevant specialists in the field. The topics covered by the conference were: White dwarf structure and evolution Progenitors and Planetary Nebulae White dwarfs in binaries: cataclysmic variables, double degenerates and other binaries White dwarfs, dust disks and planetary systems Atmospheres, chemical composition, magnetic fields Variable white dwarfs White dwarfs in stellar clusters and the halo White Dwarfs as SNIa progenitors The programme included 54 talks, and 45 posters. The oral presentations were distributed into the following sessions: Luminosity function, mass function and populations White dwarf structure and evolution White dwarf ages White dwarf catalogs and surveys Central stars of planetary nebulae Supernovae progenitors White dwarfs in novae and CVs Physical processes in white dwarfs and magnetic white dwarfs Disks, dust and planets around white dwarfs Pulsating white dwarfs Additionally we had a special open session about Spitzer and white dwarfs. The Proceedings of the 16th European Workshop on White Dwarfs are representative of the current state-of-the-art of the research field and include new and exciting results. We acknowledge the very positive attitude of the attendants to the workshop, which stimulated very fruitful discussions that took place in all the sessions and after the official schedule. Also, the meeting allowed new collaborations tp start that will undoubtedly result in significant advances in the research field. We also acknowledge the willingness of the participants to deliver their contributions before the final deadline. We sincerely

  3. Divergent variations in concentrations of chemical elements among shrub organs in a temperate desert

    PubMed Central

    He, Mingzhu; Song, Xin; Tian, Fuping; Zhang, Ke; Zhang, Zhishan; Chen, Ning; Li, Xinrong

    2016-01-01

    Desert shrubs, a dominant component of desert ecosystems, need to maintain sufficient levels of nutrients in their different organs to ensure operation of various physiological functions for the purpose of survival and reproduction. In the present study, we analyzed 10 elements in leaves, stems, and roots of 24 dominant shrub species from 52 sites across a temperate desert ecosystem in northwestern China. We found that concentrations of all 10 elements were higher in leaves than in stems and roots, that non-legumes had higher levels of leaf Na and Mg than did legumes, and that Na was more concentrated in C4 leaves than in C3 leaves. Scaling relationships of elements between the photosynthetic organ (leaf) and non-photosynthetic organs (stem and root) were allometric. Results of principal components analysis (PCA) highlighted the important role of the elements responsible for osmoregulation (K and Na) in water utilization of desert shrubs. Soil properties and taxonomy explained most variation of element concentrations in desert shrubs. Desert shrubs may not be particularly susceptible to future change in climate factors, because most elements (including N, P, K, Ca, Mn, Zn, and Cu) associated with photosynthesis, osmoregulation, enzyme activity, and water use efficiency primarily depend on soil conditions. PMID:26818575

  4. Effects of shrub encroachment on soil organic carbon in global grasslands

    NASA Astrophysics Data System (ADS)

    Li, He; Shen, Haihua; Chen, Leiyi; Liu, Taoyu; Hu, Huifeng; Zhao, Xia; Zhou, Luhong; Zhang, Pujin; Fang, Jingyun

    2016-07-01

    This study aimed to evaluate the effect of shrub encroachment on soil organic carbon (SOC) content at broad scales and its controls. We conducted a meta-analysis using paired control data of shrub-encroached grassland (SEG) vs. non-SEG collected from 142 studies worldwide. SOC contents (0–50 cm) were altered by shrub encroachment, with changes ranging from ‑50% to + 300%, with an effect size of 0.15 (p < 0.01). The SOC contents increased in semi-arid and humid regions, and showed a greater rate of increase in grassland encroached by leguminous shrubs than by non-legumes. The SOC content decreased in silty and clay soils but increased in sand, sandy loam and sandy clay loam. The SOC content increment was significantly positively correlated with precipitation and temperature as well as with soil bulk density but significantly negatively correlated with soil total nitrogen. We conclude the main effects of shrub encroachment would be to increase topsoil organic carbon content. As structural equation model revealed, soils properties seem to be the primary factors responsible for the extent of the changes, coarse textured soils having a greater capacity than fine textured soils to increase the SOC content. This increased effect appears to be secondarily enhanced by climate and plant elements.

  5. Electrostatic Interactions between Elongated Monomers Drive Filamentation of Drosophila Shrub, a Metazoan ESCRT-III Protein.

    PubMed

    McMillan, Brian J; Tibbe, Christine; Jeon, Hyesung; Drabek, Andrew A; Klein, Thomas; Blacklow, Stephen C

    2016-08-01

    The endosomal sorting complex required for transport (ESCRT) is a conserved protein complex that facilitates budding and fission of membranes. It executes a key step in many cellular events, including cytokinesis and multi-vesicular body formation. The ESCRT-III protein Shrub in flies, or its homologs in yeast (Snf7) or humans (CHMP4B), is a critical polymerizing component of ESCRT-III needed to effect membrane fission. We report the structural basis for polymerization of Shrub and define a minimal region required for filament formation. The X-ray structure of the Shrub core shows that individual monomers in the lattice interact in a staggered arrangement using complementary electrostatic surfaces. Mutations that disrupt interface salt bridges interfere with Shrub polymerization and function. Despite substantial sequence divergence and differences in packing interactions, the arrangement of Shrub subunits in the polymer resembles that of Snf7 and other family homologs, suggesting that this intermolecular packing mechanism is shared among ESCRT-III proteins. PMID:27452459

  6. Divergent variations in concentrations of chemical elements among shrub organs in a temperate desert

    NASA Astrophysics Data System (ADS)

    He, Mingzhu; Song, Xin; Tian, Fuping; Zhang, Ke; Zhang, Zhishan; Chen, Ning; Li, Xinrong

    2016-01-01

    Desert shrubs, a dominant component of desert ecosystems, need to maintain sufficient levels of nutrients in their different organs to ensure operation of various physiological functions for the purpose of survival and reproduction. In the present study, we analyzed 10 elements in leaves, stems, and roots of 24 dominant shrub species from 52 sites across a temperate desert ecosystem in northwestern China. We found that concentrations of all 10 elements were higher in leaves than in stems and roots, that non-legumes had higher levels of leaf Na and Mg than did legumes, and that Na was more concentrated in C4 leaves than in C3 leaves. Scaling relationships of elements between the photosynthetic organ (leaf) and non-photosynthetic organs (stem and root) were allometric. Results of principal components analysis (PCA) highlighted the important role of the elements responsible for osmoregulation (K and Na) in water utilization of desert shrubs. Soil properties and taxonomy explained most variation of element concentrations in desert shrubs. Desert shrubs may not be particularly susceptible to future change in climate factors, because most elements (including N, P, K, Ca, Mn, Zn, and Cu) associated with photosynthesis, osmoregulation, enzyme activity, and water use efficiency primarily depend on soil conditions.

  7. Divergent variations in concentrations of chemical elements among shrub organs in a temperate desert.

    PubMed

    He, Mingzhu; Song, Xin; Tian, Fuping; Zhang, Ke; Zhang, Zhishan; Chen, Ning; Li, Xinrong

    2016-01-01

    Desert shrubs, a dominant component of desert ecosystems, need to maintain sufficient levels of nutrients in their different organs to ensure operation of various physiological functions for the purpose of survival and reproduction. In the present study, we analyzed 10 elements in leaves, stems, and roots of 24 dominant shrub species from 52 sites across a temperate desert ecosystem in northwestern China. We found that concentrations of all 10 elements were higher in leaves than in stems and roots, that non-legumes had higher levels of leaf Na and Mg than did legumes, and that Na was more concentrated in C4 leaves than in C3 leaves. Scaling relationships of elements between the photosynthetic organ (leaf) and non-photosynthetic organs (stem and root) were allometric. Results of principal components analysis (PCA) highlighted the important role of the elements responsible for osmoregulation (K and Na) in water utilization of desert shrubs. Soil properties and taxonomy explained most variation of element concentrations in desert shrubs. Desert shrubs may not be particularly susceptible to future change in climate factors, because most elements (including N, P, K, Ca, Mn, Zn, and Cu) associated with photosynthesis, osmoregulation, enzyme activity, and water use efficiency primarily depend on soil conditions. PMID:26818575

  8. Effects of shrub encroachment on soil organic carbon in global grasslands

    PubMed Central

    Li, He; Shen, Haihua; Chen, Leiyi; Liu, Taoyu; Hu, Huifeng; Zhao, Xia; Zhou, Luhong; Zhang, Pujin; Fang, Jingyun

    2016-01-01

    This study aimed to evaluate the effect of shrub encroachment on soil organic carbon (SOC) content at broad scales and its controls. We conducted a meta-analysis using paired control data of shrub-encroached grassland (SEG) vs. non-SEG collected from 142 studies worldwide. SOC contents (0–50 cm) were altered by shrub encroachment, with changes ranging from −50% to + 300%, with an effect size of 0.15 (p < 0.01). The SOC contents increased in semi-arid and humid regions, and showed a greater rate of increase in grassland encroached by leguminous shrubs than by non-legumes. The SOC content decreased in silty and clay soils but increased in sand, sandy loam and sandy clay loam. The SOC content increment was significantly positively correlated with precipitation and temperature as well as with soil bulk density but significantly negatively correlated with soil total nitrogen. We conclude the main effects of shrub encroachment would be to increase topsoil organic carbon content. As structural equation model revealed, soils properties seem to be the primary factors responsible for the extent of the changes, coarse textured soils having a greater capacity than fine textured soils to increase the SOC content. This increased effect appears to be secondarily enhanced by climate and plant elements. PMID:27388145

  9. Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis.

    PubMed

    Eldridge, David J; Bowker, Matthew A; Maestre, Fernando T; Roger, Erin; Reynolds, James F; Whitford, Walter G

    2011-07-01

    Encroachment of woody plants into grasslands has generated considerable interest among ecologists. Syntheses of encroachment effects on ecosystem processes have been limited in extent and confined largely to pastoral land uses or particular geographical regions. We used univariate analyses, meta-analysis and structural equation modelling to test the propositions that (1) shrub encroachment does not necessarily lead to declines in ecosystem functions and (2) shrub traits influence the functional outcome of encroachment. Analyses of 43 ecosystem attributes from 244 case studies worldwide showed that some attributes consistently increased with encroachment (e.g. soil C, N), and others declined (e.g. grass cover, pH), but most exhibited variable responses. Traits of shrubs were associated with significant, though weak, structural and functional outcomes of encroachment. Our review revealed that encroachment had mixed effects on ecosystem structure and functioning at global scales, and that shrub traits influence the functional outcome of encroachment. Thus, a simple designation of encroachment as a process leading to functionally, structurally or contextually degraded ecosystems is not supported by a critical analysis of existing literature. Our results highlight that the commonly established link between shrub encroachment and degradation is not universal. PMID:21592276

  10. Modelling the shrub encroachment in a grassland with a Cellular Automata Model

    NASA Astrophysics Data System (ADS)

    Caracciolo, D.; Noto, L. V.; Istanbulluoglu, E.

    2014-09-01

    Arid and semi-arid grasslands of southwestern North America have changed dramatically over the last 150 years as a result of shrub encroachment, i.e. the increase in density, cover and biomass of indigenous shrubby plants in grasslands. Numerous studies have documented the expansion of shrublands in the southwestern American grasslands; in particular shrub encroachment has occurred strongly in part of the northern Chihuahuan desert since 1860. This encroachment has been simulated using an ecohydrological Cellular Automata model, CATGraSS. It is a spatially distributed model driven by spatially explicit irradiance and runs on a fine-resolution gridded domain. Plant competition is modelled by keeping track of mortality and establishment of plants; both are calculated probabilistically based on soil moisture stress. For this study CATGraSS has been improved with a stochastic fire module and a grazing function. The model has been implemented in a small area in Sevilleta National Wildlife Refuge (SNWR), characterized by two vegetation types (grass savanna and creosote bush shrub), considering as encroachment causes the fire return period increase, the grazing increase, the seed dispersal caused by animals, the role of wind direction and plant type competition. The model is able to reproduce the encroachment that has occurred in SNWR, simulating an increase of the shrub from 2% in 1860 to the current shrub percentage, 42%, and highlighting among the most influential factors the reduced fire frequency and the increased grazing intensity.

  11. Effects of shrub encroachment on soil organic carbon in global grasslands.

    PubMed

    Li, He; Shen, Haihua; Chen, Leiyi; Liu, Taoyu; Hu, Huifeng; Zhao, Xia; Zhou, Luhong; Zhang, Pujin; Fang, Jingyun

    2016-01-01

    This study aimed to evaluate the effect of shrub encroachment on soil organic carbon (SOC) content at broad scales and its controls. We conducted a meta-analysis using paired control data of shrub-encroached grassland (SEG) vs. non-SEG collected from 142 studies worldwide. SOC contents (0-50 cm) were altered by shrub encroachment, with changes ranging from -50% to + 300%, with an effect size of 0.15 (p < 0.01). The SOC contents increased in semi-arid and humid regions, and showed a greater rate of increase in grassland encroached by leguminous shrubs than by non-legumes. The SOC content decreased in silty and clay soils but increased in sand, sandy loam and sandy clay loam. The SOC content increment was significantly positively correlated with precipitation and temperature as well as with soil bulk density but significantly negatively correlated with soil total nitrogen. We conclude the main effects of shrub encroachment would be to increase topsoil organic carbon content. As structural equation model revealed, soils properties seem to be the primary factors responsible for the extent of the changes, coarse textured soils having a greater capacity than fine textured soils to increase the SOC content. This increased effect appears to be secondarily enhanced by climate and plant elements. PMID:27388145

  12. Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis

    PubMed Central

    Eldridge, David J.; Bowker, Matthew A.; Maestre, Fernando T.; Roger, Erin; Reynolds, James F.; Whitford, Walter G.

    2013-01-01

    Encroachment of woody plants into grasslands has generated considerable interest among ecologists. Syntheses of encroachment effects on ecosystem processes have been limited in extent and confined largely to pastoral land uses or particular geographical regions. We used univariate analyses, meta-analysis and structural equation modeling to test the propositions that 1) shrub encroachment does not necessarily lead to declines in ecosystem functions, and 2) shrub traits influence the functional outcome of encroachment. Analyses of 43 ecosystem attributes from 244 case studies worldwide showed that some attributes consistently increased with encroachment (e.g. soil C, N), and others declined (e.g. grass cover, pH), but most exhibited variable responses. Traits of shrubs were associated with significant, though weak, structural and functional outcomes of encroachment. Our review revealed that encroachment had mixed effects on ecosystem structure and functioning at global scales, and that shrub traits influence the functional outcome of encroachment. Thus, a simple designation of encroachment as a process leading to functionally, structurally or contextually degraded ecosystems is not supported by a critical analysis of existing literature. Our results highlight that the commonly established link between shrub encroachment and degradation is not universal. PMID:21592276

  13. a Simple Probabilistic, Biologically Informed Model of the Population Dynamics of Desert Shrubs

    NASA Astrophysics Data System (ADS)

    Worman, S.; Furbish, D. J.; Clarke, J. H.; Roberts, A. S.

    2010-12-01

    In arid environments, spatiotemporal variations in the processes of erosion and deposition are strongly coupled with the structure and dynamics of plant communities as well as the specific life behavior of individual plants. Understanding how physical transport processes affect the evolution of the land surface on geomorphic time-scales therefore requires considering how long-term changes in plant dynamics may in turn impact such processes. The development of this desert shrub population dynamics model is therefore motivated by the need to link rain-splash induced mound building at the shrub-scale with the unfolding ‘biological play’ occurring on a hillslope. Using the Master Equation to conserve shrub age, probabilistic and biologically informed statements for recruitment and mortality are formulated to function as source and sink terms respectively. This simple accounting framework, by tracking the number of individuals entering and leaving a population, captures the changes in shrub count that can be expected in time as the key variables driving the dynamics of these plant communities (i.e. precipitation) also change in time. The result is a tool through which it is possible to statistically describe the aggregate spatiotemporal behavior of different shrub populations, with their own characteristic life-cycles and physical dimensions, under different external forcing scenarios. This model features inputs that have a solid biophysical basis and insofar as it has the capacity to mimic key features of real processes, leads to outputs which appear consistent with findings reported in the literature.

  14. Hydraulically integrated or modular? Comparing whole-plant-level hydraulic systems between two desert shrub species with different growth forms.

    PubMed

    Espino, Susana; Schenk, H Jochen

    2009-01-01

    * Hydraulic systems of shrubs vary between hydraulically integrated and modular architectures; the latter divide the shrub into independent hydraulic units. Hydraulic systems of two common North American desert shrub species, the multi-branched Ambrosia dumosa and the single-stemmed Encelia farinosa (both Asteraceae), were compared to test for division into independent hydraulic units and the implications of such a division for water loss through leaves and roots. * Hydraulic systems of mature shrubs in the field were characterized using dye tracers and by documenting the degree of stem segmentation. Young pot-grown shrubs were subjected to heterogeneous and homogeneous watering. Spatial within-canopy variation of leaf water potentials and stomatal conductances, as well as soil water contents, were measured in response to manipulated soil water heterogeneity. * Results show that young Ambrosia shrubs are divided into independent hydraulic units long before they physically split into separate ramets as mature shrubs, and that young and mature Encelia shrubs possess integrated hydraulic systems. No hydraulic redistribution was detected for eitherspecies. * Our study shows that functional segmentation into independent hydraulic units precedes physical axis splitting, rather than being the consequence of split axes, and suggests that mature shrubs with round basal stems are likely to be hydraulically integrated. PMID:19368668

  15. Brown dwarf disks with ALMA

    SciTech Connect

    Ricci, L.; Isella, A.; Testi, L.; De Gregorio-Monsalvo, I.; Natta, A.; Scholz, A.

    2014-08-10

    We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

  16. The "stream power" of the Alpine Rivers

    NASA Astrophysics Data System (ADS)

    Salcher, Bernhard; Champagnac, Jean-Daniel

    2010-05-01

    We examine the spatial pattern of fluvial erosion on the entire European Alps and adjacent areas by applying the widely used stream power model (e.g. Whipple and Tucker, 1999). According to that model, the bedrock incision rate (E) equals the water flux (upstream contributing area (A) times rainfall (W)) multiplied by the channel slope (S) and a coefficient K which aggregates the influence of many factors, e.g. rock resistance to erosion or channel geometry. E= (Am * W) * Sn * K We apply the stream power (SP) approach as a generalized abstraction of erosional processes in the Alps using the highest available DEM (ASTER GDEM) for the entire orogen in a resolution of 1" (~30m). Climatic variability is implemented in to the SP adding a precipitation correction factor (average precipitation per year). We further average rates of large drainage basins' stream power to compare with existing post-LGM and Holocene erosion rates (Hinderer, 2001; Wittmann et al., 2007; Champagnac et al., 2009). Results show that the ice extension during the LGM is still represented in the extracted stream power. More specifically, SP values generally start to rise as soon as streams reach the areas of the former piedmont ice lobes. Outside of the LGM limits, SP values rise continuously, representing generally higher values in bedrock sections and lower values in alluvial-dominated sections. To better interpret the relative potential for erosion across the entire Alps, we use an averaged moving window on large catchments, and across the belt as a whole. At the scale of our analysis SP is used as a surrogate for the spatial pattern of erosion for which values may be used as an index of erosion (e.g. Finlaysson and Montgomery). Finally, we examine the important role of different East and West Alpine base levels on SP and discuss the associated effects on the evolution of the belt: the large eastern alpine rivers show generally higher SP values than those in the western Alps (e.g. Rhine or Rh

  17. Sensitivity of alpine watersheds to global change

    NASA Astrophysics Data System (ADS)

    Zierl, B.; Bugmann, H.

    2003-04-01

    Mountains provide society with a wide range of goods and services, so-called mountain ecosystem services. Besides many others, these services include the most precious element for life on earth: fresh water. Global change imposes significant environmental pressure on mountain watersheds. Climate change is predicted to modify water availability as well as shift its seasonality. In fact, the continued capacity of mountain regions to provide fresh water to society is threatened by the impact of environmental and social changes. We use RHESSys (Regional HydroEcological Simulation System) to analyse the impact of climate as well as land use change (e.g. afforestation or deforestation) on hydrological processes in mountain catchments using sophisticated climate and land use scenarios. RHESSys combines distributed flow modelling based on TOPMODEL with an ecophysiological canopy model based on BIOME-BGC and a climate interpolation scheme based on MTCLIM. It is a spatially distributed daily time step model designed to solve the coupled cycles of water, carbon, and nitrogen in mountain catchments. The model is applied to various mountain catchments in the alpine area. Dynamic hydrological and ecological properties such as river discharge, seasonality of discharge, peak flows, snow cover processes, soil moisture, and the feedback of a changing biosphere on hydrology are simulated under current as well as under changed environmental conditions. Results of these studies will be presented and discussed. This project is part of an over overarching EU-project called ATEAM (acronym for Advanced Terrestrial Ecosystem Analysis and Modelling) assessing the vulnerability of European ecosystem services.

  18. Tagliamento, the king of Alpine rivers

    NASA Astrophysics Data System (ADS)

    Imbriani, Nadia

    2016-04-01

    The Tagliamento river is usually described as the king of the Alpine rivers because it is an extraordinary example of braided gravel-bed river in Europe. It flows in Friuli Venezia Giulia, a region in north-eastern Italy. It has preserved its original ecosystem which has never been changed significantly by irresponsible human interference. Therefore, vegetated islands and braid bars, due to the typical network of channels the river creates, have always been an uncontaminated natural habitat for a wide variety of species of flora and fauna. The Pinzano Bridge, near San Daniele del Friuli, collapsed on 4th November 1966 because of an overflow of water from Tagliamento. From that time, lowlands territorial authorities would like to build retention basins to prevent the river from floodings. A study about the bio-geological survey carried out from a Manzini High School project, chiefly aims to study this ecosystem, which combines the dynamic nature of the Tagliamento with the biodiversity of the whole area where it flows. In the previous years, some classes were involved in this school project. After visiting the river area and taking several photographs of it, the students had the opportunity to reflect upon the devastating environmental impact which the construction of retention basins would cause. They illustrated and analyzed both the solutions offered by some local governors and the objections raised by the World Wide Fund For Nature (WWF). In the near future, other students will continue studying the Tagliamento river so as to be able to appreciate one of the local rarities nature offers, in the hope that the unique geomorphological features of this site of undoubted scientific interest could be kept intact for a very long time.

  19. Alkali content of alpine ultramafic rocks

    USGS Publications Warehouse

    Hamilton, W.; Mountjoy, W.

    1965-01-01

    The lower limit of abundance of sodium and potassium in ultramafic rocks is less than the threshold amount detectable by conventional analytical methods. By a dilutionaddition modification of the flame-spectrophotometric method, sodium and potassium have been determined in 40 specimens of alpine ultramafic rocks. Samples represent six regions in the United States and one in Australia, and include dunite, peridotite, pyroxenite, and their variably serpentinized and metamorphosed derivatives. The median value found for Na2O is 0.004 per cent, and the range of Na2O is 0.001-0.19. The median value for K2O is 0.0034 per cent and the range is 0.001-0.031 per cent. Alkali concentrations are below 0.01 per cent Na2O in 28 samples and below 0.01 per cent K2O in 35. Derivation of basalt magma from upper-mantle material similar to such ultramafic rocks, as has been postulated, is precluded by the relative amounts of sodium and potassium, which are from 200 to 600 times more abundant in basalt than in the ultramafic rocks. Similar factors apply to a number of other elements. No reasonable process could produce such concentrations in, for example, tens of thousands of cubic miles of uniform tholeiitic basalt. The ultramafic rocks might have originated either as magmatic crystal precipitates or as mantle residues left after fusion and removal of basaltic magma. Injection of ultramafic rocks to exposed positions is tectonic rather than magmatic. ?? 1965.

