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Sample records for dwarf shrub seeds

  1. Chapter 25. Shrub and forb seed production

    Treesearch

    Gordon A. Van Epps; Richard Stevens

    2004-01-01

    The success or failure of range restoration and revegetation programs depends on procurement of an adequate supply of quality grass, forb, and shrub seed. Rangeland species seed is either grown commercially or collected from wildland stands. Commercially produced seed of numerous grass species is available (Asay and Knowles 1985b; Horton and others 1990; Sours 1983). A...

  2. Users guide for seeds of western trees and shrubs.

    Treesearch

    William I. Stein; Rodger Danielson; Nancy Shaw; Scott Wolff; David. Gerdes

    1986-01-01

    Because the role of tree and shrub seed is indispensable in the renewal of forests and ranges, their identity and quality are critically important. This guide briefly covers recommended practices for maintaining the identity of seeds, for sampling them, and for testing them for quality. Practices associated with the testing and use of tree seed have developed over many...

  3. Seeds of Puerto Rican Trees and Shrubs: Second Installment

    Treesearch

    John K. Francis; Alberto Rodríguez

    1993-01-01

    Seed weights and germination information were obtained for 119 native Puerto Rican and naturalized exotic trees and shrubs. Fruit was collected from 34 of these species, and the weights were recorded. The data are presented in tables that list the species alphabetically by scientific names.

  4. 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

  5. The allocation of carbon in most common boreal dwarf shrubs compared to Scots pine seedlings

    NASA Astrophysics Data System (ADS)

    Kulmala, Liisa; del Rosario Dominguez Carrasco, Maria; Heinonsalo, Jussi

    2017-04-01

    The floor of boreal pine forests consists of a dense layer of ground vegetation consisting of dwarf shrubs, herbs, grasses, mosses and lichens. The primary productivity of this vegetation is reported to be notable but the carbon (C) dynamics of the most common dwarf shrub plant species, Calluna vulgaris, Vaccinium myrtillus and Vaccinium vitis-idaea is poorly understood. In a controlled laboratory experiment, we determined the full C balances of these dwarf shrubs for the first time and compared to Pinus sylvestris by using long-term biomass accumulation, 13C pulse labelling, CO2 exchange measurements and analysis of non-structural carbon. The observed differences in the carbon dynamics are important in estimating the origin of belowground CO2 fluxes in the field and in evaluating their biological relevance. Our results will improve current understanding of CO2 sources and sinks in boreal forests.

  6. The evolution of dwarf shrubs in alpine environments: a case study of Alchemilla in Africa

    PubMed Central

    Gehrke, Berit; Kandziora, Martha; Pirie, Michael D.

    2016-01-01

    Background and Aims Alpine and arctic environments worldwide, including high mountains, are dominated by short-stature woody plants (dwarf shrubs). This conspicuous life form asserts considerable influence on local environmental conditions above the treeline, creating its own microhabitat. This study reconstructs the evolution of dwarf shrubs in Alchemilla in the African tropical alpine environment, where they represent one of the largest clades and are among the most common and abundant plants. Methods Different phylogenetic inference methods were used with plastid and nuclear DNA sequence markers, molecular dating (BEAST and RelTime), analyses of diversification rate shifts (MEDUSA and BAMM) and ancestral character and area reconstructions (Mesquite). Key Results It is inferred that African Alchemilla species originated following long-distance dispersal to tropical East Africa, but that the evolution of dwarf shrubs occurred in Ethiopia and in tropical East Africa independently. Establishing a timeframe is challenging given inconsistencies in age estimates, but it seems likely that they originated in the Pleistocene, or at the earliest in the late Miocene. The adaptation to alpine-like environments in the form of dwarf shrubs has apparently not led to enhanced diversification rates. Ancestral reconstructions indicate reversals in Alchemilla from plants with a woody base to entirely herbaceous forms, a transition that is rarely reported in angiosperms. Conclusions Alchemilla is a clear example of in situ tropical alpine speciation. The dwarf shrub life form typical of African Alchemilla has evolved twice independently, further indicating its selective advantage in these harsh environments. However, it has not influenced diversification, which, although recent, was not rapid. PMID:26520565

  7. 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.

  8. Native shrub seed industries in the western United States and Australia: Status and outlook

    Treesearch

    N. L. Shaw; C. M. Waters

    2003-01-01

    Attempts to improve habitat for wildlife and increase forage for livestock contributed to development of native shrub seed industries in the western United States and in Australia. Shrub seedings and plantings in both countries are concentrated in areas with low and unpredictable precipitation and high probability for planting failures. In addition, both countries have...

  9. Clonality increases with snow depth in the arctic dwarf shrub Empetrum hermaphroditum.

    PubMed

    Bienau, Miriam J; Eckstein, R Lutz; Otte, Annette; Durka, Walter

    2016-12-01

    Vegetative reproduction and spread through clonal growth plays an important role in arctic-alpine ecosystems with short cool growing seasons. Local variation in winter snow accumulation leads to discrete habitat types that may provide divergent conditions for sexual and vegetative reproduction. Therefore, we studied variation in clonal structure of a dominant, evergreen, dwarf shrub (Empetrum nigrum s.l. with the two taxa E. nigrum L. s.s. and E. hermaphroditum Hagerup) along a snow cover gradient and compared clonal diversity and spatial genetic structure between habitats. We studied 374 individual shoots using 105 polymorphic AFLP markers and analyses based on hierarchical clustering, clonal diversity indices, and small-scale spatial genetic structure with pairwise kinship coefficient. We used two approaches to define a threshold of genotypic distance between two samples that are considered the same clone. Clonality was examined among three habitats (exposed ridges, sheltered depressions, birch forest) differing in snow conditions replicated in four study regions in Norway and Sweden. Clonality of E. hermaphroditum differed between habitats with an increase in clonal diversity with decreasing snow depth. Small-scale spatial genetic structure increased with decreasing clonal diversity and increasing clone size. In three study regions, E. hermaphroditum was the only species, whereas in one region E. nigrum also occurred, largely confined to exposed ridges. Our results demonstrated that snow cover in conjunction with associated habitat conditions plays an important role for the mode of propagation of the dwarf shrub E. hermaphroditum. © 2016 Botanical Society of America.

  10. Realities and myths of the Teresken Syndrome--an evaluation of the exploitation of dwarf shrub resources in the Eastern Pamirs of Tajikistan.

    PubMed

    Kraudzun, Tobias; Vanselow, Kim André; Samimi, Cyrus

    2014-01-01

    In the Eastern Pamirs extensive livestock herding is the predominant land use option and dwarf shrubs - teresken (Krascheninnikovia ceratoides) and to a lesser extent wormwood (Artemisia spp.) - are an important source of thermal energy and are crucial forage plants, particularly in winter. For the post-Soviet period, many papers and reports suggest rapidly increasing exploitation rates with sometimes alarming figures for degradation. Conventional knowledge about the Pamirs pinpoints the frightening and irreversible extraction of teresken as a dwindling resource causing land degradation - termed the 'Teresken Syndrome'. However, these publications are based on limited empirical evidence. This paper discusses the socio-economic role of dwarf shrubs as fuel and forage - today and in the past - and provides an overview of the extent of dwarf shrub distribution and degraded areas. Although our observations confirm extensive dwarf shrub exploitation, general assumptions of severe desertification as a result of dwarf shrub extraction do not yield reliable scenarios. The effects of harvesting on the vegetation cover vary widely depending on extraction practices and yields of different dwarf shrub-dominated formations. Furthermore, considerable and increasing shares of energy needs are satisfied by animal manure and imported coal. On the other hand, for low-income households harvesting dwarf shrubs is an important and reliable option to ensure both their own household energy supply and an income source. We argue that the term 'Teresken Syndrome', which was introduced after the emergency replacement of Soviet coal supplies by dwarf shrubs in the 1990s, is not appropriate anymore to describe the current use of natural resources in the Eastern Pamirs. However, under the current economic circumstances the nexus remains that the Pamir people are caught in the dilemma of using dwarf shrubs as energy and as forage resource. However, the observed negotiation practices concerning

  11. A mast-seeding desert shrub regulates population dynamics and behavior of its heteromyid dispersers

    Treesearch

    Janene Auger; Susan E. Meyer; Stephen H. Jenkins

    2016-01-01

    Granivorous rodent populations in deserts are primarily regulated through precipitation-driven resource pulses rather than pulses associated with mast-seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast-seeding in the desert shrub blackbrush (Coleogyne ramosissima), a regionally dominant species in the Mojave–Great Basin...

  12. The role of rodents in the seed fate of a thorny shrub in an ancient wood pasture

    NASA Astrophysics Data System (ADS)

    Scheper, Jeroen; Smit, Christian

    2011-03-01

    Thorny shrubs play a crucial role for the diversity and dynamics in wood pastures: they protect non-defended plants from large herbivores and thus facilitate tree establishment in the landscape through associational resistance. How thorny shrubs themselves establish in wood pastures - the main bottleneck for a dynamic shifting of grassland - shrub - woodland mosaics - is an essential unanswered question. We studied post-primary dispersal seed fate - i.e. removal, predation, secondary dispersal and survival of seeds after primary dispersal - of the thorny shrub blackthorn ( Prunus spinosa) in an ancient wood pasture in the Netherlands. Blackthorn seeds are primarily dispersed by frugivorous birds and may secondarily be dispersed by scatter-hoarding rodents. We performed two cafeteria-style experiments with blackthorn seeds placed on dishes in the dominant vegetation types. In the first we monitored seed removal in grassland, swards or blackthorn shrubs and determined rodent species abundance by live-trapping. In the second we followed tagged blackthorn seeds under shrubs and in swards to determine seed removal, predation, survival and secondary dispersal patterns. Tagged seeds were retrieved using a metal detector and by visual means. We recorded dispersal direction and distance, vegetation type, seed handling (burial, consumption) and rodent species responsible via bite marks. Seed removal and number of live-trapped rodents differed between vegetation types, with higher removal and rodent captures under shrubs than in swards and grassland. All retrieved seeds were depredated, predominantly by the wood mouse ( Apodemus sylvaticus). Disproportionally high seed numbers were retrieved in the vegetation type where originally placed (shrubs or swards). Our study suggests that rodents play an important role for blackthorn in wood pastures, predominantly as seed predators rather than secondary seed dispersers. Predation is particularly high under blackthorn shrubs

  13. Annual increments of juniper dwarf shrubs above the tree line on the central Tibetan Plateau: a useful climatic proxy

    PubMed Central

    Liang, Eryuan; Lu, Xiaoming; Ren, Ping; Li, Xiaoxia; Zhu, Liping; Eckstein, Dieter

    2012-01-01

    Background and Aims Dendroclimatology is playing an important role in understanding past climatic changes on the Tibetan Plateau. Forests, however, are mainly confined to the eastern Tibetan Plateau. On the central Tibetan Plateau, in contrast, shrubs and dwarf shrubs need to be studied instead of trees as a source of climate information. The objectives of this study were to check the dendrochronological potential of the dwarf shrub Wilson juniper (Juniperus pingii var. wilsonii) growing from 4740 to 4780 m a.s.l. and to identify the climatic factors controlling its radial growth. Methods Forty-three discs from 33 stems of Wilson juniper were sampled near the north-eastern shore of the Nam Co (Heavenly Lake). Cross-dating was performed along two directions of each stem, avoiding the compression-wood side as far as possible. A ring-width chronology was developed after a negative exponential function or a straight line of any slope had been fit to the raw measurements. Then, correlations were calculated between the standard ring-width chronology and monthly climate data recorded by a weather station around 100 km away. Key Results Our study has shown high dendrochronological potential of Wilson juniper, based on its longevity (one individual was 324 years old), well-defined growth rings, reliable cross-dating between individuals and distinct climatic signals reflected by the ring-width variability. Unlike dwarf shrubs in the circum-arctic tundra ecosystem which positively responded to above-average temperature in the growing season, moisture turned out to be growth limiting for Wilson juniper, particularly the loss of moisture caused by high maximum temperatures in May–June. Conclusions Because of the wide distribution of shrub and dwarf shrub species on the central Tibetan Plateau, an exciting prospect was opened up to extend the presently existing tree-ring networks far up into one of the largest tundra regions of the world. PMID:22210848

  14. Rapid revegetation by sowing seed mixtures of shrub and herbaceous species

    NASA Astrophysics Data System (ADS)

    Feng, J. J.; Zhang, C. L.; Zhao, T. N.

    2015-01-01

    Fast revegetation by means of sowing seed mixture of shrub and herbaceous species is a measure to prevent bare soils from wind and water erosion. 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 longer period. However, the growth of shrubs was hindered. In 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 form July to October, and a seeding density of 1.5 g m-2 is proposed for rapid revegetation.

  15. 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.

  16. Provisional tree and shrub seed zones for the Great Plains

    Treesearch

    Richard A. Cunningham

    1975-01-01

    Seed collection zones are subdivisions of land areas established to identify seed sources and to control the movement of seed and planting stock. Seed zones are needed for many species because of the genetic variation associated with their geographic distribution. Zone boundaries may be delineated from experimental data that identify genetic variation, or by analysis...

  17. 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.

  18. 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.

  19. Dormancy cycling and persistence of seeds in soil of a cold desert halophyte shrub

    PubMed Central

    Cao, Dechang; Baskin, Carol C.; Baskin, Jerry M.; Yang, Fan; Huang, Zhenying

    2014-01-01

    Background and Aims Formation of seed banks and dormancy cycling are well known in annual species, but not in woody species. In this study it was hypothesized that the long-lived halophytic cold desert shrub Kalidium gracile has a seed bank and dormancy cycling, which help restrict germination to a favourable time for seedling survival. Methods Fresh seeds were buried in November 2009 and exhumed and tested for germination monthly from May 2010 to December 2011 over a range of temperatures and salinities. Germination recovery and viability were determined after exposure to salinity and water stress. Seedling emergence and dynamics of the soil seed bank were investigated in the field. Key Results Seeds of K. gracile had a soil seed bank of 7030 seeds m−2 at the beginning of the growing season. About 72 % of the seeds were depleted from the soil seed bank during a growing season, and only 1·4 % of them gave rise to seedlings that germinated early enough to reach a stage of growth at which they could survive to overwinter. About 28 % of the seeds became part of a persistent soil seed bank. Buried seeds exhibited an annual non-dormancy/conditional dormancy (ND/CD) cycle, and germination varied in sensitivity to salinity during the cycle. Dormancy cycling is coordinated with seasonal environmental conditions in such a way that the seeds germinate in summer, when there is sufficient precipitation for seedling establishment. Conclusions Kalidium gracile has three life history traits that help ensure persistence at a site: a polycarpic perennial life cycle, a persistent seed bank and dormancy cycling. The annual ND/CD cycle in seeds of K. gracile contributes to seedling establishment of this species in the unpredictable desert environment and to maintenance of a persistent soil seed bank. This is the first report of a seed dormancy cycle in a cold desert shrub. PMID:24249808

  20. Dormancy cycling and persistence of seeds in soil of a cold desert halophyte shrub.

    PubMed

    Cao, Dechang; Baskin, Carol C; Baskin, Jerry M; Yang, Fan; Huang, Zhenying

    2014-01-01

    Formation of seed banks and dormancy cycling are well known in annual species, but not in woody species. In this study it was hypothesized that the long-lived halophytic cold desert shrub Kalidium gracile has a seed bank and dormancy cycling, which help restrict germination to a favourable time for seedling survival. Fresh seeds were buried in November 2009 and exhumed and tested for germination monthly from May 2010 to December 2011 over a range of temperatures and salinities. Germination recovery and viability were determined after exposure to salinity and water stress. Seedling emergence and dynamics of the soil seed bank were investigated in the field. Seeds of K. gracile had a soil seed bank of 7030 seeds m(-2) at the beginning of the growing season. About 72 % of the seeds were depleted from the soil seed bank during a growing season, and only 1·4 % of them gave rise to seedlings that germinated early enough to reach a stage of growth at which they could survive to overwinter. About 28 % of the seeds became part of a persistent soil seed bank. Buried seeds exhibited an annual non-dormancy/conditional dormancy (ND/CD) cycle, and germination varied in sensitivity to salinity during the cycle. Dormancy cycling is coordinated with seasonal environmental conditions in such a way that the seeds germinate in summer, when there is sufficient precipitation for seedling establishment. Kalidium gracile has three life history traits that help ensure persistence at a site: a polycarpic perennial life cycle, a persistent seed bank and dormancy cycling. The annual ND/CD cycle in seeds of K. gracile contributes to seedling establishment of this species in the unpredictable desert environment and to maintenance of a persistent soil seed bank. This is the first report of a seed dormancy cycle in a cold desert shrub.

  1. Dwarf shrub hydraulics: two Vaccinium species (Vaccinium myrtillus, Vaccinium vitis-idaea) of the European Alps compared.

    PubMed

    Ganthaler, Andrea; Mayr, Stefan

    2015-12-01

    Vaccinium myrtillus and Vaccinium vitis-idaea are two dwarf shrubs widespread in the European Alps. We studied the hydraulics of these species hypothesizing that (1) the hydraulic architecture of dwarf shrubs differs from trees, (2) hydraulic properties reflect the species' ecological amplitude and (3) hydraulic properties vary spatially and seasonally. Key hydraulic parameters (osmotic potential, turgor loss point, xylem hydraulic conductivity, vulnerability to drought-induced embolism, stomata closure, drought-induced cell damage and embolism repair) and related wood anatomical traits (conduit diameter and conduit wall reinforcement) were analyzed at four sites in Tyrol, Austria. Both species exhibited low hydraulic safety as well as low hydraulic efficiency. Fifty percentage embolism accumulated at -2.08 (V. myrtillus) and -1.97 MPa (V. vitis-idaea), 88% stomata closure was at -2.19 and -2.35 MPa, respectively. After drought, both species showed embolism repair on re-watering. Site-specific variation within species was low, while seasonal changes in embolism resistance and turgor loss point were observed. Results indicate that studied Vaccinium species have a high risk for embolism formation. This is balanced by refilling capacities, which are probably based on the small growth height of dwarf shrubs. V. vitis-idaea, which occurs on drier sites, showed more efficient repair and a lower turgor loss point than V. myrtillus.

  2. Pre-treating Seed to Enhance Germination of Desert Shrubs

    SciTech Connect

    W. K. Ostler; D. C. Anderson; D. J. Hansen

    2002-06-01

    Creosotebush [Larrea tridentata (D.C.) Cav.] and white bursage [Ambrosia dumosa (A. Gray) W.W. Payne] seeds were subjected to pre-treatments of rinsing and soaking in water and thiourea to enhance germination in laboratory experiments. The effects of darkness, temperature, seed source, and soil moisture were also evaluated in the laboratory. The best pre-treatment from the laboratory experiments, rinsing with water for 36 hours followed by drying, was field-tested at Fort Irwin, California. Two sites and two seeding dates (early March and mid April) were determined for each site. Five mulch treatments (no mulch, straw, gravel, chemical stabilizer, and plastic) were evaluated in combination with the seed pre-treatments. Field emergence was greatly enhanced with the seed pre-treatment for white bursage during the March (18-42% increase in germination) and April seedings (16-23% increase in germination). Creosotebush showed poor germination during March (2-5%) when soil temperatures averaged 15 C, but germination increased during the April trials (6-43%) when soil temperatures averaged 23 C. The seed pre-treatment during the April trials increased germination from 16-23%. The plastic mulch treatment increased germination dramatically during both the March and April trials. The plastic mulch increased soil temperatures (8-10 C)and maintained high humidity during germination. Both the chemical stabilizer and the gravel mulches improved germination over the control while the straw mulch decreased germination. These results suggest that seed pre-treatments combined with irrigation and mulch are effective techniques to establish these two dominant Mojave Desert species from seed.

  3. Growth and community responses of alpine dwarf shrubs to in situ CO₂ enrichment and soil warming.

    PubMed

    Dawes, Melissa A; Hagedorn, Frank; Zumbrunn, Thomas; Handa, Ira Tanya; Hättenschwiler, Stephan; Wipf, Sonja; Rixen, Christian

    2011-08-01

    • Rising CO₂ concentrations and the associated global warming are expected to have large impacts on high-elevation ecosystems, yet long-term multifactor experiments in these environments are rare. • We investigated how growth of dominant dwarf shrub species (Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum) and community composition in the understorey of larch and pine trees responded to 9 yr of CO₂ enrichment and 3 yr of soil warming at the treeline in the Swiss Alps. • Vaccinium myrtillus was the only species that showed a clear positive effect of CO₂ on growth, with no decline over time in the annual shoot growth response. Soil warming stimulated V. myrtillus growth even more than elevated CO₂ and was accompanied by increased plant-available soil nitrogen (N) and leaf N concentrations. Growth of Vaccinium gaultherioides and E. hermaphroditum was not influenced by warming. Vascular plant species richness declined in elevated CO₂ plots with larch, while the number of moss and lichen species decreased under warming. • Ongoing environmental change could lead to less diverse plant communities and increased dominance of the particularly responsive V. myrtillus in the studied alpine treeline. These changes are the consequence of independent CO₂ and soil warming effects, a result that should facilitate predictive modelling approaches.

  4. Impact of early and late winter icing events on sub-arctic dwarf shrubs.

    PubMed

    Preece, C; Phoenix, G K

    2014-01-01

    Polar regions are predicted to undergo large increases in winter temperature and an increased frequency of freeze-thaw cycles, which can cause ice layers in the snow pack and ice encasement of vegetation. Early or late winter timing of ice encasement could, however, modify the extent of damage caused to plants. To determine impacts of the date of ice encasement, a novel field experiment was established in sub-arctic Sweden, with icing events simulated in January and March 2008 and 2009. In the subsequent summers, reproduction, phenology, growth and mortality, as well as physiological indicators of leaf damage were measured in the three dominant dwarf shrubs: Vaccinium uliginosum, Vaccinium vitis-idaea and Empetrum nigrum. It was hypothesised that January icing would be more damaging compared to March icing due to the longer duration of ice encasement. Following 2 years of icing, E. nigrum berry production was 83% lower in January-iced plots compared to controls, and V. vitis-idaea electrolyte leakage was increased by 69%. Conversely, electrolyte leakage of E. nigrum was 25% lower and leaf emergence of V. vitis-idaea commenced 11 days earlier in March-iced plots compared to control plots in 2009. There was no effect of icing on any of the other parameters measured, indicating that overall these study species have moderate to high tolerance to ice encasement. Even much longer exposure under the January icing treatment does not clearly increase damage.

  5. Soil seed bank, factors controlling germination and establishment of a Mediterranean shrub: Pistacia lentiscus L.

    NASA Astrophysics Data System (ADS)

    García-Fayos, Patricio; Verdú, Miguel

    1998-08-01

    The recruitment strategy of Pistacia lentiscus, an evergreen sclerophyllous shrub inhabiting the Mediterranean region, was studied in order to identify the key factors controlling seedling establishment and survival. The capacity to develop a seed bank, the loss of seed viability with time, the presence of dormancy mechanisms, the conditions to promote seed germination and the seedling dynamics were investigated. The results show that P. lentiscus has a transient seed bank with rapid seed germination occurring within the year. Dormancy was not present as seeds germinated successfully without light or temperature pretreatments. Only pulp removal and a long and abundant rain event (≥ 7 days; ≥ 100 L·m -2) appeared to be necessary for germination. Seed viability decreased drastically after 1 year. More seedlings emerged under shrub canopy than in open sites, as expected by the seed dispersal pattern and canopy effects on plant establishment. The high mortality observed in the few weeks after establishment indicates that seedling survival is a bottleneck in the recruitment process of P. lentiscus in dense shrublands. Some seedlings survived in a latent mode for at least 4 years.

  6. Seed Mucilage Improves Seedling Emergence of a Sand Desert Shrub

    PubMed Central

    Yang, Xuejun; Baskin, Carol C.; Baskin, Jerry M.; Liu, Guangzheng; Huang, Zhenying

    2012-01-01

    The success of seedling establishment of desert plants is determined by seedling emergence response to an unpredictable precipitation regime. Sand burial is a crucial and frequent environmental stress that impacts seedling establishment on sand dunes. However, little is known about the ecological role of seed mucilage in seedling emergence in arid sandy environments. We hypothesized that seed mucilage enhances seedling emergence in a low precipitation regime and under conditions of sand burial. In a greenhouse experiment, two types of Artemisia sphaerocephala achenes (intact and demucilaged) were exposed to different combinations of burial depth (0, 5, 10, 20, 40 and 60 mm) and irrigation regimes (low, medium and high, which simulated the precipitation amount and frequency in May, June and July in the natural habitat, respectively). Seedling emergence increased with increasing irrigation. It was highest at 5 mm sand burial depth and ceased at burial depths greater than 20 mm in all irrigation regimes. Mucilage significantly enhanced seedling emergence at 0, 5 and 10 mm burial depths in low irrigation, at 0 and 5 mm burial depths in medium irrigation and at 0 and 10 mm burial depths in high irrigation. Seed mucilage also reduced seedling mortality at the shallow sand burial depths. Moreover, mucilage significantly affected seedling emergence time and quiescence and dormancy percentages. Our findings suggest that seed mucilage plays an ecologically important role in successful seedling establishment of A. sphaerocephala by improving seedling emergence and reducing seedling mortality in stressful habitats of the sandy desert environment. PMID:22511952

  7. 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.

  8. Effects of dispersal, shrubs, and density-dependent morality on seed and seedling distributions in temperate forests

    Treesearch

    Janneke Hille Ris Lambers; James S. Clark

    2003-01-01

    Processes limiting recruitment of trees may have large impacts on forest dynamics. In this paper, we determined the effects of dispersal, shrubs (Rhododendron maximum), and density-dependent mortality on seed and seedling distributions of Southern Appalachian trees. We quantified the spatial distribution of seed rain, seed bank densities, first-year...

  9. Potential carry-over of seeds from 11 common shrub and vine competitors of loblolly and shortleaf pines

    Treesearch

    Michael G. Shelton; Michael D. Cain

    2002-01-01

    Many of the competitors of the regeneration of loblolly and shortleaf pines (Pinus taeda, L. and Pinus echinata Mill., respectively) develop from seed disseminated on the site after reproduction cutting or from the seed bank. To evaluate the potential carry-over of the seeds from 11 shrub and vine competitors of these two...