  20. Micro Radiocarbon Dating - Applications and challenges in Alpine glaciology

    NASA Astrophysics Data System (ADS)

    Hoffmann, Helene; Bohleber, Pascal; Wagenbach, Dietmar

    2015-04-01

    The interpretation of proxy records from ice cores obtained at cold small scale Alpine glaciers is hampered first and foremost because of challenges in obtaining a reliable age scale, especially for highly thinned basal ice. Where conventional stratigraphic dating methods fail, either due to complex flow dynamics or missing layering, radiocarbon measurements of organic impurities are up to now the only option to retrieve absolute age markers. Supplementing stratigraphic records, age of basal ice itself can provide valuable information on paleoclimatic conditions, e.g. related to the onset of formation of the respective ice body. In this respect, potential targets are basal sections of Alpine ice cores and small isolated ice patches or ice caves. Organic material in ice can be separated mainly by size into DOC (Dissolved Organic Carbon) and POC (Particulate Organic Carbon). Here we focus on radiocarbon dating of the POC fraction, because the DOC fraction is known to be biased by in situ production at high Alpine sites. Concentrations of POC in high Alpine ice can be very low, ranging from about 10 µgC per kg ice to 50 µgC per kg ice. This becomes an immediate challenge when sampling ice cores, where available masses for dating are typically in the order of a few hundred grams of ice. After developing an unique sample preparation system we managed to reduce the process blank reproducibly below one microgram carbon, independent of other sample characteristics. Utilizing a gas ion source at the Accelerator Mass Spectrometer MICADAS at the Klaus-Tschira-Lab in Mannheim (Germany) we are now able to reliably date samples with concentrations as low as 10 µg carbon. Accordingly, this approach becomes applicable for high Alpine ice samples. Here we present first results from POC radiocarbon dating of Alpine ice cores along with selected basal ice samples from smaller ice caps and cave ice in order to obtain a broader picture regarding age ranges of Alpine ice bodies. For

  1. THE METALLICITY OF VOID DWARF GALAXIES

    SciTech Connect

    Kreckel, K.; Groves, B.; Croxall, K.; Pogge, R. W.; Van de Weygaert, R.

    2015-01-01

    The current ΛCDM cosmological model predicts that galaxy evolution proceeds more slowly in lower density environments, suggesting that voids are a prime location to search for relatively pristine galaxies that are representative of the building blocks of early massive galaxies. To test the assumption that void galaxies are more pristine, we compare the evolutionary properties of a sample of dwarf galaxies selected specifically to lie in voids with a sample of similar isolated dwarf galaxies in average density environments. We measure gas-phase oxygen abundances and gas fractions for eight dwarf galaxies (M{sub r} > –16.2), carefully selected to reside within the lowest density environments of seven voids, and apply the same calibrations to existing samples of isolated dwarf galaxies. We find no significant difference between these void dwarf galaxies and the isolated dwarf galaxies, suggesting that dwarf galaxy chemical evolution proceeds independent of the large-scale environment. While this sample is too small to draw strong conclusions, it suggests that external gas accretion is playing a limited role in the chemical evolution of these systems, and that this evolution is instead dominated mainly by the internal secular processes that are linking the simultaneous growth and enrichment of these galaxies.

  2. SDSS DR7 WHITE DWARF CATALOG

    SciTech Connect

    Kleinman, S. J.; Nitta, A.; Kepler, S. O.; Pelisoli, Ingrid; Pecanha, Viviane; Costa, J. E. S.; Koester, D.; Krzesinski, J.; Dufour, P.; Lachapelle, F.-R.; Bergeron, P.; Yip, Ching-Wa; Harris, Hugh C.; Eisenstein, Daniel J.; Althaus, L.; Corsico, A.

    2013-01-15

    We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log g if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.

  3. Shrub Expansion Along Arctic Alaskan Streams and Gullies Reduces Erosion Since 1980

    NASA Astrophysics Data System (ADS)

    Tape, K. D.; Verbyla, D.; Welker, J. M.

    2010-12-01

    Recent changes in the climate of arctic Alaska, including warmer summers and a lengthened growing season, have increased vegetation productivity and permafrost temperatures. In this study, we (1) examine the spatial pattern of tall shrub distribution and expansion on a landscape scale, and (2) test the effect of shrub expansion on erosion by coring lake sediments with catchments where shrub expansion is occurring and evaluating erosion trends over the last half-century. Landsat TM data from 1986 and 2009 was used to evaluate the expansion of tall shrubs across three regional subscenes in the arctic foothills in northeast Alaska. NDVI values were threshholded at 0.6 so that only tall shrubs were visible. We found that tall shrubs occupy floodplains and streams and that these habitats are conduits for shrub propagation. To examine the effect of shrub expansion on erosion, four lakes were cored near the Chandler River on the central North Slope of Alaska, where shrub expansion has been documented using repeat photography. The cores were dated assuming constant deposition and decay of 210Pb, and sediment depositional rates were used to infer the last 60-100 years of erosion in the catchments. 210Pb profiles were calibrated using 137Cs and 222Ra. Lake sediment cores 1, 3, and 4 showed a steadily increasing or fluctuating erosion rate until 1980, after which these cores show a synchronous decline. The record of erosion in lake 2 was episodic and unlike that in lakes 1, 3, and 4. We speculate that an increase in shrubs and vegetation productivity, specifically in landscape positions where soil was previously exposed to erosion, has contributed to the decline in erosion observed in lake cores 1, 3, and 4. New shrubs exploit bare soil for germination along streams and gullies, and we think that this is partly responsible for reducing erosion. It is also likely that a decrease in the magnitude and frequency of runoff events is contributing to the decline in erosion in lake

  4. Effects of added Zn, Ni and Cd on desert shrubs grown in desert soil

    SciTech Connect

    Patel, P.M.; Wallace, A.; Romney, E.M.; Alexander, G.V.

    1980-01-01

    Desert shrubs - Ambrosia dumosa, Lycium andersonii, Larrea tridenata, and Ephedra nevadensis wre grown in a glasshouse in desert (calcarous) soil with different levels of added Zn, Ni, and Cd. The objective was to study effects of the metals on growth and yield and uptake and translocation of metals in desert plant species which are common in the Mojave Desert (areas of Nevada and southeast California). Zinc and Cd considerably decreased yields of all four species. Yields of E. nevadensis were increased by Ni at 250 and 500 mg/kg applied to desert soil. Ephedra nevadensis was more tolerant of Ni than were the other three desert shrubs. Some interactions were observed among various elements: manganese concentration was increased in shrubs by Zn. Particularly, application of Ni reduced the concentrations of Zn and Mn over the control.

  5. The origin of low-mass white dwarfs

    SciTech Connect

    Rebassa-Mansergas, A.; Schreiber, M. R.; Gaensicke, B. T.; Girven, J.; Gomez-Moran, A. Nebot

    2010-11-23

    We present white dwarf mass distributions of a large sample of post common-envelope binaries and wide white dwarf main sequence binaries and demonstrate that these distributions are statistically independent. While the former contains a much larger fraction of low-mass white dwarfs, the latter is similar to single white dwarf mass distributions. Taking into account observational biases we also show that the majority of low-mass white dwarfs are formed in close binaries.

  6. The Gobbling Dwarf that Exploded

    NASA Astrophysics Data System (ADS)

    2007-07-01

    A unique set of observations, obtained with ESO's VLT, has allowed astronomers to find direct evidence for the material that surrounded a star before it exploded as a Type Ia supernova. This strongly supports the scenario in which the explosion occurred in a system where a white dwarf is fed by a red giant. ESO PR Photo 31a/07 ESO PR Photo 31a/07 Evolution of SN 2006X Spectrum Because Type Ia supernovae are extremely luminous and quite similar to one another, these exploding events have been used extensively as cosmological reference beacons to trace the expansion of the Universe. However, despite significant recent progress, the nature of the stars that explode and the physics that governs these powerful explosions have remained very poorly understood. In the most widely accepted models of Type Ia supernovae the pre-explosion white dwarf star orbits another star. Due to the close interaction and the strong attraction produced by the very compact object, the companion star continuously loses mass, 'feeding' the white dwarf. When the mass of the white dwarf exceeds a critical value, it explodes. The team of astronomers studied in great detail SN 2006X, a Type Ia supernova that exploded 70 million light-years away from us, in the splendid spiral Galaxy Messier 100 (see ESO 08/06). Their observations led them to discover the signatures of matter lost by the normal star, some of which is transferred to the white dwarf. The observations were made with the Ultraviolet and Visual Echelle Spectrograph (UVES), mounted at ESO's 8.2-m Very Large Telescope, on four different occasions, over a time span of four months. A fifth observation at a different time was secured with the Keck telescope in Hawaii. The astronomers also made use of radio data obtained with NRAO's Very Large Array as well as images extracted from the NASA/ESA Hubble Space Telescope archive. ESO PR Photo 31b/07 ESO PR Photo 31b/07 SN 2006X, before and after the Type Ia Supernova explosion "No Type Ia

  7. Warming-Induced Shrub Expansion May Enhance Future Soil Carbon Storage on the Eastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Klein, J. A.; Ojima, D.; Harte, J.; Zhao, X.

    2005-12-01

    Our objective is to quantify how ecosystem carbon storage responds to climate variability and grazing on the eastern Tibetan Plateau and to compare results across a suite of study approaches: experimental manipulations, space for time observations, and biogeochemical modeling. Four years of experimental manipulations of climate and grazing resulted in a 25gm-2yr-1 increase in shrub foliar productivity with experimental warming; grazing dampened the warming-induced shrub expansion. There was no discernable change in soil carbon storage with warming. Examination of the soil carbon in ambient plots within meadow versus shrubland habitats demonstrates 3.5% more soil carbon at the shrublands (9.4%C) than at the meadows (5.9%C). These differences in soil carbon are likely due to the highly recalcitrant nature of the shrub leaf litter, which contains 33% lignin of the total dry leaf mass. The comparable figures are 11% for forbs and 18% for graminoids. The experimental plots are likely exhibiting a delayed response to experimental warming. We predict that over the longer-term, soil carbon storage will increase with warming-induced shrub expansion. We use the CENTURY ecosystem model to illuminate the biogeochemical consequences of shrub expansion in this region and to identify temporal aspects of this transformation. While future increased carbon storage is beneficial in terms of climate mitigation, the warming-induced shrub expansion will negatively affect the availability and quality of forage resources in this region. This highlights the potential conflict between management goals in ecosystems where local livelihoods are directly dependent upon ecosystem goods and services.

  8. Spatial variation in hydraulic redistribution by the desert shrub, Sarcobatus vermiculatus, at multiple scales

    NASA Astrophysics Data System (ADS)

    Richards, J. H.; Donovan, L. A.

    2012-12-01

    Passive water movement through roots from moist to dry soils, i.e. hydraulic redistribution, can be important for plant water status, vegetation water use, nutrient acquisition and cycling, and competition/facilitation among plant species. Although hydraulic redistribution is known from many species and habitats, little is known about how it varies at multiple spatial scales across species ranges. In the Mono Basin, California ecosystem we documented variation in hydraulic redistribution by the desert halophytic shrub, Sarcobatus vermiculatus, at three spatial scales: landscape, shrub-island versus interspace, and depth. Hydraulic redistribution varied among sites across the landscape. It was most prevalent at a low salinity site with deep groundwater (9.4 m), but of lower magnitude at more saline sites with shallower groundwater. At the low salinity site, infiltration from snowmelt, the predominant precipitation input, was confined to interspaces between shrub islands. Shrub-island soils remained very dry after snowmelt, even in a year with high total snow accumulation. Shrub-island soils, however, had substantial net increases in Ψsoil during week- to month-long periods in the early part of the growing season, concomitant with self-irrigated root growth into these dry soils, as documented with mini-rhizotrons. The source of this root-system-transported water was both moist interspace soils and moist deep soil layers. Wetting up of otherwise dry shrub-island soils is likely essential for nutrient mineralization and acquisition from trapped litter, making hydraulic redistribution an important driver of landscape-scale biogeochemical cycles in these saline basins. In addition, hydraulic redistribution buffered spatial variation in water availability among sites, depths, depth to groundwater, and for plants with different root distributions, such that plant Ψpredawn and Ψmidday differed little across the landscape. Multi-scale variation in hydraulic redistribution

  9. Modeling the shrub encroachment in the Northern Chihuahuan desert Grasslands using a Cellular Automata model

    NASA Astrophysics Data System (ADS)

    Caracciolo, Domenico; Istanbulluoglu, Erkan; Noto, Leonardo V.

    2014-05-01

    Arid grasslands of southwestern North America have changed dramatically over the last 150 years as a result of the shrub encroachment, i.e. the increase in density and biomass of indigenous shrubby plants in grasslands. Numerous studies have documented the expansion of shrublands in the southwestern America Grasslands; in particular the encroachment of shrubs in american deserts has strongly occurred in the Chihuahuan deserts from 1860. The Sevilleta National Wildlife Refuge (SNWR), located in the northern Chihuahuan desert shows a dramatic encroachment front of creosote bush (i.e., shrub) into native desert grassland. This encroachment has been here simulated using an Ecohydrological Cellular Automata Model, CATGraSS. CATGraSS is a spatially distributed model driven by spatially explicit irradiance and runs on a fine-resolution gridded domain. In the model, each cell can hold a single plant type or can represent bare soil. Plant competition is modeled by keeping track of mortality and establishment of plants, both calculated probabilistically based on soil moisture stress. For this study, the model is improved with a stochastic fire and a grazing function, and its plant establishment algorithm is modified. CATGraSS is implemented in a small area (7.3 km2) in SNWR, characterized by two vegetation types: grass savanna and creosote bush. The causes that have been considered for the encroachment in this case study are: the fire return period increase, the grazing increase, the seed dispersal caused by animals, the role of wind direction and the shrub-grass inhibition effect. The model is able to reproduce the encroachment occurred in the SNWR basin, simulating an increasing of the shrub from 2% in 1860 to 42% (i.e., current shrub percentage) in 2010 highlighting as more influent factors the reduced fire frequency and the increased grazing intensity. For the future management and encroachment control, the reduction of the fire return period and the grazing removal

  10. Rapid revegetation by sowing seed mixtures of shrub and herbaceous species

    NASA Astrophysics Data System (ADS)

    Feng, J.; Zhang, C.; Zhao, T.; Zhang, Q.

    2015-05-01

    Fast revegetation by means of sowing seed mixtures of shrub and herbaceous species is a measure to prevent bare soils from wind and water erosion. A field experiment was used to test the effect of species selection and the ratio of shrub to herbaceous species on vegetation formation and shrub growth. Results showed that herbaceous species hastened cover formation and maintained a high coverage for a longer period. However, the growth of shrubs was hindered. In the North China Plain or where the soil and climate are similar, the ratio of shrub to herbaceous seeds is proposed to be 6 : 4-7 : 3 (weight ratio). Among the herbaceous species tested, Festuca arundinacea Schreb. grows relatively slow, so it should be mixed with other fast-growing species in the practice of rapid revegetation, and a seeding density lower than 6 g m-2 is proposed when applied; Orychophragmus violaceus O. E. Schulz. wilts when the seeds are ripe, leading to a significant decrease of coverage, so other species with different phenology should be involved when it is applied; Viola philippica Car. is a good ground cover plant which grows fast and maintains a stable coverage from July to October, and a seeding density of 1.5 g m-2 is proposed for rapid revegetation. Herbaceous species have different traits. Three different types of herbs were found in our experiment: slow-growing stable species (F. arundinacea), fast-growing unstable species (O. violaceus) and fast-growing stable species (V. philippica). Shrubs, slow-growing stable species and fast-growing unstable species should not be used alone because they cannot cover the ground fast or they cannot maintain a long period of good coverage. A small seeding rate of fast-growing stable species should be used to ensure a fair coverage against erosion. Because natural environmental conditions are heterogeneous and stochastic, more species should be added to enhance the stability of plant community.

  11. Brown Dwarfs at the Exoplanet Mass Boundary

    NASA Astrophysics Data System (ADS)

    Faherty, J. K.; Cruz, K. L.; Rice, E. L.; Riedel, A.

    2014-10-01

    Young brown dwarfs and directly-imaged exoplanets have enticingly similar photometric and spectroscopic characteristics, indicating that their cool, low gravity atmospheres should be studied in concert. Similarities between the peculiar shaped H band, near and mid-IR photometry as well as location on color magnitude diagrams provide important clues about how to extract physical properties of planets from current brown dwarf observations. Our team has assigned >30 brown dwarfs to 10-150 Myr nearby moving groups. In so doing, we have discovered important diversity among this extremely low-mass (10 - 30 M_{Jup}) age-calibrated sample indicating that cloud properties play a critical role in their observables.

  12. Simulations of Double White Dwarf Mergers

    NASA Astrophysics Data System (ADS)

    Motl, Patick; Staff, Jan; Marcello, Dominic; Clayton, Geoffrey; Frank, Juhan

    2016-03-01

    We present numerical simulations of double white dwarf mergers initiated by mass transfer instability. In particular, we are interested in the possible connection between such double degenerate mergers and the peculiar irregular variable R Corona Borealis stars. For the merger of a Carbon-Oxygen white dwarf with a Helium white dwarf, the degree to which Carbon from the accreting star is dredged up plays a crucial role in the appearance of the rejuvenated, merged object. We explore the amount of dredge up in the accreting star and its influence in stellar evolution models initialized from the merged object resulting from dynamical evolutions.

  13. Dwarf spheroidal galaxies: Keystones of galaxy evolution

    NASA Technical Reports Server (NTRS)

    Gallagher, John S., III; Wyse, Rosemary F. G.

    1994-01-01

    Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

  14. WHITE DWARF/M DWARF BINARIES AS SINGLE DEGENERATE PROGENITORS OF TYPE Ia SUPERNOVAE

    SciTech Connect

    Wheeler, J. Craig

    2012-10-20

    Limits on the companions of white dwarfs in the single-degenerate scenario for the origin of Type Ia supernovae (SNe Ia) have gotten increasingly tight, yet igniting a nearly Chandrasekhar mass C/O white dwarf from a condition of near hydrostatic equilibrium provides compelling agreement with observed spectral evolution. The only type of non-degenerate stars that survive the tight limits, M{sub V} {approx}> 8.4 on the SN Ia in SNR 0509-67.5 and M{sub V} {approx}> 9.5 in the remnant of SN 1572, are M dwarfs. While M dwarfs are observed in cataclysmic variables, they have special properties that have not been considered in most work on the progenitors of SNe Ia: they have small but finite magnetic fields and they flare frequently. These properties are explored in the context of SN Ia progenitors. White dwarf/M dwarf pairs may be sufficiently plentiful to provide, in principle, an adequate rate of explosions even with slow orbital evolution due to magnetic braking or gravitational radiation. Even modest magnetic fields on the white dwarf and M dwarf will yield adequate torques to lock the two stars together, resulting in a slowly rotating white dwarf, with the magnetic poles pointing at one another in the orbital plane. The mass loss will be channeled by a 'magnetic bottle' connecting the two stars, landing on a concentrated polar area on the white dwarf. This enhances the effective rate of accretion compared to spherical accretion. Luminosity from accretion and hydrogen burning on the surface of the white dwarf may induce self-excited mass transfer. The combined effects of self-excited mass loss, polar accretion, and magnetic inhibition of mixing of accretion layers give possible means to beat the 'nova limit' and grow the white dwarf to the Chandrasekhar mass even at rather moderate mass accretion rates.

  15. White Dwarf/M Dwarf Binaries as Single Degenerate Progenitors of Type Ia Supernovae

    NASA Astrophysics Data System (ADS)

    Wheeler, J. Craig

    2012-10-01

    Limits on the companions of white dwarfs in the single-degenerate scenario for the origin of Type Ia supernovae (SNe Ia) have gotten increasingly tight, yet igniting a nearly Chandrasekhar mass C/O white dwarf from a condition of near hydrostatic equilibrium provides compelling agreement with observed spectral evolution. The only type of non-degenerate stars that survive the tight limits, MV >~ 8.4 on the SN Ia in SNR 0509-67.5 and MV >~ 9.5 in the remnant of SN 1572, are M dwarfs. While M dwarfs are observed in cataclysmic variables, they have special properties that have not been considered in most work on the progenitors of SNe Ia: they have small but finite magnetic fields and they flare frequently. These properties are explored in the context of SN Ia progenitors. White dwarf/M dwarf pairs may be sufficiently plentiful to provide, in principle, an adequate rate of explosions even with slow orbital evolution due to magnetic braking or gravitational radiation. Even modest magnetic fields on the white dwarf and M dwarf will yield adequate torques to lock the two stars together, resulting in a slowly rotating white dwarf, with the magnetic poles pointing at one another in the orbital plane. The mass loss will be channeled by a "magnetic bottle" connecting the two stars, landing on a concentrated polar area on the white dwarf. This enhances the effective rate of accretion compared to spherical accretion. Luminosity from accretion and hydrogen burning on the surface of the white dwarf may induce self-excited mass transfer. The combined effects of self-excited mass loss, polar accretion, and magnetic inhibition of mixing of accretion layers give possible means to beat the "nova limit" and grow the white dwarf to the Chandrasekhar mass even at rather moderate mass accretion rates.

  16. Tourism and Water: Themes of the Alpine Convention

    NASA Astrophysics Data System (ADS)

    Imhof, R.

    2012-04-01

    1) The contribution reflects the personal opinion of the author and does not necessarily reflect the point of view of the Permanent Secretariat. The Alpine Convention is a multilateral framework treaty signed in 1991 by the eight states of the Alpine bow as well as the European Community. Its main objectives are the sustainable development of the Alpine territory and the safeguarding of the interests of the people living within it, embracing the environmental, social and economic dimensions in the broadest sense. In order to achieve its objectives, over the years the Framework Convention has been equipped with a large number of thematic protocols, e.g. on tourism. The overall objective of the Protocol on Tourism, which first came into force in 2002, is to contribute to sustainable development in the Alpine region within the existing institutional framework, by encouraging environmentally-friendly tourism through specific measures and recommendations which take the interests of both the local population and tourists into account. The provisions of the Protocol on Tourism primarily concern tourism management and controlling tourist flows, structural developments such as ski lifts and ski slopes, accommodation and the balanced development of economically weak areas. Guidelines, development plans, sectoral plans have to be adopted at the appropriate territorial level in order to enable to assess the impact of tourism development on, inter alia, water. This extends also to ski slopes developments. For example the production of artificial snow production may be authorized only if the location's hydrological, climatic and ecological conditions allow. Water is listed among the twelve themes in relation to which the Contracting Parties are supposed to take measures and coordinate their policies (Article 2 of the Framework Convention). The Alpine Convention aims to preserve and re-establish healthy water systems, especially keeping waters clean and protecting the natural

  17. Role of nurse shrubs for restoration planting of two conifers in southeast of Mu Us Sandland, China.

    PubMed

    Tian, Li; Wang, Xiaoan

    2015-01-01

    Two-year-old pine seedlings, Pinus tabulaeformis and Pinus sylvestris were planted under the canopies of three shrub species and in open areas to test for facilitation during seedling establishment in southeast of Mu Us Sandland in northern part of Shaanxi, China. Pine seedlings establishment were assessed three times within three consecutive growing seasons. Height, area and volume of shrubs were measured. Microclimate conditions (light intensity, air temperature and soil temperature and moisture) were recorded in four microhabitats. Near surface light intensity, air temperature and soil temperature were lower under shrubs, which led to higher soil moisture and pine seedlings under the canopy of shrub species. Pine seedlings survival was remarkably higher when planted under the canopy of shrub species (65.7% for P. tabulaeformis and 60.6% for P. sylvestris) as compared with open areas (22.4% for P. tabulaeformis and 38% for P. sylvestris). P. tabulaeformis with shade-tolerance trait expressed high survival of seedlings as compared to that of P. sylvestris seedlings under the canopy of shrub species (Tukey test, P < 0.05). Leguminous shrub (Caragana korshinskii and Amorpha fruticosa) showed continuously facilitation during moderate drought stress (summer 2012, 2013 and 2014), but dense and small shrub (Caragana korshinskii) reduced the establishment of seedlings possibly for light competition. Salix cheilophila showed a facilitation effect in growing seasons, but the effect of allelopathy led to high mortality of seedlings under their canopy. in addition, two pine growths were not inhibited when planted under three shrubs. In conclusions, nurse-shrub facilitation can be used as an effective restoration strategy in this sandland. However, use of shrubs as nurse plants depends on their canopy structure and ecological impacts; the selection of target species depends on their shade tolerance traits. PMID:26536812

  18. Magnetic fields in Local Group dwarf irregulars

    NASA Astrophysics Data System (ADS)

    Chyży, K. T.; Weżgowiec, M.; Beck, R.; Bomans, D. J.

    2011-05-01

    Aims: We wish to clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and to assess the role of dwarf galaxies in the magnetization of the Universe. Methods: We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100-m Effelsberg telescope at 2.64 GHz. Three galaxies were detected. A higher frequency (4.85 GHz) was used to search for polarized emission in five dwarfs that are the most luminous ones in the infrared domain, of which three were detected. Results: Magnetic fields in LG dwarfs are weak, with a mean value of the total field strength of <4.2 ± 1.8 μG, three times lower than in the normal spirals. The strongest field among all LG dwarfs of 10 μG (at 2.64 GHz) is observed in the starburst dwarf IC 10. The production of total magnetic fields in dwarf systems appears to be regulated mainly by the star-formation surface density (with the power-law exponent of 0.30 ± 0.04) or by the gas surface density (with the exponent 0.47 ± 0.09). In addition, we find systematically stronger fields in objects of higher global star-formation rate. The dwarf galaxies follow a similar far-infrared relationship (with a slope of 0.91 ± 0.08) to that determined for high surface brightness spiral galaxies. The magnetic field strength in dwarf galaxies does not correlate with their maximum rotational velocity, indicating that a small-scale rather than a large-scale dynamo process is responsible for producting magnetic fields in dwarfs. If magnetization of the Universe by galactic outflows is coeval with its metal enrichment, we show that more massive objects (such as Lyman break galaxies) can efficiently magnetize the intergalactic medium with a magnetic field strength of about 0.8 nG out to a distance of 160-530 kpc at redshifts 5-3, respectively. Magnetic fields that are several times weaker and shorter magnetization

  19. Soil development as limiting factor for shrub expansion in southwestern Greenland

    NASA Astrophysics Data System (ADS)

    Caviezel, Chatrina; Hunziker, Matthias; Zoller, Oliver; Wüthrich, Christoph; Kuhn, Nikolaus J.

    2014-05-01

    Southern Greenland currently experiences an increase in summer temperatures and a prolonged growing season (Masson-Delmotte et al. 2012), resulting in an increased shrub cover at the boreal - tundra border ecotone (Normand et al. 2013). These findings suggest the beginning of a greener Greenland in which tundra vegetation is transformed to a boreal woody flora. However, vegetation at borderline ecotones is influenced by further ecologic factors than just temperature. In this study, the ecologic conditions at a selection of sites along an elevation gradient near Igaliku in southern Greenland were examined to identify potential factors limiting the expansion of woody vegetation apart from temperature. The sites differ in elevation, topography, shrub density and soil parent material. The three study sites comprise i) well established birch shrubs growing between 50 and 180 m a.s.l., where the parent material origins from the Julianehab granite (Brooks 2012); ii) extended shrub patches at about 250 m a.s.l., where the parent material consists of Gardar Sandstones and Lavas (Brooks 2012) and iii) restricted shrub patches at an elevation of 250 m a.s.l., where the soil parent material originates from the Gardar intrusions (Brooks 2012). The extent of the shrub areas, topography and soil moisture were mapped, additionally soil samples were analyzed for C-and N-content, texture including coarse fraction and pH and used as soil development indicators. Our results show that the topographic setting regulates the existence or absence of soil while the soil parent material is an important limiting factor for soil moisture. According to these findings, we suggest that a high proportion of areas where temperature increase would allow the increase of shrub cover is not suitable for a woody flora. Brooks, Kent. 2012. "A Tale of Two Intrusions—where Familiar Rock Names No Longer Suffice." Geology Today 28 (1): 13-19. doi:10.1111/j.1365-2451.2012.00815.x. Masson-Delmotte, V., D

  20. Soil moisture redistribution as a mechanism of facilitation in savanna tree-shrub clusters.

    PubMed

    Zou, C B; Barnes, P W; Archer, S; McMurtry, C R

    2005-08-01

    Plant-soil water relations were examined in the context of a selective removal study conducted in tree-shrub communities occupying different but contiguous soil types (small discrete clusters on shallow, duplex soils versus larger, extensive groves on deep, sandy soils) in a subtropical savanna parkland. We (1) tested for the occurrence of soil moisture redistribution by hydraulic lift (HL), (2) determined the influence of edaphic factors on HL, and (3) evaluated the significance of HL for overstory tree-understory shrub interactions. Diel cycling and nocturnal increases in soil water potential (Psisoil), characteristic signatures of HL, occurred intermittently throughout an annual growth cycle in both communities over a range of moisture levels (Psisoil=-0.5 to -6.0 MPa) but only when soils were distinctly stratified with depth (dry surface/wet deep soil layers). The magnitude of mean (+/-SE) diel fluctuations in Psisoil (0.19+/-0.01 MPa) did not differ on the two community types, though HL occurred more frequently in groves (deep soils) than clusters (shallow soils). Selective removal of either Prosopis glandulosa overstory or mixed-species shrub understory reduced the frequency of HL, indicating that Prosopis and at least one other woody species was conducting HL. For Zanthoxylum fagara, a shallow-rooted understory shrub, Prosopis removal from clusters decreased leaf water potential (Psileaf) and net CO2 exchange (A) during periods of HL. In contrast, overstory removal had neutral to positive effects on more deeply-rooted shrub species (Berberis trifoliolata and Condalia hookeri). Removal of the shrub understory in groves increased A in the overstory Prosopis. Results indicate the following: (a) HL is common but temporally dynamic in these savanna tree-shrub communities; (b) edaphic factors influencing the degree of overstory/understory development, rooting patterns and soil moisture distribution influence HL; (c) net interactions between overstory and

  1. Northwest Arid Lands : an introduction to the Columbia Basin shrub-steppe

    SciTech Connect

    O'Connor, Georganne P. ); Wieda, Karen J. )

    2001-04-15

    This book explores the rich variety of life in shrub-steppe lands of the Columbia River Basin. It describes, for a non-technical audience, the flora, fauna, and geology of the lower Columbia Basin in and around the Tri-Cities, Washington. Features include color photos and maps of shrub-steppe plants and animals; lists and illustration of common plants, mammals, reptiles, amphibians, birds, fish, and species of conservation concern; tips on places to see wildflowers and wildlife; geological travel logs from the Tri-Cities to Seattle and Spokane; and a comprehensive bibliography and definition of ecological terms.

  2. Lichens and mosses on shrub-steppe soils in Southeastern Washington

    SciTech Connect

    Link, Steven O.; Ryan, Bruce D.; Downs, Janelle L. ); Cadwell, Larry L. ); Soll, Jonathan A.; Hawke, Mary Ann; Ponzetti, Jeanne

    2001-12-01

    The purpose of this study was to identify the lichens and mosses found on soils of the shrub-steppe at the Hanford Site in southeastern Washington. Thirteen sites primarily at low elevation were intensively sampled. Twenty nine lichens and six moss species were identified. Three lichens were considered undescribed species. Based on comparison with other studies and herbarium records, we conclude the soil lichen flora of the Hanford Site is substantially different than that of the Great Basin or of the shrub-steppe in Idaho.

  3. Environmental Limits of Tall Shrubs in Alaska’s Arctic National Parks

    PubMed Central

    Swanson, David K.

    2015-01-01

    We sampled shrub canopy volume (height times area) and environmental factors (soil wetness, soil depth of thaw, soil pH, mean July air temperature, and typical date of spring snow loss) on 471 plots across five National Park Service units in northern Alaska. Our goal was to determine the environments where tall shrubs thrive and use this information to predict the location of future shrub expansion. The study area covers over 80,000 km2 and has mostly tundra vegetation. Large canopy volumes were uncommon, with volumes over 0.5 m3/m2 present on just 8% of plots. Shrub canopy volumes were highest where mean July temperatures were above 10.5°C and on weakly acid to neutral soils (pH of 6 to 7) with deep summer thaw (>80 cm) and good drainage. On many sites, flooding helped maintain favorable soil conditions for shrub growth. Canopy volumes were highest where the typical snow loss date was near 20 May; these represent sites that are neither strongly wind-scoured in the winter nor late to melt from deep snowdrifts. Individual species varied widely in the canopy volumes they attained and their response to the environmental factors. Betula sp. shrubs were the most common and quite tolerant of soil acidity, cold July temperatures, and shallow thaw depths, but they did not form high-volume canopies under these conditions. Alnus viridis formed the largest canopies and was tolerant of soil acidity down to about pH 5, but required more summer warmth (over 12°C) than the other species. The Salix species varied widely from S. pulchra, tolerant of wet and moderately acid soils, to S. alaxensis, requiring well-drained soils with near neutral pH. Nearly half of the land area in ARCN has mean July temperatures of 10.5 to 12.5°C, where 2°C of warming would bring temperatures into the range needed for all of the potential tall shrub species to form large canopies. However, limitations in the other environmental factors would probably prevent the formation of large shrub canopies

  4. A simple technique for measuring rainfall interception by small shrub: interception flow collection box

    NASA Astrophysics Data System (ADS)

    Belmonte Serrato, F.; Romero Diaz, A.

    1998-03-01

    In this paper a simple technique for field measurement of rain water loss arising from interception and water flows associated with species of small Mediterranean shrub is described: the interception flow collection box. This technique solves the problem of installing devices to control stemflow in species with a multiple trunk and demonstrates its efficiency through the results obtained from the data observed for three species of semi-arid Mediterranean shrub: Juniperus oxycedrus, Rosmarinus officinalis and Thymus vulgaris. Finally, the empirical equations for the prediction of throughfall, stemflow and rain water loss through interception are presented for the three selected species and the validity of the technique employed is established.

  5. The Extraordinary Cataclysmic Binary RU Pegasi: The Hottest White Dwarf in a Dwarf Nova?

    NASA Astrophysics Data System (ADS)

    Sion, Edward M.; Urban, Joel

    2002-06-01

    We present the results of the first multicomponent synthetic spectral analysis of International Ultraviolet Explorer (IUE) archival spectra of the long-period dwarf nova RU Peg during quiescence. The best-fit, high-gravity, solar composition photosphere models yield Teff=50,000-53,000 K with scale factor distances of 250 pc. Optically thick accretion disk models imply accretion rates between 1×10-9 and 1×10-10Msolar yr-1 in order to match the steeply sloping far-UV continuum. However, the best-fit accretion disk models yield distances from 600 to 1300 pc, well beyond the estimated distance range of 130-300 pc. Using rough theoretical flux arguments and the distance estimates, we find better agreement between the observed far-UV luminosity and the predicted far-UV luminosity of a hot, massive, white dwarf model than with an accretion disk model. RU Peg appears to contain the hottest white dwarf yet found in a dwarf nova. We cannot rule out that the far-UV energy distribution is due to a multitemperature white dwarf with cooler, more slowly rotating higher latitudes and a rapidly spinning, hotter equatorial belt. We discuss implications of our analysis for theoretical predictions of the disk instability theory of dwarf nova outbursts. We discuss a comparison between RU Peg's white dwarf and the observed properties of other analyzed white dwarfs in dwarf novae.

  6. Magnetars and white dwarf pulsars

    NASA Astrophysics Data System (ADS)

    Lobato, Ronaldo V.; Malheiro, Manuel; Coelho, Jaziel G.

    2016-07-01

    The anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are a class of pulsars understood as neutron stars (NSs) with super strong surface magnetic fields, namely B ≳ 1014G, and for that reason are known as magnetars. However, in the last years, some SGRs/AXPs with low surface magnetic fields B ˜ (1012-1013)G have been detected, challenging the magnetar description. Moreover, some fast and very magnetic white dwarfs (WDs) have also been observed, and at least one showed X-ray energy emission as an ordinary pulsar. Following this fact, an alternative model based on WDs pulsars has been proposed to explain this special class of pulsars. In this model, AXPs and SGRs as dense and magnetized WDs can have surface magnetic field B ˜ 107-1010 G and rotate very fast with frequencies Ω ˜ 1rad/s, consistent with the observed rotation periods P ˜ (2-12)s.

  7. Pluto: Planet or "Dwarf Planet"?

    NASA Astrophysics Data System (ADS)

    Voelzke, M. R.; de Araújo, M. S. T.

    2010-09-01

    In August 2006 during the XXVI General Assembly of the International Astronomical Union (IAU), taken place in Prague, Czech Republic, new parameters to define a planet were established. According to this new definition Pluto will be no more the ninth planet of the Solar System but it will be changed to be a "dwarf planet". This reclassification of Pluto by the academic community clearly illustrates how dynamic science is and how knowledge of different areas can be changed and evolves through the time, allowing to perceive Science as a human construction in a constant transformation, subject to political, social and historical contexts. These epistemological characteristics of Science and, in this case, of Astronomy, constitute important elements to be discussed in the lessons, so that this work contributes to enable Science and Physics teachers who perform a basic education to be always up to date on this important astronomical fact and, thereby, carry useful information to their teaching.

  8. Inverse distributed hydrological modelling of alpine catchments

    NASA Astrophysics Data System (ADS)

    Kunstmann, H.; Krause, J.; Mayr, S.

    2005-12-01

    Even in physically based distributed hydrological models, various remaining parameters must be estimated for each sub-catchment. This can involve tremendous effort, especially when the number of sub-catchments is large and the applied hydrological model is computationally expensive. Automatic parameter estimation tools can significantly facilitate the calibration process. Hence, we combined the nonlinear parameter estimation tool PEST with the distributed hydrological model WaSiM. PEST is based on the Gauss-Marquardt-Levenberg method, a gradient-based nonlinear parameter estimation algorithm. WaSiM is a fully distributed hydrological model using physically based algorithms for most of the process descriptions. WaSiM was applied to the alpine/prealpine Ammer River catchment (southern Germany, 710 km2) in a 100×100 m2 horizontal resolution. The catchment is heterogeneous in terms of geology, pedology and land use and shows a complex orography (the difference of elevation is around 1600 m). Using the developed PEST-WaSiM interface, the hydrological model was calibrated by comparing simulated and observed runoff at eight gauges for the hydrologic year 1997 and validated for the hydrologic year 1993. For each sub-catchment four parameters had to be calibrated: the recession constants of direct runoff and interflow, the drainage density, and the hydraulic conductivity of the uppermost aquifer. Additionally, five snowmelt specific parameters were adjusted for the entire catchment. Altogether, 37 parameters had to be calibrated. Additional a priori information (e.g. from flood hydrograph analysis) narrowed the parameter space of the solutions and improved the non-uniqueness of the fitted values. A reasonable quality of fit was achieved. Discrepancies between modelled and observed runoff were also due to the small number of meteorological stations and corresponding interpolation artefacts in the orographically complex terrain. A detailed covariance analysis was performed

  9. Inverse distributed hydrological modelling of Alpine catchments

    NASA Astrophysics Data System (ADS)

    Kunstmann, H.; Krause, J.; Mayr, S.

    2006-06-01

    Even in physically based distributed hydrological models, various remaining parameters must be estimated for each sub-catchment. This can involve tremendous effort, especially when the number of sub-catchments is large and the applied hydrological model is computationally expensive. Automatic parameter estimation tools can significantly facilitate the calibration process. Hence, we combined the nonlinear parameter estimation tool PEST with the distributed hydrological model WaSiM. PEST is based on the Gauss-Marquardt-Levenberg method, a gradient-based nonlinear parameter estimation algorithm. WaSiM is a fully distributed hydrological model using physically based algorithms for most of the process descriptions. WaSiM was applied to the alpine/prealpine Ammer River catchment (southern Germany, 710 km2 in a 100×100 m2 horizontal resolution. The catchment is heterogeneous in terms of geology, pedology and land use and shows a complex orography (the difference of elevation is around 1600 m). Using the developed PEST-WaSiM interface, the hydrological model was calibrated by comparing simulated and observed runoff at eight gauges for the hydrologic year 1997 and validated for the hydrologic year 1993. For each sub-catchment four parameters had to be calibrated: the recession constants of direct runoff and interflow, the drainage density, and the hydraulic conductivity of the uppermost aquifer. Additionally, five snowmelt specific parameters were adjusted for the entire catchment. Altogether, 37 parameters had to be calibrated. Additional a priori information (e.g. from flood hydrograph analysis) narrowed the parameter space of the solutions and improved the non-uniqueness of the fitted values. A reasonable quality of fit was achieved. Discrepancies between modelled and observed runoff were also due to the small number of meteorological stations and corresponding interpolation artefacts in the orographically complex terrain. Application of a 2-dimensional numerical

  10. Permafrost aggradation in recently deglaciated alpine environments

    NASA Astrophysics Data System (ADS)

    Leopold, Matthias; Dusik, Jana; Stocker-Waldhuber, Martin; Völkel, Jörg; Becht, Michael

    2015-04-01

    Permafrost degradation is of major interest in the present discussion about alpine climate change and natural hazard prevention. Glacial retreat since the Little Ice Age (LIA) is followed by destabilisation of the surrounding mountains due to melting permafrost in bedrock and sediments. Glacial retreat also exposes huge areas of lateral and ground moraines. Areas of formerly temperate glaciers experience colder temperatures only since their ice cover has melted and basal meltwater no longer heats the ground. With a huge pore volume in the sediment body, water supply during the melt season and large daily temperature variations in high mountains, distinct freeze and thaw processes start and generate periglacial forms like patterned ground in the direct glacier forefield. Those geomorphic features are precursors for possible permafrost aggradation in proglacial areas. The work presented is part of the joint project PROSA (High-resolution measurements of morphodynamics in rapidly changing PROglacial Systems of the Alps) that aims in the quantification of a sediment budget for the upper Kaunertal valley, Austrian Central Alps. In this sense and to find out about erosion causing prerequisites and processes, permafrost and ground ice occurrence, as well as sediment thickness is measured by i.a. application of geophysical measurements, multitemporal airborne and terrestrial LiDAR, as well as aerial photographs. In this case study we examine the spatial and temporal settings for permafrost aggradation in a recently deglaciated cirque, belonging to the catchment area of the Gepatschferner glacier using electric resistivity tomography (ERT) and basal temperature of the winterly snowcover (BTS) measurements to detect the state of the permafrost, multitemporal aerial photographs dating back to 1953 to reproduce recent deglaciation of the cirque and multitemporal airborne LiDAR data to gain information about surface elevation changes. The northeast facing cirque is situated in

  11. Uncovering blue diffuse dwarf galaxies

    NASA Astrophysics Data System (ADS)

    James, Bethan L.; Koposov, Sergey; Stark, Daniel P.; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.

    2015-04-01

    Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy luminosity function. This paper presents a subsample of galaxies that were selected via a morphology-based search on Sloan Digital Sky Survey images with the aim of finding these elusive XMP galaxies. By using the recently discovered XMP galaxy, Leo P, as a guide, we obtained a collection of faint, blue systems, each with isolated H II regions embedded in a diffuse continuum, that have remained optically undetected until now. Here we show the first results from optical spectroscopic follow-up observations of 12 of ˜100 of these blue diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45 < 12 + log (O/H) < 8.0, with two galaxies being classified as XMPs. All BDDs were found to currently have a young star-forming population (<10 Myr) and relatively high ionization parameters of their H II regions. Despite their low luminosities (-11 ≲ MB ≲ -18) and low surface brightnesses (˜23-25 mag arcsec-2), the galaxies were found to be actively star forming, with current star formation rates between 0.0003 and 0.078 M⊙ yr-1. From our current subsample, BDD galaxies appear to be a population of non-quiescent dwarf irregular galaxies, or the diffuse counterparts to blue compact galaxies and as such may bridge the gap between these two populations. Our search algorithm demonstrates that morphology-based searches are successful in uncovering more diffuse metal-poor star-forming galaxies, which traditional emission-line-based searches overlook.

  12. Merging white dwarfs and thermonuclear supernovae.

    PubMed

    van Kerkwijk, M H

    2013-06-13

    Thermonuclear supernovae result when interaction with a companion reignites nuclear fusion in a carbon-oxygen white dwarf, causing a thermonuclear runaway, a catastrophic gain in pressure and the disintegration of the whole white dwarf. It is usually thought that fusion is reignited in near-pycnonuclear conditions when the white dwarf approaches the Chandrasekhar mass. I briefly describe two long-standing problems faced by this scenario, and the suggestion that these supernovae instead result from mergers of carbon-oxygen white dwarfs, including those that produce sub-Chandrasekhar-mass remnants. I then turn to possible observational tests, in particular, those that test the absence or presence of electron captures during the burning. PMID:23630372

  13. White Dwarfs, Neutron Stars and Black Holes

    ERIC Educational Resources Information Center

    Szekeres, P.

    1977-01-01

    The three possible fates of burned-out stars: white dwarfs, neutron stars and black holes, are described in elementary terms. Characteristics of these celestial bodies, as provided by Einstein's work, are described. (CP)

  14. The Missing Baryons Around Nearby Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Bregman, Joel

    2013-10-01

    Dwarf galaxies are missing nearly all of their baryons, which have presumably flowed away as a wind. This mass loss accounts for a significant fraction of all baryons lost from galaxies, so there is great interest in determining the size and scope of the gas lost. This gas is not visible in emission but is detectable through absorption features toward background AGNs. Here we propose to observe the absorbing material around three isolated dwarfs on the periphery of the Local Group: Sextans A, Sextans B, and NGC 3109. Unlike more distant dwarfs, the star formation history and cold gaseous content of these galaxies are well-studied. The isolation of these dwarfs, far from large galaxies, means that they have not yet interacted with other systems so their mass loss history is well-preserved, making them ideal targets for study.

  15. Towards understanding dynamo action in M dwarfs

    NASA Astrophysics Data System (ADS)

    Shulyak, D.; Sokoloff, D.; Kitchatinov, L.; Moss, D.

    2015-06-01

    Recent progress in observational studies of magnetic activity in M dwarfs urgently requires support from ideas of stellar dynamo theory. We propose a strategy to connect observational and theoretical studies. In particular, we suggest four magnetic configurations that appear relevant to dwarfs from the viewpoint of the most conservative version of dynamo theory, and discuss observational tests to identify the configurations observationally. As expected, any such identification contains substantial uncertainties. However, the situation in general looks less pessimistic than might be expected. Several identifications between the phenomenology of individual stars and dynamo models are suggested. Remarkably, all models discussed predict substantial surface magnetic activity at rather high stellar latitudes. This prediction looks unexpected from the viewpoint of our experience observing the Sun (which of course differs in some fundamental ways from these late-type dwarfs). We stress that a fuller understanding of the topic requires a long-term (at least 15 years) monitoring of M dwarfs by Zeeman-Doppler imaging.