  10. Seed dormancy-breaking in a cold desert shrub in relation to sand temperature and moisture.

    PubMed

    Liu, Huiliang; Abudureheman, Buhailiqiemu; Zhang, Lingwei; Baskin, Jerry M; Baskin, Carol C; Zhang, Daoyuan

    2017-01-24

    Seasonal periodicity of seed germination and its relationship to seasonal changes in temperature and soil moisture have been well studied in seeds of species with physiological dormancy. However, relatively little information is available on the role of these environmental factors in controlling germination of seeds with physical dormancy (PY). Our primary aim was to determine if seeds of the cold desert sand dune semi-shrub Eremosparton songoricum exhibits seasonal periodicity of seed germination and the relationship between seed dormancy break and soil temperature and moisture. In the laboratory, seeds incubated on dry, wet, wet-dry and dry-wet sand were exposed to a 1-year sequence of temperature regimes simulating those in the field. In the field, seeds were buried at different depths on a sand dune, and germination of periodically exhumed seeds was tested at five temperature regimes during a 2-year period. In the one-year sequence of simulated natural temperature regimes, breaking of PY was more effective under constantly wet than under constantly dry conditions, and germination percentage was significantly higher under dry-wet than under wet-dry conditions. Seeds buried in the field exhibited a distinct peak of germination in spring and little or no germination in other seasons. The final (two-year) monthly cumulative germination percentage differed among burial depths and temperature, and it was highest (47%) in seeds buried at 3 cm and tested at 25/10 °C. A seed cohort of E. songoricum likely exhibits a long-term annual periodicity of spring germination in the field, and dormancy break appears to be driven by low (winter) temperatures and relatively high sand moisture content. To our knowledge this is the first study to document seasonal periodicity in seed germination in a cold desert species with PY and to identify the mechanism (at the whole-seed level) of its occurrence.

  11. Seed dormancy-breaking in a cold desert shrub in relation to sand temperature and moisture

    PubMed Central

    Liu, Huiliang; Abudureheman, Buhailiqiemu; Zhang, Lingwei; Baskin, Jerry M.; Baskin, Carol C.

    2017-01-01

    Abstract Seasonal periodicity of seed germination and its relationship to seasonal changes in temperature and soil moisture have been well studied in seeds of species with physiological dormancy. However, relatively little information is available on the role of these environmental factors in controlling germination of seeds with physical dormancy (PY). Our primary aim was to determine if seeds of the cold desert sand dune semi-shrub Eremosparton songoricum exhibits seasonal periodicity of seed germination and the relationship between seed dormancy break and soil temperature and moisture. In the laboratory, seeds incubated on dry, wet, wet-dry and dry-wet sand were exposed to a 1-year sequence of temperature regimes simulating those in the field. In the field, seeds were buried at different depths on a sand dune, and germination of periodically exhumed seeds was tested at five temperature regimes during a 2-year period. In the 1-year sequence of simulated natural temperature regimes, breaking of PY was more effective under constantly wet than under constantly dry conditions, and germination percentage was significantly higher under dry-wet than under wet-dry conditions. Seeds buried in the field exhibited a distinct peak of germination in spring and little or no germination in other seasons. The final (2-year) monthly cumulative germination percentage differed among burial depths and temperature, and it was highest (47 %) in seeds buried at 3 cm and tested at 25/10 °C. A seed cohort of E. songoricum likely exhibits a long-term annual periodicity of spring germination in the field, and dormancy break appears to be driven by low (winter) temperatures and relatively high sand moisture content. To our knowledge this is the first study to document seasonal periodicity in seed germination in a cold desert species with PY and to identify the mechanism (at the whole-seed level) of its occurrence. PMID:28122736

  12. 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

  13. Potential toxic effect on aquatic fauna by the dwarf shrub Empetrum hermaphroditum.

    PubMed

    Brännäs, Eva; Nilsson, Marie-Charlotte; Nilsson, Linda; Gallet, Christiane; Brännäs, Kurt; Berglind, Rune; Eriksson, Lars-Ove; Leffler, Per-Erik; Zackrisson, Olle

    2004-01-01

    The common evergreen dwarf shrub Empetrum hermaphroditum has influence on the functioning of boreal terrestrial ecosystems in northern Sweden. The negative effects of E. hermaphroditum are partly attributed to the production of the dihydrostilbene, batatasin-III, which is released from leaves and litter by rain and snowmelt. In this study, we investigated whether batatasin-III is carried by runoff into streams and lakes during the snowmelt period and whether it is also potentially hazardous to aquatic fauna. Sampling of water from streams and a lake for which the surrounding terrestrial vegetation is dominated by E. hermaphroditum was done during the snowmelt period in May 1993 and in 1998, and analyzed for batatasin-III. Using 24- and 48-hr standard toxicity tests, we analyzed toxicity to brown trout (Salmo trutta) alevins and juvenile water fleas (Daphnia magna). Toxicity (proportion of dead individuals) to trout was tested at pH 6.5 and compared with that of a phenol within a range of concentrations. In the toxicity (proportion of immobilized individuals) test on D. magna, the interactive effect of pH (pH 5.5-7.0) was included. Concentration of batatasin-III was generally higher in 1998 than in 1993 and showed peak levels during snowmelt. Concentration in ephemeral runnels > the lake > streams running through clear-cuts dominated by E. hermaphroditum > control streams lacking adjacent E. hermaphroditum vegetation. The maximum concentration of batatasin-III found was 1.06 mg l(-1). The proportion of dead yolk sac alevins increased significantly (P < 0.001) with increasing concentrations of batatasin-III and time of exposure. After 24 hr, EC50 was 10 mg l(-1). It was 2 mg l(-1) after 48 hr. The effect of phenol was negligible, indicating a specific phytotoxic effect of the bibenzyl structure of batatasin-III. The proportion of mobile D. magna became significantly smaller (P < 0.001) with increasing concentrations of batatasin-III, with decreasing pH, and with

  14. Annual dormancy cycles in buried seeds of shrub species: germination ecology of Sideritis serrata (Labiatae).

    PubMed

    Copete, M A; Herranz, J M; Ferrandis, P; Copete, E

    2015-07-01

    The germination ecology of Sideritis serrata was investigated in order to improve ex-situ propagation techniques and management of their habitat. Specifically, we analysed: (i) influence of temperature, light conditions and seed age on germination patterns; (ii) phenology of germination; (iii) germinative response of buried seeds to seasonal temperature changes; (iv) temperature requirements for induction and breaking of secondary dormancy; (v) ability to form persistent soil seed banks; and (vi) seed bank dynamics. Freshly matured seeds showed conditional physiological dormancy, germinating at low and cool temperatures but not at high ones (28/14 and 32/18 °C). Germination ability increased with time of dry storage, suggesting the existence of non-deep physiological dormancy. Under unheated shade-house conditions, germination was concentrated in the first autumn. S. serrata seeds buried and exposed to natural seasonal temperature variations in the shade-house, exhibited an annual conditional dormancy/non-dormancy cycle, coming out of conditional dormancy in summer and re-entering it in winter. Non-dormant seeds were clearly induced into dormancy when stratified at 5 or 15/4 °C for 8 weeks. Dormant seeds, stratified at 28/14 or 32/18 °C for 16 weeks, became non-dormant if they were subsequently incubated over a temperature range from 15/4 to 32/18 °C. S. serrata is able to form small persistent soil seed banks. The maximum seed life span in the soil was 4 years, decreasing with burial depth. This is the second report of an annual conditional dormancy/non-dormancy cycle in seeds of shrub species.

  15. A mast-seeding desert shrub regulates population dynamics and behavior of its heteromyid dispersers.

    PubMed

    Auger, Janene; Meyer, Susan E; Jenkins, Stephen H

    2016-04-01

    Granivorous rodent populations in deserts are primarily regulated through precipitation-driven resource pulses rather than pulses associated with mast-seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast-seeding in the desert shrub blackbrush (Coleogyne ramosissima), a regionally dominant species in the Mojave-Great Basin Desert transition zone. In a 5-year study at Arches National Park, Utah, USA, we quantified spatiotemporal variation in seed resources in mast and intermast years in blackbrush-dominated and mixed desert vegetation and measured responses of Dipodomys ordii (Ord's kangaroo rat) and Perognathus flavescens (plains pocket mouse). In blackbrush-dominated vegetation, blackbrush seeds comprised >79% of seed production in a mast year, but 0% in the first postmast year. Kangaroo rat abundance in blackbrush-dominated vegetation was highest in the mast year, declined sharply at the end of the first postmast summer, and then remained at low levels for 3 years. Pocket mouse abundance was not as strongly associated with blackbrush seed production. In mixed desert vegetation, kangaroo rat abundance was higher and more uniform through time. Kangaroo rats excluded the smaller pocket mice from resource-rich patches including a pipeline disturbance and also moved their home range centers closer to this disturbance in a year of low blackbrush seed production. Home range size for kangaroo rats was unrelated to seed resource density in the mast year, but resource-poor home ranges were larger (P < 0.001) in the first postmast year, when resources were limiting. Blackbrush seeds are higher in protein and fat but lower in carbohydrates than the more highly preferred seeds of Indian ricegrass (Achnatherum hymenoides) and have similar energy value per unit of handling time. Kangaroo rats cached seeds of these two species in similar spatial configurations, implying that they were equally valued as stored food resources. Blackbrush mast

  16. Bird and ant synergy increases the seed dispersal effectiveness of an ornithochoric shrub.

    PubMed

    Camargo, Paulo H S A; Martins, Milene M; Feitosa, Rodrigo M; Christianini, Alexander V

    2016-06-01

    Seed dispersal may involve different vectors of dispersal in two or more sequential phases (i.e., diplochory). However, contributions of each phase to the overall seed dispersal effectiveness (SDE) are poorly understood and hard to evaluate due to post-dispersal processes that affect seed and seedling survival. We investigated the simultaneous bird (phase 1, in plant canopy) and ant (phase 2, on the floor) contributions to SDE with the ornithochoric shrub Erythroxylum ambiguum in a Brazilian Atlantic forest. Twelve species of birds fed on fruit and dispersed approximately 26 % of the seed crop. The remaining seed crop, 90 % of which contained viable seeds, fell to the ground beneath the parental plant. Ants either cleaned seeds in fruits or carried fallen fruit and seeds from bird feces to their nests. Although E. ambiguum has no adaptation for ant dispersal, ants were as quantitatively important as birds. Birds and ants equally increased germination rates compared to controls. However, birds deposited seeds farther from the parent, where seedling survival was higher (78 %) than it was beneath the parent (44 %), whereas ants carried seeds to their nests, where seedling survival was higher (83 %) than in controls away from their nests (63 %). Diplochory allowed a 42 % increase in SDE compared to dispersal in phase 1 alone. High lipid content in the fruit pulp of E. ambiguum may facilitate the inclusion of ants in a second step of dispersal after diaspores reach the floor. Ants can also buffer the dispersal of diplochorous plants against decreases in phase 1 dispersers.

  17. Soil seed-bank structure and seed-germination dynamics contribute to pulsed shrub encroachment in a grassland-shrubland Chihuahuan ecotone

    NASA Astrophysics Data System (ADS)

    Moreno de las Heras, Mariano; Turnbull, Laura; Wainwright, John

    2015-04-01

    Shrub encroachment is pervasive in many arid and semi-arid landscapes worldwide. Large areas of desert grasslands in southwestern USA have shifted to sparse shrublands dominated by woody species over the last 150 years, accompanied by accelerated soil erosion. A complex range of mechanisms has been suggested to explain the occurrence of this phenomenon, including land-use change, climate variations, and soil erosion feedbacks of vegetation change. An important step to understand patterns in species dominance at desert grassland-shrubland transitions is the understanding of limitations on plant establishment imposed by the shrub-encroachment process. We analyze the structure of soil seed banks and the environmental limitations for seed germination (i.e. soil-water availability and temperature) of dominant species (black grama and creosotebush) across a Chihuahuan grassland-shrubland ecotone (Sevilleta National Wildlife Refuge, New Mexico). Seed density in soils across the ecotone is generally low (200-400 seeds m-2), although is largely concentrated in vegetation clumps (reaching peaks up to 800-1200 seeds m-2 in grass and shrub patches). Species composition in the soil seed-bank is strongly affected by shrub encroachment, with seed densities of grass species (and particularly for black grama) sharply decreasing in shrub-dominated areas. Optimal temperature for seed germination of both black grama and creosotebush (20-25°C) suggests synchronization of plant establishment with the summer monsoonal period. Water-level limitations for seed germination are similar for the two species (about 8-10% soil moisture), although creosotebush seeds need a longer time under optimal water-availability conditions for germination (about 12 days) than black grama seeds (about 7 days). Analysis of temporal series of field-based and simulated soil-moisture levels suggests that creosotebush requires very strong monsoonal precipitation for plant establishment, and therefore shrub

  18. Dense understory dwarf bamboo alters the retention of canopy tree seeds

    NASA Astrophysics Data System (ADS)

    Qian, Feng; Zhang, Tengda; Guo, Qinxue; Tao, Jianping

    2016-05-01

    Tree seed retention is thought to be an important factor in the process of forest community regeneration. Although dense understory dwarf bamboo has been considered to have serious negative effects on the regeneration of forest community species, little attention has been paid to the relationship between dwarf bamboo and seed retention. In a field experiment we manipulated the density of Fargesia decurvata, a common understory dwarf bamboo, to investigate the retention of seeds from five canopy tree species in an evergreen and deciduous broad-leaved mixed forest in Jinfoshan National Nature Reserve, SW China. We found that the median survival time and retention ratio of seeds increased with the increase in bamboo density. Fauna discriminately altered seed retention in bamboo groves of different densities. Arthropods reduced seed survival the most, and seeds removed decreased with increasing bamboo density. Birds removed or ate more seeds in groves of medium bamboo density and consumed fewer seeds in dense or sparse bamboo habitats. Rodents removed a greater number of large and highly profitable seeds in dense bamboo groves but more small and thin-husked seeds in sparse bamboo groves. Seed characteristics, including seed size, seed mass and seed profitability, were important factors affecting seed retention. The results suggested that dense understory dwarf bamboo not only increased seeds concealment and reduced the probability and speed of seed removal but also influenced the trade-off between predation and risk of animal predatory strategies, thereby impacting the quantity and composition of surviving seeds. Our results also indicated that dense understory dwarf bamboo and various seed characteristics can provide good opportunities for seed storage and seed germination and has a potential positive effect on canopy tree regeneration.

  19. 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

  20. 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.

  1. Reciprocal carbon and nitrogen transfer between an ericaceous dwarf shrub and fungi isolated from Piceirhiza bicolorata ectomycorrhizas.

    PubMed

    Grelet, Gwen-Aëlle; Johnson, David; Paterson, Eric; Anderson, Ian C; Alexander, Ian J

    2009-01-01

    The overstorey coniferous trees and understorey ericaceous dwarf shrubs of northern temperate and boreal forests have previously been considered to form mycorrhizas with taxonomically and functionally distinct groups of fungi. Here, we tested the hypothesis that Meliniomyces variabilis and Meliniomyces bicolor, isolated from Piceirhiza bicolorata ectomycorrhizas of pine, can function as ericoid mycorrhizal symbionts with Vaccinium vitis-idaea. We used split-compartment microcosms to measure the reciprocal exchange of (13)C and (15)N between V. vitis-idaea and three fungal isolates in the Hymenoscyphus ericae aggregate isolated from Scots pine ectomycorrhizas (M. variabilis and M. bicolor) or Vaccinium roots (M. variabilis). The extramatrical fungal mycelium of labelled mycorrhizal plants was significantly enriched in (13)C, and the leaves were significantly enriched in (15)N, compared with nonmycorrhizal and nonlabelled controls. * These findings show for the first time that fungi in the H. ericae aggregate, isolated from pine ectomycorrhizas, can transfer C and N and can thus form functional ericoid mycorrhizas in an understorey ericaceous shrub.

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

    PubMed Central

    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

    2014-01-01

    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

  3. Shrub seed banks in mixed conifer forests of northern California and the role of fire in regulating abundance

    Treesearch

    Eric E. Knapp; Phillip C. Weatherspoon; Carl N. Skinner

    2012-01-01

    Understory shrubs play important ecological roles in forests of the western US, but they can also impede early tree growth and lead to fire hazard concerns when very dense. Some of the more common genera (Ceanothus, Arctostaphylos, and Prunus) persist for long periods in the seed bank, even in areas where plants have been...

  4. Habitat fragmentation and altered fire regime create trade-offs for an obligate seeding shrub.

    PubMed

    Regan, Helen M; Crookston, John B; Swab, Rebecca; Franklin, Janet; Lawson, Dawn M

    2010-04-01

    Habitat loss is widely considered the greatest threat to biodiversity. However, habitat loss brings with it myriad other threats that exacerbate impacts to biodiversity. For instance, altered fire regime is associated with habitat loss and fragmentation with unknown consequences to biodiversity. Plant functional groups that rely on fire to complete their life cycle may be adversely affected by disruptions to the natural fire regime, particularly when coupled with population declines due to habitat loss. We used a spatially explicit stochastic population model linked with fire hazard functions to investigate the cumulative effects of habitat loss, fragmentation, and altered fire regime on the expected minimum abundance of a long-lived obligate-seeding shrub, Ceanothus greggii var. perplexans. This species is endemic to the California Floristic Province, a biodiversity hotspot, and is representative of a functional group of plants found in many fire-prone ecosystems. We tested the impact of a range of different fire frequencies under three different combinations of fuel accumulation and weather. The best average fire return interval for population abundance was consistently in the range of 30-50 years. However, observed average fire return intervals in highly fragmented areas can be approximately 20 years or less, and model results show this to be detrimental to C. greggii populations. Results also show that if fires are uncorrelated across habitat fragments then the impact of altered fire regime on populations is worse than the impact of habitat fragmentation because of spatial and temporal decoupling of fire events across the landscape. However, the negative impacts of altered fire regime are outweighed by habitat loss as fragmentation increases. Our results show that large unplanned fires, operating under an altered fire regime, are ultimately detrimental to perennial obligate-seeding shrubs in fragmented landscapes.

  5. Seed production and dispersal by dwarf mistletoe in overstory jeffrey pines in California

    Treesearch

    Robert F. Scharpf; J. R. Parmeter Jr.

    1971-01-01

    Studies in northeastern California showed that the number of dwarf mistletoe (Arceuthobium campylopodum) seeds trapped declined at a logaithmic rate as the distance from overstory source of infection increased. The most seeds were dispersed in the direction of preuading winds. It Is quite likely that storms also aid dispersal. Total numbers of seeds...

  6. Thermogenesis-triggered seed dispersal in dwarf mistletoe

    PubMed Central

    deBruyn, Rolena A.J.; Paetkau, Mark; Ross, Kelly A.; Godfrey, David V.; Friedman, Cynthia Ross

    2015-01-01

    Lodgepole pine dwarf mistletoe (DM), Arceuthobium americanum, is a parasitic flowering plant and forest pathogen in North America. Seed dispersal in DM occurs by explosive discharge. Notably, slight warming of ripe DM fruit in the laboratory can trigger explosions. Previously, we showed that alternative oxidase, a protein involved in endogenous heat production (thermogenesis) in plants, is present in DM fruit. These observations have led us to investigate if thermogenesis induces discharge. Here, infrared thermographs reveal that ripe DM fruits display an anomalous increase in surface temperature by an average of 2.1±0.8 °C over an average time of 103±29 s (n=9, 95% confidence interval) before dehiscence. Furthermore, both non-isothermal and isothermal modulated differential scanning calorimetry consistently show an exothermic event (~1 J g−1) in the non-reversible heat flow just prior to discharge. These results support thermogenesis-triggered seed discharge, never before observed in any plant. PMID:25662062

  7. Thermogenesis-triggered seed dispersal in dwarf mistletoe.

    PubMed

    deBruyn, Rolena A J; Paetkau, Mark; Ross, Kelly A; Godfrey, David V; Friedman, Cynthia Ross

    2015-02-09

    Lodgepole pine dwarf mistletoe (DM), Arceuthobium americanum, is a parasitic flowering plant and forest pathogen in North America. Seed dispersal in DM occurs by explosive discharge. Notably, slight warming of ripe DM fruit in the laboratory can trigger explosions. Previously, we showed that alternative oxidase, a protein involved in endogenous heat production (thermogenesis) in plants, is present in DM fruit. These observations have led us to investigate if thermogenesis induces discharge. Here, infrared thermographs reveal that ripe DM fruits display an anomalous increase in surface temperature by an average of 2.1±0.8 °C over an average time of 103±29 s (n=9, 95% confidence interval) before dehiscence. Furthermore, both non-isothermal and isothermal modulated differential scanning calorimetry consistently show an exothermic event (~1 J g(-1)) in the non-reversible heat flow just prior to discharge. These results support thermogenesis-triggered seed discharge, never before observed in any plant.

  8. Invasive exotic shrub modifies a classic animal-habitat relationship and alters patterns of vertebrate seed predation.

    PubMed

    Guiden, Peter W; Orrock, John L

    2017-02-01

    Recent evidence suggests that invasive exotic plants can provide novel habitats that alter animal behavior. However, it remains unclear whether classic animal-habitat associations that influence the spatial distribution of plant-animal interactions, such as small mammal use of downed woody debris, persist in invaded habitats. We removed an invasive exotic shrub (buckthorn, Rhamnus cathartica) from 7 of 15 plots in Wisconsin. In each plot, we deployed 200 tagged Quercus rubra seeds in November 2014. After five months, tags were recovered to track spatial patterns of small mammal seed predation. Most recovered tags were associated with consumed seeds (95%); live-trapping, ancillary camera-trapping, and previous behavioral studies suggest that white-footed mice (Peromyscus leucopus) were responsible for most seed predation. In habitats without R. cathartica, most seed predation occurred near woody debris. In habitats with R. cathartica, small mammals rarely consumed seeds near woody debris, and seed predation occurred farther from the plot center and was less spatially clustered. Our results illustrate that invasive exotic shrubs can disrupt an otherwise common animal-habitat relationship. Failing to account for changes in habitat use may diminish our ability to predict animal distributions and outcomes of species interactions in novel habitats created by invasive exotic plants. © 2016 by the Ecological Society of America.

  9. The formation of the patterns of desert shrub communities on the Western Ordos Plateau, China: the roles of seed dispersal and sand burial.

    PubMed

    Wang, Yange; Yang, Xiaohui; Shi, Zhongjie

    2013-01-01

    The western Ordos Plateau is a key area of shrub diversity and a National Nature Reserve of endangered shrub species in north-west China. Desert expansion is becoming the most important threat to these endangered species. However, little is known about the effects of sand burial on the dynamics of the shrub community. This study aims to investigate how the shrubs as a community and as different individual shrubs respond to the disturbances caused by the desert expansion. The approach used by this study is to separate the seed-dispersal strategy from the sand-burial forces that are involved in structuring the shrub communities at different disturbance stages. Four communities for different disturbance stages were surveyed by using 50×50 m plots. The individual shrubs were classified into coloniser and successor groups at the seed-dispersal stage and strong and weak sand-burial tolerance groups at the sand-expansion stage. We employed spatial point pattern analysis with null models for each community to examine the seed-dispersal strategy and sand-burial forces affecting community distribution patterns. At the seed-dispersal stage, the interactions between the colonisers and the successors showed significant positive correlation at a scale of 0-1 m and significant negative correlation at a scale of 2 m; significant negative correlations between the groups with strong and weak sand-burial tolerance in the early stage of sand expansion at scales of 3-6 m, and significant positive correlation in the later stage of sand expansion at a scale of 13 m, were found. Seed-dispersal strategy is a reasonable mechanism to explain the shrub community pattern formation in the earlier stages, whereas sand burial is the primary reason for the disappearance of shrubs with weak sand-burial tolerance, this irreversible disturbance causes homogenisation of the community structure and produces aging populations of shrub species. This has an important influence on the succession direction

  10. Growth responses of low-alpine dwarf-shrub heath species to nitrogen deposition and management.

    PubMed

    Britton, Andrea J; Fisher, Julia M

    2008-06-01

    Nitrogen deposition is a continuing problem in European alpine regions. We hypothesised that, despite climatic limitations, low-alpine Calluna heathland would respond to nitrogen addition with increased shoot growth and flowering and that fire and grazing would modify responses. In a five-year study, 0-50kgNha(-1)y(-1) were added, combined with burning (+/-) and clipping (+/-). Calluna vulgaris responded with increased shoot extension, but effects on flowering were variable. Burning enhanced the positive effect of nitrogen addition and negative effects of clipping. Sub-dominant shrubs generally did not respond to nitrogen. C. vulgaris shoot extension was stimulated by nitrogen addition of 10kgNha(-1)y(-1) (above background) supporting suggestions that alpine heathlands are sensitive to low levels of nitrogen deposition. Increased C. vulgaris growth could negatively impact on important lichen components of this vegetation through increased shading and competition. Climatic factors constrain productivity in this community, but do not prevent rapid responses to nitrogen deposition by some species.

  11. Irrigation and fertilization effects on seed number, size, germination and seedling growth: implications for desert shrub establishment.

    PubMed

    Breen, A N; Richards, J H

    2008-08-01

    Plants with limited resources adjust partitioning among growth, survival, and reproduction. We tested the effects of water and nutrient amendments on seed production, size, and quality in Sarcobatus vermiculatus (greasewood) to assess the magnitude and importance of changes in reproductive partitioning. In addition, we assessed interactions among the environment of seed-producing plants (adult plant scale), seed size, and seedling microenvironment (seedling scale) on successful seedling establishment. Interactions of these factors determine the scale of resource heterogeneity that affects seedling establishment in deserts. Both total number of seeds produced per plant and seed quality (weight and germination) increased significantly in the enriched treatment in a 3-year field experiment. Seedling length 3 days after germination and seed N concentration, other measures of seed quality, were higher for seed from both irrigated and enriched plants than for seed from control plants. Field S. vermiculatus seed production and quality can be substantially increased with irrigation and nutrient enrichment at the adult plant scale and this allows management of seed availability for restoration. However, based on a greenhouse study, seedling environment, not the environment of the seed-producing plant or seed size, was the most important factor affecting seedling germination, survival, and growth. Thus it appears that production of more seed may be more important than improved seed quality, because higher quality seed did not compensate for a low-resource seedling environment. For both natural establishment and restoration this suggests that heterogeneity at the scale of seedling microsites, perhaps combined with fertilization of adult shrubs (or multi-plant patches), would produce the greatest benefit for establishing seedlings in the field.

  12. Bottom-up effects of nutrient availability on flower production, pollinator visitation, and seed output in a high-Andean shrub.