  16. Neutral Hydrogen in Local Group Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Grcevich, Jana

    The gas content of the faintest and lowest mass dwarf galaxies provide means to study the evolution of these unique objects. The evolutionary histories of low mass dwarf galaxies are interesting in their own right, but may also provide insight into fundamental cosmological problems. These include the nature of dark matter, the disagreement between the number of observed Local Group dwarf galaxies and that predicted by lambda cold dark matter models, and the discrepancy between the observed census of baryonic matter in the Milky Way's environment and theoretical predictions. This thesis explores these questions by studying the neutral hydrogen (HI) component of dwarf galaxies. First, limits on the HI mass of the ultra-faint dwarfs are presented, and the HI content of all Local Group dwarf galaxies is examined from an environmental standpoint. We find that those Local Group dwarfs within 270 kpc of a massive host galaxy are deficient in HI as compared to those at larger galactocentric distances. Ram-pressure arguments are invoked, which suggest halo densities greater than 2-3 x 10-4 cm-3 out to distances of at least 70 kpc, values which are consistent with theoretical models and suggest the halo may harbor a large fraction of the host galaxy's baryons. We also find that accounting for the incompleteness of the dwarf galaxy count, known dwarf galaxies whose gas has been removed could have provided at most 2.1 x 108 M⊙ of HI gas to the Milky Way. Second, we examine the possibility of discovering unknown gas-rich ultra-faint galaxies in the Local Group using HI. The GALFA-HI Survey catalog is searched for compact, isolated HI clouds which are most similar to the expected HI characteristics of low mass dwarf galaxies. Fifty-one Local Group dwarf galaxy candidates are identified through column density, brightness temperature, and kinematic selection criteria, and their properties are explored. Third, we present hydrodynamic simulations of dwarf galaxies experiencing a

  17. Alpine Skiing: Special Olympics Sports Skills Instructional Program.

    ERIC Educational Resources Information Center

    Joseph P. Kennedy, Jr. Foundation, Washington, DC.

    The first of five guides in the Sports Skills Instructional Program focuses on teaching alpine skiing to mentally retarded students. Each unit contains the following elements: overview, long-term goal, short-term objectives, modifications and adaptations, sports skill assessment, teaching skill, skill sequence, task analysis, teaching suggestions,…

  18. Efficiency of Energy Utilization by Lactating Alpine Goats

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Thirty-six lactating Alpine does (50.5 ± 1.2 kg BW) were used to determine the effect of stage of lactation on energy utilization. Twelve does were assigned for measurement periods in early, mid-, and late lactation (28-35, 91-98, and 189 to 196 d of lactation). For six does of each group, after m...

  19. Shrub encroachment in North American grasslands: Shifts in growth form dominance rapidly alters control of ecosystem carbon inputs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Shrub encroachment into grass-dominated biomes is occurring globally due to a variety of anthropogenic activities, but the consequences for carbon (C) inputs, storage and cycling remain unclear. We studied eight North American graminoid-dominated ecosystems invaded by shrubs, from arctic tundra to ...

  20. RECONSIDERATION OF USING WATER PONDING DIKES TO REESTABLISH NATIVE GRASSES IN SHRUB-INVADED AREAS OF THE SOUTHWEST

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Many rangeland treatments have been tested to cause a reversal in the process of shrub invasion into desert grasslands. It seems that, because of the harsh nature of the arid environment, just removing shrubs and even subsequent seeding with native or introduced grasses is not enough to reverse the...

  1. Does shrub invasion indirectly limit grass establishment via seedling herbivory? A test at grassland-shrubland ecotones

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Does shrub invasion at ecotones indirectly limit grass establishment by increasing mammalian seedling herbivory, Chihuahuan Desert, New Mexico? We tested the hypothesis that herbivore-related mortality of seedlings of the dominant perennial grass Bouteloua eriopoda would be highest in shrub-dominate...

  2. Accretion Flows in Magnetic White Dwarf Systems

    NASA Technical Reports Server (NTRS)

    Imamura, James N.

    2005-01-01

    We received Type A and B funding under the NASA Astrophysics Data Program for the analysis and interpretation of hard x-ray data obtained by the Rossi X-ray Timing Explorer and other NASA sponsored missions for Intermediate Polars (IPS) and Polars. For some targets, optical data was available. We reduced and analyzed the X-ray spectra and the X-ray and optical (obtained at the Cerro Tololo Inter-American Observatory) timing data using detailed shock models (which we constructed) to place constraints on the properties of the accreting white dwarfs, the high energy emission mechanisms of white dwarfs, and the large-scale accretion flows of Polars and IPS. IPS and Polars are white dwarf mass-transfer binaries, members of the larger class of cata,clysmic variables. They differ from the bulk of the cataclysmic variables in that they contain strongly magnetic white dwarfs; the white dwarfs in Polars have B, = 7 to 230 MG and those in IPS have B, less than 10 MG. The IPS and Polars are both examples of funneled accretion flows in strong magnetic field systems. The IPS are similar to x-ray pulsars in that accretion disks form in the systems which are disrupted by the strong stellar magnetic fields of the white dwarfs near the stellar surface from where the plasma is funneled to the surface of the white dwarf. The localized hot spots formed at the footpoints of the funnels coupled with the rotation of the white dwarf leads to coherent pulsed x-ray emission. The Polars offer an example of a different accretion topology; the magnetic field of the white dwarf controls the accretion flow from near the inner Lagrangian point of the system directly to the stellar surface. Accretion disks do not form. The strong magnetic coupling generally leads to synchronous orbital/rotational motion in the Polars. The physical system in this sense resembles the Io/Jupiter system. In both IPS and Polars, pulsed emission from the infrared to x-rays is produced as the funneled flows merge onto the

  3. L' AND M' Photometry Of Ultracool Dwarfs

    NASA Technical Reports Server (NTRS)

    Marley, M. S.; Tsvetanov, Z. I.; Vrba, F. J.; Henden, A. A.; Luginbuhl, C. B.

    2004-01-01

    We have compiled L' (3.4-4.1 microns) and M' (4.6- 4.8 microns) photometry of 63 single and binary M, L, and T dwarfs obtained at the United Kingdom Infrared Telescope using the Mauna Kea Observatory filter set. This compilation includes new L' measurements of eight L dwarfs and 13 T dwarfs and new M' measurements of seven L dwarfs, five T dwarfs, and the M1 dwarf Gl 229A. These new data increase by factors of 0. 6 and 1.6, respectively, the numbers of ultracool dwarfs T (sub eff) dwarfs whose flux-calibrated JHK spectra, L' photometry, and trigonometric parallaxes are available, and we estimate these quantities for nine other dwarfs whose parallaxes and flux-calibrated spectra have been obtained. BC(SUB K) is a well-behaved function of near-infrared spectral type with a dispersion of approx. 0.1 mag for types M6-T5 it is significantly more scattered for types T5-T9. T (sub eff) declines steeply and monotonically for types M6-L7 and T4-T9, but it is nearly constant at approx. 1450 K for types L7-T4 with assumed ages of approx. 3 Gyr. This constant T(sub eff) is evidenced by nearly unchanging values of L'-M' between types L6 and T3. It also supports recent models that attribute the changing near-infrared luminosities and spectral features across the L-T transition to the rapid migration, disruption, and/or thinning of condensate clouds over a narrow range of T(sub eff). The L' and M' luminosities of early-T dwarfs do not exhibit the pronounced humps or inflections previously noted in l through K bands, but insufficient data exist for types L6-T5 to assert that M(Sub L') and M(sub M') are strictly monotonic within this range of typew. We compare the observed K, L', and M' luminosities of L and T dwarfs in our sample with those predicted by precipitation-cloud-free models for varying surface gravities and sedimentation efficiencies.

  4. The Metamorphosis of Tidally Stirred Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Mayer, Lucio; Governato, Fabio; Colpi, Monica; Moore, Ben; Quinn, Thomas; Wadsley, James; Stadel, Joachim; Lake, George

    2001-10-01

    We present results from high-resolution N-body/SPH (smoothed particle hydrodynamic) simulations of rotationally supported dwarf irregular galaxies moving on bound orbits in the massive dark matter halo of the Milky Way. The dwarf models span a range in disk surface density and the masses and sizes of their dark halos are consistent with the predictions of cold dark matter cosmogonies. We show that the strong tidal field of the Milky Way determines severe mass loss in their halos and disks and induces bar and bending instabilities that transform low surface brightness dwarfs (LSBs) into dwarf spheroidals (dSphs) and high surface brightness dwarfs (HSBs) into dwarf ellipticals (dEs) in less than 10 Gyr. The final central velocity dispersions of the remnants are in the range 8-30 km s-1 and their final v/σ falls to values less than 0.5, matching well the kinematics of early-type dwarfs. The transformation requires the orbital time of the dwarf to be <~3-4 Gyr, which implies a halo as massive and extended as predicted by hierarchical models of galaxy formation to explain the origin of even the farthest dSph satellites of the Milky Way, Leo I, and Leo II. We show that only dwarfs with central dark matter densities as high as those of Draco and Ursa Minor can survive for 10 Gyr in the proximity of the Milky Way. A correlation between the central density and the distance of the dwarfs from the primary galaxy is indeed expected in hierarchical models, in which the densest objects should have small orbital times because of their early formation epochs. Part of the gas is stripped and part is funneled to the center because of the bar, generating one strong burst of star formation in HSBs and smaller, multiple bursts in LSBs. Therefore, the large variety of star formation histories observed in Local Group dSphs arises because different types of dIrr progenitors respond differently to the external perturbation of the Milky Way. Our evolutionary model naturally explains the

  5. ANS ultraviolet observations of dwarf Cepheids

    NASA Technical Reports Server (NTRS)

    Sturch, C. R.; Wu, C.-C.

    1983-01-01

    Ultraviolet observations of three dwarf Cepheids (VZ Cnc, SX Phe, and AI Vel) are presented. The UV light curves are consistent with those in the visual region. When compared to standard stars, all three dwarf Cepheids exhibit flux deficiencies at the shortest observed wavelengths. The most extreme deficiencies appear for SX Phe; these may be related to the other properties previously noted for this star, including low metallicity, high space motion, and low luminosity.

  6. New White Dwarfs in the SDSS DR10

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Pelisoli, I.; Koester, D.; Ourique, G.; Kleinman, S. J.; Romero, A. D.; Nitta, A.; Eisenstein, D. J.; Costa, J. E. S.; Külebi, B.; Jordan, S.; Dufour, P.; Giommi, P.; Rebassa-Mansergas, A.

    2015-06-01

    We report the discovery of 8 991 new spectroscopically confirmed white dwarfs and subdwarfs in the Sloan Digital Sky Survey Data Release 10. We obtain Teff, log g and mass for hydrogen atmosphere white dwarf stars (DAs) and helium atmosphere white dwarf stars (DBs), and estimate the calcium/helium abundances for the white dwarf stars with metallic lines (DZs) and carbon/helium for cool carbon dominated spectra DQs. We found 2 new oxygen dominated spectra white dwarfs, 69 DQs, 42 hot DO/PG1159s, 175 white dwarf+main sequence star binaries, 206 magnetic DAHs, 325 continuum dominated DCs, 397 metal polluted white dwarfs, 450 helium dominated white dwarfs, 636 subdwarfs and 6796 new hydrogen dominated white dwarf stars.

  7. Nonlinear Analysis of Pulsating White Dwarf Lightcurves

    NASA Astrophysics Data System (ADS)

    Provencal, J. L.; Montgomery, M. H.; Shipman, H.; WET TEam

    2015-06-01

    Convection remains one of the largest sources of theoretical uncertainty in our understanding of stellar physics. For example, Bergeron (1995) show that basic parameters such as flux, line profiles, energy distribution, color indices, and equivalent widths are extremely sensitive to the assumed convective parameterization. This is compelling, since we use our knowledge of these basic parameters to calibrate white dwarf cooling sequences, provide detailed estimates for the ages of individual white dwarfs, and determine the age of the Galactic disk. The Whole Earth Telescope (WET) is engaged in a long term project to empirically calibrate the physical properties of convection in pulsating white dwarfs by combining asteroseismology and analysis of nonlinear light curves. Nonsinusoidal distortions, in the form of narrow peaks and wider valleys, are observed in many pulsating white dwarf light curves. These are a reflection of the local depth of the convection zone, a value which varies during a pulsation cycle. Applying asteroseismology and convective light curve fitting to a wide sample of pulsating white dwarfs provides an empirical map of how the convective response time (the convection zone “depth”) varies as a function of effective temperature, and this can be compared with theoretical models, both MLT and hydrodynamic. This project has resulted in a large database of white dwarf lightcurves and pulsation frequencies. We present current results for DA and DB pulsators, and provide a few examples of interesting pulsation behavior seen along the way.

  8. Morphology and Structures of Nearby Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Seo, Mira; Ann, HongBae

    2015-08-01

    We performed an analysis of the structure of nearby dwarf galaxies based on a 2-dimensional decomposition of galaxy images using GALFIT. The present sample consists of ~1,100 dwarf galaxies with redshift less than z = 0.01, which is is derived from the morphology catalog of the Visually classified galaxies in the local universe (Ann, Seo, and Ha 2015). In this catalog, dwarf galaxies are divided into 5 subtypes: dS0, dE, dSph, dEbc, dEblue with distinction of the presence of nucleation in dE, dSph, and dS0. We found that dSph and dEblue galaxies are fainter than other subtypes of dwarf galaxies. In most cases, single component, represented by the Sersic profile with n=1~1.5, well describes the luminosity distribution of dwarf galaxies in the present sample. However, a significant fraction of dS0, dEbc, and dEbue galaxies show sub-structures such as spiral arms and rings. We will discuss the morphology dependent evolutionary history of the local dwarf galaxies.

  9. MICROLENSING BINARIES WITH CANDIDATE BROWN DWARF COMPANIONS

    SciTech Connect

    Shin, I.-G.; Han, C.; Gould, A.; Skowron, J.; Udalski, A.; Szymanski, M. K.; Kubiak, M.; Soszynski, I.; Pietrzynski, G.; Poleski, R.; Ulaczyk, K.; Pietrukowicz, P.; Kozlowski, S.; Wyrzykowski, L.; Sumi, T.; Dominik, M.; Beaulieu, J.-P.; Tsapras, Y.; Bozza, V.; Abe, F.; Collaboration: OGLE Collaboration; MOA Collaboration; muFUN Collaboration; and others

    2012-12-01

    Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing events discovered during the 2004-2011 observation seasons. Based on the low mass ratio criterion of q < 0.2, we found seven candidate events: OGLE-2004-BLG-035, OGLE-2004-BLG-039, OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334, MOA-2011-BLG-104/OGLE-2011-BLG-0172, MOA-2011-BLG-149, and MOA-201-BLG-278/OGLE-2011-BLG-012N. Among them, we are able to confirm that the companions of the lenses of MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149 are brown dwarfs by determining the mass of the lens based on the simultaneous measurement of the Einstein radius and the lens parallax. The measured masses of the brown dwarf companions are 0.02 {+-} 0.01 M {sub Sun} and 0.019 {+-} 0.002 M {sub Sun} for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low-mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events with well-covered light curves increases with new-generation searches.

  10. Model Assessment of Permafrost Development for a Large Alpine Catchment

    NASA Astrophysics Data System (ADS)

    Voelksch, I.; Lehning, M.

    2005-12-01

    The extremely hot summer of 2003 saw increased rockfall and slope instability problems in the European Alps. This is generally attributed to permafrost thawing. Therefore, the development of permafrost in steep Alpine terrain under the observed warming trend needs to be investigated. We use ALPINE3D, a detailed model of Alpine surface processes to assess permafrost occurrence under the current climate and to predict an expected change under the warming scenario that future summers will be on average as the summer 2003. The ALPINE3D modules consist of a radiation balance model using a view factor approach and include short-wave scattering and long-wave emission from terrain and tall vegetation. The processes in the atmosphere are coupled to a distributed one-dimensional model of vegetation, snow and soil (SNOWPACK) using the assumption that lateral exchange is small in these media. Snow and soil processes are treated in much detail with adaptive multi-layer finite elements. The model modules can be run in a parallel (distributed) mode using a GRID infrastructure to allow such computationally demanding tasks. The application of ALPINE3D to the Cordevole river basin in the northern Italian Dolomites has been based on weather station data from seven locations in the area. A spatial resolution of 200 m is used for the simulation, which covers approximately 900 square kilometers. Typically, mass and energy exchange processes for 20 soil layers and up to 30 snow layers are calculated with an hourly time step and 15 years of data. In the steep terrain of the southern Alps, only a small area fraction has permafrost. Permafrost disappears almost completely under the warming scenario, which is achieved by simulating repeatedly the 2003 year.

  11. Relevance of wet deposition of organic matter for alpine ecosystems

    NASA Astrophysics Data System (ADS)

    Mladenov, N.; Williams, M. W.; Schmidt, S. K.; Goss, N. R.; Reche, I.

    2011-12-01

    In barren, alpine environments, carbon inputs from atmospheric deposition may be very important for ecological processes. Recent findings suggest that atmospheric deposition influences the quality of dissolved organic matter (DOM) in alpine lakes on a global scale. Here, we evaluate the inputs of DOM in atmospheric wet deposition to alpine terrestrial ecosystems, in terms of both quantity and quality. We show that at the Niwot Ridge Long Term Ecological Research Station (Colorado, USA) wet deposition represents a seasonally variable (Figure 1) mass input of organic carbon, depositing on average 6 kg C/ha/yr or roughly 1500 kg C to the Green Lake 4 watershed at Niwot Ridge. Wet deposition is, therefore, a substantial input of dissolved organic carbon (DOC) to the catchment when compared to the annual DOC yield from Green Lake 4, estimated at just over 1800 kg C. In terms of DOM bioavailability for alpine microorganisms, our optical spectroscopic results showing high amounts of amino acid-like fluorescence and low aromaticity suggest that DOM in wet deposition may be particularly labile, especially in the summer months. The heterotrophic processing of this organic carbon input has important implications for the cycling of other nutrients, such as nitrogen, in alpine environments. We have also shown that the sources of DOM in wet deposition include bioaerosols, such as pollen, which represent much of the summer DOC loading. However, relationships with inorganic N and sulfate also suggest that organic pollutants in the atmosphere may have an equally important influence on DOM in wet deposition. Additionally, the quality of wet deposition DOM in the spring is similar to that of dust deposition observed near the Sahara and may be influenced by dust events, as shown from air mass trajectories originating in or near the Colorado Plateau. The seasonality of DOM quality appears to be related to these varying sources and is, therefore, a critical topic for future research.

  12. Stable isotopes in alpine precipitation as tracers of atmospheric deposition

    NASA Astrophysics Data System (ADS)

    Wasiuta, V. L.; Lafreniere, M. J.; Kyser, T. K.; Norman, A. L.; Mayer, B.; Wieser, M.

    2010-12-01

    Alpine ecosystems, which are generally nutrient poor and exist under extreme climatic conditions, are particularly sensitive to environmental and climatic stressors. Studies in the USA Rocky Mountains and European Alps have shown that alpine terrestrial and aquatic ecosystems are particularly sensitive to enhanced deposition of reactive nitrogen and can show ecologically destructive responses at relatively low levels of nitrogen deposition. However, there is no base line for atmospheric deposition of natural and anthropogenic contaminants in the Canadian alpine. Preliminary results of isotopic and chemical analyses of precipitation from an elevational transect on a glaciated alpine site in the Canadian Rockies are presented. Precipitation accumulating from early autumn through to spring (2008/2009 and 2009/2010) was sampled by means of seasonal snow cover on alpine glaciers. Summer precipitation was sampled through July and August 2010 using bulk collectors installed at the sites of winter sampling. The isotope ratios of dissolved sulphate (δ34S, δ18O), nitrogen (δ15N, δ18O), as well as precipitation (δ2H, δ18O) are utilized in addition to major ion concentrations and trace metal concentrations. Results from 2008/2009 snowpack samples indicate a strong seasonal trend in sulphate (SO42-) and nitrogen (NO3-) deposition which is consistent across the altitudinal transect. Snow horizons representing early autumn and spring precipitation show higher SO42- and NO3- concentrations in contrast to lower concentrations in winter horizons. The aforementioned suite of isotopic and chemical analyses are used to investigate the variability in dominant geographic source regions for atmospheric SO42- and NO3- (local, regional, or long range transported contaminants), as well as to identify contributions from the major biogeochemical source types (e.g. hydrocarbon combustion, lithogenic dust, agricultural emissions).

  13. Shrub encroachment across North America: A multi-site synthesis of patterns, mechanisms, and consequences

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In North America, the expansion of shrubs within ecosystems previously dominated by herbaceous species has been documented in barrier islands off the Virginia coast, mesic grasslands of the Great Plains, sub-tropical savannas of Texas, desert grasslands of the Southwest, across the Intermountain Wes...

  14. Delineating native and invasive plant functional groups in shrub-steppe vegetation using bidirectional reflectance

    NASA Astrophysics Data System (ADS)

    Naupari, Javier A.; Vierling, Lee A.; Eitel, Jan U. H.

    2013-01-01

    Delineating invasive and native plant types using remote sensing is important for managing rangelands. Remote characterization of rangeland vegetation often utilizes only the nadir view, which can be complicated by background soil reflectance. We therefore collected bidirectional radiometric measurements on a shrub-steppe vegetated landscape throughout the mid- to late-growing season to: (1) quantify the BRFs of four rangeland vegetation functional groups (native shrub, native grasses, invasive annual grasses, and forbs), and (2) examine ways in which bidirectional reflectance values may help delineate native and invasive vegetation types. We found that the invasive grass medusahead rye (Taeniatherum caput-medusae [L.] Nevski) could be discriminated from other vegetation types at nadir and across four forward-viewing zenith angles because this species exhibited structural changes when leaf orientation changed from erectophile to planophile during and after the filling of seedheads. We also confirmed that native shrubs exhibited the highest anisotropy in all wavebands, as the relatively complex structure of the shrub canopy and concomitant shadowing greatly affected values of normalized difference vegetation index across all view angles. In order to delineate rangeland vegetation types at coarser scales, further study is needed to quantify the spectral angular signatures of these plant groups using satellite-based images.

  15. Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Doubling atmospheric carbon dioxide concentrations [CO2] over native Colorado shortgrass steppe progressively increased plant cover over a five year period in Artemisia frigida Willd, fringed sage, a common shrub of North American and Asian native grasslands. Plant community species composition in ...

  16. Hydraulic redistribution by two semi-arid shrub species: Implications for Sahelianagro-ecosystems

    EPA Science Inventory

    Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulat...

  17. Demographic effects on fruit set in the dioecious shrub Canada buffaloberry (Shepherdia canadensis)

    PubMed Central

    Johnson, Kate M.

    2014-01-01

    The effects of pollen limitation on reproductive success in plants have been well-documented using pollen supplementation experiments. However, the role of local demographics in determining pollen limitation, particularly in terms of the additive and interactive effects of pollen availability and competition are not well known. We measured fruit set in the dioecious shrub Canada buffaloberry (Shepherdia canadensis) in Central Alberta, Canada to evaluate whether local demographics measured at three spatial scales (25, 50, and 100 m2) affect fruit set in buffaloberry. We test whether density-dependence (population density), pollen donor (measured as male density, distance to nearest male plant and size of nearest male plant), female competitor (measured as female density and distance to nearest female plant), or the combined pollen donor and competitor hypotheses best explain natural variations in fruit set for a population of Canada buffaloberry. Support was highest for the combined pollen donor and competitor hypothesis at an intermediate spatial scale of 50 m2. Proportion fruit set increased with male shrub density (pollen donors) and decreased with female shrub density (pollen competitors), but was more affected by the presence of males than females. This illustrates that access to male shrubs within a 3.99 m radius affects pollen availability, while nearby females compete intra-specifically for pollen. PMID:25165635

  18. Relationship between shrubs and foods in mountain plover habitat in Park County, Colorado

    USGS Publications Warehouse

    Schneider, S.C.; Wunder, Michael B.; Knopf, F.L.

    2006-01-01

    We explored habitat use in terms of vegetation structure and potential forage availability for mountain plovers (Charadrius montanus) in Park County, Colorado. We quantified the percentage cover of bare ground, percentage cover of shrubs (Chrysothamnus visadiflorus), linear distance to nearest shrub, arthropod biomass, and grasshopper density for 102 plots of 1,963 m2, 51 of which were occupied by plovers and 51 of which were selected randomly within previously-classified potential habitat. We modeled the probability of habitat use by plovers based on these measurements. We further subdivided the occupied plots to model probability of habitat use by adults with broods as compared with use by pre-nesting and post-nesting adults. Percentage of bare ground and probability of habitat use for adults with broods were related inversely, but not so for adults without broods. Grasshopper density was positively related to probability of habitat use by adults without broods, whereas proximity to nearest shrub was negatively related. We propose that habitat use by plovers in South Park is influenced by the amount of available shrub-grassland edge habitat and the availability of forage.

  19. EFFECTS OF PLANT SIZE ON PHOTOSYNTHESIS AND WATER RELATIONS IN THE DESERT SHRUB PROSOPIS GLANDULOSA (FABACEAE)

    EPA Science Inventory

    The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial gra...

  20. Permafrost collapse after shrub removal shifts tundra ecosystem to a methane source

    NASA Astrophysics Data System (ADS)

    Nauta, Ake L.; Heijmans, Monique M. P. D.; Blok, Daan; Limpens, Juul; Elberling, Bo; Gallagher, Angela; Li, Bingxi; Petrov, Roman E.; Maximov, Trofim C.; van Huissteden, Jacobus; Berendse, Frank

    2015-01-01

    Arctic tundra ecosystems are warming almost twice as fast as the global average. Permafrost thaw and the resulting release of greenhouse gases from decomposing soil organic carbon have the potential to accelerate climate warming. In recent decades, Arctic tundra ecosystems have changed rapidly, including expansion of woody vegetation, in response to changing climate conditions. How such vegetation changes contribute to stabilization or destabilization of the permafrost is unknown. Here we present six years of field observations in a shrub removal experiment at a Siberian tundra site. Removing the shrub part of the vegetation initiated thawing of ice-rich permafrost, resulting in collapse of the originally elevated shrub patches into waterlogged depressions within five years. This thaw pond development shifted the plots from a methane sink into a methane source. The results of our field experiment demonstrate the importance of the vegetation cover for protection of the massive carbon reservoirs stored in the permafrost and illustrate the strong vulnerability of these tundra ecosystems to perturbations. If permafrost thawing can more frequently trigger such local permafrost collapse, methane-emitting wet depressions could become more abundant in the lowland tundra landscape, at the cost of permafrost-stabilizing low shrub vegetation.

  1. Influence of secondary compound complementarity and species diversity on consumption of Mediterranean shrubs by sheep

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Generalist herbivores foraging in chemically diverse grazing ecosystems like the Mediterranean maquis increase intake on mixed diets, suggesting they are more able to meet nutritional needs and avoid toxicosis. Thus, our objectives were to determine how shrub species diversity and complementary inte...

  2. A synthetic review of feedbacks and drivers of shrub encroachment in arid grasslands

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Many arid grasslands around the world are affected by woody plant encroachment and the replacement of a relatively continuous grass cover with shrub patches bordered by bare soil. This shift in plant community composition is often abrupt in space and time, suggesting that it is likely sustained by p...

  3. Diseases of Ornamental and Shade Trees, Shrubs, Vines, and Ground Covers.

    ERIC Educational Resources Information Center

    Nichols, Lester P.

    This agriculture extension service publication from Pennsylvania State University covers the identification and control of common ornamental trees, shrubs, and ground cover diseases. The publication is divided into sections. The first section discusses the diseases of ornamental and shade trees, including general diseases and diseases of specific…

  4. Insects and Related Pests of Trees, Shrubs, and Lawns. MP-25R.

    ERIC Educational Resources Information Center

    Spackman, Everett W.; Lawson, Fred A.

    This document discusses identification and control of the pests of trees and shrubs. The insects are grouped according to feeding habits and the type of damage caused to plants. Categories include the sucking insects and mites, leaf eating insects, pests attacking trunks and branches, and gall causing insects. (CS)

  5. Postfire shrub cover dynamics: a 70-year fire history in mountain big sagebrush communities

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Fire is a natural process in sagebrush (Artemisia L.) communities. Land managers use fire to meet rangeland management objectives. This study was conducted to quantify, from present conditions, the effect of time since last burn (TSLB) on shrub cover over 70 yr of fire history. We sampled mountain...

  6. Postfire shrub-cover dynamics: a 70-year fire history in big sagebrush communities.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Land managers use prescribed fire to meet rangeland management objectives. This study was conducted to quantify, from present conditions, the effect of time since last burn (TSLB) on shrub cover over 70 yr of fire history. We sampled mountain big sagebrush communities at the USDA, ARS, U.S. Sheep ...

  7. Runoff responses to long-term rainfall variability in a shrub-dominated catchment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In this study we investigate how rainfall has changed between two nine year periods (1977e1985 and 2003e2011), and evaluate the effects of changes in rainfall on runoff from a shrub-dominated catchment in the southwestern USA. Analysis of rainfall characteristics shows that between these two periods...

  8. Global Survey of Anthropogenic Neighborhood Threats to Conservation of Grass-Shrub and Forest Vegetation

    EPA Science Inventory

    The ecological functions of natural vegetation are threatened when it is subsumed in anthropogenic landscapes. We report the first comparative global survey of anthropogenic landscape threats to forest and grass-shrub vegetation. Using a global land-cover map derived from remote...

  9. Modeling shrub population dynamics in response to overgrazing and climate change in the southwestern US desert

    NASA Astrophysics Data System (ADS)

    Stabert, E. C.; Furbish, D. J.

    2010-12-01

    The environmental health and well-being of semi-arid southwestern US deserts strongly depend on the state of the region’s vegetation. Desertification has resulted in the degradation of semi-arid lands and thus these deserts exhibit less vegetated, arid-like conditions whereby soil and associated vital nutrients are vulnerable to aeolian and hydrologic erosion. This process of desertification has been exacerbated by overgrazing and possibly climate change, and there is the possibility that such disturbances can lead to an irreversible shift from semi-arid to arid-like conditions with low relative biomass and loss of land productivity. We expand on the work of Worman (2010), who developed a probabilistic model of shrub population dynamics in response to variations in precipitation and associated soil moisture conditions, distinguishing the effects of summer versus winter precipitation on seedling recruitment and shrub mortality. Specifically, we have modified the model to mimic effects of grazing on the likelihood of shrub mortality, and we have incorporated stochastic descriptions of variations in the timing and magnitude of precipitation that are likely to occur over decadal to century timescales. By evaluating the response of shrub populations (focusing on rabbitbrush and broom snakeweed), the model provides insights regarding the likelihood of land productivity loss.

  10. Badger (Taxidea taxus) disturbances increase soil heterogeneity in a degraded shrub-steppe ecosystem

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In the western United States, overgrazing, weed invasion and wildfire have resulted in the conversion of shrub-steppe to annual grasslands, with substantial effects on ecosystem function. In these landscapes, badgers disturb large areas of soil while foraging for prey. Mounds created by badgers cont...

  11. PRECIPITATION TIMING ALTERS SOIL C STORAGE IN A GREAT BASIN SHRUB-STEPPE ECOSYSTEM

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Predictions of precipitation responses to global warming vary in timing, magnitude and inter-annual variability. Most research investigating impacts of precipitation timing have focused on plant responses but little is known concerning soil C responses. In a Great Basin shrub-steppe ecosystem, we qu...

  12. Antecedent conditions influence soil respiration differences in shrub and grass patches

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Quantifying the response of soil respiration to past environmental conditions is critical for predicting how future climate and vegetation change will impact ecosystem carbon balance. Increased shrub dominance in semiarid grasslands has potentially large effects on soil carbon cycling. The goal of t...

  13. Energy-dense liquid fuel intermediates by pyrolysis of guayule (Parthenium argentatum) shrub and bagasse

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Guayule is a perennial shrub grown in the southwestern United States that is used to produce high quality, natural rubber latex. However, only about 10% of the plant material is used for latex production; the remaining biomass, called bagasse, can be used for renewable fuel production. Fast pyroly...

  14. Shrub expansion in northern Chihuahuan Desert grasslands: Spatial patterns of transition and biophysical constraints

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Among the greatest contemporary threats to the structure, function and biological diversity of desert grassland and shrub savanna ecosystems of the southwestern United States is the displacement of mesophytic grasses by xerophytic woody plants. Through a combination of field sampling and spatial mod...

  15. The Hunt for Missing Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-11-01

    Theories of galaxy formation and evolution predict that there should be significantly more dwarf galaxies than have been observed. Are our theories wrong? Or are dwarf galaxies just difficult to detect? Recent results from a survey of a galaxy cluster 62 million light-years away suggest there may be lots of undiscovered dwarf galaxies hiding throughout the universe!Hiding in FaintnessThe missing dwarf problem has had hints of a resolution with the recent discovery of Ultra-Diffuse Galaxies (UDGs) in the Coma and Virgo galaxy clusters. UDGs have low masses and large radii, resulting in a very low surface brightness that makes them extremely difficult to detect. If many dwarfs are UDGs, this could well explain why weve been missing them!But the Coma and Virgo galaxy clusters are similar in that theyre both very massive. Are there UDGs in other galaxy clusters as well? To answer this question, an international team of scientists is running the Next Generation Fornax Survey (NGFS), a survey searching for faint dwarf galaxies in the central 30 square degrees of the Fornax galaxy cluster.The NGFS uses near-UV and optical observations from the Dark Energy Camera mounted on the 4m Blanco Telescope in Chile. The survey is still underway, but in a recent publication led by Roberto P. Muoz (Institute of Astrophysics at the Pontifical Catholic University of Chile), the team has released an overview of the first results from only the central 3 square degrees of the NGFS field.Surprising DetectionGalaxy radii vs. their absolute i-band magnitudes, for the dwarfs found in NGFS as well as other stellar systems in the nearby universe. The NGFS dwarfs are similar to the ultra-diffuse dwarfs found in the Virgo and Coma clusters, but are several orders of magnitude fainter. [Muoz et al. 2015]In just this small central field, the team has found an astounding 284 low-surface-brightness dwarf galaxy candidates 158 of them previously undetected. At the bright end of this sample are dwarf

  16. The Hunt for Dwarf Galaxies' Ancestors

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-01-01

    Dwarf galaxies are typically very faint, and are therefore hard to find. Given that, what are our chances of finding their distant ancestors, located billions of light-years away? A recent study aims to find out.Ancient CounterpartsDwarf galaxies are a hot topic right now, especially as we discover more and more of them nearby. Besides being great places to investigate a variety of astrophysical processes, local group dwarf galaxies are also representative of the most common type of galaxy in the universe. For many of these dwarf galaxies, their low masses and typically old stellar populations suggest that most of their stars were formed early in the universes history, and further star formation was suppressed when the universe was reionized at redshifts of z ~ 610. If this is true, most dwarf galaxies are essentially fossils: theyve evolved little since that point.To test this theory, wed like to find counterparts to our local group dwarf galaxies at these higher redshifts of z = 6 or 7. But dwarf galaxies, since they dont exhibit lots of active star formation, have very low surface brightnesses making them very difficult to detect. What are the chances that current or future telescope sensitivities will allow us to detect these? Thats the question Anna Patej and Abraham Loeb, two theorists at Harvard University, have addressed in a recent study.Entering a New RegimeThe surface brightness vs. size for 73 local dwarf galaxies scaled back to redshifts of z=6 (top) and z=7 (bottom). So far weve been able to observe high-redshift galaxies within the boxed region of the parameter space. JWST will open the shaded region of the parameter space, which includes some of the dwarf galaxies. [Patej Loeb 2015]Starting from observational data for 87 Local-Group dwarf galaxies, Patej and Loeb used a stellar population synthesis code to evolve the galaxies backward in time to redshifts of z = 6 and 7. Next, they narrowed this sample to only those dwarfs for which most star

  17. Seasonal Distribution and Diversity of Ground Arthropods in Microhabitats Following a Shrub Plantation Age Sequence in Desertified Steppe

    PubMed Central

    Liu, Rentao; Zhu, Fan; Song, Naiping; Yang, Xinguo; Chai, Yongqing

    2013-01-01

    In desertified regions, shrub-dominated patches are important microhabitats for ground arthropod assemblages. As shrub age increases, soil, vegetation and microbiological properties can change remarkably and spontaneously across seasons. However, relatively few studies have analyzed how ground arthropods respond to the microhabitats created by shrubs of different plantation ages across seasons. Using 6, 15, 24 and 36 year-old plantations of re-vegetated shrubs (Caragana koushinskii) in the desert steppe of northwestern China as a model system, we sampled ground arthropod communities using a pitfall trapping method in the microhabitats under shrubs and in the open areas between shrubs, during the spring, summer and autumn. The total ground arthropod assemblage was dominated by Carabidae, Melolonthidae, Curculionidae, Tenebrionidae and Formicidae that were affected by plantation age, seasonal changes, or the interaction between these factors, with the later two groups also influenced by microhabitat. Overall, a facilitative effect was observed, with more arthropods and a greater diversity found under shrubs as compared to open areas, but this was markedly affected by seasonal changes. There was a high degree of similarity in arthropod assemblages and diversity between microhabitats in summer and autumn. Shrub plantation age significantly influenced the distribution of the most abundant groups, and also the diversity indices of the ground arthropods. However, there was not an overall positive relationship between shrub age and arthropod abundance, richness or diversity index. The influence of plantation age on arthropod communities was also affected by seasonal changes. From spring through summer to autumn, community indices of ground arthropods tended to decline, and a high degree of similarity in these indices (with fluctuation) was observed among different ages of shrub plantation in autumn. Altogether the recovery of arthropod communities was markedly affected by

  18. Novel wildlife in the Arctic: the influence of changing riparian ecosystems and shrub habitat expansion on snowshoe hares.

    PubMed

    Tape, Ken D; Christie, Katie; Carroll, Geoff; O'Donnell, Jonathan A

    2016-01-01

    Warming during the 20th century has changed the arctic landscape, including aspects of the hydrology, vegetation, permafrost, and glaciers, but effects on wildlife have been difficult to detect. The primary aim of this study is to examine the physical and biological processes contributing to the expanded riparian habitat and range of snowshoe hares (Lepus americanus) in northern Alaska. We explore linkages between components of the riparian ecosystem in Arctic Alaska since the 1960s, including seasonality of stream flow, air temperature, floodplain shrub habitat, and snowshoe hare distributions. Our analyses show that the peak discharge during spring snowmelt has occurred on average 3.4 days per decade earlier over the last 30 years and has contributed to a longer growing season in floodplain ecosystems. We use empirical correlations between cumulative summer warmth and riparian shrub height to reconstruct annual changes in shrub height from the 1960s to the present. The effects of longer and warmer growing seasons are estimated to have stimulated a 78% increase in the height of riparian shrubs. Earlier spring discharge and the estimated increase in riparian shrub height are consistent with observed riparian shrub expansion in the region. Our browsing measurements show that snowshoe hares require a mean riparian shrub height of at least 1.24-1.36 m, a threshold which our hindcasting indicates was met between 1964 and 1989. This generally coincides with observational evidence we present suggesting that snowshoe hares became established in 1977 or 1978. Warming and expanded shrub habitat is the most plausible reason for recent snowshoe hare establishment in Arctic Alaska. The establishment of snowshoe hares and other shrub herbivores in the Arctic in response to increasing shrub habitat is a contrasting terrestrial counterpart to the decline in marine mammals reliant on decreasing sea ice. PMID:26527375

  19. Greater deciduous shrub abundance extends the annual period of maximum tundra greenness and increases modeled net CO2 uptake

    NASA Astrophysics Data System (ADS)

    Sweet, S. K.; Griffin, K. L.; Steltzer, H.; Gough, L.; Boelman, N.

    2014-12-01

    Satellite studies of the terrestrial Arctic report increased summer greening and longer green seasons over the past several decades, which may increase productivity and lengthen the period of carbon uptake. These trends have been attributed largely to increasing air temperatures and reduced snow cover duration. However, deciduous shrubs are concurrently becoming increasingly abundant in tundra landscapes, which may also impact canopy phenology and productivity. Our aim in this research was to determine the influence of greater deciduous shrub abundance on tundra canopy phenology and subsequent impacts on net ecosystem carbon exchange (NEE) over the growing season in the northern foothills of the Brooks Range, Alaska (68º38' N, 149º34' W). We compared deciduous shrub-dominated and evergreen/graminoid-dominated community-level canopy phenology using the normalized difference vegetation index (NDVI) and piecewise linear regression modeling. We used a tundra plant-community specific leaf area index (LAI) model to estimate LAI throughout the season. We then used a tundra specific NEE model to estimate the impact of greater deciduous shrub abundance and associated shifts in leaf area and canopy phenology on tundra carbon flux. We found that deciduous shrub canopies reached the onset of maximum greenness significantly earlier than evergreen/graminoid canopies, but both communities reached the onset of senescence at similar times, resulting in a net extension of the peak green season in deciduous shrub communities compared to evergreen/graminoid communities. The combined effect of a longer peak green season and greater leaf area of deciduous shrub canopies increased the net carbon uptake in deciduous shrub communities compared to evergreen/graminoid communities. However, the longer peak season alone significantly increased carbon uptake in deciduous shrub communities, suggesting that greater deciduous shrub abundance increases carbon uptake not only due to greater leaf

  20. Performance of shrub willows (Salix spp.) as an evapotranspiration cover on Solvay wastebeds

    NASA Astrophysics Data System (ADS)

    Mirck, Jaconette

    2009-12-01

    Soda ash (Na2CO3) production in the Syracuse New York area created 607 ha of wastebeds over the course of about 100 years. Today the primary concern of the Solvay wastebeds is high chloride concentrations in the leachate and storm water that may end up in the groundwater and nearby Onondaga Lake. The potential of shrub willow evapotranspiration (ET) covers to minimize leaching and to manage storm water was assessed in two studies. A sap flow sensor field study to estimate transpiration rates of four shrub willow varieties over an entire growing season. A greenhouse study focused on recycling saline Solvay storm water onto shrub willows. Annual sap flow and crop coefficients (Kc) were similar among four shrub willows, but differences were present over the course of the growing season. Peak K c values did not coincide with peak leaf area index (LAI), as might be expected if LAI were the main driver of transpiration. Rather than solely being driven by LAI, coupling with the atmosphere was an important factor in stand level sap flow. Estimates of ET were measured during both experiments, the ET/sap flow rankings of the shrub willow varieties were similar; Salix miyabeana (SX64)< S. purpurea (9882-34)< S. miyabeana x S. sachalinensis (9870-23 or 9870-40). In the greenhouse study, Solvay storm water that contained 1,625 mg Cl - L-1 (close to the average storm water concentration) did not significantly decrease ET values or growth for any of the willow varieties. Mass balances of sodium and chloride were carried out to assess the potentials of recycling saline Solvay storm water back onto a shrub willow ET cover during the growing season. During a ten-week study the combination of a shallow depth soil (33 cm) and a high irrigation regime (170% of average precipitation in the Syracuse NY area) resulted in the accumulation of at least 62% of both sodium and chloride in the plant/soil system for all five Solvay storm water treatments. Both studies indicated that shrub

  1. Potential effects of tree-to-shrub type conversion on streamflow in California's Sierra Nevada

    NASA Astrophysics Data System (ADS)

    Baguskas, S. A.; Bart, R.; Molinari, N.; Tague, C.; Moritz, M.

    2014-12-01

    There is widespread concern that changes in climate and fire regime may lead to vegetation change across California, which in turn may influence watershed hydrology. Although plant cover is known to affect numerous hydrological processes, sensitivities to vegetation type and spatial arrangement of species within watersheds are not well understood. The primary objective of our research was to generate mechanistically-based projections of how potential type conversion from forested to shrub dominated systems may affect streamflow. During the 2014 growing season, we measured ecophysiological responses (plant water status and leaf gas exchange rates) of two dominant tree and shrub species to changes in seasonal water availability at two sites within the southern Sierra Nevada Critical Zone Observatory. Plant physiological observations were used to parameterize a process-based eco-hydrological model, RHESSys. This model was used to evaluate the impact of changes in seasonal water availability and vegetation type-conversion on streamflow. Based on our field observations, shrubs and trees had similar access to water through the early part of the growing season (April-early June); however, by late July, available water to shrubs was twice that of trees (shrubs, -0.55 ± 0.08 MPa; trees, -1.07 ± 0.08 MPa, p<0.05). Likewise, maximum transpiration (E) and carbon assimilation (A) rates per unit leaf area were twice as high for shrubs then trees in July (shrubs, A= 21 ± 2.3 μmol m-2 s-1, E=6.6 ± 1.8 mmol m-2 s-1; trees, A=8.2 ± 1.9 μmol m-2 s-1, E=2.4 ± 0.3 mmol m-2 s-1). Preliminary modeled changes in streamflow following simulated vegetation conversion were found to affect both the timing and amount of discharge. Controls on pre vs. post-conversion streamflow included changes in interception, rooting depth, energy balance, and plant response to changes in seasonal water availability. Our research demonstrates how linking strategic field data collection and mechanistic

  2. Kinematics and luminosities of brown dwarfs with the BDNYC group .

    NASA Astrophysics Data System (ADS)

    Riedel, A. R.

    Due to magnitude limits, the Gaia survey will not delve as deeply into the local population of brown dwarfs as it will other stellar populations. While hundreds or thousands of brown dwarfs will be measured by Gaia, we propose a different, indirect method wherein studies using Gaia data will help teach us about brown dwarfs: Identifying moving groups that contain brown dwarfs. This use of Gaia data will directly help attempts to disentangle the effects of age and mass on brown dwarf spectra, which opens the possibilities for determining empirical constraints on brown dwarf evolution.

  3. Pulsating white dwarfs in cataclysmic variables: The marriage of ZZ Cet and dwarf nova

    NASA Astrophysics Data System (ADS)

    Warner, Brian; Woudt, Patrick A.

    2004-05-01

    There are now four dwarf novae known with white dwarf primaries that show large amplitude non-radial oscillations of the kind seen in ZZ Cet stars. We compare the properties of these stars and point out that by the end of Sloan Digital Sky Survey more than 30 should be known.