    PubMed

    Muñoz, Alejandro A; Celedon-Neghme, Constanza; Cavieres, Lohengrin A; Arroyo, Mary T K

    2005-03-01

    Soil nutrient availability directly enhances vegetative growth, flowering, and fruiting in alpine ecosystems. However, the impacts of nutrient addition on pollinator visitation, which could affect seed output indirectly, are unknown. In a nutrient addition experiment, we tested the hypothesis that seed output in the insect-pollinated, self-incompatible shrub, Chuquiraga oppositifolia (Asteraceae) of the Andes of central Chile, is enhanced by soil nitrogen (N) availability. We aimed to monitor total shrub floral display, size of flower heads (capitula), pollinator visitation patterns, and seed output during three growing seasons on control and N addition shrubs. N addition did not augment floral display, size of capitula, pollinator visitation, or seed output during the first growing season. Seed mass and viability were 25-40% lower in fertilised shrubs. During the second growing season only 33% of the N addition shrubs flowered compared to 71% of controls, and a significant (50%) enhancement in vegetative growth occurred in fertilised shrubs. During the third growing season, floral display in N addition shrubs was more than double that of controls, received more than twice the number of insect pollinator visits, and seed output was three- to four-fold higher compared to controls. A significant (50%) enhancement in vegetative growth again occurred in N addition shrubs. Results of this study strongly suggest that soil N availability produces strong positive bottom-up effects on the reproductive output of the alpine shrub C. oppositifolia. Despite taking considerably longer to be manifest in comparison to the previously reported top-down indirect negative effects of lizard predators in the same study system, our results suggest that both bottom-up and top-down forces are important in controlling the reproductive output of an alpine shrub.

  13. 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.

  14. Spread of dwarf mistletoe from discrete seed sources into young stands of ponderosa and Jeffrey pines

    Treesearch

    J. R. Parmeter Jr.

    1972-01-01

    The maximum distance of spread of dwarf mistletoes from isolated overstory pines into surrounding reproduction averages 120 feet. The rate of infection in young trees declined as distance from the seed source increased and was generally greatest in the direction of prevailing winds. This pattern of infection was similar to the previously reported pattern of seed...

  15. Impacts of winter icing events on the growth, phenology and physiology of sub-arctic dwarf shrubs.

    PubMed

    Preece, Catherine; Callaghan, Terry V; Phoenix, Gareth K

    2012-12-01

    The Arctic is experiencing the greatest climate change in winter, including increases in freeze-thaw cycles that can result in ice encasement of vegetation. Ice encasement can expose plants to hypoxia and greater temperature extremes, but currently the impacts of icing on plants in the field remain little understood. With this in mind, a unique field manipulation experiment was established in heathland in northern Sweden with ice encasement simulated in early March 2008, 2009 and 2010 until natural thaw each spring. In the following summers we assessed the impacts on flowering, bud phenology, shoot growth and mortality and leaf damage (measured by chlorophyll fluorescence and electrolyte leakage) of the three dominant dwarf shrub species Empetrum nigrum, Vaccinium vitis-idaea (both evergreen) and Vaccinium myrtillus (deciduous). Two consecutive winters of icing decreased V. vitis-idaea flowering by 57%, while flowering of V. myrtillus and E. nigrum remained unaffected. Vaccinium myrtillus showed earlier budburst but shoot growth for all species was unchanged. Shoot mortality of V. myrtillus and V. vitis-idaea increased after the first year (by 70 and 165%, respectively) and again for V. myrtillus following the third year (by 67%), while E. nigrum shoot mortality remained unaffected, as were chlorophyll fluorescence and electrolyte leakage in all species. Overall, the sub-arctic heathland was relatively tolerant to icing, but the considerable shoot mortality of V. myrtillus contrasting with the general tolerance of E. nigrum suggests plant community structure in the longer term could change if winters continue to see a greater frequency of icing events.

  16. 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.

  17. 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.

  18. 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

  19. The influence of spruce on acidity and nutrient content in soils of Northern Taiga dwarf shrub-green moss spruce forests

    NASA Astrophysics Data System (ADS)

    Orlova, M. A.; Lukina, N. V.; Smirnov, V. E.; Artemkina, N. A.

    2016-11-01

    Presently, among the works considering the influence of forest trees on soil properties, the idea that spruce ( Picea abies) promotes the acidification of soils predominates. The aim of this work is to assess the effects of spruce trees of different ages and Kraft classes on the acidity and content of available nutrient compounds in the soils under boreal dwarf shrub-green moss spruce forests by the example of forest soils in the Kola Peninsula. The soils are typical iron-illuvial podzols (Albic Rustic Podzols (Arenic)). Three probable ways of developing soils under spruce forests with the moss-dwarf shrub ground cover are considered. The soils under windfall-soil complexes of flat mesodepressions present the initial status. The acidity of organic soil horizons from the initial stage of mesodepression overgrowth to the formation of adult trees changed nonlinearly: the soil acidity reached its maximum under the 30-40-year-old trees and decreased under the trees older than 100 years. The contents of nitrogen and available nutrients increased. The acidity of the mineral soil horizons under the trees at the ages of 110-135 and 190-220 years was comparable, but higher than that under the 30-40-year-old trees. The differences in the strength and trends of the trees' effect on the soils are explained by the age of spruce trees and their belonging to different Kraft classes.

  20. The Formation of the Patterns of Desert Shrub Communities on the Western Ordos Plateau, China: The Roles of Seed Dispersal and Sand Burial

    PubMed Central

    Wang, Yange; Yang, Xiaohui; Shi, Zhongjie

    2013-01-01

    The western Ordos Plateau is a key area of shrub diversity and a National Nature Reserve of endangered shrub species in north-west China. Desert expansion is becoming the most important threat to these endangered species. However, little is known about the effects of sand burial on the dynamics of the shrub community. This study aims to investigate how the shrubs as a community and as different individual shrubs respond to the disturbances caused by the desert expansion. The approach used by this study is to separate the seed-dispersal strategy from the sand-burial forces that are involved in structuring the shrub communities at different disturbance stages. Four communities for different disturbance stages were surveyed by using 50×50 m plots. The individual shrubs were classified into coloniser and successor groups at the seed-dispersal stage and strong and weak sand-burial tolerance groups at the sand-expansion stage. We employed spatial point pattern analysis with null models for each community to examine the seed-dispersal strategy and sand-burial forces affecting community distribution patterns. At the seed-dispersal stage, the interactions between the colonisers and the successors showed significant positive correlation at a scale of 0–1 m and significant negative correlation at a scale of 2 m; significant negative correlations between the groups with strong and weak sand-burial tolerance in the early stage of sand expansion at scales of 3–6 m, and significant positive correlation in the later stage of sand expansion at a scale of 13 m, were found. Seed-dispersal strategy is a reasonable mechanism to explain the shrub community pattern formation in the earlier stages, whereas sand burial is the primary reason for the disappearance of shrubs with weak sand-burial tolerance, this irreversible disturbance causes homogenisation of the community structure and produces aging populations of shrub species. This has an important influence on the succession

  1. Seed viability, germination, and radicle growth of dwarf mistletoe in California

    Treesearch

    Robert F. Scharpf

    1970-01-01

    Two species of dwarf mistletoe were studied: Arceuthobium abietinum (Engelm.) Hawksworth and Wiens and A. occidentale Engelm. Viability of fresh seeds was high and not significantly influenced by year of collection, where collected, or plant from which collected. Temperature affected viability most noticeably. It also significantly...

  2. One seed source of Jeffrey pine shows resistance to dwarf mistletoe

    Treesearch

    Robert F. Scharpf; Bohun B. Kinloch; James L. Jenkinson

    1992-01-01

    Four seed sources of Jeffrey pine (Pinus jeffreyi) were selected for testing through controlled inoculation for resistance to dwarf mistletoe (Arceuthobium campylopodum). The pines were 7 years old and part of a progeny test planting established by the USDA Forest Service's Institute of Forest Genetics, Placewille,...

  3. Two decades of demography reveals that seed and seedling transitions limit population persistence in a translocated shrub

    PubMed Central

    Gross, C. L.; Mackay, D.

    2014-01-01

    Background and Aims Olearia flocktoniae is an endangered shrub that was passively translocated from its natural ecosystem, where it has since gone extinct. This study aimed to determine sensitivities vital to populations persisting in human-created areas. Methods Population colonization, longevity and extinction were investigated over 20 years using 133 populations. Seed-bank longevity was determined from germination trials of seeds exhumed from extinct and extant sites via a 10-year glasshouse trial and by in situ sowing experiments. From 27 populations, 98 cohorts were followed and matrix models of transitions from seeds to adults were used to evaluate the intrinsic rate of population growth against disturbance histories. Ten populations (38 cohorts) with different disturbance histories were used to evaluate sensitivities in vital rates. Key Results Most populations had few individuals (∼30) and were transient (<5 years above ground). The intrinsic population growth rate was rarely >1 and all but two populations were extinct at year 20. Seeds were short-lived in situ. Although >1000 seeds per plant were produced annually in most populations, sensitivity analysis showed that the transition to the seed bank and the transition from the seed bank to seedlings are key vulnerabilities in the life-cycle. Conclusions Seedling establishment is promoted by recent disturbance. Increasing the number of disturbance events in populations, even severe disturbances that almost extirpate populations, significantly increases longer-term population persistence. Only populations that were disturbed annually survived the full 20 years of the study. The results show that translocated populations of O. flocktoniae will fail to persist without active management. PMID:24844983

  4. Two decades of demography reveals that seed and seedling transitions limit population persistence in a translocated shrub.

    PubMed

    Gross, C L; Mackay, D

    2014-07-01

    Olearia flocktoniae is an endangered shrub that was passively translocated from its natural ecosystem, where it has since gone extinct. This study aimed to determine sensitivities vital to populations persisting in human-created areas. Population colonization, longevity and extinction were investigated over 20 years using 133 populations. Seed-bank longevity was determined from germination trials of seeds exhumed from extinct and extant sites via a 10-year glasshouse trial and by in situ sowing experiments. From 27 populations, 98 cohorts were followed and matrix models of transitions from seeds to adults were used to evaluate the intrinsic rate of population growth against disturbance histories. Ten populations (38 cohorts) with different disturbance histories were used to evaluate sensitivities in vital rates. Most populations had few individuals (∼30) and were transient (<5 years above ground). The intrinsic population growth rate was rarely >1 and all but two populations were extinct at year 20. Seeds were short-lived in situ. Although >1000 seeds per plant were produced annually in most populations, sensitivity analysis showed that the transition to the seed bank and the transition from the seed bank to seedlings are key vulnerabilities in the life-cycle. Seedling establishment is promoted by recent disturbance. Increasing the number of disturbance events in populations, even severe disturbances that almost extirpate populations, significantly increases longer-term population persistence. Only populations that were disturbed annually survived the full 20 years of the study. The results show that translocated populations of O. flocktoniae will fail to persist without active management. © The Author 2014. Published by Oxford University Press on behalf of the Annals of Botany Company.

  5. What are the consequences of ant-seed interactions on the abundance of two dry-fruited shrubs in a Mediterranean scrub?

    PubMed

    Arnan, Xavier; Rodrigo, A; Retana, J

    2011-12-01

    Strong interactions between dry-fruited shrubs and seed-harvesting ants are expected in early successional scrubs, where both groups have a major presence. We have analysed the implications of the seed characteristics of two dry-fruited shrub species (Coronilla minima and Dorycnium pentaphyllum) on seed predation and dispersal mediated by harvester ants and the consequences of these processes on spatio-temporal patterns of plant abundance in a heterogeneous environment. We found that large C. minima seeds were collected much more (39%) than small D. pentaphyllum seeds (2%). However, not all of the removed seeds of these plant species were consumed, and 12.8% of the seeds were lost along the trails, which increased dispersal distances compared with abiotic dispersal alone. Seed dropping occurred among all microhabitats of the two plant species, but especially in open microhabitats, which are the most suitable ones for plant establishment. The two plant species increased their presence in the study area during the study period: C. minima in open microhabitats and D. pentaphyllum in high vegetation. The large size of C. minima seeds probably limited the primary seed dispersal of this species, but may have allowed strong interaction with ants. Thus, seed dispersal by ants resulted in C. minima seeds reaching more suitable microhabitats by means of increasing dispersal distance and redistribution among microhabitats. In contrast, the smaller size of D. pentaphyllum seeds arguably allows abiotic seed dispersal over longer distances and colonization of all types of microhabitats, although it probably also limits their interaction with ants and, consequently, their redistribution in suitable microhabitats. We suggest that dyszoochory could contribute to the success of plant species with different seed characteristics in scrub habitats where seeds are abundantly collected by seed-harvesting ants.

  6. Wet-season Dormancy Release in Seed Banks of a Tropical Leguminous Shrub is Determined by Wet Heat

    PubMed Central

    VAN KLINKEN, RIEKS D.; FLACK, LLOYD K.; PETTIT, WILLIAM

    2006-01-01

    • Background and Aims Hard-seeded (physical) dormancy is common among plants, yet mechanisms for dormancy release are poorly understood, especially in the tropics. The following questions are asked: (a) whether dormancy release in seed banks of the tropical shrub Parkinsonia aculeata (Caesalpiniaceae) is determined by wet heat (incubation under wet, warm to hot, conditions); and (b) whether its effect is modified by microclimate. • Methods A seed burial trial was conducted in the wet–dry tropics (northern Australia) to compare dormancy release across different habitats (open, artificial cover, ground cover and canopy cover), burial depths (0, 3 and 20 cm) and burial durations (2, 6 and 14 weeks). Results were compared with predictions using a laboratory-derived relationship between wet heat and dormancy release, and microclimate data collected during the trial. • Key Results Wet heat (defined as the soil temperature above which seeds were exposed to field capacity or higher for a cumulative total of 24 h) was 43·6 °C in the 0 cm open treatment, and decreased with increasing shade and depth to 29·5 °C at 20 cm under canopy cover. The dormancy release model showed that wet heat was a good predictor of the proportion of seeds remaining dormant. Furthermore, dormancy release was particularly sensitive to wet heat across the temperature range encountered across treatments. This resulted in a 16-fold difference in dormancy levels between open (<5 % of seeds still dormant) and covered (82 %) microhabitats. • Conclusions These results demonstrate that wet heat is the principal dormancy release mechanism for P. aculeata when conditions are hot and wet. They also highlight the potential importance of microclimate in driving the population dynamics of such species. PMID:16891334

  7. Wet-season dormancy release in seed banks of a tropical leguminous shrub is determined by wet heat.

    PubMed

    van Klinken, Rieks D; Flack, Lloyd K; Pettit, William

    2006-10-01

    Hard-seeded (physical) dormancy is common among plants, yet mechanisms for dormancy release are poorly understood, especially in the tropics. The following questions are asked: (a) whether dormancy release in seed banks of the tropical shrub Parkinsonia aculeata (Caesalpiniaceae) is determined by wet heat (incubation under wet, warm to hot, conditions); and (b) whether its effect is modified by microclimate. A seed burial trial was conducted in the wet-dry tropics (northern Australia) to compare dormancy release across different habitats (open, artificial cover, ground cover and canopy cover), burial depths (0, 3 and 20 cm) and burial durations (2, 6 and 14 weeks). Results were compared with predictions using a laboratory-derived relationship between wet heat and dormancy release, and microclimate data collected during the trial. Wet heat (defined as the soil temperature above which seeds were exposed to field capacity or higher for a cumulative total of 24 h) was 43.6 degrees C in the 0 cm open treatment, and decreased with increasing shade and depth to 29.5 degrees C at 20 cm under canopy cover. The dormancy release model showed that wet heat was a good predictor of the proportion of seeds remaining dormant. Furthermore, dormancy release was particularly sensitive to wet heat across the temperature range encountered across treatments. This resulted in a 16-fold difference in dormancy levels between open (<5 % of seeds still dormant) and covered (82 %) microhabitats. These results demonstrate that wet heat is the principal dormancy release mechanism for P. aculeata when conditions are hot and wet. They also highlight the potential importance of microclimate in driving the population dynamics of such species.

  8. Dwarf

    USDA-ARS?s Scientific Manuscript database

    Alfalfa dwarf occurs rarely in alfalfa fields. Dwarf has been identified only in California, where it is found at a low frequency. Plants with symptoms of dwarf were reported in the 1950s in Mississippi, Georgia, and Rhode Island, but experimental confirmation of the disease in those States was no...

  9. Long-term experimental warming, shading and nutrient addition affect the concentration of phenolic compounds in arctic-alpine deciduous and evergreen dwarf shrubs.

    PubMed

    Hansen, Anja H; Jonasson, Sven; Michelsen, Anders; Julkunen-Tiitto, Riitta

    2006-02-01

    Environmental changes are likely to alter the chemical composition of plant tissues, including content and concentrations of secondary compounds, and thereby affect the food sources of herbivores. After 10 years of experimental increase of temperature, nutrient levels and light attenuation in a sub-arctic, alpine ecosystem, we investigated the effects on carbon based secondary compounds (CBSC) and nitrogen in one dominant deciduous dwarf shrub, Salix herbacea x polaris and two dominant evergreen dwarf shrubs, Cassiope tetragona and Vaccinium vitis-idaea throughout one growing season. The main aims were to compare the seasonal course and treatment effects on CBSC among the species, life forms and leaf cohorts and to examine whether the responses in different CBSC were consistent across compounds. The changes in leaf chemistry both during the season and in response to the treatments were higher in S. herbacea x polaris than in the corresponding current year's leaf cohort of the evergreen C. tetragona. The changes were also much higher than in the 1-year-old leaves of the two evergreens probably due to differences in dilution and turnover of CBSC in growing and mature leaves paired with different rates of allocation. Most low molecular weight phenolics in the current year's leaves decreased in all treatments. Condensed tannins and the tannin-to-N ratio, however, either increased or decreased, and the strength and even direction of the responses varied among the species and leaf cohorts, supporting views of influential factors additional to resource-based or developmental controls, as e.g. species specific or genetic controls of CBSC. The results indicate that there is no common response to environmental changes across species and substances. However, the pronounced treatment responses imply that the quality of the herbivore forage is likely to be strongly affected in a changing arctic environment, although both the direction and strength of the responses will be

  10. Effect of Temperature, Light and Salinity on Seed Germination and Radicle Growth of the Geographically Widespread Halophyte Shrub Halocnemum strobilaceum

    PubMed Central

    Qu, Xiao-Xia; Huang, Zhen-Ying; Baskin, Jerry M.; Baskin, Carol C.

    2008-01-01

    Background and Aims The small leafy succulent shrub Halocnemum strobilaceum occurs in saline habitats from northern Africa and Mediterranean Europe to western Asia, and it is a dominant species in salt deserts such as those of north-west China. The effects of temperature, light/darkness and NaCl salinity were tested on seed germination, and the effects of salinity were tested on seed germination recovery, radicle growth and radicle elongation recovery, using seeds from north-west China; the results were compared with those previously reported on this species from ‘salt steppes’ in the Mediterranean region of Spain. Methods Seed germination was tested over a range of temperatures in light and in darkness and over a range of salinities at 25 °C in the light. Seeds that did not germinate in the NaCl solutions were tested for germination in deionized water. Seeds from which radicles had barely emerged in deionized water were transferred to NaCl solutions for 10 d and then back to deionized water for 10 d to test for radicle growth and recovery. Key Results Seeds germinated to higher percentages in light than in darkness and at high than at low temperatures. Germination percentages decreased with an increase in salinity from 0·1 to 0·75 m NaCl. Seeds that did not germinate in NaCl solutions did so after transfer to deionized water. Radicle elongation was increased by low salinity, and then it decreased with an increase in salinity, being completely inhibited by ≥2·0 m NaCl. Elongation of radicles from salt solutions <3·0 m resumed after seedlings were transferred to deionized water. Conclusions The seed and early seedling growth stages of the life cycle of H. strobilaceum are very salt tolerant, and their physiological responses differ somewhat between the Mediterranean ‘salt steppe’ of Spain and the inland cold salt desert of north-west China. PMID:17428834

  11. Nutritive value and qualitative assessment of secondary compounds in seeds of eight tropical browse, shrub and pulse legumes.

    PubMed

    Babayemi, O J; Demeyer, D; Fievez, V

    2004-01-01

    Seeds of four tropical multipurpose trees (Albizia saman, Albizia lebbeck, Albizia rhizonse, Leucaena leucocephala), two shrubs (Tephrosia candida, Tephrosia bracteolata) and two pulse legume (Lablab purpureus, Canavalia ensiformis) were chemically analysed for dry matter (DM), ash, crude protein (CP), neutral detergent fibre (NDF) and ether extract (EE). Qualitative evaluation of secondary metabolites (saponins, phenols, steroids, and alkaloids) was elucidated. The DM, ash, CP, NDF and EE ranged between 88.9-93.6 %, 3.0-5.4 %, 24.8-38.2 %, 22.1-46.9 % and 2.0-17.0 % respectively. All seed species contained at least one group of secondary plant metabolites and steroids were common to all except C. ensiformis that was not implicated for any. A. lebbeck and A. rhizonse showed low saponin content. Indications for water soluble tannins were reported for L. leucocephala while the two species of Tephrosia contained flavonoids or condensed tannins. The study suggested the potentials of the legumes seed species as a feed source for ruminants.

  12. Effects of seed bank disturbance on the fine-scale genetic structure of populations of the rare shrub Grevillea macleayana.

    PubMed

    England, P R; Whelan, R J; Ayre, D J

    2003-11-01

    Dispersal in most plants is mediated by the movement of seeds and pollen, which move genes across the landscape differently. Grevillea macleayana is a rare, fire-dependent Australian shrub with large seeds lacking adaptations for dispersal; yet it produces inflorescences adapted to pollination by highly mobile vertebrates (eg birds). Interpreting fine-scale genetic structure in the light of these two processes is confounded by the recent imposition of anthropogenic disturbances with potentially contrasting genetic consequences: (1) the unusual foraging behaviour of exotic honeybees and 2. widespread disturbance of the soil-stored seedbank by road building and quarrying. To test for evidence of fine-scale genetic structure within G. macleayana populations and to test the prediction that such structure might be masked by disturbance of the seed bank, we sampled two sites in undisturbed habitat and compared their genetic structure with two sites that had been strongly affected by road building using a test for spatial autocorrelation of genotypes. High selfing levels inferred from genotypes at all four sites implies that pollen dispersal is limited. Consistent with this, we observed substantial spatial clustering of genes at 10 m or less in the two undisturbed populations and argue that this reflects the predicted effects of both high selfing levels and limited seed dispersal. In contrast, at the two sites disturbed by road building, spatial autocorrelation was weak. This suggests there has been mixing of the seed bank, counteracting the naturally low dispersal and elevated selfing due to honeybees. Pollination between near neighbours with reduced relatedness potentially has fitness consequences for G. macleayana in disturbed sites.

  13. Consumers limit the abundance and dynamics of a perennial shrub with a seed bank

    USGS Publications Warehouse

    Kauffman, M.J.; Maron, J.L.

    2006-01-01

    For nearly 30 years, ecologists have argued that predators of seeds and seedlings seldom have population-level effects on plants with persistent seed banks and density-dependent seedling survival. We parameterized stage-based population models that incorporated density dependence and seed dormancy with data from a 5.5-year experiment that quantified how granivorous mice and herbivorous voles influence bush lupine (Lupinus arboreus) demography. We asked how seed dormancy and density-dependent seedling survival mediate the impacts of these consumers in dune and grassland habitats. In dune habitat, mice reduced analytical ?? (the intrinsic rate of population growth) by 39%, the equilibrium number of above-ground plants by 90%, and the seed bank by 98%; voles had minimal effects. In adjacent grasslands, mice had minimal effects, but seedling herbivory by voles reduced analytical ?? by 15% and reduced both the equilibrium number of aboveground plants and dormant seeds by 63%. A bootstrap analysis demonstrated that these consumer effects were robust to parameter uncertainty. Our results demonstrate that the quantitative strengths of seed dormancy and density-dependent seedling survival-not their mere existence-critically mediate consumer effects. This study suggests that plant population dynamics and distribution may be more strongly influenced by consumers of seeds and seedlings than is currently recognized. ?? 2006 by The University of Chicago.

  14. Low Rate of Between-Population Seed Dispersal Restricts Genetic Connectivity and Metapopulation Dynamics in a Clonal Shrub

    PubMed Central

    Merwin, Laura; He, Tianhua; Lamont, Byron B.; Enright, Neal J.; Krauss, Siegfried L.

    2012-01-01

    Clonal species normally have low seed production, low recruitment rates and long lifespans, and it is expected that the rates of long-distance dispersal (LDD) of seeds will be low as well. Banksia candolleana is a clonal shrub in Mediterranean-type, fire-prone sclerophyll shrublands of southwestern Australia, whose reproductive biology and population dynamics contrast with those of co-occurring nonclonal congeneric species, all of which are restricted to a mosaic of sand dunes set within a matrix of inhospitable swales. Using microsatellite markers, we genotyped 499 plants in all 15 populations of B. candolleana within a 12-km2 area, assessed population genetic differentiation, and quantified the effective rate of interpopulation seed dispersal through genetic assignment of individuals to populations. We measured life history, reproductive and demographic attributes, and compared these with two co-occurring Banksia species, a non-clonal resprouter and a nonsprouter. B. candolleana has much higher levels of population genetic differentiation, and one-third the rate of interpopulation seed migration, as the other two species (2.2% vs 5.5−6.8% of genotyped plants inferred to be immigrants), though distances reached by LDD are comparable (0.3−2.3 km). The low rate of interpopulation dispersal was supported by an analysis of the age structure of three populations that suggests a mean interdune migration rate of <800 m in 200 years, and 60% of suitable dunes remain uninhabited. Thus, B. candolleana has poor properties for promoting long-distance dispersal. It is unclear if these are idiosyncratic to this species or whether such properties are to be expected of clonal species in general where LDD is less critical for species survival. PMID:23209839

  15. Strong dependence of a pioneer shrub on seed dispersal services provided by an endemic endangered lizard in a Mediterranean island ecosystem

    PubMed Central

    Santamaría, Luís; Calviño-Cancela, María

    2017-01-01

    The accelerating rate of vertebrate extinctions and population declines threatens to disrupt important ecological interactions, altering key ecosystem processes such as animal seed dispersal. The study of highly specialized mutualistic interactions is crucial to predict the consequences of population declines and extinctions. Islands offer unique opportunities to study highly specialized interactions, as they often have naturally depauperated faunas and are experiencing high rates of human-driven extinctions. In this study, we assess the effect of seed dispersal on seedling recruitment of Ephedra fragilis (Ephedraceae) on a Mediterranean island ecosystem. We used field data and stochastic simulation modeling to estimate seed fate and recruitment patterns of this pioneer shrub typical of arid and semiarid areas, and to estimate the dependence of recruitment on the lizard Podarcis lilfordi (Lacertidae), its only known seed disperser. Ephedra fragilis recruitment highly depended on lizards: lizards produced 3.8 times more newly-emerged seedlings than non-dispersed seeds and no seedlings from undispersed seeds survived the study period. Seed dispersal by lizards was mostly to open sites, which was key for the increased success observed, while undispersed seeds, falling under mother plants, suffered higher predation and lower seedling emergence and survival. The ability of this pioneer shrub to get established in open ground is crucial for vegetation colonization and restoration, especially on degraded lands affected by desertification, where they act as nurse plants for other species. Lizards are key in this process, which has important consequences for community structure and ecosystem functioning. PMID:28827820

  16. Effect of cold stratification treatments on germination of drought tolerant shrubs seeds.

    PubMed

    Olmez, Zafer; Temel, Fatih; Gokturk, Askin; Yahyaoglu, Zeki

    2007-04-01

    This study was carried out to determine effects of different durations (20, 40, 60 days and control) of cold stratification treatments on seed germination and to overcome dormancy in seeds of twelve different drought tolerant plants. The species used in this study were Arbutus andrachne L., Cistus creticus L., Colutea armena Bois. Huet., Cotinus coggygria Scop., Cotoneaster numullaria Fisch. and Mey, Elaeagnus angustifolia L., Jasminum fruticans L., Paliurus spina-christii Mill., Punica granatum L., Pyracantha coccinea Roem., Rhus coriaria L., and Ziziphus jujuba Mill. The seeds were sown in polyethylene pots under greenhouse and on seedbeds under open field conditions. Statistical design was a randomized complete block design with three replications. Germinated seeds were counted and observed periodically for 90 days after sowing to determine germination percentages (GP) and germination rates (GR). While the highest GP were determined according to duration of cold stratification under greenhouse conditions for each species were 44.2% for 60 days, 2.5% for 20 days, 85.6% for 60 days, 13.5% for 20 and 60 days, 64.3% for 20 days, 11.2% for 60 days, 8.2% for 20 days and 14.1% for 20 days for Cotinus coggygria, Cotoneaster numullaria, Jasminum fruticans, Paliurus spina-christii, Pyracantha coccinea, Punica granatum, Rhus coriaria and Ziziphus jujuba respectively The highest GP were 16.5% forArbutus andrachne and 91.3% for Colutea armena for 20 days cold stratified seeds and sown under open field conditions. Furthermore, the highest GP were obtained from seeds of Cistus creticus (27.5%) and Elaeagnus angustifolia (56.2%) in control sowing.

  17. Fruit Size Determines the Role of Three Scatter-Hoarding Rodents as Dispersers or Seed Predators of a Fleshy-Fruited Atacama Desert Shrub.

    PubMed

    Luna, Claudia A; Loayza, Andrea P; Squeo, Francisco A

    2016-01-01

    Scatter-hoarding rodents can act as both predators and dispersers for many large-seeded plants because they cache seeds for future use, but occasionally forget them in sites with high survival and establishment probabilities. The most important fruit or seed trait influencing rodent foraging behavior is seed size; rodents prefer large seeds because they have higher nutritional content, but this preference can be counterbalanced by the higher costs of handling larger seeds. We designed a cafeteria experiment to assess whether fruit and seed size of Myrcianthes coquimbensis, an endangered desert shrub, influence the decision-making process during foraging by three species of scatter-hoarding rodents differing in body size: Abrothrix olivaceus, Phyllotis darwini and Octodon degus. We found that the size of fruits and seeds influenced foraging behavior in the three rodent species; the probability of a fruit being harvested and hoarded was higher for larger fruits than for smaller ones. Patterns of fruit size preference were not affected by rodent size; all species were able to hoard fruits within the entire range of sizes offered. Finally, fruit and seed size had no effect on the probability of seed predation, rodents typically ate only the fleshy pulp of the fruits offered and discarded whole, intact seeds. In conclusion, our results reveal that larger M. coquimbensis fruits have higher probabilities of being harvested, and ultimately of its seeds being hoarded and dispersed by scatter-hoarding rodents. As this plant has no other dispersers, rodents play an important role in its recruitment dynamics.

  18. The influence of interplant distance and number of flowers on seed set in dwarf bear-poppy (Arctomecon humilis)

    Treesearch

    K. T. Harper; Renee Van Buren; Zachary T. Aanderud

    2001-01-01

    Samples from three isolated populations of the dwarf bear-poppy (Arctomecon humilis Cov.) demonstrate that both flower pollination (fruit set) and seed set per fruit decline as interplant distances increase and the number of flowers per plant declines. Interplant distance and number of flowers per plant tend to interact with reproduction. Seed set per plant is most...

  19. Evolutionary drivers of mast-seeding in a long-lived desert shrub

    Treesearch

    Susan E. Meyer; Burton K. Pendleton

    2015-01-01

    Patterns of reproductive output in blackbrush did not track current growing season precipitation, but instead were regulated by prior-year weather cues. The strength of the response to the masting cue depended on habitat quality, with higher mean reproductive output, shorter intervals between years of high seed production, and lower CVp at more favorable sites...

  20. Effects of kin-structured seed dispersal on the genetic structure of the clonal dioecious shrub ilex leucoclada.

    PubMed

    Torimaru, T; Tani, N; Tsumura, Y; Nishimura, N; Tomaru, N

    2007-06-01

    Nonrandom patterns of gene dispersal have been identified as possible causes of genetic structuring within populations. Attempts to model these patterns have generally focused solely on the effects of isolation by distance, but the processes involved are more complex than such modeling suggests. Here, we extend considerations of gene dispersal processes beyond simple isolation by distance effects by directly evaluating the effects of kin-structured gene dispersal mediated by the group dispersal of related seeds within fruits (i.e., kin-structured seed dispersal) by birds on genetic structure in Ilex leucoclada, a clonal dioecious shrub. To examine the genetic structure patterns, we established two 30x30 m plots (one with immature soils in old-growth forest and one in secondary forest, designated IM and SC, respectively) with different I. leucoclada stem densities. In these two plots 145 and 510 stems were found, representing 78 and 85 genets, respectively, identified by analyzing their genotypes at eight microsatellite loci. The clonal structure was stronger in the SC plot than in the IM plot. Correlograms of coancestry for genets in both plots exhibited significant, positive, high values in the shortest distance class, indicating the presence of strong genetic structure. However, Sp statistics revealed that the pattern of the genetic structure differed between the plots. In addition, to estimate the family structure within fruits, we sampled forty fruits, in total, from 15 randomly selected plants in the area around the IM and SC plots, and found that 80% of the fruits were multiseeded and 42-100% of the multiseeded fruits contained at least one pair of full sibs. Simulations based on these estimates demonstrated that the group dispersal of related seeds produced through correlated mating both within and across fruits, but not unstructured half-sib dispersal, could generate the observed magnitude and trends of genetic structure found in the IM plot. Furthermore

  1. Differential effects of two explosive compounds on seed germination and seedling morphology of a woody shrub, Morella cerifera.

    PubMed

    Via, Stephen M; Zinnert, Julie C; Young, Donald R

    2015-01-01

    Soils contaminated with explosive compounds occur on a global scale. Research demolition explosive (RDX) (hexahydro-1,3,5-trinitro-1,3,5-triazine) and trinitrotoluene (TNT) (2-methyl-1,3,5-trinitrobenzene) are the most common explosive compounds in the environment. These compounds, by variably impacting plant health, can affect species establishment in contaminated areas. Our objective was to quantify comparative effects of RDX and TNT on a woody shrub, Morella cerifera, commonly found on bombing ranges along the Atlantic Coast of the United States. Two life stages of M. cerifera, Seeds and juvenile plants, were exposed to soil amended with concentrations of RDX and TNT representative of field levels; RDX up to 1,500 ppm and TNT up to 900 ppm. Percent germination was recorded for 3 weeks; morphological metrics of necrotic, reduced, and curled leaves, in addition to shoot length and number measured at the end of the experiment (8 weeks) for juvenile plants. All concentrations of RDX inhibited seed germination while TNT did not have an effect at any concentration. As contaminant concentration increased, significant increases in seedling morphological damage occurred in the presence of RDX, whereas TNT did not affect seedling morphology at any concentration. Overall the plants were more sensitive to the presence of RDX. Species specific responses to explosive compounds in the soil have the potential to act as a physiological filter, altering plant recruitment and establishment. This filtering of species may have a number of large scale impacts including: altering species composition and ecological succession.

  2. Ericaceous dwarf shrubs affect ectomycorrhizal fungal community of the invasive Pinus strobus and native Pinus sylvestris in a pot experiment.

    PubMed

    Kohout, Petr; Sýkorová, Zuzana; Bahram, Mohammad; Hadincová, Věroslava; Albrechtová, Jana; Tedersoo, Leho; Vohník, Martin

    2011-07-01

    This study aimed to elucidate the relationship between ericaceous understorey shrubs and the diversity and abundance of ectomycorrhizal fungi (EcMF) associated with the invasive Pinus strobus and native Pinus sylvestris. Seedlings of both pines were grown in mesocosms and subjected to three treatments simulating different forest microhabitats: (a) grown in isolation and grown with (b) Vaccinium myrtillus or (c) Vaccinium vitis-idaea. Ericaceous plants did not act as a species pool of pine mycobionts and inhibited the ability of the potentially shared species Meliniomyces bicolor to form ectomycorrhizae. Similarly, Ericaceae significantly reduced the formation of Thelephora terrestris ectomycorrhizae in P. sylvestris. EcMF species composition in the mesocosms was strongly affected by both the host species and the presence of an ericaceous neighbour. When grown in isolation, P. strobus root tips were predominantly colonised by Wilcoxina mikolae, whereas those of P. sylvestris were more commonly colonised by Suillus and Rhizopogon spp. Interestingly, these differences were less evident (Suillus + Rhizopogon spp.) or absent (W. mikolae) when the pines were grown with Ericaceae. P. strobus exclusively associated with Rhizopogon salebrosus s.l., suggesting the presence of host specificity at the intrageneric level. Ericaceous plants had a positive effect on colonisation of P. strobus root tips by R. salebrosus s.l. This study demonstrates that the interaction of selective factors such as host species and presence of ericaceous plants may affect the realised niche of the ectomycorrhizal fungi.

  3. Fruit Size Determines the Role of Three Scatter-Hoarding Rodents as Dispersers or Seed Predators of a Fleshy-Fruited Atacama Desert Shrub

    PubMed Central

    Loayza, Andrea P.; Squeo, Francisco A.

    2016-01-01

    Scatter-hoarding rodents can act as both predators and dispersers for many large-seeded plants because they cache seeds for future use, but occasionally forget them in sites with high survival and establishment probabilities. The most important fruit or seed trait influencing rodent foraging behavior is seed size; rodents prefer large seeds because they have higher nutritional content, but this preference can be counterbalanced by the higher costs of handling larger seeds. We designed a cafeteria experiment to assess whether fruit and seed size of Myrcianthes coquimbensis, an endangered desert shrub, influence the decision-making process during foraging by three species of scatter-hoarding rodents differing in body size: Abrothrix olivaceus, Phyllotis darwini and Octodon degus. We found that the size of fruits and seeds influenced foraging behavior in the three rodent species; the probability of a fruit being harvested and hoarded was higher for larger fruits than for smaller ones. Patterns of fruit size preference were not affected by rodent size; all species were able to hoard fruits within the entire range of sizes offered. Finally, fruit and seed size had no effect on the probability of seed predation, rodents typically ate only the fleshy pulp of the fruits offered and discarded whole, intact seeds. In conclusion, our results reveal that larger M. coquimbensis fruits have higher probabilities of being harvested, and ultimately of its seeds being hoarded and dispersed by scatter-hoarding rodents. As this plant has no other dispersers, rodents play an important role in its recruitment dynamics. PMID:27861550

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

    PubMed Central

    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

  5. 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

  6. A Novel Cytochrome P450 Is Implicated in Brassinosteroid Biosynthesis via the Characterization of a Rice Dwarf Mutant, dwarf11, with Reduced Seed Length

    PubMed Central

    Tanabe, Sumiyo; Ashikari, Motoyuki; Fujioka, Shozo; Takatsuto, Suguru; Yoshida, Shigeo; Yano, Masahiro; Yoshimura, Atsushi; Kitano, Hidemi; Matsuoka, Makoto; Fujisawa, Yukiko; Kato, Hisaharu; Iwasaki, Yukimoto

    2005-01-01

    We have characterized a rice (Oryza sativa) dwarf mutant, dwarf11 (d11), that bears seeds of reduced length. To understand the mechanism by which seed length is regulated, the D11 gene was isolated by a map-based cloning method. The gene was found to encode a novel cytochrome P450 (CYP724B1), which showed homology to enzymes involved in brassinosteroid (BR) biosynthesis. The dwarf phenotype of d11 mutants was restored by the application of the brassinolide (BL). Compared with wild-type plants, the aberrant D11 mRNA accumulated at higher levels in d11 mutants and was dramatically reduced by treatment with BL, implying that the gene is feedback-regulated by BL. Precise determination of the defective step(s) in BR synthesis in d11 mutants proved intractable because of tissue specificity and the complex control of BR accumulation in plants. However, 6-deoxotyphasterol (6-DeoxoTY) and typhasterol (TY), but not any upstream intermediates before these compounds, effectively restored BR response in d11 mutants in a lamina joint bending assay. Multiple lines of evidence together suggest that the D11/CYP724B1 gene plays a role in BR synthesis and may be involved in the supply of 6-DeoxoTY and TY in the BR biosynthesis network in rice. PMID:15705958

  7. A novel cytochrome P450 is implicated in brassinosteroid biosynthesis via the characterization of a rice dwarf mutant, dwarf11, with reduced seed length.

    PubMed

    Tanabe, Sumiyo; Ashikari, Motoyuki; Fujioka, Shozo; Takatsuto, Suguru; Yoshida, Shigeo; Yano, Masahiro; Yoshimura, Atsushi; Kitano, Hidemi; Matsuoka, Makoto; Fujisawa, Yukiko; Kato, Hisaharu; Iwasaki, Yukimoto

    2005-03-01

    We have characterized a rice (Oryza sativa) dwarf mutant, dwarf11 (d11), that bears seeds of reduced length. To understand the mechanism by which seed length is regulated, the D11 gene was isolated by a map-based cloning method. The gene was found to encode a novel cytochrome P450 (CYP724B1), which showed homology to enzymes involved in brassinosteroid (BR) biosynthesis. The dwarf phenotype of d11 mutants was restored by the application of the brassinolide (BL). Compared with wild-type plants, the aberrant D11 mRNA accumulated at higher levels in d11 mutants and was dramatically reduced by treatment with BL, implying that the gene is feedback-regulated by BL. Precise determination of the defective step(s) in BR synthesis in d11 mutants proved intractable because of tissue specificity and the complex control of BR accumulation in plants. However, 6-deoxotyphasterol (6-DeoxoTY) and typhasterol (TY), but not any upstream intermediates before these compounds, effectively restored BR response in d11 mutants in a lamina joint bending assay. Multiple lines of evidence together suggest that the D11/CYP724B1 gene plays a role in BR synthesis and may be involved in the supply of 6-DeoxoTY and TY in the BR biosynthesis network in rice.

  8. 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

  9. 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

  10. Hydrated mucilage reduces post-dispersal seed removal of a sand desert shrub by ants in a semiarid ecosystem.

    PubMed

    Yang, Xuejun; Baskin, Carol C; Baskin, Jerry M; Gao, Ruiru; Yang, Fan; Wei, Lingling; Li, Leilei; He, Hongju; Huang, Zhenying

    2013-12-01

    Post-dispersal seed removal by animals can lead to extensive seed loss and thus is an important factor in structuring plant communities. However, we know much less about post-dispersal seed predation than about other forms of herbivory. Mucilage plays many ecological roles in adaptation of plants to diverse environments; nevertheless, until now the role of mucilage in ant-mediated seed movement remains largely hypothetical. We studied the role of mucilage in seed removal of Artemisia sphaerocephala by ants in Mu Us Sandland in Inner Mongolia, China. Messor aciculatus was the most active seed predator of Artemisia sphaerocephala. Time to first ant collecting (T 1st) of wet intact seeds was longest and significantly different from that for dry intact seeds, wet demucilaged seeds, and dry demucilaged seeds; number of seeds removed to ant nests was lowest for wet intact seeds. After they were collected by ants, 5 % of wet intact seeds were dropped during transport. Our results indicate that seed mucilage of Artemisia sphaerocephala may play a significant role in post-dispersal seed removal by (1) making seeds less attractive to ants, thus resulting in a delay of collection time; (2) forming a strong bond to soil particles, making it difficult for ants to remove seeds; and (3) making seeds more likely to be dropped during transport, thereby allowing them to escape from predation even after collection by ants. This study demonstrates the importance of mucilage in reducing seed removal by ants and thus in anchoring seeds of desert plants in the vicinity of mother plants.

  11. Temporal patterns of genetic variation across a 9-year-old aerial seed bank of the shrub Banksia hookeriana (Proteaceae).

    PubMed

    Barrett, Luke G; He, Tianhua; Lamont, Byron B; Krauss, Siegfried L

    2005-11-01

    The pattern of accumulation of genetic variation over time in seed banks is poorly understood. We examined the genetic structure of the aerial seed bank of Banksia hookeriana within a single 15-year-old population in fire-prone southwestern Australia, and compared genetic variation between adults and each year of a 9-year-old seed bank using amplified fragment length polymorphism (AFLP). B. hookeriana is well suited to the study of seed bank dynamics due to the canopy storage of its seeds, and because each annual crop can be identified. A total of 304 seeds from nine crop years and five maternal plants were genotyped, along with 113 plants from the adult population. Genetic variation, as assessed by the proportion of polymorphic markers (P(p)) and Shannon's index (I), increased slightly within the seed bank over time, while gene diversity (H(j)), did not change. P(p), I, and H(j) all indicated that genetic variation within the seed bank quickly approached the maximal level detected. Analysis of molecular variance revealed that less than 4% of variation could be accounted for by variation among seeds produced in different years, whereas there was greater differentiation among maternal plants (12.7%), and among individual seeds produced by different maternal plants (83.4%). With increasing population age, offspring generated each year were slightly more outbred, as indicated by an increase in the mean number of nonmaternal markers per offspring. There were no significant differences for H(j) or I between adults and the seed bank. Viability of seeds decreased with age, such that the viability of 9-year-old seeds was half that of 2-year-old seeds. These results suggest that variable fire frequencies have only limited potential to influence the amount of genetic variation stored within the seed bank of B. hookeriana.

  12. Genetic structure and seed-mediated dispersal rates of an endangered shrub in a fragmented landscape: a case study for Juniperus communis in northwestern Europe

    PubMed Central

    2011-01-01

    Background Population extinction risk in a fragmented landscape is related to the differential ability of the species to spread its genes across the landscape. The impact of landscape fragmentation on plant population dynamics will therefore vary across different spatial scales. We quantified successful seed-mediated dispersal of the dioecious shrub Juniperus communis in a fragmented landscape across northwestern Europe by using amplified fragment length polymorphism (AFLP) markers. Furthermore we investigated the genetic diversity and structure on two spatial scales: across northwestern Europe and across Flanders (northern Belgium). We also studied whether seed viability and populations size were correlated with genetic diversity. Results Unexpectedly, estimated seed-mediated dispersal rates were quite high and ranged between 3% and 14%. No population differentiation and no spatial genetic structure were detected on the local, Flemish scale. A significant low to moderate genetic differentiation between populations was detected at the regional, northwest European scale (PhiPT = 0.10). In general, geographically nearby populations were also genetically related. High levels of within-population genetic diversity were detected but no correlation was found between any genetic diversity parameter and population size or seed viability. Conclusions In northwestern Europe, landscape fragmentation has lead to a weak isolation-by-distance pattern but not to genetic impoverishment of common juniper. Substantial rates of successful migration by seed-mediated gene flow indicate a high dispersal ability which could enable Juniperus communis to naturally colonize suitable habitats. However, it is not clear whether the observed levels of migration will suffice to counterbalance the effects of genetic drift in small populations on the long run. PMID:21859457

  13. Distribution of three congeneric shrub species along an aridity gradient is related to seed germination and seedling emergence

    PubMed Central

    Lai, Liming; Tian, Yuan; Wang, Yongji; Zhao, Xuechun; Jiang, Lianhe; Baskin, Jerry M.; Baskin, Carol C.; Zheng, Yuanrun

    2015-01-01

    Environmental tolerance of a species has been shown to correlate positively with its geographical range. On the Ordos Plateau, three Caragana species are distributed sequentially along the precipitation gradient. We hypothesized that this geographical distribution pattern is related to environmental tolerances of the three Caragana species during seed germination and seedling emergence stages. To test this hypothesis, we examined seed germination under different temperature, light and water potentials, and monitored seedling emergence for seeds buried at eight sand depths and given different amounts of water. Seeds of C. korshinskii germinated to high percentages at 5 : 15 to 25 : 35 °C in both light and darkness, while those of C. intermedia and C. microphylla did so only at 15 : 25 and 25 : 35 °C, respectively. Nearly 30 % of the C. korshinskii seeds germinated at −1.4 MPa at 20 and 25 °C, while no seeds of the other two species did so. Under the same treatments, seedling emergence percentages of C. korshinskii were higher than those of the other two species. The rank order of tolerance to drought and sand burial of the three species is C. korshinskii > C. intermedia > C. microphylla. The amount of precipitation and sand burial depth appear to be the main selective forces responsible for the geographical distribution of these species. PMID:26139184

  14. Development and Practical Use of RT-PCR for Seed-transmitted Prune dwarf virus in Quarantine

    PubMed Central

    Lee, Siwon; Shin, Yong-Gil

    2014-01-01

    Among imported plants, seeds are the items that have many latent pathogens and are difficult to inspect. Also, they are the import and export items whose market is expected to expand. The biggest problem with seeds is viruses. Prune dwarf virus (PDV) is the virus that is commonly inspected in Prunus cerasifera, P. persica, P. armeniaca, P. mandshurica, P. cerasus, P. avium or P. serotina seeds. In this study, two RT-PCR primer sets, which can promptly and specifically diagnose plant quarantine seed-transmitted PDV, were developed; and nested PCR primers, where products amplify 739 and 673 nucleotides (nt), and an nested PCR-product, 305 nt, can be obtained as these products are amplified again, were developed. Also, a modified-positive control plasmid was developed, where the restriction enzyme XhoI, which can identify the contamination of samples from the control, was inserted. The method developed in this study has detected PDV in 18 cases since 2007, and is expected to continuously contribute to the plant quarantine in Korea. PMID:25289000

  15. Development and Practical Use of RT-PCR for Seed-transmitted Prune dwarf virus in Quarantine.

    PubMed

    Lee, Siwon; Shin, Yong-Gil

    2014-06-01

    Among imported plants, seeds are the items that have many latent pathogens and are difficult to inspect. Also, they are the import and export items whose market is expected to expand. The biggest problem with seeds is viruses. Prune dwarf virus (PDV) is the virus that is commonly inspected in Prunus cerasifera, P. persica, P. armeniaca, P. mandshurica, P. cerasus, P. avium or P. serotina seeds. In this study, two RT-PCR primer sets, which can promptly and specifically diagnose plant quarantine seed-transmitted PDV, were developed; and nested PCR primers, where products amplify 739 and 673 nucleotides (nt), and an nested PCR-product, 305 nt, can be obtained as these products are amplified again, were developed. Also, a modified-positive control plasmid was developed, where the restriction enzyme XhoI, which can identify the contamination of samples from the control, was inserted. The method developed in this study has detected PDV in 18 cases since 2007, and is expected to continuously contribute to the plant quarantine in Korea.

  16. Population size, center-periphery, and seed dispersers' effects on the genetic diversity and population structure of the Mediterranean relict shrub Cneorum tricoccon.

    PubMed

    Lázaro-Nogal, Ana; Matesanz, Silvia; García-Fernández, Alfredo; Traveset, Anna; Valladares, Fernando

    2017-09-01

    The effect of population size on population genetic diversity and structure has rarely been studied jointly with other factors such as the position of a population within the species' distribution range or the presence of mutualistic partners influencing dispersal. Understanding these determining factors for genetic variation is critical for conservation of relict plants that are generally suffering from genetic deterioration. Working with 16 populations of the vulnerable relict shrub Cneorum tricoccon throughout the majority of its western Mediterranean distribution range, and using nine polymorphic microsatellite markers, we examined the effects of periphery (peripheral vs. central), population size (large vs. small), and seed disperser (introduced carnivores vs. endemic lizards) on the genetic diversity and population structure of the species. Contrasting genetic variation (HE: 0.04-0.476) was found across populations. Peripheral populations showed lower genetic diversity, but this was dependent on population size. Large peripheral populations showed high levels of genetic diversity, whereas small central populations were less diverse. Significant isolation by distance was detected, indicating that the effect of long-distance gene flow is limited relative to that of genetic drift, probably due to high selfing rates (FIS = 0.155-0.887), restricted pollen flow, and ineffective seed dispersal. Bayesian clustering also supported the strong population differentiation and highly fragmented structure. Contrary to expectations, the type of disperser showed no significant effect on either population genetic diversity or structure. Our results challenge the idea of an effect of periphery per se that can be mainly explained by population size, drawing attention to the need of integrative approaches considering different determinants of genetic variation. Furthermore, the very low genetic diversity observed in several small populations and the strong among

  17. Maize dwarf mosaic in sweet corn contributes to weed growth and seed production

    USDA-ARS?s Scientific Manuscript database

    Maize dwarf mosaic (MDM) stunts corn growth, delays development, and is the most prevalent viral disease of sweet corn. Although weeds evade control in most sweet corn fields, the extent to which MDM influences the crop’s weed suppressive ability is unknown. Field studies were conducted over a three...

  18. A statistical analysis of seeds and other high-contrast exoplanet surveys: massive planets or low-mass brown dwarfs?

    SciTech Connect

    Brandt, Timothy D.; Spiegel, David S.; McElwain, Michael W.; Grady, C. A.; Turner, Edwin L.; Mede, Kyle; Kuzuhara, Masayuki; Schlieder, Joshua E.; Brandner, W.; Feldt, M.; Wisniewski, John P.; Abe, L.; Biller, B.; Carson, J.; Currie, T.; Egner, S.; Golota, T.; Guyon, O.; Goto, M.; Hashimoto, J.; and others

    2014-10-20

    We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections (κ And b, two ∼60 M {sub J} brown dwarf companions in the Pleiades, PZ Tel B, and CD–35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of ∼30-100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at ∼5 M {sub J}, with a single power-law distribution. We find that p(M, a)∝M {sup –0.65} {sup ±} {sup 0.60} a {sup –0.85} {sup ±} {sup 0.39} (1σ errors) provides an adequate fit to our data, with 1.0%-3.1% (68% confidence) of stars hosting 5-70 M {sub J} companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs.