  4. Evidence of physiological decoupling from grassland ecosystem drivers by an encroaching woody shrub.

    PubMed

    Nippert, Jesse B; Ocheltree, Troy W; Orozco, Graciela L; Ratajczak, Zak; Ling, Bohua; Skibbe, Adam M

    2013-01-01

    Shrub encroachment of grasslands is a transformative ecological process by which native woody species increase in cover and frequency and replace the herbaceous community. Mechanisms of encroachment are typically assessed using temporal data or experimental manipulations, with few large spatial assessments of shrub physiology. In a mesic grassland in North America, we measured inter- and intra-annual variability in leaf δ(13)C in Cornus drummondii across a grassland landscape with varying fire frequency, presence of large grazers and topographic variability. This assessment of changes in individual shrub physiology is the largest spatial and temporal assessment recorded to date. Despite a doubling of annual rainfall (in 2008 versus 2011), leaf δ(13)C was statistically similar among and within years from 2008-11 (range of -28 to -27‰). A topography*grazing interaction was present, with higher leaf δ(13)C in locations that typically have more bare soil and higher sensible heat in the growing season (upland topographic positions and grazed grasslands). Leaf δ(13)C from slopes varied among grazing contrasts, with upland and slope leaf δ(13)C more similar in ungrazed locations, while slopes and lowlands were more similar in grazed locations. In 2011, canopy greenness (normalized difference vegetation index - NDVI) was assessed at the centroid of individual shrubs using high-resolution hyperspectral imagery. Canopy greenness was highest mid-summer, likely reflecting temporal periods when C assimilation rates were highest. Similar to patterns seen in leaf δ(13)C, NDVI was highest in locations that typically experience lowest sensible heat (lowlands and ungrazed). The ability of Cornus drummondii to decouple leaf physiological responses from climate variability and fire frequency is a likely contributor to the increase in cover and frequency of this shrub species in mesic grassland and may be generalizable to other grasslands undergoing woody encroachment. PMID

  5. Effects of seed origin and irrigation on survival and growth of transplanted shrubs

    SciTech Connect

    Winkel, V.K.

    1995-10-01

    Revegetation is difficult in the Mojave Desert due to limited, erratic precipitation and extreme temperatures. Establishing plant cover by transplanting native shrubs is known to be a promising technique, but many questions still remain regarding its use on a large operational scale. A study was initiated on the US Department of Energy Nevada Test Site (NTS) to determine the effects of seed origin and irrigation on survival and growth of transplanted shrubs. Plants of three species (Larrea tridentata, Ambrosia dumosa, and Atriplex canescens) were grown in a greenhouse and hardened outdoors. Plants of all three species were produced from two seed sources: (1) seed collected from the NTS (Mojave Desert), and (2) commercially available seed collected from outside the NTS. One-year-old containerized plants (180 of each species) were transplanted to a site on the NTS and irrigated with two liters of water at one of the following frequencies: (1) at time of planting only, (2) at time of planting and monthly during the first growing season, and (3) at time of planting and twice monthly during the first growing season. After 16 months, survival of all species was generally greater than 80% and was unaffected by irrigation treatments. Survival of fourwing saltbush was significantly greater from local versus non-local seed. Survival of bursage and creosotebush was generally unaffected by seed origin. Shrub volumes regardless of species or seed origin increased during the first growing season, and then decreased during the second growing season. Shrub volumes for fourwing saltbush were significantly greater for shrubs from local versus non-local seed.

  6. Is the WBE model appropriate for semi-arid shrubs subjected to clear cutting?

    PubMed

    Issoufou, Hassane Bil-Assanou; Rambal, Serge; Le Dantec, Valérie; Oï, Monique; Laurent, Jean-Paul; Saadou, Mahamane; Seghieri, Josiane

    2015-02-01

    It is crucial to understand the adaptive mechanisms of woody plants facing periodic drought to assess their vulnerability to the increasing climate variability predicted in the Sahel. Guiera senegalensis J.F.Gmel is a semi-evergreen Combretaceae commonly found in Sahelian rangelands, fallows and crop fields because of its value as an agroforestry species. We compared canopy leafing, and allometric measurements of leaf area, stem area and stem length and their relationships with leaf water potential, stomatal conductance (gs) and soil-to-leaf hydraulic conductance (KS-L), in mature and current-year resprouts of G. senegalensis in Sahelian Niger. In mature shrubs, seasonal drought reduced the ratio of leaf area to cross-sectional stem area (AL : AS), mainly due to leaf shedding. The canopy of the current-year resprouts remained permanently leafed as the shrubs produced leaves and stems continuously, and their AL : AS ratio increased throughout the dry season. Their KS-L increased, whereas gs decreased. West, Brown and Enquist's (WBE) model can thus describe allometric trends in the seasonal life cycle of undisturbed mature shrubs, but not that of resprouts. Annual clear cutting drives allometric scaling relationships away from theoretical WBE predictions in the current-year resprouts, with scaling exponents 2.5 times greater than those of mature shrubs. High KS-L (twice that of mature shrubs) supports this intensive regeneration process. The adaptive strategy described here is probably common to many woody species that have to cope with both severe seasonal drought and regular disturbance over the long term. PMID:25716875

  7. Living with Aliens: Effects of Invasive Shrub Honeysuckles on Avian Nesting

    PubMed Central

    Gleditsch, Jason M.; Carlo, Tomás A.

    2014-01-01

    Invasive species have come to the forefront of conservation biology as a major threat to native biodiversity. Habitats dominated by shrub honeysuckles (Lonicera spp.) in the United States have been characterized as “ecological traps” by ecologists. Here we tested this hypothesis by investigating the effects of shrub honeysuckles on the nesting ecology of native birds in seven study sites in central Pennsylvania, USA. We examined how the abundance of shrub honeysuckles influenced the selection of nesting substrates and habitat for a community of common songbirds, and the parental-care behavior and nestling development of gray catbirds (Dumetella carolinensis). We found that birds had a strong bias towards nesting in honeysuckle shrubs, but not necessarily for nesting in honeysuckle-dominated habitats. Nest predation rates were affected by the density of nests in a habitat, but not by the overall abundance of honeysuckles in such habitats. Honeysuckle abundance in the habitat did show significant effects on some parental-care behavioral parameters: catbirds had higher nest visitation rates and shorter visit lengths in areas of high honeysuckle density. On average, Gray catbirds fed fruit 12%±0.31 s.e. of their nestling-feeding bouts, mostly fruits of shrub honeysuckles. Nestlings in sites with high honeysuckle density also showed higher mass:tarsus ratios, suggesting a good (possibly better) physiological condition of catbird nestlings at the time of fledging. Our study shows that honeysuckle-dominated habitats could have equivocal effects on nesting parameters of common species of native birds. We advise more caution in the widespread denomination of novel plant communities with high densities of honeysuckle as “ecological traps” as effects can be null or positive on native birds in certain localities. PMID:25229633

  8. Ecological benefits of myrmecochory for the endangered chaparral shrub Fremontodendron decumbens (Sterculiaceae).

    PubMed

    Boyd, R S

    2001-02-01

    Fremontodendron decumbens grows in a single county in central California, USA. Prior research showed that its elaiosome-bearing seeds are dispersed by the harvester ant Messor andrei. I tested several hypotheses regarding the positive role of ant-mediated dispersal to F. decumbens: (1) Does ant-mediated seed dispersal facilitate seed escape from rodent predation?; (2) Does ant processing of seeds stimulate germination?; (3) Are ant middens more suitable microsites for seed or seedling survival in unburned chaparral areas?; and (4) Do survival benefits of dispersal occur post-fire in the form of differences in seedling survival probabilities and, if so, why? Results of tests of each hypothesis were: (1) similar percentages of seeds placed on ant middens and under F. decumbens shrub canopies were destroyed by rodents, but seeds from which elaiosomes had been removed were more likely to escape rodent predation; (2) seeds processed by ants did not germinate more readily than seeds removed directly from shrub branches; (3) seedling predation was a major cause of mortality in unburned chaparral on both ant middens and under shrubs, and overall seedling survival did not differ between the two microsites; (4) post-burn seedling survival was significantly greater for seedlings dispersed away from F. decumbens shrub canopies, because dispersed seedlings were both less likely to be killed by predators and more likely to be growing in a gap created by the fire-caused death of an established shrub. I concluded that the major ecological benefit to F. decumbens of ant-mediated seed dispersal was elevated post-fire seedling survival resulting from enhanced escape by dispersed seedlings from both predation and competition. PMID:11222246

  9. Plant-soil interactions promote co-occurrence of three nonnative woody shrubs.

    PubMed

    Kuebbing, Sara E; Classen, Aimée T; Call, Jaime J; Henning, Jeremiah A; Simberloff, Daniel

    2015-08-01

    Ecosystems containing multiple nonnative plant species are common, but mechanisms promoting their co-occurrence are understudied. Plant-soil interactions contribute to the dominance of singleton species in nonnative ranges because many nonnatives experience stronger positive feedbacks relative to co-occurring natives. Plant-soil interactions could impede other nonnatives if an individual nonnative benefits from its soil community to a greater extent than its neighboring nonnatives, as is seen with natives. However, plant-soil interactions could promote nonnative co-occurrence if a nonnative accumulates beneficial soil mutualists that also assist other nonnatives. Here, we use greenhouse and field experiments to ask whether plant-soil interactions (1) promote the codominance of two common nonnative shrubs (Ligustrum sinense and Lonicera maackii) and (2) facilitate the invasion of a less-common nonnative shrub (Rhamnus davurica) in deciduous forests of the southeastern United States. In the greenhouse, we found that two of the nonnatives, L. maackii and R. davurica, performed better in soils conditioned by nonnative shrubs compared to uninvaded forest soils, which. suggests that positive feedbacks among co-occurring nonnative shrubs can promote continued invasion of a site. In both greenhouse and field experiments, we found consistent signals that the codominance of the nonnatives L. sinense and L. maackii may be at least partially explained by the increased growth of L. sinense in L. maackii soils. Overall, significant effects of plant-soil interactions on shrub performance indicate that plant-soil interactions can potentially structure the co-occurrence patterns of these nonnatives. PMID:26405753

  10. Soil Modification by Native Shrubs Boosts Crop Productivity in Sudano-Sahelian Agroforestry System

    NASA Astrophysics Data System (ADS)

    Bogie, N. A.; Bayala, R.; Diedhiou, I.; Ghezzehei, T. A.; Dick, R.

    2014-12-01

    A changing climate along with human and animal population pressure can have a devastating effect on crop yields and food security in the Sudano-Sahel. Agricultural solutions to address soil degradation and crop water stress are needed to combat this increasingly difficult situation. Significant differences in crop success have been observed in peanut and millet grown in association with two native evergreen shrubs Piliostigma reticulatum, and Guiera senegalensis at the sites of Nioro du Rip and Keur Matar, respectively.We investigate how farmers can increase crop productivity by capitalizing on the evolutionary adaptation of native shrubs to the harsh Sudano-Sahelian environment as well as the physical mechanisms at work in the system that can lead to more robust yields. Soil moisture and water potential data were collected during a dry season millet irrigation experiment where stress was imposed in the intercropped system. Despite lower soil moisture content, crops grown in association with shrubs have increased biomass production and a faster development cycle. Hydraulic redistribution is thought to exist in this system and we found diurnal fluctuations in water potential within the intercropped system that increased in magnitude of to 0.4 Mpa per day as the soil dried below 1.0 Mpa during the stress treatment. An isotopic tracer study investigating hydraulic redistribution was carried out by injecting labeled water into shrub roots and sampling shrubs and nearby crops for isotopic analysis of plant water. These findings build on work that was completed in 2004 at the site, but point to lower overall magnitude of diurnal soil water potential fluctuations in dry soils. Using even the limited resources that farmers possess, this agroforestry technique can be expanded over wide swaths of the Sahel.

  11. Cold Brown Dwarfs with WISE: Y Dwarfs and the Field Mass Function

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, J. Davy

    2012-01-01

    Why study Brown Dwarf stars? They re the lowest mass byproducts of star formation.. They provide time capsules across the age of the Galaxy.. They show what low-T(sub eff) atmospheres look like.. They may be some of our closest neighbors in space..WISE is a 40cm Earth-orbiting telescope. There are 211 stars and only 33 brown dwarfs in this volume.. This means that stars outnumber brown dwarfs by a factor of 6:1 currently.. The number of brown dwarfs will continue to increase if:: (a) more nearby Y dwarf candidates are confirmed, or (b) our distances to known Y s are overestimated, or (c) there are colder BDs invisible to WISE..

  12. RE 0044+09: A new K dwarf rapid rotator with a white dwarf companion

    NASA Technical Reports Server (NTRS)

    Kellett, Barry J.; Bromage, Gordon E.; Brown, Alexander; Jeffries, Robin D.; James, David J.; Kilkenny, David; Robb, Russell M.; Wonnacott, David; Lloyd, Christopher; Clayton, C.

    1995-01-01

    We report the discovery of a new K dwarf rapid rotator with a potential white dwarf companion. The white dwarf accounts for over 90% of the observed extreme ultraviolet flux detected from this system. Analysis of ROSAT Wide Field Camera (WFC) and IUE data both suggest a white dwarf temperature of approximately 28,700 K. Optical photometry and the IUE long wavelength prime (LWP) spectrum (with the white dwarf contribution removed) imply that the late-type star has a spectral type of K1-3 V, and a distance of 55 +/- 5 pc. Using this distance, the observed IUE SWP flux, and the best-fit temperature results in a white dwarf radius of 0.0088 solar radius. The estimated white dwarf mass is then approximately 0.91 solar mass; somewhat over-massive compared to field white dwarfs. Optical photometry of the K star reveals a 'spot' modulation period of approximately 10 hr (now observed over 3 yr). However, radial velocity observations have revealed no significant variations. Spectroscopic observations place a low limit on the lithium abundance, but do show rapid rotation with a v sin i of 90 +/- 10 km/s. The K star was detected as a radio source at 3.6 cm (on two occasions) and 6 cm by the Very Large Array (VLA). The most likely evolutionary scenario is that the K star and hot white dwarf from either a wide binary or common proper motion pair with an age of 0.1-0.1 Gyr-consistent with the evolutionary timescale of the white dwarf and the rapid rotation of the K star. However, from the proper motion of the K star, this system does not seem to be associated with any of the known young stellar groups.

  13. Spatial and temporal patterns of water availability in a grass-shrub ecotone and implications for grassland recovery in arid environments

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Encroachment of woody shrubs into historic desert grasslands is a major problem throughout the world. Conversion of grasslands to shrub-dominated systems may result in significant alteration of biogeochemical processes and reduced resource availability in shrub interspaces, making grassland recover...

  14. Water clouds in Y dwarfs and exoplanets

    SciTech Connect

    Morley, Caroline V.; Fortney, Jonathan J.; Marley, Mark S.; Lupu, Roxana; Greene, Tom; Saumon, Didier; Lodders, Katharina

    2014-05-20

    The formation of clouds affects brown dwarf and planetary atmospheres of nearly all effective temperatures. Iron and silicate condense in L dwarf atmospheres and dissipate at the L/T transition. Minor species such as sulfides and salts condense in mid- to late T dwarfs. For brown dwarfs below T {sub eff} ∼ 450 K, water condenses in the upper atmosphere to form ice clouds. Currently, over a dozen objects in this temperature range have been discovered, and few previous theoretical studies have addressed the effect of water clouds on brown dwarf or exoplanetary spectra. Here we present a new grid of models that include the effect of water cloud opacity. We find that they become optically thick in objects below T {sub eff} ∼ 350-375 K. Unlike refractory cloud materials, water-ice particles are significantly nongray absorbers; they predominantly scatter at optical wavelengths through the J band and absorb in the infrared with prominent features, the strongest of which is at 2.8 μm. H{sub 2}O, NH{sub 3}, CH{sub 4}, and H{sub 2} CIA are dominant opacity sources; less abundant species may also be detectable, including the alkalis, H{sub 2}S, and PH{sub 3}. PH{sub 3}, which has been detected in Jupiter, is expected to have a strong signature in the mid-infrared at 4.3 μm in Y dwarfs around T {sub eff} = 450 K; if disequilibrium chemistry increases the abundance of PH{sub 3}, it may be detectable over a wider effective temperature range than models predict. We show results incorporating disequilibrium nitrogen and carbon chemistry and predict signatures of low gravity in planetary mass objects. Finally, we make predictions for the observability of Y dwarfs and planets with existing and future instruments, including the James Webb Space Telescope and Gemini Planet Imager.

  15. Water Clouds in Y Dwarfs and Exoplanets

    NASA Astrophysics Data System (ADS)

    Morley, Caroline V.; Marley, Mark S.; Fortney, Jonathan J.; Lupu, Roxana; Saumon, Didier; Greene, Tom; Lodders, Katharina

    2014-05-01

    The formation of clouds affects brown dwarf and planetary atmospheres of nearly all effective temperatures. Iron and silicate condense in L dwarf atmospheres and dissipate at the L/T transition. Minor species such as sulfides and salts condense in mid- to late T dwarfs. For brown dwarfs below T eff ~ 450 K, water condenses in the upper atmosphere to form ice clouds. Currently, over a dozen objects in this temperature range have been discovered, and few previous theoretical studies have addressed the effect of water clouds on brown dwarf or exoplanetary spectra. Here we present a new grid of models that include the effect of water cloud opacity. We find that they become optically thick in objects below T eff ~ 350-375 K. Unlike refractory cloud materials, water-ice particles are significantly nongray absorbers; they predominantly scatter at optical wavelengths through the J band and absorb in the infrared with prominent features, the strongest of which is at 2.8 μm. H2O, NH3, CH4, and H2 CIA are dominant opacity sources; less abundant species may also be detectable, including the alkalis, H2S, and PH3. PH3, which has been detected in Jupiter, is expected to have a strong signature in the mid-infrared at 4.3 μm in Y dwarfs around T eff = 450 K if disequilibrium chemistry increases the abundance of PH3, it may be detectable over a wider effective temperature range than models predict. We show results incorporating disequilibrium nitrogen and carbon chemistry and predict signatures of low gravity in planetary mass objects. Finally, we make predictions for the observability of Y dwarfs and planets with existing and future instruments, including the James Webb Space Telescope and Gemini Planet Imager.

  16. Tracking star formation in dwarf cluster galaxies

    NASA Astrophysics Data System (ADS)

    Rude, Cody Millard

    The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of star formation in cluster dwarf galaxies by measuring and comparing the r- and u-band luminosity functions of 15 low redshift Abell galaxy clusters using archival data from the Canada-France-Hawaii Telescope (CFHT). Luminosity functions, dwarf-to-giant ratios, and blue fractions are measured in four cluster-centric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. The outer region of the cluster sample shows an increase in the faint-end slope of the u-band luminosity function relative to the r-band, indicating star formation in dwarf galaxies. The blue fraction for dwarf galaxies steadily rises with increasing cluster-centric radii. The change in the blue fraction of giant galaxies also increases, but at a lower rate. Additionally, the inner regions of clusters ranging from 0.185 < z < 0.7 from the "Cluster Lensing and Supernova survey with Hubble (CLASH)" are used to generate blue- and red-band luminosity functions, dwarf-to-giant ratios, and blue fractions. Comparisons of the inner region of the CLASH and CFHT clusters show an increase in the blue fraction of dwarf galaxies with redshift that is not present in giant galaxies.

  17. Size-related change in Nitraria sphaerocarpa patches shifts the shrub-annual interaction in an arid desert, northwestern China

    NASA Astrophysics Data System (ADS)

    Zhang, Gefei; Yang, Qiyue; Wang, Xiaofen; Zhao, Wenzhi

    2015-11-01

    In arid and semi-arid ecosystems, the effect of shrubs on their understory plants has been frequently reported. Many previous studies have shown that both facilitation and competition act simultaneously, and their balance changes in response to spatial or temporal variations in environmental stresses. Yet, we know little about how the interaction varies between shrubs and their understory plants in vegetation patches with different characteristics. Here, an empirical investigation was conducted in Hexi desert region of northwest China, to evaluate how the net effect of Nitraria sphaerocarpa shrubs on the herbaceous species varies across different sizes of N. sphaerocarpa patches. Our study showed that herbaceous species perform better on small shrub patches. But the magnitude of this facilitative effect decreased with increasing patch size, and finally shifted to interference in large patches. The results indicated that these negative shifts in plant interactions were not clearly related to 'shrub-island effect' in terms of nutrient accumulation or soil properties improvement, but may be explained by the variation in other abiotic factors, such as soil moisture and available light. Changes in root distribution and canopy structure of N. sphaerocarpa shrubs with the increase of patch size seem to also partly explain the variation in shrub-understory species interactions, as a result of increased above- and below-ground niche overlaps.

  18. Detecting the Differences in Responses of Stomatal Conductance to Moisture Stresses between Deciduous Shrubs and Artemisia Subshrubs

    PubMed Central

    Gao, Qiong; Yu, Mei; Zhou, Chan

    2013-01-01

    Shrubs and subshrubs can tolerate wider ranges of moisture stresses in both soil and air than other plant life forms, and thus represent greater nonlinearity and uncertainty in ecosystem physiology. The objectives of this paper are to model shrub/subshrub stomatal conductance by synthesizing the field leaf gas exchanges data of 24 species in China, in order to detect the differences between deciduous shrubs and Artemisia subshrubs in their responses of stomatal conductance to changes in the moisture stresses. We revised a model of stomatal conductance by incorporating the tradeoff between xylem hydraulic efficiency and cavitation loss risk. We then fit the model at the three hierarchical levels: global (pooling all data as a single group), three functional groups (deciduous non-legume shrubs, deciduous legume shrubs, and subshrubs in Artemisia genus), and individual observations (species × sites). Bayesian inference with Markov Chain Monte Carlo method was applied to obtain the model parameters at the three levels. We found that the model at the level of functional groups is a significant improvement over that at the global level, indicating the significant differences in the stomatal behavior among the three functional groups. The differences in tolerance and sensitivities to changes in moisture stresses are the most evident between the shrubs and the subshrubs: The two shrub groups can tolerate much higher soil water stress than the subshrubs. The analysis at the observation level is also a significant improvement over that at the functional group level, indicating great variations within each group. Our analysis offered a clue for the equivocal issue of shrub encroachment into grasslands: While the invasion by the shrubs may be irreversible, the dominance of subshrubs, due to their lower resistance and tolerance to moisture stresses, may be put down by appropriate grassland management. PMID:24386351

  19. Rapid carbon turnover beneath shrub and tree vegetation is associated with low soil carbon stocks at a subarctic treeline.