  19. A Statistical Analysis of SEEDS and Other High-contrast Exoplanet Surveys: Massive Planets or Low-mass Brown Dwarfs?

    NASA Astrophysics Data System (ADS)

    Brandt, Timothy D.; McElwain, Michael W.; Turner, Edwin L.; Mede, Kyle; Spiegel, David S.; Kuzuhara, Masayuki; Schlieder, Joshua E.; Wisniewski, John P.; Abe, L.; Biller, B.; Brandner, W.; Carson, J.; Currie, T.; Egner, S.; Feldt, M.; Golota, T.; Goto, M.; Grady, C. A.; Guyon, O.; Hashimoto, J.; Hayano, Y.; Hayashi, M.; Hayashi, S.; Henning, T.; Hodapp, K. W.; Inutsuka, S.; Ishii, M.; Iye, M.; Janson, M.; Kandori, R.; Knapp, G. R.; Kudo, T.; Kusakabe, N.; Kwon, J.; Matsuo, T.; Miyama, S.; Morino, J.-I.; Moro-Martín, A.; Nishimura, T.; Pyo, T.-S.; Serabyn, E.; Suto, H.; Suzuki, R.; Takami, M.; Takato, N.; Terada, H.; Thalmann, C.; Tomono, D.; Watanabe, M.; Yamada, T.; Takami, H.; Usuda, T.; Tamura, M.

    2014-10-01

    We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections (κ And b, two ~60 M J brown dwarf companions in the Pleiades, PZ Tel B, and CD-35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of ~30-100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at ~5 M J, with a single power-law distribution. We find that p(M, a)vpropM -0.65 ± 0.60 a -0.85 ± 0.39 (1σ errors) provides an adequate fit to our data, with 1.0%-3.1% (68% confidence) of stars hosting 5-70 M J companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  20. Globulettes as Seeds of Brown Dwarfs and Free-Floating Planetary-Mass Objects

    NASA Astrophysics Data System (ADS)

    Gahm, G. F.; Grenman, T.; Fredriksson, S.; Kristen, H.

    2007-04-01

    previous studies and also much longer than the free-fall time. We conclude that a large number of our globulettes have time to form central low-mass objects long before the ionization front, driven by the impinging Lyman photons, has penetrated far into the globulette. Hence, the globulettes may be one source in the formation of brown dwarfs and free-floating planetary-mass objects in the galaxy. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

  1. Hemlock Dwarf Mistletoe (FIDL)

    Treesearch

    Paul E. Hennon; Jerome S. Beatty; Diane Hildebrand

    2001-01-01

    Hemlock dwarf mistletoe, Arceuthobium tsugense (Rosendahl) G.N. Jones, causes a serious disease of western hemlock and several other tree species along the Pacific Coast of North America. This small, seed-bearing plant lives exclusively as a parasite on living trees. Throughout its range, hemlock dwarf mistletoe occurs in patch-like patterns in the forests. Some...

  2. Chapter 22. Rosaceous shrubs

    Treesearch

    Nancy L. Shaw; Stephen B. Monsen; Richard Stevens

    2004-01-01

    Important shrubs of the Rose Family (Rosaceae) in the Intermountain region are distributed from blackbrush and salt desert shrub communities through high elevation forests and meadows. Growth habits of this group vary from trailing brambles to upright shrubs and small trees. Some species are evergreen while others are deciduous. Many of these species are highly valued...

  3. Yield and seed oil content response of dwarf, rapid-cycling Brassica to nitrogen treatments, planting density, and carbon dioxide enrichment

    NASA Technical Reports Server (NTRS)

    Frick, J.; Nielsen, S. S.; Mitchell, C. A.

    1994-01-01

    Effects of N level (15 to 30 mM), time of N increase (14 to 28 days after planting), and planting density (1163 to 2093 plants/m2) were determined for crop yield responses of dwarf, rapid-cycling brassica (Brassica napus L., CrGC 5-2, Genome: ACaacc). Crops were grown in solid-matrix hydroponic systems and under controlled-environment conditions, including nonsupplemented (ambient) or elevated CO2 concentrations (998 +/- 12 micromoles mol-1). The highest seed yield rate obtained (4.4 g m-2 day-1) occurred with the lowest N level (15 mM) applied at the latest treatment time (day 28). In all trials, CO2 enrichment reduced seed yield rate and harvest index by delaying the onset of flowering and senescence and stimulating vegetative shoot growth. The highest shoot biomass accumulation rate (55.5 g m-2 day-1) occurred with the highest N level (30 mM) applied at the earliest time (day 14). Seed oil content was not significantly affected by CO2 enrichment. Maximum seed oil content (30% to 34%, dry weight basis) was obtained using the lowest N level (15 mM) initiated at the latest treatment time (day 28). In general, an increase in seed oil content was accompanied by a decrease in seed protein. Seed carbohydrate, moisture, and ash contents did not vary significantly in response to experimental treatments. Effects of N level and time of N increase were consistently significant for most crop responses. Planting density was significant only under elevated CO2 conditions.

  4. Yield and seed oil content response of dwarf, rapid-cycling Brassica to nitrogen treatments, planting density, and carbon dioxide enrichment.

    PubMed

    Frick, J; Nielsen, S S; Mitchell, C A

    1994-11-01

    Effects of N level (15 to 30 mM), time of N increase (14 to 28 days after planting), and planting density (1163 to 2093 plants/m2) were determined for crop yield responses of dwarf, rapid-cycling brassica (Brassica napus L., CrGC 5-2, Genome: ACaacc). Crops were grown in solid-matrix hydroponic systems and under controlled-environment conditions, including nonsupplemented (ambient) or elevated CO2 concentrations (998 +/- 12 micromoles mol-1). The highest seed yield rate obtained (4.4 g m-2 day-1) occurred with the lowest N level (15 mM) applied at the latest treatment time (day 28). In all trials, CO2 enrichment reduced seed yield rate and harvest index by delaying the onset of flowering and senescence and stimulating vegetative shoot growth. The highest shoot biomass accumulation rate (55.5 g m-2 day-1) occurred with the highest N level (30 mM) applied at the earliest time (day 14). Seed oil content was not significantly affected by CO2 enrichment. Maximum seed oil content (30% to 34%, dry weight basis) was obtained using the lowest N level (15 mM) initiated at the latest treatment time (day 28). In general, an increase in seed oil content was accompanied by a decrease in seed protein. Seed carbohydrate, moisture, and ash contents did not vary significantly in response to experimental treatments. Effects of N level and time of N increase were consistently significant for most crop responses. Planting density was significant only under elevated CO2 conditions.

  5. Yield and seed oil content response of dwarf, rapid-cycling Brassica to nitrogen treatments, planting density, and carbon dioxide enrichment

    NASA Technical Reports Server (NTRS)

    Frick, J.; Nielsen, S. S.; Mitchell, C. A.

    1994-01-01

    Effects of N level (15 to 30 mM), time of N increase (14 to 28 days after planting), and planting density (1163 to 2093 plants/m2) were determined for crop yield responses of dwarf, rapid-cycling brassica (Brassica napus L., CrGC 5-2, Genome: ACaacc). Crops were grown in solid-matrix hydroponic systems and under controlled-environment conditions, including nonsupplemented (ambient) or elevated CO2 concentrations (998 +/- 12 micromoles mol-1). The highest seed yield rate obtained (4.4 g m-2 day-1) occurred with the lowest N level (15 mM) applied at the latest treatment time (day 28). In all trials, CO2 enrichment reduced seed yield rate and harvest index by delaying the onset of flowering and senescence and stimulating vegetative shoot growth. The highest shoot biomass accumulation rate (55.5 g m-2 day-1) occurred with the highest N level (30 mM) applied at the earliest time (day 14). Seed oil content was not significantly affected by CO2 enrichment. Maximum seed oil content (30% to 34%, dry weight basis) was obtained using the lowest N level (15 mM) initiated at the latest treatment time (day 28). In general, an increase in seed oil content was accompanied by a decrease in seed protein. Seed carbohydrate, moisture, and ash contents did not vary significantly in response to experimental treatments. Effects of N level and time of N increase were consistently significant for most crop responses. Planting density was significant only under elevated CO2 conditions.

  6. Shrub encroachment is linked to extirpation of an apex predator.

    PubMed

    Gordon, Christopher E; Eldridge, David J; Ripple, William J; Crowther, Mathew S; Moore, Ben D; Letnic, Mike

    2017-01-01

    The abundance of shrubs has increased throughout Earth's arid lands. This 'shrub encroachment' has been linked to livestock grazing, fire-suppression and elevated atmospheric CO2 concentrations facilitating shrub recruitment. Apex predators initiate trophic cascades which can influence the abundance of many species across multiple trophic levels within ecosystems. Extirpation of apex predators is linked inextricably to pastoralism, but has not been considered as a factor contributing to shrub encroachment. Here, we ask if trophic cascades triggered by the extirpation of Australia's largest terrestrial predator, the dingo (Canis dingo), could be a driver of shrub encroachment in the Strzelecki Desert, Australia. We use aerial photographs spanning a 51-year period to compare shrub cover between areas where dingoes are historically rare and common. We then quantify contemporary patterns of shrub, shrub seedling and mammal abundances, and use structural equation modelling to compare competing trophic cascade hypotheses to explain how dingoes could influence shrub recruitment. Finally, we track the fate of seedlings of an encroaching shrub, hopbush (Dodonaea viscosa angustissima), during a period optimal for seedling recruitment, and quantify removal rates of hopbush seeds by rodents from enriched seed patches. Shrub cover was 26-48% greater in areas where dingoes were rare than common. Our structural equation modelling supported the hypothesis that dingo removal facilitates shrub encroachment by triggering a four level trophic cascade. According to this model, increased mesopredator abundance in the absence of dingoes results in suppressed abundance of consumers of shrub seeds and seedlings, rodents and rabbits respectively. In turn, suppressed abundances of rodents and rabbits in the absence of dingoes relaxed a recruitment bottleneck for shrubs. The results of our SEM were supported by results showing that rates of hopbush seedling survival and seed removal were 1

  7. Members of the gibberellin receptor gene family GID1 (GIBBERELLIN INSENSITIVE DWARF1) play distinct roles during Lepidium sativum and Arabidopsis thaliana seed germination

    PubMed Central

    Voegele, Antje; Linkies, Ada; Müller, Kerstin; Leubner-Metzger, Gerhard

    2011-01-01

    Germination of endospermic seeds is partly regulated by the micropylar endosperm, which acts as constraint to radicle protrusion. Gibberellin (GA) signalling pathways control coat-dormancy release, endosperm weakening, and organ expansion during seed germination. Three GIBBERELLIN INSENSITIVE DWARF1 (GID1) GA receptors are known in Arabidopsis thaliana: GID1a, GID1b, and GID1c. Molecular phylogenetic analysis of angiosperm GID1s reveals that they cluster into two eudicot (GID1ac, GID1b) groups and one monocot group. Eudicots have at least one gene from each of the two groups, indicating that the different GID1 receptors fulfil distinct roles during plant development. A comparative Brassicaceae approach was used, in which gid1 mutant and whole-seed transcript analyses in Arabidopsis were combined with seed-tissue-specific analyses of its close relative Lepidium sativum (garden cress), for which three GID1 orthologues were cloned. GA signalling via the GID1ac receptors is required for Arabidopsis seed germination, GID1b cannot compensate for the impaired germination of the gid1agid1c mutant. Transcript expression patterns differed temporarily, spatially, and hormonally, with GID1b being distinct from GID1ac in both species. Endosperm weakening is mediated, at least in part, through GA-induced genes encoding cell-wall-modifying proteins. A suppression subtraction hybridization (SSH) cDNA library enriched for sequences that are highly expressed during early germination in the micropylar endosperm contained expansins and xyloglucan endo-transglycosylases/hydrolases (XTHs). Their transcript expression patterns in both species strongly suggest that they are regulated by distinct GID1-mediated GA signalling pathways. The GID1ac and GID1b pathways seem to fulfil distinct regulatory roles during Brassicaceae seed germination and seem to control their downstream targets distinctly. PMID:21778177

  8. Factors influencing the scarification and germination of three montane Sierra Nevada shrubs

    Treesearch

    J. Boone Kaufmann; R. E. Martin

    1991-01-01

    Following fires in the forested ecosystems of the northern Sierra Nevada, California, early successional communities are often dominated by shrubs that arise from seeds that have remained viable in soil seedbanks for long periods. The germination response of seeds of three seral montane shrub species was investigated following exposure to differing types of heat (wet...

  9. The SEEDS High-Contrast Imaging Survey: Exoplanet and Brown Dwarf Survey for Nearby Young Stars Dated with Gyrochronology and Activity Age Indicators

    NASA Astrophysics Data System (ADS)

    Kuzuhara, Masayuki; Tamura, Motohide; Helminiak, Kris; Mede, Kyle; Brandt, Timothy; Janson, Markus; Kandori, Ryo; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Hashimoto, Jun

    2015-12-01

    The SEEDS campaign has successfully discovered and characterized exoplanets, brown dwarfs, and circumstellar disks since it began in 2009, via the direct imaging technique. The survey has targeted nearby young stars, as well as stars associated to star-forming regions, the Pleiades open cluster, moving groups, and debris disks. We selected the nearby young stars that have been dated with age indicators based on stellar rotation periods (i.e., gyrochronology) and chromoshperic/coronal activities. Of these, nearly 40 were observed, with ages mainly between 100 and 1000 Myr and distances less than 40 pc. Our observations typically attain the contrast of ~6 x 10-6 at 1'' and better than ~1 x 10-6 beyond 2'', enabling us to detect a planetary-mass companion even around such old stars. Indeed, the SEEDS team reported the discovery that the nearby Sun-like star GJ 504 hosts a Jovian companion GJ 504b, which has a mass of 3-8.5 Jupiter masses that is inferred according to the hot-start cooling models and our estimated system age of 100-510 Myr. The remaining observations out of the selected ~40 stars have resulted in no detection of additional planets or brown dwarf companions. Meanwhile, we have newly imaged a low-mass stellar companion orbiting the G-type star HIP 10321, for which the presence of companion was previously announced via radial velocity technique. The astrometry and radial velocity measurements are simultaneously analyzed to determine the orbit, providing constraints on the dynamical mass of both objects and stellar evolution models. Here we summarize our direct imaging observations for the nearby young stars dated with gyrochrolorogy and activity age indicators. Furthermore, we report the analysis for the HIP 10321 system with the imaged low-mass companion.

  10. Mechanisms for maintenance of dominance in a nonclonal desert shrub

    Treesearch

    Stanley G. Kitchen; Susan E. Meyer; Stephanie L. Carlson

    2015-01-01

    Blackbrush (Coleogyne ramosissima: Rosaceae) is a slow-growing, non-clonal shrub that is regionally dominant on xeric, shallow soils in the North American Mojave Desert-Great Basin transition zone and southern Colorado Plateau. Blackbrush seed production is concentrated in mast years, and most seeds are cached and later consumed by heteromyid rodents....

  11. Nutrients intake, performance and nitrogen balance of West African dwarf sheep fed graded levels of toasted Enterolobium cyclocarpum seeds as supplement to Panicum maximum.

    PubMed

    Idowu, O J; Arigbede, O M; Dele, P A; Olanite, J A; Adelusi, O O; Ojo, V O A; Sunmola, A S

    2013-12-01

    A study was conducted to assess the nutritive value of Enterolobium cyclocarpum seeds as supplementary feed for ruminant animals during the dry season when grasses are either not available or of low quality. Matured fruits of E. cyclocarpum were collected, toasted, peeled and then used for the trial. Thirty two West African Dwarf (WAD) sheep aged between 12 +/- 2 months with an average body weight of 10 +/- 2 kg were used in assessing the nutritive value of graded levels of toasted Enterolobium cyclocarpum seed in a concentrate diets as supplement to Panicum maximum basal diet. The percent compositions of the experimental diets were toasted E. cyclocarpum seeds at various levels of inclusion (0, 10, 20 and 30%) for diets 1, 2, 3 and 4. respectively. The diets (1-4) were consecutively fed to each animal at 50 g kg(-1) b.wt. for 12 weeks in a completely randomized design. Parameters taken were weekly body weights, daily feed intake, nutrient utilization and nitrogen balance status for each animal. Diet 2 had the highest significant (p < 0.05) nutrients intake being 871.88, 137.13, 147.59, 33.26 and 69.86 g day(-1) for DM, CP, CF, EE and ASH respectively. The Dry Matter Digestibility (DMD) coefficients decreased significantly (p < 0.05) with increased inclusion levels of toasted E. cyclocarpum seeds supplementation. Sheep fed diet 4 had the lowest feed conversion ratio (8.61) and the highest daily average gain of 58.93 g. However the animals fed Diet 2 had the highest nitrogen retension and converted their feed to flesh.

  12. Sowing the seeds of massive black holes in small galaxies: Young clusters as the building blocks of ultracompact dwarf galaxies

    SciTech Connect

    Amaro-Seoane, Pau; Konstantinidis, Symeon; Freitag, Marc Dewi; Coleman Miller, M.; Rasio, Frederic A. E-mail: simos@ari.uni-heidelberg.de E-mail: miller@astro.umd.edu

    2014-02-20

    Interacting galaxies often have complexes of hundreds of young stellar clusters of individual masses ∼10{sup 4}-10{sup 6} M {sub ☉} in regions that are a few hundred parsecs across. These cluster complexes interact dynamically, and their coalescence is a candidate for the origin of some ultracompact dwarf galaxies. Individual clusters with short relaxation times are candidates for the production of intermediate-mass black holes of a few hundred solar masses, via runaway stellar collisions prior to the first supernovae in a cluster. It is therefore possible that a cluster complex hosts multiple intermediate-mass black holes that may be ejected from their individual clusters due to mergers or binary processes, but bound to the complex as a whole. Here we explore the dynamical interaction between initially free-flying massive black holes and clusters in an evolving cluster complex. We find that, after hitting some clusters, it is plausible that the massive black hole will be captured in an ultracompact dwarf forming near the center of the complex. In the process, the hole typically triggers electromagnetic flares via stellar disruptions, and is also likely to be a prominent source of gravitational radiation for the advanced ground-based detectors LIGO and VIRGO. We also discuss other implications of this scenario, notably that the central black hole could be considerably larger than expected in other formation scenarios for ultracompact dwarfs.

  13. A napin-like polypeptide from dwarf Chinese white cabbage seeds with translation-inhibitory, trypsin-inhibitory, and antibacterial activities.

    PubMed

    Ngai, P H K; Ng, T B

    2004-02-01

    Napins are 1:1 disulfide-linked complexes of a smaller (ca. 4kDa) subunit and a larger (ca. 10kDa) subunit. The intent of the present study was to ascertain the production of napin by the seeds of a Brassica species that has not been examined previously, and also to explore new biological activities of the napin. A heterodimeric 11-kDa napin-like polypeptide has been isolated from Chinese white cabbage (Brassica chinensis cv dwarf) seeds with a protocol comprising ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, fast protein liquid chromatography (FPLC)-ion exchange chromatography on Mono S and FPLC-gel filtration on Superdex 75. The N-terminal sequence of the 7-kDa subunit manifests striking similarity to napin large chain, albumin and trypsin inhibitor. The N-terminal sequence of the 4-kDa subunit is homologous to napin large chain and an antimicrobial peptide. The napin-like polypeptide inhibited translation in the rabbit reticulocyte system with an IC50 of 18.5nM. This translation-inhibitory activity was stable between pH 4 and 11, and between 10 and 40 degrees C. The polypeptide inhibited trypsin with a higher potency ( IC50 = 8.5 microM) than it inhibited chymotrypsin (IC50 = 220 microM), but was devoid of ribonuclease and antifungal activities. It manifested antibacterial activity against Pseudomonas aeruginosia, Bacillus subtilis, Bacillus cereus, and Bacillus megaterium. The results revealed that the napin-like polypeptide from Chinese white cabbage seeds exhibited some potentially exploitable activities.

  14. Lodgepole Pine Dwarf Mistletoe

    Treesearch

    Frank G. Hawksworth; Oscar J. Dooling

    1984-01-01

    Lodgepole pine dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) is a native, parasitic, seed plant that occurs essentially throughout the range of lodgepole pine in North America. It is the most damaging disease agent in lodgepole pine, causing severe growth loss and increased tree mortality. Surveys in the Rocky Mountains show that the parasite is found in...

  15. Chapter 21. Composite shrubs

    Treesearch

    E. Durant McArthur; Richard Stevens

    2004-01-01

    The sunflower family (Compositae or Asteraceae) is the largest family of flowering plants. Its many species occur around the world as annual and perennial herbs and as shrubs and trees (Benson 1957; Cronquist 1968; Wagenitz 1977). Three shrubby genera of the family-sagebrush (Artemisia), rabbitbrush (Chrysothamnus), and matchbrush...

  16. Measuring carbon in shrubs. Chapter 5

    Treesearch

    David C. Chojnacky; Mikaila. Milton

    2008-01-01

    Although shrubs are a small component of the overall carbon budget, shrub lands and shrub cover within forested lands warrant monitoring with consistent procedures to account for carbon in shrubs and to track carbon accumulation as communities change from shrubs to trees and vice versa. Many different procedures have been used to sample and measure shrubs (Bonham 1989...

  17. 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.

  18. First-order fire effects on herbs and Shrubs: present knowledge and process modeling needs

    Treesearch

    Kirsten Stephan; Melanie Miller; Matthew B. Dickinson

    2010-01-01

    Herbaceous plants and shrubs have received little attention in terms of fire effects modeling despite their critical role in ecosystem integrity and resilience after wildfires and prescribed burns. In this paper, we summarize current knowledge of direct effects of fire on herb and shrub (including cacti) vegetative tissues and seed banks, propose key components for...

  19. A preliminary investigation on the feasibility of preharvest burning for shrub control

    Treesearch

    J. Boone Kauffman; R. E. Martin

    1985-01-01

    Historically, fire was a natural component in ponderosa pine (Pinus ponderosa)-mixed conifer ecosystems in the Sierra Nevada of California. Wildfires may have reduced the number of shrub seeds in the soil, as well as the density of mature shrubs and young hardwoods, thereby allowing conifers to reinvade a site after disturbance, and grow with reduced competition. With...

  20. Seedling establishment in a masting desert shrub parallels the pattern for forest trees

    Treesearch

    Susan E. Meyer; Burton K. Pendleton

    2015-01-01

    The masting phenomenon along with its accompanying suite of seedling adaptive traits has been well studied in forest trees but has rarely been examined in desert shrubs. Blackbrush (Coleogyne ramosissima) is a regionally dominant North American desert shrub whose seeds are produced in mast events and scatter-hoarded by rodents. We followed the fate of seedlings in...

  1. 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.

  2. Establishing big sagebrush and other shrubs from planting stock

    Treesearch

    Nancy L. Shaw; Anne Halford; J. Kent McAdoo

    2015-01-01

    Bareroot or container seedlings can be used to quickly re-establish big sagebrush and other native shrubs in situations where direct seeding is not feasible or unlikely to succeed. Guidelines are provided for developing a planting plan and timeline, arranging for seedling production, and installing and managing outplantings.

  3. 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

  4. Growing Shrubs at the George O. White State Forest Nursery: What Has Worked and What Has Not

    Treesearch

    Gregory Hoss

    2006-01-01

    At the George O. White State Forest Nursery in Licking, MO, we annually grow about 20 species of shrubs. That number has been larger in some years. For most species, we purchase seeds locally and process them at our nursery. Our shrubs are used for wetland restoration, windbreaks, visual screens, riparian buffers, and wildlife plantings.

  5. 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.

  6. 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

  7. 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

  8. What if plant functional types conceal species-specific responses to environment? Study on arctic shrub communities.

    PubMed

    Saccone, Patrick; Hoikka, Kristiina; Virtanen, Risto

    2017-06-01

    Plant functional types (PFT) are increasingly used to outline biome-scale plant-environment relationship and predict global change effects on community structure. However, the potentials and limitations of the PFT approach have to be tested as they can be less sensitive than trait-based or species-level approaches. Here, we compare the responses of deciduous-evergreen shrub PFTs and species to gradual snow-related environmental conditions by also considering effects of aboveground architectural traits and neighboring shrubs. Five deciduous species and four evergreen dwarf shrub species were transplanted to be exposed to four levels of winter snow cover across mesotopographic gradients in northern Fennoscandian tundra. The survival and growth of individually tagged shoots were monitored over one year, and the change in cover of shrubs was monitored over four years. Evergreen species showed higher resistance to environmental severity and generally benefitted from higher abundance of neighboring shrubs. Deciduous species exhibited negligible to drastic responses to snow thickness and neighboring shrubs tended to have a negative effect on their performance and survival. Tall shoots of deciduous shrubs survived poorly under the thinnest snow cover. Overall, deciduous and evergreen PFTs showed modest differences in their performances along the gradient. Our results show that deciduous-evergreen leaf phenology categories predict shrub responses to changing environmental conditions only to a limited extent. Our findings highlight strong species-specific responses especially among deciduous shrubs, and a differential role of plant-plant interactions for shrubs. Our results emphasize that distribution patterns of arctic-alpine shrubs and shrub community responses to altered snow regimes depend on species-level plant functional attributes, species interactions and species-specific sensitivities to environmental severity. © 2017 by the Ecological Society of America.

  9. Will greater shrub abundance greatly impact tundra surface-atmosphere exchanges of energy and carbon?

    NASA Astrophysics Data System (ADS)

    Humphreys, E.; Lafleur, P.

    2015-12-01

    Increasing deciduous shrub abundance, productivity, and range in the Arctic comes with the potential for both negative and positive feedbacks to the climate system. This study presents six seasons of eddy covariance measurements of carbon dioxide (CO2) and latent and sensible heat fluxes along a shrub gradient in Canada's Low Arctic. Three flux tower sites with 17, 45, and 64% dwarf birch cover were established within a few kilometers of each other to investigate differences in microclimate, energy and carbon exchanges. As expected, there was greater winter snow depth but less summer soil thaw with greater shrub cover. However, snowmelt timing and speed were usually similar among sites. Despite a reduction in albedo in spring and greater leaf area through summer, latent heat fluxes were consistently lower with greater shrub cover. Offset by small differences in sensible heat fluxes, total seasonal atmospheric heating (combined sensible and latent heat fluxes) was similar among sites. We anticipated greater net uptake of CO2 through the growing season with greater shrub cover. However, that was only the case in some years. There was much more week-to-week and year-to-year variability in CO2 fluxes at the shrubbiest site suggesting photosynthesis and respiration processes were more sensitive to weather variations. Shrub abundance does impact tundra surface-atmosphere exchanges of energy and carbon but these observations also highlight the complexity involved in predicting the net climate feedback effect of current and future Arctic vegetation change.

  10. Coping with shrub secondary metabolites by ruminants

    USDA-ARS?s Scientific Manuscript database

    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 ...

  11. 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

  12. Chapter 23. Shrubs of other families

    Treesearch

    Stephen B. Monsen; Richard Stevens; Nancy L. Shaw

    2004-01-01

    Numerous genera and species of shrubs occur throughout the Intermountain region in addition to those included in the Asteraceae, Chenopodiaceae, and Rosaceae families. Although shrubs are widespread throughout this region and dominate many areas, species richness is low compared to the shrub flora of the Pacific United States, Chile, western Australia, and South Africa...

  13. Increased spring freezing vulnerability for alpine shrubs under early snowmelt.

    PubMed

    Wheeler, J A; Hoch, G; Cortés, A J; Sedlacek, J; Wipf, S; Rixen, C

    2014-05-01

    Alpine dwarf shrub communities are phenologically linked with snowmelt timing, so early spring exposure may increase risk of freezing damage during early development, and consequently reduce seasonal growth. We examined whether environmental factors (duration of snow cover, elevation) influenced size and the vulnerability of shrubs to spring freezing along elevational gradients and snow microhabitats by modelling the past frequency of spring freezing events. We sampled biomass and measured the size of Salix herbacea, Vaccinium myrtillus, Vaccinium uliginosum and Loiseleuria procumbens in late spring. Leaves were exposed to freezing temperatures to determine the temperature at which 50% of specimens are killed for each species and sampling site. By linking site snowmelt and temperatures to long-term climate measurements, we extrapolated the frequency of spring freezing events at each elevation, snow microhabitat and per species over 37 years. Snowmelt timing was significantly driven by microhabitat effects, but was independent of elevation. Shrub growth was neither enhanced nor reduced by earlier snowmelt, but decreased with elevation. Freezing resistance was strongly species dependent, and did not differ along the elevation or snowmelt gradient. Microclimate extrapolation suggested that potentially lethal freezing events (in May and June) occurred for three of the four species examined. Freezing events never occurred on late snow beds, and increased in frequency with earlier snowmelt and higher elevation. Extrapolated freezing events showed a slight, non-significant increase over the 37-year record. We suggest that earlier snowmelt does not enhance growth in four dominant alpine shrubs, but increases the risk of lethal spring freezing exposure for less freezing-resistant species.

  14. 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

  15. Seed dispersal of desert annuals.

    PubMed

    Venable, D Lawrence; Flores-Martinez, Arturo; Muller-Landau, Helene C; Barron-Gafford, Greg; Becerra, Judith X

    2008-08-01

    We quantified seed dispersal in a guild of Sonoran Desert winter desert annuals at a protected natural field site in Tucson, Arizona, USA. Seed production was suppressed under shrub canopies, in the open areas between shrubs, or both by applying an herbicide prior to seed set in large, randomly assigned removal plots (10-30 m diameter). Seedlings were censused along transects crossing the reproductive suppression borders shortly after germination. Dispersal kernels were estimated for Pectocarya recurvata and Schismus barbatus from the change in seedling densities with distance from these borders via inverse modeling. Estimated dispersal distances were short, with most seeds traveling less than a meter. The adhesive seeds of P. recurvata went farther than the small S. barbatus seeds, which have no obvious dispersal adaptation. Seeds dispersed farther downslope than upslope and farther when dispersing into open areas than when dispersing into shrubs. Dispersal distances were short relative to the pattern of spatial heterogeneity created by the shrub and open space mosaic. This suggests that dispersal could contribute to local population buildup, possibly facilitating species coexistence. Overall, these results support the hypothesis that escape in time via delayed germination is likely to be more important for desert annuals than escape in space.

  16. New White Dwarf-Brown Dwarf Binaries

    NASA Astrophysics Data System (ADS)

    Casewell, S. L.; Geier, S.; Lodieu, N.

    2017-03-01

    We present follow-up spectroscopy to 12 candidate white dwarf-brown dwarf binaries. We have confirmed that 8 objects do indeed have a white dwarf primary (7 DA, 1 DB) and two are hot subdwarfs. We have determined the Teff and log g for the white dwarfs and subdwarfs, and when combining these values with a model spectrum and the photometry, we have 3 probable white dwarf-substellar binaries with spectral types between M6 and L6.

  17. The Woody Plant Seed Manual

    Treesearch

    Franklin T. Bonner; Robert P. Karrfalt

    2008-01-01

    The first comprehensive handbook on the seeds of trees and shrubs produced by the USDA Forest Service was USDA Misc. Pub. 654, Woody-Plant Seed Manual. The manuscript was ready for publication in 1941, but World War II delayed publication until 1948. The boom in tree planting in the 1950s and 1960s created a large demand for seeds and exposed the gaps in our knowledge...

  18. Postfire drill-seeding of Great Basin plants: Effects of contrasting drills on seeded and nonseeded species

    Treesearch

    Jeffrey E. Ott; Robert D. Cox; Nancy L. Shaw; Beth A. Newingham; Amy C. Ganguli; Mike Pellant; Bruce A. Roundy; Dennis L. Eggett

    2016-01-01

    Objectives of postfire seeding in the Great Basin include reestablishment of perennial cover, suppression of exotic annual weeds, and restoration of diverse plant communities. Nonconventional seeding techniques may be required when seeding mixes of grasses, forbs, and shrubs containing seeds of different sizes. We conducted an operational-scale experiment to...

  19. A story of the permafrost small-scale collapse at the deciduous shrub patches in the northeast Siberian tundra

    NASA Astrophysics Data System (ADS)

    Li, Bingxi; Heijmans, Monique; Sass-Klaassen, Ute; Berendse, Frank

    2014-05-01

    The recent climate change is believed to accelerate the permafrost degradation in the arctic tundra. It also, meanwhile, drove the greening of the arctic (the expansion of the deciduous shrubs). The switch of the vegetation type might largely affect the local permafrost dynamics. Previous research indicated that the cover of deciduous shrubs mitigates the local permafrost degradation. From our observations, the active layer of permafrost at the deciduous shrub patch is normally the thinnest during the growing season. However, at our northeast Siberian tundra research site we also observed the drowning of shrubs due to small-scale permafrost collapse which happened in the shrub patches. This phenomenon is still far from understood. In this study we tried to explore the reasons that triggered these events. We hypothesized that the shrub cover can no longer protect the permafrost if dying of the oldest deciduous shrubs starts. Without sufficient shrub protection, the small-scale collapse of permafrost happens. Thus, we expected that the oldest deciduous shrub (in our study is dwarf birch Betula nana) individuals existed at small-scale permafrost collapse sites and the more younger stems appeared at the margin, compared with those at the center of the patches. The lack of long-term monitoring record increased the difficulties of the study. To achieve this target, a dendrochoronolgical method was implemented in this study, helping us measuring the shrub ages precisely. From the results of the study, we concluded that the dynamics of these patches were more complicated than our original hypotheses. Although there were some evidence supporting our expectation, the other results were against that. The vegetation dynamics of the B. nana patch probably was not the main reason of the local small-scale permafrost collapse. It was further implied that the local permafrost dynamics probably play a vital role on the patch dynamics in turn.

  20. Ecosystem response to removal of exotic riparian shrubs and a transition to upland vegetation

    USGS Publications Warehouse

    Reynolds, Lindsay V.; Cooper, David J.

    2011-01-01

    Understanding plant community change over time is essential for managing important ecosystems such as riparian areas. This study analyzed historic vegetation using soil seed banks and the effects of riparian shrub removal treatments and channel incision on ecosystem and plant community dynamics in Canyon de Chelly National Monument, Arizona. We focused on how seeds, nutrients, and ground water influence the floristic composition of post-treatment vegetation and addressed three questions: (1) How does pre-treatment soil seed bank composition reflect post-treatment vegetation composition? (2) How does shrub removal affect post-treatment riparian vegetation composition, seed rain inputs, and ground water dynamics? and (3) Is available soil nitrogen increased near dead Russian olive plants following removal and does this influence post-treatment vegetation? We analyzed seed bank composition across the study area, analyzed differences in vegetation, ground water levels, and seed rain between control, cut-stump and whole-plant removal areas, and compared soil nitrogen and vegetation near removed Russian olive to areas lacking Russian olive. The soil seed bank contained more riparian plants, more native and fewer exotic plants than the extant vegetation. Both shrub removal methods decreased exotic plant cover, decreased tamarisk and Russian olive seed inputs, and increased native plant cover after 2 years. Neither method increased ground water levels. Soil near dead Russian olive trees indicated a short-term increase in soil nitrogen following plant removal but did not influence vegetation composition compared to areas without Russian olive. Following tamarisk and Russian olive removal, our study sites were colonized by upland plant species. Many western North American rivers have tamarisk and Russian olive on floodplains abandoned by channel incision, river regulation or both. Our results are widely applicable to sites where drying has occurred and vegetation

  1. Seed dispersers, seed predators, and browsers act synergistically as biotic filters in a mosaic landscape.

    PubMed

    Zamora, Regino; Matías, Luis

    2014-01-01

    In this study, we analize the functional influence of animals on the plants they interact with in a mediterranean mountain. We hypothesise that seed dispersers, seed predators, and browsers can act as biotic filters for plant communities. We analyse the combined effects of mutualistic (seed dispersal) and antagonistic (seed predation, herbivory) animal interactions in a mosaic landscape of Mediterranean mountains, basing our results on observational and experimental field. Most of the dispersed seeds came from tree species, whereas the population of saplings was composed predominantly of zoochorous shrub species. Seed predators preferentially consumed seeds from tree species, whereas seeds from the dominant fleshy-fruited shrubs had a higher probability of escaping these predators. The same pattern was repeated among the different landscape units by browsers, since they browsed selectively and far more intensely on tree-species saplings than on the surrounding shrubs. In synthesis, our work identifies the major biotic processes that appear to be favoring a community dominated by shrubs versus trees because seed dispersers, predators, and herbivores together favored shrub dispersal and establishment versus trees.

  2. Seed Dispersers, Seed Predators, and Browsers Act Synergistically as Biotic Filters in a Mosaic Landscape

    PubMed Central

    Zamora, Regino; Matías, Luis

    2014-01-01

    In this study, we analize the functional influence of animals on the plants they interact with in a mediterranean mountain. We hypothesise that seed dispersers, seed predators, and browsers can act as biotic filters for plant communities. We analyse the combined effects of mutualistic (seed dispersal) and antagonistic (seed predation, herbivory) animal interactions in a mosaic landscape of Mediterranean mountains, basing our results on observational and experimental field. Most of the dispersed seeds came from tree species, whereas the population of saplings was composed predominantly of zoochorous shrub species. Seed predators preferentially consumed seeds from tree species, whereas seeds from the dominant fleshy-fruited shrubs had a higher probability of escaping these predators. The same pattern was repeated among the different landscape units by browsers, since they browsed selectively and far more intensely on tree-species saplings than on the surrounding shrubs. In synthesis, our work identifies the major biotic processes that appear to be favoring a community dominated by shrubs versus trees because seed dispersers, predators, and herbivores together favored shrub dispersal and establishment versus trees. PMID:25233342

  3. Shrub removal in reforested post-fire areas increases native plant species richness

    Treesearch

    Gabrielle N. Bohlman; Malcolm North; Hugh D. Safford

    2016-01-01

    Large, high severity fires are becoming more prevalent in Sierra Nevada mixed-conifer forests, largely due to heavy fuel loading and forest densification caused by past and current management practices. In post-fire areas distant from seed trees, conifers are often planted to re-establish a forest and to prevent a potential type-conversion to shrub fields. Typical...

  4. Shrubs stimulate heterotrophic respiration in arctic soils

    NASA Astrophysics Data System (ADS)

    Phillips, C. A.; Wurzburger, N.

    2016-12-01

    The response of arctic ecosystems to global change will have critical effects on future climate. Climate warming has already triggered the expansion of shrubs across tundra, raising questions about how shrubs will affect ecosystem carbon balance. Shrub litter quality and mycorrhizal symbionts may accelerate the activity of soil microorganisms that facilitate the release of large stores of soil carbon. We investigated how shrubs affect the activity of soil microorganisms by creating soil mesocosms from areas with and without shrub species as dominants of the plant community in arctic Alaska. We hypothesized that relative to their non-shrub counterparts, heterotrophic respiration of shrub soils would: (1) be greater, (2) demonstrate greater response to additions of shrub litter, and (3) be less nutrient limited. We created mesocosms with root-free soils at constant moisture and temperature, and quantified basal heterotrophic soil respiration rates, and the response of respiration to litter and nutrient inputs in a series of laboratory experiments inputs. (1) We found that the presence of shrubs generally produced higher rates of basal soil respiration in both horizons, suggesting that shrubs stimulate microbial activity. (2) Litter addition increased respiration across both horizons with no differences in response between shrub and non-shrub soils. (3) N additions did not increase heterotrophic respiration, but P and N+P additions induced a short respiratory pulse in all soils, suggesting mild P limitation. Collectively, these findings provide evidence that shrubs stimulate heterotrophic microbial activity to enhance carbon loss, but generate new questions about the mechanisms driving these patterns.

  5. Dwarf Galaxies with Active Massive Black Holes

    NASA Astrophysics Data System (ADS)

    Reines, Amy E.; Greene, J. E.; Geha, M. C.

    2014-01-01

    Supermassive black holes (BHs) live at the heart of essentially all massive galaxies with bulges, power AGN, and are thought to be important agents in the evolution of their hosts. However, the birth and growth of the first supermassive BH "seeds" is far from understood. While direct observations of these distant BHs in the infant Universe are unobtainable with current capabilities, massive BHs in present-day dwarf galaxies can place valuable constraints on the masses, formation path, and hosts of supermassive BH seeds. Using optical spectroscopy from the SDSS, we have systematically assembled the largest sample of dwarf galaxies hosting active massive BHs to date. These dwarf galaxies have stellar masses comparable to the Magellanic Clouds and contain some of the least-massive supermassive BHs known.

  6. 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)

  7. 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)

  8. Uncovering AGN Fueling and Feedback in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Mushotzky, Richard

    2014-09-01

    While massive black holes (BHs) are ubiquitous in massive galaxies, their presence in dwarf galaxies is less certain. This constitutes a major gap in our understanding of BH-galaxy co-evolution. Identifying low-mass BHs in local dwarfs could also constrain BH seed formation at high z. Active BHs in dwarfs can reveal BH fueling and feedback in a vastly different regime than the well-studied AGN in massive hosts. Most AGN feedback models focus on the latter, as star formation is thought to suffice to drive feedback in dwarfs. However, AGN are increasingly found in dwarfs, where their effect on hosts may be most dramatic. We propose an unprecedented program to detect and characterize AGN fueling and feedback in the low-mass regime, using a unique sample of Swift-BAT AGN in dwarf

  9. 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.

  10. Recent expansion of erect shrubs in the Low Arctic: evidence from Eastern Nunavik

    NASA Astrophysics Data System (ADS)

    Tremblay, Benoît; Lévesque, Esther; Boudreau, Stéphane

    2012-09-01

    In order to characterize shrub response near the treeline in Eastern Nunavik (Québec), a region under extensive warming since the 1990s, we compared two series (1964 and 2003) of vertical aerial photos from the vicinity of Kangiqsualujjuaq. Our study revealed a widespread increase in erect woody vegetation cover. During the 40 years spanning the two photo series, erect shrub and tree cover increased markedly on more than half of the land surface available for new colonization or infilling. Within the 7.2 km2 analysed, areas with dense shrub and tree cover (>90%) increased from 34% to 44% whereas areas with low cover (<10%) shrank from 45% to 29%. This increase in cover of trees and shrubs occurred throughout the landscape regardless of altitude, slope angle and exposure, although to varying extents. The main shrub species involved in this increase was Betula glandulosa Michx. (dwarf birch), which was present in 98% and dominant in 85% of the 345 plots. In addition, numerous seedlings and saplings of Larix laricina (Du Roi) K Koch (eastern larch) were found above the treeline (25% of the plots), suggesting that the altitudinal treeline might shift upslope in the near future. Sites that remained devoid of erect woody vegetation in 2003 were either characterized by the absence of a suitable seedbed or by harsh local microclimatic conditions (wind exposure or excessive drainage). Our results indicate dramatic increases in shrub and tree cover at a Low Arctic site in Eastern Nunavik, contributing to a growing number of observations of woody vegetation change from various areas around the North.

  11. 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

  12. 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.

  13. Comparison of postfire seeding practices for Wyoming big sagebrush

    Treesearch

    Jeffrey E. Ott; Robert D. Cox; Nancy L. Shaw

    2017-01-01

    Wildfires in the Great Basin have resulted in widespread loss of Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young), an ecologically important shrub that has proven difficult to establish from seed.We sought to identify optimal seeding practices forWyoming big sagebrush in the context of postfire seeding operations involving...

  14. Direct seeding woody species for restoration of bottomlands

    Treesearch

    Daniel J. Twedt

    2006-01-01

    I direct seeded (broadcast) seeds of 39 species of trees and shrubs using an ATV-mounted rotary spreader to initiate restoration of bottomland forest on retired agricultural sites. Four sites were planted during February, 2000, and 13 additional sites were planted during April and May, 2001. After two growing seasons, stem density of direct-seeded species varied...

  15. Pondberry (Lindera melissifolia) seed predators

    Treesearch

    Fernanda Maria Abilio; Carl Smith; Colin Tidwell; Paul Hamel; Margaret Devall; Ted Leininger

    2008-01-01

    Pondberry is an endangered, dioecious, deciduous shrub that grows in periodically flooded forests of the southeastern United States of America. Pondbeny is a clonal plant. Each female stem grows up to two meters tall and may produce many red drupes. The probability of dispersed seeds to survive to germination and beyond is unknown in the species. For this study, six...

  16. DISPERSAL OF SEEDS AS NEST MATERIAL BY THE CACTUS WREN

    EPA Science Inventory

    Cactus wren (Campylorhynchus brunneicapillus) nests from the southern Chihuahuan Desert contained viable seeds of grasses, forbs, and shrubs. The most common plants used as construction material in these nests were Muhlenbergia porteri, Boerhavia spicata, and the alien grass Era...

  17. DISPERSAL OF SEEDS AS NEST MATERIAL BY THE CACTUS WREN

    EPA Science Inventory

    Cactus wren (Campylorhynchus brunneicapillus) nests from the southern Chihuahuan Desert contained viable seeds of grasses, forbs, and shrubs. The most common plants used as construction material in these nests were Muhlenbergia porteri, Boerhavia spicata, and the alien grass Era...

  18. Sowing the Seeds of Planets? Artist Concept

    NASA Image and Video Library

    2005-10-20

    This artist concept shows microscopic crystals in the dusty disk surrounding a brown dwarf, or failed star. The crystals, made up of a green mineral found on Earth called olivine, are thought to help seed the formation of planets.

  19. Mortality of resprouting chaparral shrubs after a fire and during a record drought: physiological mechanisms and demographic consequences.

    PubMed

    Pratt, R Brandon; Jacobsen, Anna L; Ramirez, Aaron R; Helms, Anjel M; Traugh, Courtney A; Tobin, Michael F; Heffner, Marcus S; Davis, Stephen D

    2014-03-01

    We examined postfire regeneration of chaparral shrubs during an intense drought. This study focused on the demography and physiology of shrub species that resprout from a basal lignotuber following fire. We found significant levels of resprout mortality when intense drought occurred in the year following fire during the period of shrub recovery. Three of the seven sampled resprouting species had the greatest or near greatest levels of mortality ever recorded when compared to previous studies. Most shrub mortality occurred during the drought after individuals had resprouted (i.e. individuals survived fire, resprouted and then subsequently died). Physiological measurements of species with high mortality suggested that resprout stems were highly embolized and xylem hydraulic conductivities were close to zero during the peak of the drought. In addition, lignotubers of two of the three species experiencing high mortality were depleted of starch. Population densities of most shrub species declined after the drought compared with their prefire levels, with the exception of one drought tolerant obligate seeding species. Resprouting shrub species may deplete their carbohydrate reserves during the resprouting process, making them particularly vulnerable to drought because of the need to transpire water to acquire the CO2 that is used to supply energy to a large respiring root system. Drought appears to interact with fire by altering postfire shrub recovery and altering species abundances and composition of chaparral communities. © 2013 John Wiley & Sons Ltd.

  20. Empty Seeds Are Not Always Bad: Simultaneous Effect of Seed Emptiness and Masting on Animal Seed Predation

    PubMed Central

    Perea, Ramón; Venturas, Martin; Gil, Luis

    2013-01-01

    Seed masting and production of empty seeds have often been considered independently as different strategies to reduce seed predation by animals. Here, we integrate both phenomena within the whole assemblage of seed predators (both pre and post-dispersal) and in two contrasting microsites (open vs. sheltered) to improve our understanding of the factors controlling seed predation in a wind-dispersed tree (Ulmus laevis). In years with larger crop sizes more avian seed predators were attracted with an increase in the proportion of full seeds predated on the ground. However, for abundant crops, the presence of empty seeds decreased the proportion of full seeds predated. Empty seeds remained for a very long period in the tree, making location of full seeds more difficult for pre-dispersal predators and expanding the overall seed drop period at a very low cost (in dry biomass and allocation of C, N and P). Parthenocarpy (non-fertilized seeds) was the main cause of seed emptiness whereas seed abortion was produced in low quantity. These aborted seeds fell prematurely and, thus, could not work as deceptive seeds. A proportion of 50% empty seeds significantly reduced ground seed predation by 26%. However, a high rate of parthenocarpy (beyond 50% empty seeds) did not significantly reduce seed predation in comparison to 50% empty seeds. We also found a high variability and unpredictability in the production of empty seeds, both at tree and population level, making predator deception more effective. Open areas were especially important to facilitate seed survival since rodents (the main post-dispersal predators) consumed seeds mostly under shrub cover. In elm trees parthenocarpy is a common event that might work as an adaptive strategy to reduce seed predation. Masting per se did not apparently reduce the overall proportion of seeds predated in this wind-dispersed tree, but kept great numbers of seeds unconsumed. PMID:23776503

  1. Empty seeds are not always bad: simultaneous effect of seed emptiness and masting on animal seed predation.

    PubMed

    Perea, Ramón; Venturas, Martin; Gil, Luis

    2013-01-01

    Seed masting and production of empty seeds have often been considered independently as different strategies to reduce seed predation by animals. Here, we integrate both phenomena within the whole assemblage of seed predators (both pre and post-dispersal) and in two contrasting microsites (open vs. sheltered) to improve our understanding of the factors controlling seed predation in a wind-dispersed tree (Ulmus laevis). In years with larger crop sizes more avian seed predators were attracted with an increase in the proportion of full seeds predated on the ground. However, for abundant crops, the presence of empty seeds decreased the proportion of full seeds predated. Empty seeds remained for a very long period in the tree, making location of full seeds more difficult for pre-dispersal predators and expanding the overall seed drop period at a very low cost (in dry biomass and allocation of C, N and P). Parthenocarpy (non-fertilized seeds) was the main cause of seed emptiness whereas seed abortion was produced in low quantity. These aborted seeds fell prematurely and, thus, could not work as deceptive seeds. A proportion of 50% empty seeds significantly reduced ground seed predation by 26%. However, a high rate of parthenocarpy (beyond 50% empty seeds) did not significantly reduce seed predation in comparison to 50% empty seeds. We also found a high variability and unpredictability in the production of empty seeds, both at tree and population level, making predator deception more effective. Open areas were especially important to facilitate seed survival since rodents (the main post-dispersal predators) consumed seeds mostly under shrub cover. In elm trees parthenocarpy is a common event that might work as an adaptive strategy to reduce seed predation. Masting per se did not apparently reduce the overall proportion of seeds predated in this wind-dispersed tree, but kept great numbers of seeds unconsumed.

  2. 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.

  3. Brown Dwarf Comparison

    NASA Image and Video Library

    2009-11-17

    NASA Wide-field Infrared Survey Explorer will uncover many failed stars, or brown dwarfs, in infrared light. This diagram shows a brown dwarf in relation to Earth, Jupiter, a low-mass star and the sun.

  4. Tree seed handling, processing, testing, and storage at Hayward State Nursery, Wisconsin Department of Natural Resources

    Treesearch

    Gordon Christians

    2008-01-01

    The Hayward State Nursery, Wisconsin grows more than 40 species from seeds. Up to 6000 bushels of raw unprocessed tree and shrub seeds are collected each year, and all seeds are collected in Wisconsin or adjacent states. All white spruce (Picea glauca) and some white pine seeds (Pinus strobus) are collected from orchards containing...

  5. Pacific Northwest forest tree seed zones: a template for native plants?

    Treesearch

    GR Johnson; Frank C Sorensen; J Bradley St Clair; Richard C. Cronn

    2004-01-01

    Seed movement guidelines for restoration activities are lacking for most native grasses, forbs, and shrubs. The forestry community has decades of experience in establishing seed zones and seed movement guidelines that may be of value to restoration managers. We review the history of seed zone development in forest trees, with emphasis on the Pacific Northwest, and make...

  6. Treating downy brome with herbicide and seeding with native shrubs

    Treesearch

    Suzanne Owen; Carolyn Sieg

    2011-01-01

    Downy brome or cheatgrass (Bromus tectorum L.) is one of the most invasive and widespread exotic plants in North America. Downy brome can reduce soil nutrient availability, alter native plant community composition, and increase fire frequencies. The effectiveness of Plateau® imazapic herbicide in reducing downy brome cover has been variable, and there is uncertainty...

  7. 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

  8. Proceedings - Symposium on cheatgrass invasion, shrub die-off, and other aspects of shrub biology and management

    Treesearch

    E. Durant McArthur; Evan M. Romney; Stanley D. Smith; Paul T. Tueller

    1990-01-01

    Includes 45 papers and accounts of field trips from a symposium focused on a recent shrub die-off phenomenon and a perennial problem, cheatgrass invasion, on western rangelands. Contributions also cover shrub establishment, shrub ecosystem ecology and physiology, and plant and shrub ecosystems.

  9. Pulsating white dwarfs

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Romero, Alejandra D.