    PubMed

    Parker, Thomas C; Subke, Jens-Arne; Wookey, Philip A

    2015-05-01

    Climate warming at high northern latitudes has caused substantial increases in plant productivity of tundra vegetation and an expansion of the range of deciduous shrub species. However significant the increase in carbon (C) contained within above-ground shrub biomass, it is modest in comparison with the amount of C stored in the soil in tundra ecosystems. Here, we use a 'space-for-time' approach to test the hypothesis that a shift from lower-productivity tundra heath to higher-productivity deciduous shrub vegetation in the sub-Arctic may lead to a loss of soil C that out-weighs the increase in above-ground shrub biomass. We further hypothesize that a shift from ericoid to ectomycorrhizal systems coincident with this vegetation change provides a mechanism for the loss of soil C. We sampled soil C stocks, soil surface CO2 flux rates and fungal growth rates along replicated natural transitions from birch forest (Betula pubescens), through deciduous shrub tundra (Betula nana) to tundra heaths (Empetrum nigrum) near Abisko, Swedish Lapland. We demonstrate that organic horizon soil organic C (SOCorg ) is significantly lower at shrub (2.98 ± 0.48 kg m(-2) ) and forest (2.04 ± 0.25 kg m(-2) ) plots than at heath plots (7.03 ± 0.79 kg m(-2) ). Shrub vegetation had the highest respiration rates, suggesting that despite higher rates of C assimilation, C turnover was also very high and less C is sequestered in the ecosystem. Growth rates of fungal hyphae increased across the transition from heath to shrub, suggesting that the action of ectomycorrhizal symbionts in the scavenging of organically bound nutrients is an important pathway by which soil C is made available to microbial degradation. The expansion of deciduous shrubs onto potentially vulnerable arctic soils with large stores of C could therefore represent a significant positive feedback to the climate system. PMID:25367088

  20. Rapid carbon turnover beneath shrub and tree vegetation is associated with low soil carbon stocks at a subarctic treeline

    PubMed Central

    Parker, Thomas C; Subke, Jens-Arne; Wookey, Philip A

    2015-01-01

    Climate warming at high northern latitudes has caused substantial increases in plant productivity of tundra vegetation and an expansion of the range of deciduous shrub species. However significant the increase in carbon (C) contained within above-ground shrub biomass, it is modest in comparison with the amount of C stored in the soil in tundra ecosystems. Here, we use a ‘space-for-time’ approach to test the hypothesis that a shift from lower-productivity tundra heath to higher-productivity deciduous shrub vegetation in the sub-Arctic may lead to a loss of soil C that out-weighs the increase in above-ground shrub biomass. We further hypothesize that a shift from ericoid to ectomycorrhizal systems coincident with this vegetation change provides a mechanism for the loss of soil C. We sampled soil C stocks, soil surface CO2 flux rates and fungal growth rates along replicated natural transitions from birch forest (Betula pubescens), through deciduous shrub tundra (Betula nana) to tundra heaths (Empetrum nigrum) near Abisko, Swedish Lapland. We demonstrate that organic horizon soil organic C (SOCorg) is significantly lower at shrub (2.98 ± 0.48 kg m−2) and forest (2.04 ± 0.25 kg m−2) plots than at heath plots (7.03 ± 0.79 kg m−2). Shrub vegetation had the highest respiration rates, suggesting that despite higher rates of C assimilation, C turnover was also very high and less C is sequestered in the ecosystem. Growth rates of fungal hyphae increased across the transition from heath to shrub, suggesting that the action of ectomycorrhizal symbionts in the scavenging of organically bound nutrients is an important pathway by which soil C is made available to microbial degradation. The expansion of deciduous shrubs onto potentially vulnerable arctic soils with large stores of C could therefore represent a significant positive feedback to the climate system. PMID:25367088

  1. White Dwarfs in the GALEX Survey

    NASA Technical Reports Server (NTRS)

    Kawka, Adela; Vennes, Stephane

    2007-01-01

    We have cross-correlated the 2dF QSO Redshift Survey (2QZ) white dwarf catalog with the GALEX 2nd Data Release and the Sloan Digital Sky Survey (SDSS) data release 5 to obtain ultraviolet photometry (FUV, NUV) for approximately 700 objects and optical photometry (ugriz) for approximately 800 objects. We have compared the optical-ultraviolet colors to synthetic white dwarf colors to obtain temperature estimates for approximately 250 of these objects. These white dwarfs have effective temperatures ranging from 10 000 K (cooling age of about 1Gyr) up to about 40000 K (cooling age of about 3 Myrs), with a few that have even higher temperatures. We found that to distinguish white dwarfs from other stellar luminosity classes both optical and ultraviolet colors are necessary, in particular for the hotter objects where there is contamination from B and 0 main-sequence stars. Using this sample we build a luminosity function for the DA white dwarfs with Mv < 12 mag.

  2. White dwarf stars with carbon atmospheres.

    PubMed

    Dufour, P; Liebert, J; Fontaine, G; Behara, N

    2007-11-22

    White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch. PMID:18033290

  3. Observing Dwarf Galaxies in the Local Universe

    NASA Astrophysics Data System (ADS)

    Simon, Joshua

    2016-03-01

    Dwarf galaxies in the Local Group are key probes of both dark matter and galaxy formation. They are the smallest, oldest, most dark matter-dominated, and least chemically enriched stellar systems currently known. However, despite two decades of major computational, theoretical, and observational advances in this field, we are still working toward a complete understanding of star and galaxy formation at the faint end of the galaxy luminosity function. In the last year, large sky surveys such as the Dark Energy Survey and Pan-STARRS have made an unprecedented series of discoveries, nearly doubling the population of Milky Way satellite galaxies that was known at the start of 2015. This increase in the number of nearby dwarfs may significantly improve the sensitivity of searches for dark matter annihilation radiation. Many of these new dwarfs are likely to have originated as satellites of the Magellanic Clouds, providing a unique opportunity to study the effect of galactic environment on the formation of the faintest dwarfs. I will provide an overview of recent discoveries and how they fit in to the previously known population of nearby dwarf galaxies, highlighting a few of the most interesting objects from the perspective of dark matter and stellar nucleosynthesis.

  4. Gravitational Interactions of White Dwarf Double Stars

    NASA Astrophysics Data System (ADS)

    McKeough, James; Robinson, Chloe; Ortiz, Bridget; Hira, Ajit

    2016-03-01

    In the light of the possible role of White Dwarf stars as progenitors of Type Ia supernovas, we present computational simulations of some astrophysical phenomena associated with a study of gravitationally-bound binary stars, composed of at least one white dwarf star. Of particular interest to astrophysicists are the conditions inside a white dwarf star in the time frame leading up to its explosive end as a Type Ia supernova, for an understanding of the massive stellar explosions. In addition, the studies of the evolution of white dwarfs could serve as promising probes of theories of gravitation. We developed FORTRAN computer programs to implement our models for white dwarfs and other stars. These codes allow for different sizes and masses of stars. Simulations were done in the mass interval from 0.1 to 2.5 solar masses. Our goal was to obtain both atmospheric and orbital parameters. The computational results thus obtained are compared with relevant observational data. The data are further analyzed to identify trends in terms of sizes and masses of stars. We will extend our computational studies to blue giant and red giant stars in the future. Funding from National Science Foundation.

  5. Discovery of a cool brown dwarf

    NASA Astrophysics Data System (ADS)

    Nakajima, T.; Oppenheimer, B. R.; Kulkarni, S. R.; Golimowski, D. A.; Matthews, K.; Durrance, S. T.

    1995-11-01

    BROWN dwarfs are starlike objects with masses less than 0.08 times that of the Sun, which are unable to sustain hydrogen fusion in their interiors1-4. They are very hard to detect, as most of the energy of gravitational contraction is radiated away within ~108 yr, leaving only a very low residual luminosity. Accordingly, almost all searches for brown dwarfs have been directed towards clusters of young stars-a strategy that has recently proved successful5,6. But there are only modest observable differences between young brown dwarfs and very lowmass stars, making it difficult to identify the former without appealing to sophisticated models7. Older brown dwarfs should have a more distinctive appearance, and if they are companions to nearby stars, their luminosity can be determined unambiguously. Here we report the discovery of a probable companion to the nearby star G1229, with no more than onetenth the luminosity of the least luminous hydro-gen-burning star. We conclude that the companion, G1229B, is a brown dwarf with a temperature of less than 1,200 K, and a mass ~20-50 times that of Jupiter.

  6. T Dwarfs and the Substellar Mass Function

    NASA Astrophysics Data System (ADS)

    Burgasser, A. J.; 2MASS Rare Objects Team

    2001-12-01

    The recent sky surveys 2MASS, SDSS, and DENIS have unveiled a vast population of substellar objects in the Solar Neighborhood, and have appended two new spectral classes onto the familiar MK system: L and T dwarfs. With hundreds of these objects now known, we can address one of the fundamental questions that initiated the search for brown dwarfs in the first place - what is their contribution to the Galactic mass budget? I present results on the field substellar mass function, based on a sample of T dwarfs identified in the 2MASS survey. Using the evolutionary models of Burrows et al. and a Monte Carlo simulation of the Solar Neighborhood, I show that the number of T dwarfs identified in this sample is consistent with a shallow power-law mass function, 0.5 < α < 1.0, similar to values derived from young clusters but inconsistent with previous estimates in the field. I discuss possible reasons for this discrepancy, and ways in which we may improve our census of nearby brown dwarfs. Support for this work was provided by NASA through a Hubble Fellowship grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incoporated, under NASA contract NAS5-26555.

  7. The Potential of White Dwarf Cosmochronology

    NASA Astrophysics Data System (ADS)

    Fontaine, G.; Brassard, P.; Bergeron, P.

    2001-04-01

    In the light of recent significant progress on both the observational and theoretical fronts, we review the status of white dwarf stars as cosmochronometers. These objects represent the end products of stellar evolution for the vast majority of stars and, as such, can be used to constrain the ages of various populations of evolved stars in the Galaxy. For example, the oldest white dwarfs in the solar neighborhood (the remnants of the very first generation of intermediate-mass stars in the Galactic disk) are still visible and can be used, in conjunction with cooling theory, to estimate the age of the disk. More recent observations suggest the tantalizing possibility that a population of very old white dwarfs inhabits the Galactic halo. Such a population may contribute significantly to baryonic ``dark'' matter in the Milky Way and may be used to obtain an independent estimate of the age of the halo. In addition, white dwarf cosmochronology is likely to play a very significant role in the coming era of giant 8-10 m telescopes when faint white dwarf populations should be routinely discovered and studied in open and globular clusters. Based, in part, on the C. S. Beals Lecture presented by G. Fontaine at the Annual General Meeting of the Canadian Astronomical Society held in Vancouver (2000 May).

  8. THE MASSES OF POPULATION II WHITE DWARFS

    SciTech Connect

    Kalirai, Jason S.; Davis, D. Saul; Richer, Harvey B.; Bergeron, P.; Catelan, Marcio; Hansen, Brad M. S.; Michael Rich, R. E-mail: sdavis@astro.ubc.c E-mail: bergeron@astro.umontreal.c E-mail: hansen@astro.ucla.ed

    2009-11-01

    Globular star clusters are among the first stellar populations to have formed in the Milky Way, and thus only a small sliver of their initial spectrum of stellar types are still burning hydrogen on the main sequence today. Almost all of the stars born with more mass than 0.8 M{sub sun} have evolved to form the white dwarf cooling sequence of these systems, and the distribution and properties of these remnants uniquely holds clues related to the nature of the now evolved progenitor stars. With ultra-deep Hubble Space Telescope imaging observations, rich white dwarf populations of four nearby Milky Way globular clusters have recently been uncovered, and are found to extend impressive 5-8 mag in the faint-blue region of the Hertzsprung-Russell diagram. In this paper, we characterize the properties of these population II remnants by presenting the first direct mass measurements of individual white dwarfs near the tip of the cooling sequence in the nearest of the Milky Way globulars, M4. Based on Gemini/GMOS and Keck/LRIS multiobject spectroscopic observations, our results indicate that 0.8 M{sub sun} population II main-sequence stars evolving today form 0.53 +- 0.01 M{sub sun} white dwarfs. We discuss the implications of this result as it relates to our understanding of stellar structure and evolution of population II stars and for the age of the Galactic halo, as measured with white dwarf cooling theory.

  9. Are All Dwarf Carbon Stars Binary?

    NASA Astrophysics Data System (ADS)

    Farihi, Jay; Harris, Hugh; Subasavage, John; Bergfors, Carolina; Green, Paul; Gansicke, Boris

    2014-08-01

    The origin of dwarf carbon stars is a persistent astrophysical curiosity dating back to 1977. Only giant stars dredge up interior carbon, and hence the discovery of an unevolved dwarf star with C/O >1 was a big surprise. Astronomers are no closer to understanding these rare and spectrally peculiar stars 37 years later(!). The bulk of dwarf carbon stars show no sign of an evolved companion necessary to account for their externally polluted atmospheres. These stars are sensitive tracers of Galactic chemical evolution and star formation, and provide strong constraints on the potential for carbon-dominated (single star) planetary systems. We propose to conclusively validate or refute the hypothetical binary nature of dwarf carbon stars, and hence their chemical and physical formation channel(s). For all binaries, we will initially constrain and eventually measure orbital periods. By determining their physical separation during the previous epoch of mass transfer, we will distinguish between the Roche lobe overflow and wind capture models for the creation of carbon dwarfs.

  10. Keck Imaging of Binary L Dwarfs.

    PubMed

    Koerner; Kirkpatrick; McElwain; Bonaventura

    1999-11-20

    We present Keck near-infrared imaging of three binary L dwarf systems, all of which are likely to be substellar. Two are lithium dwarfs, and a third exhibits an L7 spectral type, making it the coolest binary known to date. All have component flux ratios near 1 and projected physical separations between 5 and 10 AU, assuming distances of 18-26 pc from recent measurements of trigonometric parallax. These surprisingly similar binaries represent the sole detections of companions in 10 L dwarf systems that were analyzed in the preliminary phase of a much larger dual-epoch imaging survey. The detection rate prompts us to speculate that binary companions to L dwarfs are common, that similar-mass systems predominate, and that their distribution peaks at radial distances in accord both with M dwarf binaries and with the radial location of Jovian planets in our own solar system. To fully establish these conjectures against doubts raised by biases inherent in this small preliminary survey, however, will require quantitative analysis of a larger volume-limited sample that has been observed with high resolution and dynamic range. PMID:10534453

  11. Identifying uncertainties for quantifying shrub encroachment in Northern Alaska using LiDAR

    NASA Astrophysics Data System (ADS)

    Magney, T. S.; Vierling, L. A.; Eitel, J.; Greaves, H.; Boelman, N.; Griffin, K. L.; Praeger, C.

    2013-12-01

    Climatic warming in the tundra biome has occurred at rates two to three times higher than the global average during the last 150 years, and is continuing at an unprecedented pace. Over the past few decades, Arctic tundra ecosystems have responded to climatic warming via shifts in vegetation composition and increased woody biomass. The resulting increases in size, abundance, and range of deciduous shrubs has affected ecosystem processes, causing shifts in carbon (C) and nitrogen (N) pools that could result in both positive and negative climate feedbacks. In Northern Alaska, the expansion of shrubs has increased by roughly 16% in land area since 1950; however, progress towards quantifying the impact of shrub expansion on biogeochemical cycling at regional scales is limited. Satellite remote sensing of the arctic has been proposed by many as a key tool to better quantify change and ecosystem responses to a warming tundra over large spatial extents, but has primarily only been inferred from multi-year trends of the Normalized Difference Vegetation Index (NDVI). These, and other passive remote sensing studies, have been complicated by the high cloud cover, low solar angle, and low levels of sunlight inherent to the arctic. Additionally, many such studies lack necessary ground validation, resulting in high levels of error, uncertainty, and misinterpretation of results. Improved techniques are therefore needed to quantify and scale how the dramatic biophysical and ecological changes occurring in arctic tundra ecosystems will affect C and N pools at local and regional scales. To address these problems, we tested the ability of active remote sensing (terrestrial (TLS) and airborne lidar (ALS)) at multiple spatial resolutions to better quantify aboveground shrub biomass, vertical, and horizontal canopy cover. Uncertainties in the ability of ALS to quantify shrub allometrics was determined using regression analysis with a stepwise selection procedure to determine the ideal

  12. Partitioning Evapotranspiration to Illustrate the Effects of Shrub Competition and Soil Water on Ecosystem State Transitions

    NASA Astrophysics Data System (ADS)

    Schreiner-McGraw, A.; Vivoni, E. R.; Browning, D. M.

    2015-12-01

    Woody-plant encroachment over the last 100 years has shaped the deserts in the southwestern United States. In this work, we examine the process of woody-plant encroachment in the Chihuahuan Desert at the Jornada Experimental Range in New Mexico. Our hypothesis is that differences in shrub phenology among mesquite, tarbush, and creosotebush relative to the seasonal timing of plant available water have governed the historic shifts in shrub-dominated states. This work tests that hypothesis using data obtained from a dense instrument network along with aerial images and phenological measurements. We installed sap flow sensors on 9 shrubs, 3 each of mesquite, tarbush, and creosotebush, to measure seasonal and interspecies variations in transpiration (T). These sensors are located within the footprint of an eddy covariance tower used to measure ecosystem-scale evapotranspiration (ET). We use a network of soil moisture sensors as well as a cosmic-ray sensing soil moisture sensor to measure soil water and relate this to overall ET and species-level transpiration. We partitioned ET into its components, bare soil evaporation (E) and T, using an empirical approach based on soil temperature and soil moisture. For the pre-monsoon and monsoon seasons of 2013 (2014), we found that T/ET was 0.26 (0.24) and 0.70 (0.71), respectively. We use a hydrologic model to partition the ET during this period to compare to the observations from the empirical approach. We further partitioned T into shrub components using sapflow data. We then analyze the activity of each species throughout the year and how they compete for water by examining time series of rainfall, soil moisture, soil temperature, ET, shrub phenological data and vegetation greenness. Our evaluations provide a first look into how plant phenology can impact shrub competition and the implications this has on short-term soil water availability and ET as well as long-term state dynamics in mixed shrublands of the Chihuahuan Desert.

  13. Phosphorus biogeochemistry in alpine ecosystems of the Northern Caucasus

    NASA Astrophysics Data System (ADS)

    Makarov, Mikhail; Vaganov, Ivan

    2010-05-01

    The study of phosphorus biogeochemistry in an alpine landscape of the Northern Caucasus has been spent in the Teberda Biosphere Reserve on the experimental plot with total area of 3.9 ha (150 m wide, 260 m long, altitude differences 100 m) and on the plots of long-term experiment on studying of nutrients application influence on alpine ecosystems located in the eastern slope of Mt. Malaya Khatipara. Results of studying of phosphorus concentrations and store in alpine soils and plant phytomass indicated differences for diverse alpine ecosystems along geochemical gradient. Although biological accumulation of phosphorus in the upper part of soil profiles was general characteristic of all ecosystems, it is shown that geochemical redistribution of phosphorus from eluvial to accumulative parts of a landscape is the main thing in the course of phosphorus and its labile compounds accumulation in soils of the alpine communities of accumulative habitats. In turn, biological accumulation of phosphorus in soils of different alpine ecosystems redistributes an element in a soil profile with different intensity depending on capacity of biological cycle. The biological factor causes also prevalence of organic compounds among of phosphorus migrating forms in modern soils and in a landscape. As inorganic (0.01-0.02 mg/L) as organic (up to 0.17 mg/L) phosphorus leaching in the eluvial soils was from 2 to 5 times lower compared with soils of accumulative positions in a landscape. Soil phosphorus fractionation on organic and inorganic compounds of different geochemical mobility and biological availability indicated differences of phosphorus state for diverse alpine ecosystems along the experimental plot. The minor proportion of 0.5 M NaHCO3 (pH 8.5) extractable labile organic and inorganic phosphates was general characteristic of all studied soils, although especially low proportion of labile phosphorus compounds was typical for lichen heath soil, while soils of snow-bed communities

  14. Red Dwarfs and the End of the Main Sequence

    NASA Astrophysics Data System (ADS)

    Adams, F. C.; Graves, G. J. M.; Laughlin, G.

    2004-12-01

    This paper celebrates the contributions of Peter Bodenheimer to our understanding of stellar evolution by focusing on the long term development of red dwarf stars. We show that these diminutive stellar objects remain convective over most of their lives, they continue to burn hydrogen for trillions of years, and they do not experience red giant phases in their old age. Instead, red dwarfs turn into blue dwarfs and finally white dwarfs. This work shows (in part) why larger stars do become red giants.

  15. A Search for Fine Wines: Discovering Close Red Dwarf-White Dwarf Binaries

    NASA Astrophysics Data System (ADS)

    Boyd, Mark; Finch, C. T.; Hambly, N. C.; Henry, T. J.; Jao, W.; Riedel, A. R.; Subasavage, J. P.; Winters, J. G.; RECONS

    2012-01-01

    Like fine wines, stars come in both red and white varieties. Here we present initial results of the Fine Wines Project that targets red dwarf-white dwarf pairs. The two scientific goals of Fine Wines are (1) to develop methods to estimate ages for red dwarfs based on the cooling ages of the white dwarfs, and (2) to identify suitable pairs for dynamical mass determinations of white dwarfs to probe their interior structures. Here we focus on the search for Fine Wines, including sample selection, elimination of false positives, and initial reconnaissance. The sample was extracted via color-color plots from a pool of more than 30,000 proper motion systems examined during the SuperCOSMOS-RECONS (SCR) and UCAC3 Proper Motion (UPM) surveys. The initial sample of 75 best candidates is being observed for BVRI photometry and 3500-9500 A spectroscopy to confirm whether or not the systems are red dwarf-white dwarf pairs. Early results indicate that roughly 50% of the candidates selected are indeed Fine Wine systems. This effort is supported by the NSF through grant AST 09-08402 and via observations made possible by the SMARTS Consortium.

  16. THE LINK BETWEEN PLANETARY SYSTEMS, DUSTY WHITE DWARFS, AND METAL-POLLUTED WHITE DWARFS

    SciTech Connect

    Debes, John H.; Walsh, Kevin J.; Stark, Christopher

    2012-03-10

    It has long been suspected that metal-polluted white dwarfs (types DAZ, DBZ, and DZ) and white dwarfs with dusty disks possess planetary systems, but a specific physical mechanism by which planetesimals are perturbed close to a white dwarf has not yet been fully posited. In this paper, we demonstrate that mass loss from a central star during post-main-sequence evolution can sweep planetesimals into interior mean motion resonances with a single giant planet. These planetesimals are slowly removed through chaotic excursions of eccentricity that in time create radial orbits capable of tidally disrupting the planetesimal. Numerical N-body simulations of the solar system show that a sufficient number of planetesimals are perturbed to explain white dwarfs with both dust and metal pollution, provided other white dwarfs have more massive relic asteroid belts. Our scenario requires only one Jupiter-sized planet and a sufficient number of asteroids near its 2:1 interior mean motion resonance. Finally, we show that once a planetesimal is perturbed into a tidal crossing orbit, it will become disrupted after the first pass of the white dwarf, where a highly eccentric stream of debris forms the main reservoir for dust-producing collisions. These simulations, in concert with observations of white dwarfs, place interesting limits on the frequency of planetary systems around main-sequence stars, the frequency of planetesimal belts, and the probability that dust may obscure future terrestrial planet finding missions.

  17. The White Dwarf Binary Pathways Survey I: A sample of FGK stars with white dwarf companions

    NASA Astrophysics Data System (ADS)

    Parsons, S. G.; Rebassa-Mansergas, A.; Schreiber, M. R.; Gänsicke, B. T.; Zorotovic, M.; Ren, J. J.

    2016-08-01

    The number of spatially unresolved white dwarf plus main-sequence star binaries has increased rapidly in the last decade, jumping from only ˜30 in 2003 to over 3000. However, in the majority of known systems the companion to the white dwarf is a low mass M dwarf, since these are relatively easy to identify from optical colours and spectra. White dwarfs with more massive FGK type companions have remained elusive due to the large difference in optical brightness between the two stars. In this paper we identify 934 main-sequence FGK stars from the Radial Velocity Experiment (RAVE) survey in the southern hemisphere and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey in the northern hemisphere, that show excess flux at ultraviolet wavelengths which we interpret as the likely presence of a white dwarf companion. We obtained Hubble Space Telescope ultraviolet spectra for nine systems which confirmed that the excess is indeed caused, in all cases, by a hot compact companion, eight being white dwarfs and one a hot subdwarf or pre-helium white dwarf, demonstrating that this sample is very clean. We also address the potential of this sample to test binary evolution models and type Ia supernovae formation channels.