    2017-09-01

    The Sloan Digital Sky Survey has allowed us to increase the number of known white dwarfs by a factor of five and consequently the number of known pulsating white dwarfs also by a factor of five. It has also led to the discovery of new types of variable white dwarfs, as the variable hot DQs, and the pulsating Extremely Low Mass white dwarfs. With the Kepler Mission, it has been possible to discover new phenomena, the outbursts present in a few pulsating white dwarfs.

  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.

  11. 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.

  12. Effects of habitat and season on removal and hoarding of seeds of wild apricot (Prunus armeniaca) by small rodents

    NASA Astrophysics Data System (ADS)

    Ji-Qi, Lu; Zhi-Bin, Zhang

    2004-12-01

    The wild apricot (Prunus armeniaca) is widely distributed in the Donglingshan Mountains of Mentougou District of Beijing, China, where its seeds may be an important food resource for rodents. Predation, removal and hoarding of seeds by rodents will inevitably affect the spatio-temporal pattern of seed fate of wild apricot in this area. By marking and releasing tagged seeds of wild apricot, we investigated seeds survival, scatter-hoarding, cache size and seedling establishment, and the preference of micro-habitats used by rodents to store seeds. The results showed that: (1) rodents in this area hoarded food intensively in autumn, as well as in spring and summer. (2) There were significant effects of habitat and season on removal rate of tagged seeds at releasing plots. In both two types of habitats, Low and High shrub, tagged seeds were removed most rapidly by rodents in autumn, at intermediate rates in spring and least rapidly in summer. (3) During three seasons, mean dispersal distance of scatter-hoarded seeds in Low shrub habitat was greater than that in High shrub. Most removed seeds were buried within 21.0 m of the releasing plots. (4) In both two types of habitats, Low and High shrub, rodents tended to carry seeds to US (Under shrub) and SE (Shrub edge) microhabitats for scatter-hoarding or predation. (5) Among the caches made by rodents, most caches contained only one seed, but up to three seeds were observed; caches of 2-3 seeds were common in autumn. (6) By comparing dental marks, we determined that large field mice (Apodemus peninsulae) and David's rock squirrels (Sciurotamias davidianus) contributed to removal and predation of released tagged seeds. However, only the large field mice exerted a pivotal and positive role on the burial of dispersed seeds. (7) Establishment of three seedlings originated from seeds buried by rodents was documented in High shrub habitat.

  13. 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

  14. 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

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

    PubMed

    Myers-Smith, Isla H; Hik, David S

    2013-10-01

    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.

  16. 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.

  17. Variation in semi-arid soil seed banks

    SciTech Connect

    Boudell-Flanary, J.A.; Link, S.O. |

    1995-09-01

    Seeds recovered from soils in the semi-arid shrub-steppe were compared to test for differences between the seed banks found beneath and cryptogamic crust and the crevices in the crust. Seed quantity found within the crevices was 56% higher than that under the cryptogamic crust. Pseudoroegneria spicata, Poa sandbergii, Bromus tectorum, and Artemisia tridentata are the common species found at the research site. Seeds of Bromus tectorum, Erigeron spp., and Poa spp. were found in the crevices of the crust. Seeds of Artemisia tridentata were not found in the seed banks of either the cryptogamic crust or the crevices in the crust. The higher amount of seeds found in the crevices of the cryptogamic crust suggests that the crevices play a significant role in determining the distributional pattern of shrub-steppe vegetation.

  18. Biomass estimation for five shrubs from northeastern Minnesota.

    Treesearch

    Lewis F. Ohmann; David F. Grigal; Robert B. Brander

    1976-01-01

    Describes the derivation and use of biomass prediction equations for five shrub species from northeastern Minnesota. The various equations predict four weight variables based on four shrub dimensions used as independent variables.

  19. T Dwarf Explorer

    NASA Astrophysics Data System (ADS)

    Fazio, Giovanni; Hora, Joseph; Luhman, Kevin; Marengo, Massimo; Patten, Brian; Sonnett, Sarah; Stauffer, John

    2007-05-01

    With the basic colors and photometry for M, L, and T dwarfs in the IRAC bandpasses established (Patten et al. 2006), we wish to shift our focus to the differences seen among objects with similar T_eff and, in particular, to expand on the exploration of the T dwarfs. While some of the observed dispersion of T dwarf colors and magnitudes in the near- and mid-IR for objects of the same sub-type can be explained by differences in metallicity and gravity, some of this scatter may also be due to binarity and intrinsic variability (i.e., 'brown dwarf weather'). We are curious as to whether or not the observed scatter with color in the infrared, which appears to be largest in the mid-T dwarfs, really tapers off and grows smaller in the late-T dwarfs, or if we are simply not seeing the whole picture due to small number statistics. On the warmer end of the T sequence, recent results suggest that the transition from the late-L to early-T types in brown dwarf temperature progresses very quickly in an evolutionary sense. Therefore, objects with early T types should be relatively rare. Many of the early-T brown dwarfs used in the in the Patten et al. 2006 study (and others) have turned out to be very close binaries (e.g. Burgasser et al. 2006), which has resulted in a deficit of true, single early-T brown dwarfs with well-determined mid-infrared colors and photometry. We are proposing to acquire IRAC photometry for an additional ~23 T-type dwarfs in order to allow us to better characterize trending with color and spectral type for the T dwarfs. These new T dwarf data will be combined with the existing T dwarf data previously acquired by IRAC to produce the color-color and color-magnitude diagrams necessary to compare observation to theory for the coolest sub-stellar mass objects known. These data will prove invaluable in constraining searches in color and magnitude space for brown dwarf companions to nearby stars as well as for free-floating brown dwarfs in the field.

  20. Shrubs and vines for northeastern wildlife

    Treesearch

    John D. Gill; William M. Healy

    1974-01-01

    A non-technical handbook in which 34 authors discuss management of 97 native and 3 naturalized shrubs or woody vines most important to wildlife in the Northeast,-Kentucky to Maryland to Newfoundland to Ontario. Topics include range, habitat, life history, uses, propagation, and management; but not identification.

  1. 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…

  2. 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…

  3. 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.

  4. Seed germination and seedling emergence of Scotch broom (Cytisus scoparius)

    Treesearch

    Timothy B. Harrington

    2009-01-01

    Scotch broom is a large, leguminous shrub that has invaded 27 U.S. states. The species produces seeds with a hard coat that remain viable in the soil for years. Growth-chamber studies were conducted to determine effects of temperature regime and cold-stratification period on seed germination. Seedling emergence, mortality, and biomass also were studied in response to...

  5. Weak Evidence of Regeneration Habitat but Strong Evidence of Regeneration Niche for a Leguminous Shrub

    PubMed Central

    Delerue, Florian; Gonzalez, Maya; Michalet, Richard; Pellerin, Sylvain; Augusto, Laurent

    2015-01-01

    The identification of an ecological niche specific to the regeneration phase has mobilised significant attention. However, the importance of the regeneration niche concept remains unclear. Our main objective was to study the existence of such a regeneration niche for a leguminous shrub, Ulex europaeus. This study was carried out in southwest France in the context of water and nutrient stresses (mainly phosphorus limitation) due to the presence of nutrient-poor sandy soils. We analysed the regeneration of the species from the germination of seeds and emergence of new seedlings until the seedlings reached young shrub size. Our design included a P fertilisation treatment. We also investigated microsite characteristics (micro-topography and vegetation development) as they can interact with meteorological conditions and determine water availability for seeds and seedlings. We found that P availability controlled seedling growth and the time necessary to reach young shrub size. Water availability appeared to impact the species germination and seedlings survival. We also found that P and water availability depended on the interactions between microsite characteristics and climatic variations. Finally we found evidence that P and water availability are important ecological factors shaping the regeneration niche of the species, but we found weak evidence that any microsite would be appropriate for the regeneration of the species in the long term. Future studies regarding regeneration niches need to distinguish more clearly the ecological factors important for regeneration (the regeneration niche per se) and the physical world where the seedlings appear and develop (the regeneration habitat). PMID:26098877

  6. Weak Evidence of Regeneration Habitat but Strong Evidence of Regeneration Niche for a Leguminous Shrub.

    PubMed

    Delerue, Florian; Gonzalez, Maya; Michalet, Richard; Pellerin, Sylvain; Augusto, Laurent

    2015-01-01

    The identification of an ecological niche specific to the regeneration phase has mobilised significant attention. However, the importance of the regeneration niche concept remains unclear. Our main objective was to study the existence of such a regeneration niche for a leguminous shrub, Ulex europaeus. This study was carried out in southwest France in the context of water and nutrient stresses (mainly phosphorus limitation) due to the presence of nutrient-poor sandy soils. We analysed the regeneration of the species from the germination of seeds and emergence of new seedlings until the seedlings reached young shrub size. Our design included a P fertilisation treatment. We also investigated microsite characteristics (micro-topography and vegetation development) as they can interact with meteorological conditions and determine water availability for seeds and seedlings. We found that P availability controlled seedling growth and the time necessary to reach young shrub size. Water availability appeared to impact the species germination and seedlings survival. We also found that P and water availability depended on the interactions between microsite characteristics and climatic variations. Finally we found evidence that P and water availability are important ecological factors shaping the regeneration niche of the species, but we found weak evidence that any microsite would be appropriate for the regeneration of the species in the long term. Future studies regarding regeneration niches need to distinguish more clearly the ecological factors important for regeneration (the regeneration niche per se) and the physical world where the seedlings appear and develop (the regeneration habitat).

  7. White Dwarf Mergers on Adaptive Meshes

    NASA Astrophysics Data System (ADS)

    Katz, Maximilian Peter

    The mergers of binary white dwarf systems are potential progenitors of astrophysical explosions such as Type Ia supernovae. These white dwarfs can merge either by orbital decay through the emission of gravitational waves or by direct collisions as a result of orbital perturbations. The coalescence of the stars may ignite nuclear fusion, resulting in the destruction of both stars through a thermonuclear runaway and ensuing detonation. The goal of this dissertation is to simulate binary white dwarf systems using the techniques of computational fluid dynamics and therefore to understand what numerical techniques are necessary to obtain accurate dynamical evolution of the system, as well as to learn what conditions are necessary to enable a realistic detonation. For this purpose I have used software that solves the relevant fluid equations, the Poisson equation for self-gravity, and the systems governing nuclear reactions between atomic species. These equations are modeled on a computational domain that uses the technique of adaptive mesh refinement to have the highest spatial resolution in the areas of the domain that are most sensitive to the need for accurate numerical evolution. I have identified that the most important obstacles to accurate evolution are the numerical violation of conservation of energy and angular momentum in the system, and the development of numerically seeded thermonuclear detonations that do not bear resemblance to physically correct detonations. I then developed methods for ameliorating these problems, and determined what metrics can be used for judging whether a given white dwarf merger simulation is trustworthy. This involved the development of a number of algorithmic improvements to the simulation software, which I describe. Finally, I performed high-resolution simulations of typical cases of white dwarf mergers and head-on collisions to demonstrate the impacts of these choices. The results of these simulations and the corresponding

  8. A Panchromatic View of Brown Dwarf Aurorae

    NASA Astrophysics Data System (ADS)

    Pineda, J. Sebastian; Hallinan, Gregg; Kao, Melodie M.

    2017-09-01

    Stellar coronal activity has been shown to persist into the low-mass star regime, down to late M-dwarf spectral types. However, there is now an accumulation of evidence suggesting that at the end of the main sequence, there is a transition in the nature of the magnetic activity from chromospheric and coronal to planet-like and auroral, from local impulsive heating via flares and MHD wave dissipation to energy dissipation from strong large-scale magnetospheric current systems. We examine this transition and the prevalence of auroral activity in brown dwarfs through a compilation of multiwavelength surveys of magnetic activity, including radio, X-ray, and optical. We compile the results of those surveys and place their conclusions in the context of auroral emission as a consequence of large-scale magnetospheric current systems that accelerate energetic electron beams and drive the particles to impact the cool atmospheric gas. We explore the different manifestations of auroral phenomena, like Hα, in brown dwarf atmospheres and define their distinguishing characteristics. We conclude that large-amplitude photometric variability in the near-infrared is most likely a consequence of clouds in brown dwarf atmospheres, but that auroral activity may be responsible for long-lived stable surface features. We report a connection between auroral Hα emission and quiescent radio emission in electron cyclotron maser instability pulsing brown dwarfs, suggesting a potential underlying physical connection between quiescent and auroral emissions. We also discuss the electrodynamic engines powering brown dwarf aurorae and the possible role of satellites around these systems both to power the aurorae and seed the magnetosphere with plasma.

  9. Simple methods for raising tree and shrub seedlings in Afghanistan

    Treesearch

    R. Kasten Dumroese; Thomas D. Landis; Tara Luna; George Hernandez

    2008-01-01

    Growing trees and shrubs in nurseries is rewarding. You may wish to grow trees and shrubs for many reasons: 1) reforestation; 2) land stabilization; 3) fire wood (energy); 4) improving water quality; 5) urban landscapes; 6) providing shade; 7) producing fruits or nuts. If you enjoy growing plants, you are more likely to produce better trees and shrubs (Figure 1.1). In...

  10. Tall shrub dynamics in northern Minnesota aspen and conifer forests.

    Treesearch

    James C. Galogh; David F. Grigal

    1988-01-01

    Tall shrub dynamics were examined in upland stands in northern Minnesota. Mortality rates of shrub stems did not differ among the stands. Shrub stem regeneration did differ among the stands and was related to overstory characteristics, soil moisture, and soil nutrients. Stem density was regulated by annual regeneration.

  11. Larch Dwarf Mistletoe (FIDL)

    Treesearch

    Jerome S. Beatty; Gregory M. Filip; Robert L. Mathiason

    1997-01-01

    Larch dwarf mistletoe (Arceuthobium laricis (Piper) St. John) is a common and damaging parasite of western larch (Larix occidentalis Nutt.) in the Pacific Northwest and southern British Columbia. Larch dwarf mistletoe occurs commonly throughout the range of western larch in British Columbia, northern and central Idaho, western Montana and east of the Cascades in...

  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. Tolerance of an expanding subarctic shrub, Betula glandulosa, to simulated caribou browsing.

    PubMed

    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.

  14. Incidence of viruses in fescue (Festuca sp.) seed production fields in the Willamette Valley in 2016

    USDA-ARS?s Scientific Manuscript database

    Tall Fescue seed production fields of Western Oregon were sampled and tested for the presence or absence of three viruses, Barley yellow dwarf virus (BYDV) -MAV and -PAV, and Cereal yellow dwarf virus (CYDV). There was no BYDV-MAV detected in any of the Fescue seed fields. The BYDV-PAV occurred in ...

  15. Cultivation and irrigation of fernleaf biscuitroot (Lomatium dissectum) for seed production

    Treesearch

    Myrtle P. Shock; Clinton C. Shock; Erik G. B. Feibert; Nancy L. Shaw; Lamont D. Saunders; Ram K. Sampangi

    2012-01-01

    Native grass, forb, and shrub seed is needed to restore rangelands of the U.S. Intermountain West. Fernleaf biscuitroot [Lomatium dissectum (Nutt.) Mathias & Constance] is a desirable component of rangelands. Commercial seed production is necessary to provide the quantity and quality of seed needed for rangeland restoration and reclamation efforts. Fernleaf...

  16. Pollinating bees crucial to farming wildflower seed for U.S. habitat restoration

    Treesearch

    James H. Cane

    2008-01-01

    Federal land managers desire seed of Great Basin perennial wildflowers, mixed with grass and shrub seed, for restoration of millions of acres of sagebrush communities degraded by altered wildfire regimes, and exotic grasses and forbs. For 15 candidate wildflower species to be farmed for seed production, all were found to need pollinators, typically bees (Apiformes),...

  17. Seed ecology of Lindera melissifolia (Lauraceae) as it relates to rarity of the species

    Treesearch

    Tracy Hawkins; Jeffery L. Walck; Siti N. Hidayati

    2011-01-01

    The seed ecology of the federally endangered shrub, Lindera melissifolia was investigated to determine if this aspect of the species life history contributes to the rarity of the species. Lindera melissifolia has the capacity to form a short-lived (two growing seasons) persistent soil seed bank if fruit pulp remains on seeds following dispersal and subsequent winter...

  18. Big sagebrush seed bank densities following wildfires

    USDA-ARS?s Scientific Manuscript database

    Big sagebrush (Artemisia spp.) is a critical shrub to many wildlife species including sage grouse (Centrocercus urophasianus), mule deer (Odocoileus hemionus), and pygmy rabbit (Brachylagus idahoensis). Big sagebrush is killed by wildfires and big sagebrush seed is generally short-lived and do not s...

  19. Advanced techniques to prepare seed to sow

    Treesearch

    Robert P. Karrfalt

    2013-01-01

    This paper reviews research on improving the basic technique of cold stratification for tree and shrub seeds. Advanced stratification techniques include long stratification, stratification re-dry, or multiple cycles of warm-cold stratification. Research demonstrates that careful regulation of moisture levels and lengthening the stratification period have produced a...

  20. Artemisia tridenata seed bank densities following wildfires

    USDA-ARS?s Scientific Manuscript database

    Big sagebrush (Artemisia spp.) is a critical shrub to such sagebrush obligate species as sage grouse, (Centocercus urophasianus), mule deer (Odocoileus hemionus), and pygmy rabbit (Brachylagus idahoensis). Big sagebrush do not sprout after wildfires and big sagebrush seed is generally short-lived a...

  1. Big Sagebrush Seed Bank Densities Following Wildfires

    USDA-ARS?s Scientific Manuscript database

    Big sagebrush (Artemisia sp.) is a critical shrub to such sagebrush obligate species as sage grouse, (Centocercus urophasianus), mule deer (Odocoileus hemionus), and pygmy rabbit (Brachylagus idahoensis). Big sagebrush do not sprout after wildfires wildfires and big sagebrush seed is generally sho...

  2. The dwarf saltwort (Salicornia bigelovii Torr.): Evaluation of breeding populations

    USDA-ARS?s Scientific Manuscript database

    Breeding populations of the dwarf saltwort (Salicornia bigelovii Torr. [Chenopodiaceae]) have been evaluated under high seawater salinity (45 dS m-1) for phenotypic, morphometric, biomass and seed traits in an effort to select suitable families and genotypes within families for breeding purposes and...

  3. Astrophysics with white dwarfs

    NASA Astrophysics Data System (ADS)

    Kalirai, Jasonjot Singh

    2004-10-01

    White dwarfs are the end products of the entire stellar evolutionary process in all intermediate and low mass stars. Over 99% of all stars in our Galaxy will eventually end their lives as white dwarfs. Observationally, studying white dwarfs has proven to be very difficult, primarily due to the faintness of the objects. Bright white dwarfs with M V = 11 have a luminosity only 1/300th of the Sun's intrinsic brightness, while the faintest white dwarfs are 100,000 x fainter than the Sun. In this thesis, we describe three related projects aimed at better understanding white dwarfs themselves, as well as their role as inhabitants of our Galaxy. The data that we have acquired to study these faint stars are of unprecedented quality and depth, thereby making possible several scientific results that have eluded investigation in decades of previous effort. First, we provide new insight into one of the most important questions in astrophysics today, what is the nature of the dark matter? Specifically, we are able to marginally rule out the most likely candidates based on microlensing results, namely white dwarfs, as a strong contribution to the dark matter. This study represents the deepest ever look into the Galactic halo and uses Hubble Space Telescope (HST) data. Secondly, we present results from the continuing study of open star clusters in the Canada France Hawaii Telescope (CFHT) Open Star Cluster Survey. This work has improved the quality of the photometry of open star clusters by over an order of magnitude compared to what had been previously possible. We present our findings for two very young clusters, NGC 2168 (M35) and NGC 2323 (M50), including a study of their white dwarf populations. These two clusters, and the white dwarfs that we have found within them, will prove to be crucial in constraining one of the most fundamental relations in stellar evolution, the initial-final mass relationship. In the third project, we use the 8-metre Gemini North and 10- metre Keck

  4. Astrometric Binaries: White Dwarfs?

    NASA Astrophysics Data System (ADS)

    Oliversen, Nancy A.

    We propose to observe a selection of astrometric or spectroscopicastrometric binaries nearer than about 20 pc with unseen low mass companions. Systems of this type are important for determining the luminosity function of low mass stars (white dwarfs and very late main sequence M stars), and their contribution to the total mass of the galaxy. Systems of this type are also important because the low mass, invisible companions are potential candidates in the search for planets. Our target list is selected primarily from the list of 31 astrometric binaries near the sun by Lippincott (1978, Space Sci. Rev., 22, 153), with additional candidates from recent observations by Kamper. The elimination of stars with previous IUE observations, red companions resolved by infrared speckle interferometry, or primaries later than M1 (because if white dwarf companions are present they should have been detected in the visible region) reduces the list to 5 targets which need further information. IUE SWP low dispersion observations of these targets will show clearly whether the remaining unseen companions are white dwarfs, thus eliminating very cool main sequence stars or planets. This is also important in providing complete statistical information about the nearest stars. The discovery of a white dwarf in such a nearby system would provide important additional information about the masses of white dwarfs. Recent results by Greenstein (1986, A. J., 92, 859) from binary systems containing white dwarfs imply that 80% of such systems are as yet undetected. The preference of binaries for companions of approximately equal mass makes the Lippincott-Kamper list of A through K primaries with unseen companions a good one to use to search for white dwarfs. The mass and light dominance of the current primary over the white dwarf in the visible makes ultraviolet observations essential to obtain an accurate census of white dwarf binaries.

  5. Spectroscopy of Brown Dwarfs

    NASA Astrophysics Data System (ADS)

    Rebolo, R.

    Recent searches for brown dwarfs have succeeded in finding these elusive objects. Massive brown dwarfs (40-70 Jupiter masses) have been found in the Pleiades, orbiting around a nearby star and, very recently, in the field. A review is given of their observed photometric and spectroscopic properties in the optical and near-infrared. The diagnosis of substellar nature based on lithium lines and methane bands is discussed in detail. While lithium has proved useful to test brown dwarfs with effective temperatures hotter than ~1600 K, methane is a substellar indicator at lower temperatures.

  6. 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.

  7. Canopy-snow Interaction in a sub-Arctic Shrub Tundra With Shrubs Buried by Snow

    NASA Astrophysics Data System (ADS)

    Bartlett, P. A.; Marsh, P.; Mackay, M.; Pohl, S.; Onclin, C.; Russell, M.

    2008-12-01

    The accumulation and ablation of the winter snowpack is strongly affected by the structure and distribution of vegetation. Near the tree-line where the boreal forest transitions to sub-Arctic tundra, wind scours snow from the open tundra and deposits it near the edges of shrub tundra and forests. The Trail Valley Creek (TVC) watershed is located just north of the forest-tundra transition at 68°45'N, 133°30'W in the Northwest Territories and is characterized by gently rolling hills with some deeply incised river valleys. Tundra vegetation dominates much of the upland areas, with shrub tundra and sparse black spruce found on hill slopes and in the valley bottoms. Typically, open tundra and areas with short shrubs are snow-covered for most of the winter and exhibit a high winter albedo (~0.8) characteristic of the snowpack, whereas dense forests are very efficient at trapping solar radiation and can maintain a low albedo (~0.2-0.3) for much of the winter. The winter albedo of sparse forests and unburied shrubs falls between these values. Tall shrubs are interesting because the effect of the shrubs on the snowpack and energy exchange is dependent on whether the shrubs remain standing during the winter, or are bent over and buried by the snowpack, subsequently springing up during the spring melt. In this study the influence of the canopy on snowmelt and energy exchanges is examined at a tall tundra shrub (TTS) site in the TVC basin for the 2003 spring melt. The shrubs were bent over and buried during the winter and sprang up over a short period during the spring melt. Measurements from a nearby tundra upland (TUP) site serve as a basis of comparison and the interpretation is aided using simulations performed with the Canadian Land Surface Scheme (CLASS). Snow accumulation was higher at TTS than at TUP, but lower than the over-winter snowfall, suggesting that transport out of TTS by wind and/or sublimation was significant. The albedo was similar at the two sites (~0

  8. Spectral vegetation indices for estimating shrub cover, green phytomass and leaf turnover in a sedge-shrub tundra

    NASA Astrophysics Data System (ADS)

    Kushida, K.; Kim, Y.; Tsuyuzaki, S.; Fukuda, M.

    2008-12-01

    Using field observations, we determined the relationships between spectral indices and the shrub ratio, green phytomass and leaf turnover of a sedge-shrub tundra community in the Arctic National Wildlife Refuge, Alaska, USA. We established a 50-m ~ 50-m plot (69.73°N 143.62°W) located on a floodplain of the refuge. The willow shrub (Salix lanata) and sedge (Carex bigelowii) dominated the plot vegetation. In July to August 2007, we established ten 0.5-m ~ 0.5-m quadrats on both shrub- covered ground (shrub quadrats) and on ground with no shrubs (sedge quadrats). All the shrubs within the shrub quadrats were harvested, and the photosynthetic and non-photosynthetic parts were weighed. Subsequently, the remaining green phytomass was also harvested and weighed. The shrub quadrats were measured spectrally before and after harvesting the shrubs. The sedge quadrats were also measured spectrally. The shrub ratio was more strongly correlated with the normalized difference vegetation index (NDVI, R2 of 0.57) than the normalized difference infrared index (NDII), the soil-adjusted vegetation index (SAVI) or the enhanced vegetation index (EVI). On the other hand, for both green phytomass and leaf turnover, the strongest correlation was with NDII (R2 of 0.63 and 0.79, respectively).

  9. Population dynamics of dwarf mistletoe on young true firs in the central Sierra Nevada, California

    Treesearch

    Robert E Scharpf; J. R. Jr. Parmeter

    1982-01-01

    Young red firs (Abies magnifica A. Murr.) and white firs (A. concolor [Gord. & Glend.] Lindl. ex Hildebr.) on the Stanislaus National Forest, California, were inoculated with seeds of dwarf mistletoe (Arceuthobium abietinum) for 5 successive years. Only 3 to 4 percent of about 7000 seeds placed on branches...

  10. Understanding Brown Dwarf Variability

    NASA Technical Reports Server (NTRS)

    Marley, Mark S.

    2013-01-01

    Surveys of brown dwarf variability continue to find that roughly half of all brown dwarfs are variable. While variability is observed amongst all types of brown dwarfs, amplitudes are typically greatest for L-T transition objects. In my talk I will discuss the possible physical mechanisms that are responsible for the observed variability. I will particularly focus on comparing and contrasting the effects of changes in atmospheric thermal profile and cloud opacity. The two different mechanisms will produce different variability signatures and I will discuss the extent to which the current datasets constrain both mechanisms. By combining constraints from studies of variability with existing spectral and photometric datasets we can begin to construct and test self-consistent models of brown dwarf atmospheres. These models not only aid in the interpretation of existing objects but also inform studies of directly imaged giant planets.