  18. Alpine exhumation of the central Cantabrian Mountains, Northwest Spain

    NASA Astrophysics Data System (ADS)

    Fillon, C.; Pedreira, D.; Beek, P. A.; Huismans, R. S.; Barbero, L.; Pulgar, J. A.

    2016-02-01

    The Cantabrian Mountains extend along the Atlantic coast of northern Spain and are known to have experienced an Alpine phase of deformation, reactivating well-expressed Variscan structures. They form the westward continuation of the Pyrenean range and were similarly uplifted consequently to the convergence between the Iberian and European plates. Nevertheless, due to the scarcity of syntectonic sediments and structural markers in a large outcrop of Variscan basement, little is known about the precise timing and amount of the Alpine exhumation phase in the Cantabrian Mountains. We present a new low-temperature thermochronology data set, composed of nine apatite fission track (AFT) and six zircon (U-Th)/He (ZHe) ages, sampled along structurally well-constrained N-S profiles through the central part of the Cantabrian Mountains and complemented by 3-D thermokinematic modeling. The occurrence of Eocene-Oligocene AFT and ZHe ages in the center of the profiles allows us to frame the period of Alpine exhumation from 39 to 29 Ma, at a rate of 0.24-0.3 km Myr-1. Moreover, the reset ZHe ages imply significant burial of the samples, by up to 8-10 km in the center of the range. Therefore, the Alpine exhumation phase was significant, and synchronous to the main phase of exhumation in the central Pyrenees, although exhumation rates were an order of magnitude lower. Three-dimensional thermokinematic modeling of the data confirms the timing of uplift of this area, but its resolution is limited by the relatively small number of reset ages over a large area.

  19. Identifying key conservation threats to Alpine birds through expert knowledge.

    PubMed

    Chamberlain, Dan E; Pedrini, Paolo; Brambilla, Mattia; Rolando, Antonio; Girardello, Marco

    2016-01-01

    Alpine biodiversity is subject to a range of increasing threats, but the scarcity of data for many taxa means that it is difficult to assess the level and likely future impact of a given threat. Expert opinion can be a useful tool to address knowledge gaps in the absence of adequate data. Experts with experience in Alpine ecology were approached to rank threat levels for 69 Alpine bird species over the next 50 years for the whole European Alps in relation to ten categories: land abandonment, climate change, renewable energy, fire, forestry practices, grazing practices, hunting, leisure, mining and urbanization. There was a high degree of concordance in ranking of perceived threats among experts for most threat categories. The major overall perceived threats to Alpine birds identified through expert knowledge were land abandonment, urbanization, leisure and forestry, although other perceived threats were ranked highly for particular species groups (renewable energy and hunting for raptors, hunting for gamebirds). For groups of species defined according to their breeding habitat, open habitat species and treeline species were perceived as the most threatened. A spatial risk assessment tool based on summed scores for the whole community showed threat levels were highest for bird communities of the northern and western Alps. Development of the approaches given in this paper, including addressing biases in the selection of experts and adopting a more detailed ranking procedure, could prove useful in the future in identifying future threats, and in carrying out risk assessments based on levels of threat to the whole bird community. PMID:26966659

  20. Scenario Calculations for Alpine Snow Cover and Runoff

    NASA Astrophysics Data System (ADS)

    Bavay, M.; Lehning, M.; Jonas, T.; Loewe, H.

    2009-04-01

    The snow cover in the Alps is heavily affected by climate change. Recent data show that at altitudes below 1200 m a.s.l. a time-continuous winter snow cover is becoming an exception rather than the rule. This will also change the timing and characteristics of river runoff in Alpine catchments. A numerical study of the impact of climate change on snow cover and runoff has been conducted using ALPINE3D, a model for the high resolution simulation of alpine surface processes, in particular snow, soil and vegetation processes. We present here an assessment of future snow and runoff in two Alpine catchments, the larger Inn catchment (1945 km2) and the smaller Dischma catchment (43 km2), based on two common climate change scenarios (IPCC A2 and B2). The predicted changes in snow and runoff are drastic. While the current climate still supports permanent snow and ice at the altitudes of the highest peaks above 3000 m a.s.l., this zone will disappear under the future climate. The changes in snow cover can be summarized by approximately shifting the elevation zones down by 900 m. The corresponding changes in runoff are also severe: While the current climate shows a significant contribution from snow melt until mid to late summer, future climate will feature a much narrower snow melt runoff peak in spring. A further observation is that heavy precipitation events in the fall will change from mainly snow to mainly rain and will have a higher probability to produce flooding.

  1. Identifying key conservation threats to Alpine birds through expert knowledge

    PubMed Central

    Pedrini, Paolo; Brambilla, Mattia; Rolando, Antonio; Girardello, Marco

    2016-01-01

    Alpine biodiversity is subject to a range of increasing threats, but the scarcity of data for many taxa means that it is difficult to assess the level and likely future impact of a given threat. Expert opinion can be a useful tool to address knowledge gaps in the absence of adequate data. Experts with experience in Alpine ecology were approached to rank threat levels for 69 Alpine bird species over the next 50 years for the whole European Alps in relation to ten categories: land abandonment, climate change, renewable energy, fire, forestry practices, grazing practices, hunting, leisure, mining and urbanization. There was a high degree of concordance in ranking of perceived threats among experts for most threat categories. The major overall perceived threats to Alpine birds identified through expert knowledge were land abandonment, urbanization, leisure and forestry, although other perceived threats were ranked highly for particular species groups (renewable energy and hunting for raptors, hunting for gamebirds). For groups of species defined according to their breeding habitat, open habitat species and treeline species were perceived as the most threatened. A spatial risk assessment tool based on summed scores for the whole community showed threat levels were highest for bird communities of the northern and western Alps. Development of the approaches given in this paper, including addressing biases in the selection of experts and adopting a more detailed ranking procedure, could prove useful in the future in identifying future threats, and in carrying out risk assessments based on levels of threat to the whole bird community. PMID:26966659

  2. HAWAII QUASAR AND T DWARF SURVEY. I. METHOD AND DISCOVERY OF FAINT FIELD ULTRACOOL DWARFS ,

    SciTech Connect

    Kakazu, Yuko; Capak, Peter L.; Hu, Esther M.; Liu, Michael C.; Wainscoat, Richard J.; Wang Weihao

    2010-11-01

    The Hawaii Quasar and T dwarf survey (HQT Survey) is a wide-field, red optical survey carried out with the Suprime-Cam mosaic CCD camera on the 8.2 m Subaru telescope. The HQT survey is designed to search for low-luminosity (M{sub AB1450} < -23) quasars at high redshift (z>5.7) as well as T dwarfs, both of which are selected by their very red I - z' colors. We use an optical narrowband filter NB816 to break a well-known I - z' color degeneracy between high-z quasars and foreground M and L dwarfs, which are more numerous than quasars. This paper is the first in a series of papers from the HQT survey and we report on the discovery of six faint (19 {<=} J {<=} 20) ultracool dwarfs found over a {approx}9.3 deg{sup 2} area with a limiting magnitude of z'{sub AB} {<=} 23.3. These dwarfs were confirmed by near-IR imaging and/or spectroscopy conducted at various facilities on Mauna Kea. With estimated distances of 60-170 pc, these are among the most distant spectroscopically confirmed field brown dwarfs to date. Limits on the proper motions of these ultracool dwarfs suggest that they are old members of the Galactic disk, though future follow-up observations are necessary to minimize errors. Our finding rate of ultracool dwarfs is within model predictions of Liu et al. However, the large brightening amplitude ({approx}1 mag) previously reported for the L/T transition objects appears to overpredict the numbers. We also examine how the survey field latitude affects the survey sensitivity to the vertical scale height of ultracool dwarfs.

  3. Prospecting in ultracool dwarfs: measuring the metallicities of mid- and late-M dwarfs

    SciTech Connect

    Mann, Andrew W.; Deacon, Niall R.; Gaidos, Eric; Ansdell, Megan; Liu, Michael C.; Magnier, Eugene A.; Aller, Kimberly M.; Brewer, John M.

    2014-06-01

    Metallicity is a fundamental parameter that contributes to the physical characteristics of a star. The low temperatures and complex molecules present in M dwarf atmospheres make it difficult to measure their metallicities using techniques that have been commonly used for Sun-like stars. Although there has been significant progress in developing empirical methods to measure M dwarf metallicities over the last few years, these techniques have been developed primarily for early- to mid-M dwarfs. We present a method to measure the metallicity of mid- to late-M dwarfs from moderate resolution (R ∼ 2000) K-band (≅ 2.2 μm) spectra. We calibrate our formula using 44 wide binaries containing an F, G, K, or early-M primary of known metallicity and a mid- to late-M dwarf companion. We show that similar features and techniques used for early-M dwarfs are still effective for late-M dwarfs. Our revised calibration is accurate to ∼0.07 dex for M4.5-M9.5 dwarfs with –0.58 < [Fe/H] < +0.56 and shows no systematic trends with spectral type, metallicity, or the method used to determine the primary star metallicity. We show that our method gives consistent metallicities for the components of M+M wide binaries. We verify that our new formula works for unresolved binaries by combining spectra of single stars. Lastly, we show that our calibration gives consistent metallicities with the Mann et al. study for overlapping (M4-M5) stars, establishing that the two calibrations can be used in combination to determine metallicities across the entire M dwarf sequence.

  4. Responses Of Alpine Vegetation To Global Warming: Insights From Comparing Alpine-Restricted And Broad-Ranging Herbs Along Snowmelt Gradients

    NASA Astrophysics Data System (ADS)

    Butz, R. J.; Reinhardt, K. S.; Germino, M. J.; Kueppers, L. M.

    2009-12-01

    Many alpine plant species face habitat fragmentation and loss, and even extinction because their narrow elevation, precipitation, and temperature tolerances limit their geographic distribution. In order to assess the impacts of climate change on sensitive native alpine communities we used a variety of methods to look at the seasonal timing of life stages (phenology) and the stress responses (physiology) of alpine species along a natural environmental gradient at Niwot Ridge in the Colorado Rocky Mountains to address the following question: Will alpine plants be impaired in their existing range as a result of climate change? We collected data on date of snowmelt and vegetative and flowering phenology of all alpine species present from snowmelt to senescence in 80 1m2 plots above treeline. In addition, we measured soil temperature and moisture, plant water potential and leaf-level gas exchange early, mid, and late-season on three alpine-restricted and three broader-ranging alpine species: Geum rossii, Artemisia scopulorum, Carex rupestris, Lewisia pygmaea, Tetraneuris grandiflora, and Sibbaldia procumbens. In 2009, the natural variation in snowmelt timing was 40 days (approximately 5.5 weeks) over the 80 plots. Our results suggest that with earlier snowmelt, the number of vascular species per plot increases. However, this increase is almost exclusively attributable to wider ranging species not restricted to the alpine. Plots with intermediate natural snowmelt dates had a higher diversity of alpine-restricted species, photosynthesis, and water-use efficiency, thereby potentially increasing long-term survival rates amongst alpine species. Water stress increased in all species as the season progressed, especially in plots where snow melted earliest. Photosynthetic productivity and diversity of alpine-restricted species was greatest in plots having intermediate melt dates. These findings suggest that shifts in snowmelt date under a warming climate will likely impact the

  5. The benefit of amateur observations for research in dwarf novae

    NASA Technical Reports Server (NTRS)

    La Dous, Constanze

    1992-01-01

    Contributions of amateur astronomers to research on dwarf novae, which are based on carefully monitoring the outburst behavior of these objects, are reviewed. These contributions range from scheduling of observations to the observational basis for research on the dwarf nova outburst mechanism. It is suggested, that, with better equipment, observations of orbital light variations in dwarf novae might be performed by amateur astronomers.

  6. Aspects on muscle properties and use in competitive Alpine skiing.

    PubMed

    Tesch, P A

    1995-03-01

    This brief report describes the physiological demands in competitive Alpine skiing as well as the physiological profile of elite skiers. Maximal heart rate is typically attained by the end of either of the four Alpine ski disciplines. The giant slalom probably calls for the largest reliance upon aerobic energy metabolism and oxygen uptake may increase to 75%-100% of maximal aerobic power. Although high caliber skiers typically show increased maximal aerobic power, it is unlikely that this is an important factor determining success in skiing. Also, anaerobic energy provision accounts for more than half of the total energy yield. Accordingly, plasma and muscle lactate accumulation is substantial after a single race. Similarly, during skiing there is a high rate of glycogen utilization that eventually may result in depletion of muscle glycogen stores by the end of a day of intense skiing. Muscles of Alpine skiers do not possess a distinct fiber type composition and, if anything, skiers tend to show a preponderance of slow twitch fibers. This concords with the recruitment of both muscle fiber types during slalom or giant slalom. Elite skiers show increased knee extensor strength. This seems warranted because there is great reliance upon slow and forceful eccentric muscle actions when performing turns in the giant slalom or slalom. PMID:7752855

  7. Slip localization on the southern Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Barth, N. C.; Boulton, C.; Carpenter, B. M.; Batt, G. E.; Toy, V. G.

    2013-06-01

    of a detailed field study of the southern onshore portion of New Zealand's Alpine Fault reveal that for 75 km along-strike, dextral-normal slip on this long-lived structure is highly localized in phyllosilicate-rich fault core gouges and along their contact with more competent rocks. At three localities (Martyr River, McKenzie Creek, and Hokuri Creek), we document complete cross sections through the fault. New 40Ar/39Ar dates on mylonites, combined with microstructural and mechanical data on phyllosilicate-rich fault core gouges show that modern slip is localized onto a single, steeply dipping 1 to 12 m-thick fault core composed of impermeable (k = 10-20 to 10-22 m2), frictionally weak (μs = 0.12-0.37), velocity-strengthening, illite-chlorite, and saponite-chlorite-lizardite fault gouges. Fault core materials are (1) comparable to those of other major weak-cored faults (e.g., San Andreas Fault) and (2) most compatible with fault creep, despite paleoseismic evidence of quasiperiodic large magnitude earthquakes (Mw > 7) on this portion of the Alpine Fault. We conclude that frictional properties of gouges at the surface do not characterize the overall seismogenic behavior of the southern Alpine Fault.

  8. Numerical simulation of a turning alpine ski during recreational skiing.

    PubMed

    Hirano, Y; Tada, N

    1996-09-01

    While downhill snow skiing, recreational alpine skiers enjoy making turning motions with their skis. These motions are mainly induced by skidding, while turning by alpine ski racers is made by carving a trace in the snow. In the present study we treat the turning motions by recreational alpine skiers. This "skidding" turning motion is made possible by centripetal forces acting on the ski and skier dynamic motion systems, with these forces arising due to the skier placing the ski's longitudinal axis at an angle that is inclined away from the velocity vector and edging the ski into the snow. When snow is soft, the edged ski creates a snow impacting force, whereas a snow cutting force occurs when it is hard. Here, we calculate the former force using a three-dimensional water jet analogy, while the latter one using conventional metal cutting theory, after which the corresponding equations of motion for each system are derived and numerically solved. This methodology enables simulating the curvilinear and rotational motion of the ski and skier systems. Resultant simulations quantitatively show for the first time that the resultant radius of curvature of a ski track while downhill skiing is strongly dependent on the location of the ski boot on the ski's longitudinal axis and also on its side-cut (midlength taper). PMID:8883012

  9. Comparison modeling for alpine vegetation distribution in an arid area.

    PubMed

    Zhou, Jihua; Lai, Liming; Guan, Tianyu; Cai, Wetao; Gao, Nannan; Zhang, Xiaolong; Yang, Dawen; Cong, Zhentao; Zheng, Yuanrun

    2016-07-01

    Mapping and modeling vegetation distribution are fundamental topics in vegetation ecology. With the rise of powerful new statistical techniques and GIS tools, the development of predictive vegetation distribution models has increased rapidly. However, modeling alpine vegetation with high accuracy in arid areas is still a challenge because of the complexity and heterogeneity of the environment. Here, we used a set of 70 variables from ASTER GDEM, WorldClim, and Landsat-8 OLI (land surface albedo and spectral vegetation indices) data with decision tree (DT), maximum likelihood classification (MLC), and random forest (RF) models to discriminate the eight vegetation groups and 19 vegetation formations in the upper reaches of the Heihe River Basin in the Qilian Mountains, northwest China. The combination of variables clearly discriminated vegetation groups but failed to discriminate vegetation formations. Different variable combinations performed differently in each type of model, but the most consistently important parameter in alpine vegetation modeling was elevation. The best RF model was more accurate for vegetation modeling compared with the DT and MLC models for this alpine region, with an overall accuracy of 75 % and a kappa coefficient of 0.64 verified against field point data and an overall accuracy of 65 % and a kappa of 0.52 verified against vegetation map data. The accuracy of regional vegetation modeling differed depending on the variable combinations and models, resulting in different classifications for specific vegetation groups. PMID:27307276

  10. Abiotic and biotic controls of spatial pattern at alpine treeline

    USGS Publications Warehouse

    Malanson, George P.; Xiao, Ningchuan; Alftine, K.J.; Bekker, Mathew; Butler, David R.; Brown, Daniel G.; Cairns, David M.; Fagre, Daniel; Walsh, Stephen J.

    2000-01-01

    At alpine treeline, trees and krummholz forms affect the environment in ways that increase their growth and reproduction. We assess the way in which these positive feedbacks combine in spatial patterns to alter the environment in the neighborhood of existing plants. The research is significant because areas of alpine tundra are susceptible to encroachment by woody species as climate changes. Moreover, understanding the general processes of plant invasion is important. The importance of spatial pattern has been recognized, but the spatial pattern of positive feedbacks per se has not been explored in depth. We present a linked set of models of vegetation change at an alpine forest-tundra ecotone. Our aim is to create models that are as simple as possible in order to test specific hypotheses. We present results from a model of the resource averaging hypothesis and the positive feedback switch hypothesis of treelines. We compare the patterns generated by the models to patterns observed in fine scale remotely sensed data.

  11. White dwarfs as tracers of galactic evolution

    NASA Astrophysics Data System (ADS)

    Isern, J.; Hernanz, M.; García-Berro, E.; Salaris, M.

    White dwarfs are the final remnants of low and intermediate mass stars. Their evolution is essentially a cooling process that lasts for ~ 10 Gyr and allows to obtain information about the age of the Galaxy as well as about the past stellar formation rate in the solar neighborhood. We show in this paper the state of the art of the white dwarf cooling theory and the uncertainties still remaining. We also provide some applications of the theory of cooling white dwarfs to escrutiny the past history of the Milky Way. These applications range from an independent derivation of the past history of the local star formation rate to a determination of the properties of the halo.

  12. Youth Indicators of Late-M Dwarfs

    NASA Astrophysics Data System (ADS)

    Feldman, Daniel; Cruz, K.; Lépine, S.; Alpert, N.

    2011-01-01

    We present a study in which we searched for a correlation between weak Na absorption doublet (8183Å, 8194Å) and strong H-Alpha emission (6563Å) in late-M dwarf stars (M6-M9), as both are indicative of youth. Our sample consists of late-M Dwarfs from the LSPM Survey (Lépine and Shara, 2005), which contain stars with measured proper motions of mu > 40 mas/yr. Measurements for emission and absorption strength were made using spectral indices. Our preliminary results are presented; future work will include a similar analysis of early type M Dwarfs, as well as kinematics. This work was funded by the CUNY Summer Undergraduate Research Program, as well as the CUNY Macaulay Honors College, and we acknowledge the hospitality of the American Museum of Natural History.

  13. Stellar feedback in dwarf galaxy formation.

    PubMed

    Mashchenko, Sergey; Wadsley, James; Couchman, H M P

    2008-01-11

    Dwarf galaxies pose substantial challenges for cosmological models. In particular, current models predict a dark-matter density that is divergent at the center, which is in sharp contrast with observations that indicate a core of roughly constant density. Energy feedback, from supernova explosions and stellar winds, has been proposed as a major factor shaping the evolution of dwarf galaxies. We present detailed cosmological simulations with sufficient resolution both to model the relevant physical processes and to directly assess the impact of stellar feedback on observable properties of dwarf galaxies. We show that feedback drives large-scale, bulk motions of the interstellar gas, resulting in substantial gravitational potential fluctuations and a consequent reduction in the central matter density, bringing the theoretical predictions in agreement with observations. PMID:18048653

  14. Be stars with white dwarf companions

    NASA Astrophysics Data System (ADS)

    Orio, Marina; Luna, Gerardo; Zemko, Polina; Kotulla, Ralf; Gallagher, Jay; Harbeck, Daniel

    2016-07-01

    A handful of supersoft X-ray sources in the Magellanic Clouds that could not be identified with transient nova outbursts turned out to be mainly massive close binaries. Recently, we have clearly identified a Be binary in M31, and are currently collecting data for another candidate in that galaxy. Work is in progress to assess whether the compact object companion really is a hydrogen burning white dwarf (the alternative being a massive stellar-mass black hole). If we can prove that Be+white dwarf interacting close binaries are common, and that hydrogen is often ignited on the white dwarf in these systems, we have discovered a new promising channel towards the explosion of supernovae of type Ia in star forming regions, without invoking double degenerate systems

  15. Recombination energy in double white dwarf formation

    NASA Astrophysics Data System (ADS)

    Nandez, J. L. A.; Ivanova, N.; Lombardi, J. C.

    2015-06-01

    In this Letter, we investigate the role of recombination energy during a common envelope event. We confirm that taking this energy into account helps to avoid the formation of the circumbinary envelope commonly found in previous studies. For the first time, we can model a complete common envelope event, with a clean compact double white dwarf binary system formed at the end. The resulting binary orbit is almost perfectly circular. In addition to considering recombination energy, we also show that between 1/4 and 1/2 of the released orbital energy is taken away by the ejected material. We apply this new method to the case of the double white dwarf system WD 1101+364, and we find that the progenitor system at the start of the common envelope event consisted of an ˜1.5 M⊙ red giant star in an ˜30 d orbit with a white dwarf companion.

  16. Charged condensate and helium dwarf stars

    SciTech Connect

    Gabadadze, Gregory; Rosen, Rachel A E-mail: rar339@nyu.edu

    2008-10-15

    White dwarf stars composed of carbon, oxygen and heavier elements are expected to crystallize as they cool down below certain temperatures. Yet, simple arguments suggest that the helium white dwarf cores may not solidify, mostly because of zero-point oscillations of the helium ions that would dissolve the crystalline structure. We argue that the interior of the helium dwarfs may instead form a macroscopic quantum state in which the charged helium-4 nuclei are in a Bose-Einstein condensate, while the relativistic electrons form a neutralizing degenerate Fermi liquid. We discuss the electric charge screening, and the spectrum of this substance, showing that the bosonic long-wavelength fluctuations exhibit a mass gap. Hence, there is a suppression at low temperatures of the boson contribution to the specific heat-the latter being dominated by the specific heat of the electrons near the Fermi surface. This state of matter may have observational signatures.

  17. White dwarfs, the Galaxy and Dirac's cosmology

    NASA Technical Reports Server (NTRS)

    Stothers, R.

    1976-01-01

    The additive and multiplicative versions of Dirac's cosmological hypothesis relating the gravitational constant variation with elapsed time and number of particles populating the universe is invoked to account for the deficiency or absence of white dwarfs fainter than about 0.0001 solar luminosity. An estimate is made of white dwarf luminosity in accordance with the two