  11. Seedling establishment in a masting desert shrub parallels the pattern for forest trees

    NASA Astrophysics Data System (ADS)

    Meyer, Susan E.; Pendleton, Burton K.

    2015-05-01

    The masting phenomenon along with its accompanying suite of seedling adaptive traits has been well studied in forest trees but has rarely been examined in desert shrubs. Blackbrush (Coleogyne ramosissima) is a regionally dominant North American desert shrub whose seeds are produced in mast events and scatter-hoarded by rodents. We followed the fate of seedlings in intact stands vs. small-scale disturbances at four contrasting sites for nine growing seasons following emergence after a mast year. The primary cause of first-year mortality was post-emergence cache excavation and seedling predation, with contrasting impacts at sites with different heteromyid rodent seed predators. Long-term establishment patterns were strongly affected by rodent activity in the weeks following emergence. Survivorship curves generally showed decreased mortality risk with age but differed among sites even after the first year. There were no detectable effects of inter-annual precipitation variability or site climatic differences on survival. Intraspecific competition from conspecific adults had strong impacts on survival and growth, both of which were higher on small-scale disturbances, but similar in openings and under shrub crowns in intact stands. This suggests that adult plants preempted soil resources in the interspaces. Aside from effects on seedling predation, there was little evidence for facilitation or interference beneath adult plant crowns. Plants in intact stands were still small and clearly juvenile after nine years, showing that blackbrush forms cohorts of suppressed plants similar to the seedling banks of closed forests. Seedling banks function in the absence of a persistent seed bank in replacement after adult plant death (gap formation), which is temporally uncoupled from masting and associated recruitment events. This study demonstrates that the seedling establishment syndrome associated with masting has evolved in desert shrublands as well as in forests.

  12. Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities

    NASA Astrophysics Data System (ADS)

    Myers-Smith, Isla H.; Forbes, Bruce C.; Wilmking, Martin; Hallinger, Martin; Lantz, Trevor; Blok, Daan; Tape, Ken D.; Macias-Fauria, Marc; Sass-Klaassen, Ute; Lévesque, Esther; Boudreau, Stéphane; Ropars, Pascale; Hermanutz, Luise; Trant, Andrew; Siegwart Collier, Laura; Weijers, Stef; Rozema, Jelte; Rayback, Shelly A.; Schmidt, Niels Martin; Schaepman-Strub, Gabriela; Wipf, Sonja; Rixen, Christian; Ménard, Cécile B.; Venn, Susanna; Goetz, Scott; Andreu-Hayles, Laia; Elmendorf, Sarah; Ravolainen, Virve; Welker, Jeffrey; Grogan, Paul; Epstein, Howard E.; Hik, David S.

    2011-12-01

    Recent research using repeat photography, long-term ecological monitoring and dendrochronology has documented shrub expansion in arctic, high-latitude and alpine tundra ecosystems. Here, we (1) synthesize these findings, (2) present a conceptual framework that identifies mechanisms and constraints on shrub increase, (3) explore causes, feedbacks and implications of the increased shrub cover in tundra ecosystems, and (4) address potential lines of investigation for future research. Satellite observations from around the circumpolar Arctic, showing increased productivity, measured as changes in ‘greenness’, have coincided with a general rise in high-latitude air temperatures and have been partly attributed to increases in shrub cover. Studies indicate that warming temperatures, changes in snow cover, altered disturbance regimes as a result of permafrost thaw, tundra fires, and anthropogenic activities or changes in herbivory intensity are all contributing to observed changes in shrub abundance. A large-scale increase in shrub cover will change the structure of tundra ecosystems and alter energy fluxes, regional climate, soil-atmosphere exchange of water, carbon and nutrients, and ecological interactions between species. In order to project future rates of shrub expansion and understand the feedbacks to ecosystem and climate processes, future research should investigate the species or trait-specific responses of shrubs to climate change including: (1) the temperature sensitivity of shrub growth, (2) factors controlling the recruitment of new individuals, and (3) the relative influence of the positive and negative feedbacks involved in shrub expansion.

  13. 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. Copyright (c) 2005 Wiley-Liss, Inc.

  14. Burial increases seed longevity of two Artemisia tridentata (Asteraceae) subspecies.

    PubMed

    Wijayratne, Upekala C; Pyke, David A

    2012-03-01

    Seed longevity and persistence in soil seed banks may be especially important for population persistence in ecosystems where opportunities for seedling establishment and disturbance are unpredictable. The fire regime, an important driver of population dynamics in sagebrush steppe ecosystems, has been altered by exotic annual grass invasion. Soil seed banks may play an active role in postfire recovery of the foundation shrub Artemisia tridentata, yet conditions under which seeds persist are largely unknown. We investigated seed longevity of two Artemisia tridentata subspecies in situ by retrieving seed bags that were placed at varying depths over a 2 yr period. We also sampled naturally dispersed seeds in litter and soil immediately after seed dispersal and before flowering in subsequent seasons to estimate seed persistence. After 24 mo, seeds buried at least 3 cm below the soil surface retained 30-40% viability whereas viability of seeds on the surface and under litter declined to 0 and < 11%, respectively. The density of naturally dispersed seeds in the seed bank was highly heterogeneous both spatially and temporally, and attrition varied significantly by region. Our study suggests that Artemisia tridentata has the potential to form a short-term soil seed bank that persists longer than has been commonly assumed, and that burial is necessary for seed longevity. Use of seeding techniques that promote burial of some seeds to aid in formation of a soil seed bank may increase restoration potential.

  15. [Predation and removal of rodents on the seeds with different size and pericarp traits].

    PubMed

    Zhou, Li-biao; Yan, Xing-fu; Wang, Jian-li; Zhou, Yun-feng

    2013-08-01

    A field survey was conducted in the Quercus wutaishanica shrubs in Liupan Mountains of Ningxia, Northwest China to study the predation and removal of rodents on the seeds of Q. wutaishanica, Prunus salicina and Pinus armandii, aimed to explore the effects of seed size and pericarp traits on the predation and removal behaviors of rodents. The in situ seed predation rates of smaller Q. wutaishanica seeds and P. armandii seeds were significantly higher than those of larger Q. wutaishanica seeds and P. salicina seeds. The P. salicina seeds with hard and thick pericarp (endocarp) had the highest predation rate and hoarding rate after the removal by rodents. The movement distance of larger Q. wutaishanica seeds during predation events was the longest (3.10 m), and the seed hoarding distance of this species (6.48 m) was significantly longer than that of the three other types of seeds. Over 80% of sites were used as the predation sites by rodents for the seeds, except that the P. salicina seeds contained only a single seed and the cache sites contained a single seed accounted for over 90% for all types of seeds. Few predation and cache sites containing over two seeds were detected. Higher proportion of P. armandii seeds were predated in microhabitats except at the base of shrubs and in the holes after removal by rodent, while the seeds of other three types were predated mainly at the base of shrubs and in the holes after removal by rodents. The seed hoarding patterns after removal by rodents were primarily determined by pericarp traits, and higher proportion of soil burial that the rodents hoarded seeds with hard pericarp (endocarp) was detected.

  16. Post-fire seeding of great basin native plants using conventional and minimum-till rangeland drills

    USDA-ARS?s Scientific Manuscript database

    Objectives of post-fire seeding in the Great Basin include reestablishment of perennial cover, suppression of exotic annual weeds, and increasingly restoration of diverse plant communities. Non-conventional seeding techniques may be required when seeding mixes of grasses, forbs and shrubs containing...

  17. 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.

  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. 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

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

    USDA-ARS?s Scientific Manuscript database

    Drylands comprise 40% of Earth’s land mass and are critical to imperiled wildlife species, food security and carbon sequestration. Exotic weed invasions, overgrazing, energy extraction, and other factors have left many of the planet’s drylands in various states of degradation, and this has prompted...

  1. Photometric Variability of Y Dwarfs

    NASA Astrophysics Data System (ADS)

    Trucks, Jesica; Cushing, M.; Hardegree-Ullman, K.; Gelino, C. R.; Kirkpatrick, J. D.; Mace, G. N.; Gizis, J.; Marley, M. S.; Morley, C.; Fortney, J. J.

    2014-01-01

    Condensate clouds are present in brown dwarf atmospheres due to their low surface temperatures. As the coolest (Teff < 600 K) class of brown dwarfs currently known, Y dwarfs allow us to study the unique atmospheric physics that occur at these temperatures including the formation of sulfide, chloride, and water clouds. Dynamic inhomogeneities in cloud cover should manifest as photometric variabilities in the observed light curves of brown dwarfs. This phenomenon was originally documented in two brown-dwarfs by Morales-Calderón et al. (2006) at 4.5 microns, and in one brown dwarf by Heinze et al. (2013) at 3.6 microns. We describe our ongoing program to monitor fourteen Y dwarfs for photometric variability at 3.6 and 4.5 microns with the Spitzer Space Telescope and present initial results including the first detection of Y dwarf variability.

  2. Brown Dwarf Microlensing (Illustration)

    NASA Image and Video Library

    2016-11-10

    This illustration depicts a newly discovered brown dwarf, an object that weighs in somewhere between our solar system's most massive planet (Jupiter) and the least-massive-known star. This brown dwarf, dubbed OGLE-2015-BLG-1319, interests astronomers because it may fall in the "desert" of brown dwarfs. Scientists have found that, for stars roughly the mass of our sun, less than 1 percent have a brown dwarf orbiting within 3 AU (1 AU is the distance between Earth and the sun). This brown dwarf was discovered when it and its star passed between Earth and a much more distant star in our galaxy. This created a microlensing event, where the gravity of the system amplified the light of the background star over the course of several weeks. This microlensing was observed by ground-based telescopes looking for these uncommon events, and was the first to be seen by two space-based telescopes: NASA's Spitzer and Swift missions. http://photojournal.jpl.nasa.gov/catalog/PIA21076

  3. 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.

  4. 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.

  5. Seedling Responses to Water Pulses in Shrubs with Contrasting Histories of Grassland Encroachment

    PubMed Central

    Woods, Steven R.; Archer, Steven R.; Schwinning, Susan

    2014-01-01

    Woody plant encroachment into grasslands has occurred worldwide, but it is unclear why some tree and shrub species have been markedly more successful than others. For example, Prosopis velutina has proliferated in many grasslands of the Sonoran Desert in North America over the past century, while other shrub species with similar growth form and life history, such as Acacia greggii, have not. We conducted a glasshouse experiment to assess whether differences in early seedling development could help explain why one species and not the other came to dominate many Sonoran Desert grasslands. We established eight watering treatments mimicking a range of natural precipitation patterns and harvested seedlings 16 or 17 days after germination. A. greggii had nearly 7 times more seed mass than P. velutina, but P. velutina emerged earlier (by 3.0±0.3 d) and grew faster (by 8.7±0.5 mg d−1). Shoot mass at harvest was higher in A. greggii (99±6 mg seedling−1) than in P. velutina (74±2 mg seedling−1), but there was no significant difference in root mass (54±3 and 49±2 mg seedling−1, respectively). Taproot elongation was differentially sensitive to water supply: under the highest initial watering pulse, taproots were 52±19 mm longer in P. velutina than in A. greggii. Enhanced taproot elongation under favorable rainfall conditions could give nascent P. velutina seedlings growth and survivorship advantages by helping reduce competition with grasses and maintain contact with soil water during drought. Conversely, A. greggii's greater investment in mass per seed appeared to provide little return in early seedling growth. We suggest that such differences in recruitment traits and their sensitivities to environmental conditions may help explain ecological differences between species that are highly similar as adults and help identify pivotal drivers of shrub encroachment into grasslands. PMID:24475263

  6. Seedling responses to water pulses in shrubs with contrasting histories of grassland encroachment.

    PubMed

    Woods, Steven R; Archer, Steven R; Schwinning, Susan

    2014-01-01

    Woody plant encroachment into grasslands has occurred worldwide, but it is unclear why some tree and shrub species have been markedly more successful than others. For example, Prosopis velutina has proliferated in many grasslands of the Sonoran Desert in North America over the past century, while other shrub species with similar growth form and life history, such as Acacia greggii, have not. We conducted a glasshouse experiment to assess whether differences in early seedling development could help explain why one species and not the other came to dominate many Sonoran Desert grasslands. We established eight watering treatments mimicking a range of natural precipitation patterns and harvested seedlings 16 or 17 days after germination. A. greggii had nearly 7 times more seed mass than P. velutina, but P. velutina emerged earlier (by 3.0±0.3 d) and grew faster (by 8.7±0.5 mg d⁻¹). Shoot mass at harvest was higher in A. greggii (99±6 mg seedling⁻¹) than in P. velutina (74±2 mg seedling⁻¹), but there was no significant difference in root mass (54±3 and 49±2 mg seedling⁻¹, respectively). Taproot elongation was differentially sensitive to water supply: under the highest initial watering pulse, taproots were 52±19 mm longer in P. velutina than in A. greggii. Enhanced taproot elongation under favorable rainfall conditions could give nascent P. velutina seedlings growth and survivorship advantages by helping reduce competition with grasses and maintain contact with soil water during drought. Conversely, A. greggii's greater investment in mass per seed appeared to provide little return in early seedling growth. We suggest that such differences in recruitment traits and their sensitivities to environmental conditions may help explain ecological differences between species that are highly similar as adults and help identify pivotal drivers of shrub encroachment into grasslands.

  7. Low functional redundancy among mammalian browsers in regulating an encroaching shrub (Solanum campylacanthum) in African savannah.

    PubMed

    Pringle, Robert M; Goheen, Jacob R; Palmer, Todd M; Charles, Grace K; DeFranco, Elyse; Hohbein, Rhianna; Ford, Adam T; Tarnita, Corina E

    2014-06-22

    Large herbivorous mammals play an important role in structuring African savannahs and are undergoing widespread population declines and local extinctions, with the largest species being the most vulnerable. The impact of these declines on key ecological processes hinges on the degree of functional redundancy within large-herbivore assemblages, a subject that has received little study. We experimentally quantified the effects of three browser species (elephant, impala and dik-dik) on individual- and population-level attributes of Solanum campylacanthum (Solanum incanum sensu lato), an encroaching woody shrub, using semi-permeable exclosures that selectively removed different-sized herbivores. After nearly 5 years, shrub abundance was lowest where all browser species were present and increased with each successive species deletion. Different browsers ate the same plant species in different ways, thereby exerting distinct suites of direct and indirect effects on plant performance and density. Not all of these effects were negative: elephants and impala also dispersed viable seeds and indirectly reduced seed predation by rodents and insects. We integrated these diffuse positive effects with the direct negative effects of folivory using a simple population model, which reinforced the conclusion that different browsers have complementary net effects on plant populations, and further suggested that under some conditions, these net effects may even differ in direction.

  8. Low functional redundancy among mammalian browsers in regulating an encroaching shrub (Solanum campylacanthum) in African savannah

    PubMed Central

    Pringle, Robert M.; Goheen, Jacob R.; Palmer, Todd M.; Charles, Grace K.; DeFranco, Elyse; Hohbein, Rhianna; Ford, Adam T.; Tarnita, Corina E.

    2014-01-01

    Large herbivorous mammals play an important role in structuring African savannahs and are undergoing widespread population declines and local extinctions, with the largest species being the most vulnerable. The impact of these declines on key ecological processes hinges on the degree of functional redundancy within large-herbivore assemblages, a subject that has received little study. We experimentally quantified the effects of three browser species (elephant, impala and dik-dik) on individual- and population-level attributes of Solanum campylacanthum (Solanum incanum sensu lato), an encroaching woody shrub, using semi-permeable exclosures that selectively removed different-sized herbivores. After nearly 5 years, shrub abundance was lowest where all browser species were present and increased with each successive species deletion. Different browsers ate the same plant species in different ways, thereby exerting distinct suites of direct and indirect effects on plant performance and density. Not all of these effects were negative: elephants and impala also dispersed viable seeds and indirectly reduced seed predation by rodents and insects. We integrated these diffuse positive effects with the direct negative effects of folivory using a simple population model, which reinforced the conclusion that different browsers have complementary net effects on plant populations, and further suggested that under some conditions, these net effects may even differ in direction. PMID:24789900

  9. Ecological longevity of Polaskia chende (Cactaceae) seeds in the soil seed bank, seedling emergence and survival.

    PubMed

    Ordoñez-Salanueva, C A; Orozco-Segovia, A; Canales-Martínez, M; Seal, C E; Pritchard, H W; Flores-Ortiz, C M

    2017-08-08

    Soil seed banks are essential elements of plant population dynamics, enabling species to maintain genetic variability, withstand periods of adversity and persist over time, including for cactus species. However knowledge of the soil seed bank in cacti is scanty. In this study, over a 5-year period we studied the seed bank dynamics, seedling emergence and nurse plant facilitation of Polaskia chende, an endemic columnar cactus of central Mexico. P. chende seeds were collected for a wild population in Puebla, Mexico. Freshly collected seeds were sown at 25 °C and 12-h photoperiod under white light, far-red light and darkness. The collected seeds were divided in two lots, the first was stored in the laboratory and the second was use to bury seeds in open areas and beneath a shrub canopy. Seeds were exhumed periodically over 5 years. At the same time seeds were sown in open areas and beneath shrub canopies; seedling emergence and survival were recorded over different periods of time for 5 years. The species forms long-term persistent soil seed banks. The timing of seedling emergence via germination in the field was regulated by interaction between light, temperature and soil moisture. Seeds entered secondary dormancy at specific times according to the expression of environmental factors, demonstrating irregular dormancy cycling. Seedling survival of P. chende was improved under Acacia constricta nurse plants. Finally, plant facilitation affected the soil seed bank dynamics as it promoted the formation of a soil seed bank, but not its persistence. © 2017 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.

  10. Characterizing the population of active galactic nuclei in dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Baldassare, Vivienne F.; Reines, Amy E.; Gallo, Elena; Greene, Jenny E.

    2017-01-01

    Clues to super-massive black hole (BH) formation and growth reside in the population and properties of BHs in local dwarf galaxies. The masses of BHs in these systems are our best observational constraint on the masses of the first BH "seeds" at high redshift. Moreover, present-day dwarf galaxies are unlikely to have undergone major mergers, making them a relatively pristine testbed for studying triggers of BH accretion. However, in order to find BHs in dwarf galaxies outside the Local Group, it is necessary to search for signatures of accretion, i.e., active galactic nuclei (AGN). Until recently, only a handful of dwarf galaxies were known to contain AGN. However, large surveys such as the SDSS have led to the production of samples of over a hundred dwarf galaxies with AGN signatures (see e.g., Reines et al. 2013). My dissertation work has involved in-depth, multi-wavelength follow-up of nearby (z<0.055) dwarf galaxies with optical spectroscopic AGN signatures in SDSS.I analyzed high resolution spectra of dwarf galaxies with narrow-line AGN, which led to the discovery of a 50,000 MSun BH in the nucleus of RGG 118 - the smallest BH yet reported in a galaxy nucleus (Baldassare et al. 2015). I also used multi-epoch optical spectroscopy to study the nature of broad H-alpha emission in dwarf galaxies. A characteristic signature of dense gas orbiting around a BH, broad emission can also be produced by transient stellar processes. I showed that broad H-alpha in star-forming dwarf galaxies fades over a baseline of 5-10 years, and is likely produced by e.g., a Type II SN as opposed to an AGN. However, broad emission in dwarf galaxies with AGN/composite narrow lines is persistent and consistent across observations, suggesting an AGN origin (Baldassare et al. 2016). Finally, I analyzed X-ray and UV observations of dwarf galaxies with broad and narrow-line AGN signatures. All targets had nuclear X-ray detections at levels significantly higher than expected from X-ray binaries

  11. Experimental investigation of fire propagation in single live shrubs

    Treesearch

    Jing Li; Shankar Mahalingam; David R. Weise

    2017-01-01

    This work focuses broadly on individual, live shrubs and, more specifically, it examines bulk density in chaparral and its combined effects with wind and ignition location on the resulting fire behaviour. Empirical functions to predict bulk density as a function of height for 4-year-old chaparral were developed for two typical species of shrub fuels in southern...

  12. Little response of true fir saplings to understory shrub removal

    Treesearch

    William W. Oliver; Fabian C.C. Uzoh

    2002-01-01

    The ability of white fir and California red fir to become established, persist, and eventually dominate montane shrub fields is well known. When the firs have eventually dominated do the understory shrubs continue to inhibit growth? In a small study in the southern Cascade Range of northeastern California, we tested the growth response of a thinned stand of saplings to...

  13. Comparative wood anatomy of some shrubs native to the Northern Rocky Mountains

    Treesearch

    Arlene Dale

    1968-01-01

    This paper describes some xylem characteristics of the more important shrub species of the Northern Rockies and presents a key for identifying shrub-wood specimens by microscopic characters. The paper contains photomicrographs of 55 shrub woods.

  14. Origins, Evolution, and Fate of Brown Dwarfs

    NASA Technical Reports Server (NTRS)

    Martin, Eduardo

    2003-01-01

    Research related to the origins, evolution and fate of brown dwarfs is presented. The topics include: 1) Imaging surveys for brown dwarfs; 2) Companion detection techniques; 3) Measurements of fundamental properties of brown dwarfs; 4) Classification schemes for ultracool dwarfs; 5) Origins and evolution of brown dwarfs; 6) Ultracool atmospheres and interiors; 7) Time variable phenomena in brown dwarfs; 8) Comparisons between brown dwarfs and planets; 9) Substellar mass functions; and 10) Future facilities.

  15. Burial increases seed longevity of two Artemisia tridentata (Asteraceae) subspecies

    USGS Publications Warehouse

    Wijayratne, Upekala C.; Pyke, David A.

    2012-01-01

    Premise of the study: Seed longevity and persistence in soil seed banks may be especially important for population persistence in ecosystems where opportunities for seedling establishment and disturbance are unpredictable. The fire regime, an important driver of population dynamics in sagebrush steppe ecosystems, has been altered by exotic annual grass invasion. Soil seed banks may play an active role in postfire recovery of the foundation shrub Artemisia tridentata, yet conditions under which seeds persist are largely unknown. Methods: We investigated seed longevity of two Artemisia tridentata subspecies in situ by retrieving seed bags that were placed at varying depths over a 2 yr period. We also sampled naturally dispersed seeds in litter and soil immediately after seed dispersal and before flowering in subsequent seasons to estimate seed persistence. Key results: After 24 mo, seeds buried at least 3 cm below the soil surface retained 30–40% viability whereas viability of seeds on the surface and under litter declined to 0 and Artemisia tridentata has the potential to form a short-term soil seed bank that persists longer than has been commonly assumed, and that burial is necessary for seed longevity. Use of seeding techniques that promote burial of some seeds to aid in formation of a soil seed bank may increase restoration potential.

  16. Quercus ilex L. carbon sequestration capability related to shrub size.

    PubMed

    Gratani, Loretta; Catoni, Rosangela; Varone, Laura

    2011-07-01

    CO(2) sequestration capacity of Quercus ilex L., an evergreen species developing in shrub and forest communities widely distributed in the Mediterranean Basin, was analysed. Experiments were carried out in the period of January to December 2009 on 20 shrubs of different size, growing at the Botanical Garden of Rome. At shrub level, the largest differences concern total photosynthetic leaf surface area per shrub and shrub volume. Shrubs structure significantly contribute to reduce total irradiance and air temperature below the canopy. Leaf mass per area is higher in sun leaves than in shade ones (20 ± 1 and 12 ± 2 mg cm( -2), respectively). Sun leaves are also characterised by the highest leaf thickness (78% higher in sun than in shade leaves), the spongy parenchyma thickness (71% higher in sun than in shade leaves) and the highest adaxial cuticle thickness (7.2 ± 1.2 and 4.7 ± 0.5 μm, respectively). Net photosynthetic rates (P (N)) of sun and shade leaves are the highest in spring, and shade leaves contribute 6% to the whole shrub P (N). Q. ilex CO(2) sequestration depends on shrub size. In particular, the CO(2) sequestration per shrub was 0.20 ± 0.02 Kg CO(2) year( -1) in small shrubs, and it was 75% and 98% lower than in medium and large ones. The highest CO(2) sequestration is measured in spring, decreasing 77% during drought. Q. ilex may play a significant role in mitigating carbon dioxide concentration and lowering air and soil temperature in areas around the Mediterranean Basin.

  17. 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.

  18. Among-individual variation in pollen limitation and inbreeding depression in a mixed-mating shrub

    PubMed Central

    González-Varo, Juan P.; Traveset, Anna

    2010-01-01

    Background and Aims Variation in inbreeding depression (δ) among individual plants is considered to play a central role in mating system evolution and population genetics. Moreover, such variation could be linked to individual susceptibility to pollen limitation (PL) because those individuals strongly affected by δ for seed production will require more outcross pollen for setting a given number of fruits or seeds. However, no study has tested explicitly for associations between PL and δ at the individual plant level. This study assesses the extent of among-individual variation in PL and δ, the consistency of δ across life stages, and the relationships between individual PL and δ in the mixed-mating shrub Myrtus communis. Methods Controlled hand-pollinations were performed in a natural M. communis population. Marked flowers were monitored until fruit production and a greenhouse experiment was conducted with the seeds produced. Key Results Compared with selfing, outcross-pollination enhanced seed number per fruit, germination rate and seedling growth, but did not enhance fruit-set. Only seed number per fruit was pollen limited and, thus, cumulative pollen limitation depended more on pollen quality (outcross pollen) than on quantity. The effects of δ varied considerably across life stages and individual plants. Cumulative δ was high across individuals (mean δ = 0·65), although there were no positive correlations between δ values at different life stages. Interestingly, maternal plants showing stronger δ for seed production were more pollen limited, but they were also less affected by δ for seedling growth because of a seed size/number trade-off. Conclusions Results show a general inconsistency in δ across life stages and individuals, suggesting that different deleterious loci are acting at different stages. The association between δ and PL at the individual level corroborates the idea that pollen limitation may be ‘genotype-dependent’ regardless of

  19. High male fertility in males of a subdioecious shrub in hand-pollinated crosses

    PubMed Central

    Wang, Hui; Matsushita, Michinari; Tomaru, Nobuhiro; Nakagawa, Michiko

    2016-01-01

    Female reproductive success in females versus hermaphrodites has been well documented. However, documenting a potential advantage in male fertility of male versus hermaphrodite individuals in subdioecious species is also essential for understanding the evolutionary pathway toward dioecy from hermaphroditism via gynodioecy. Siring success in terms of fruit set, fruit mass, number of seeds and mean seed mass was compared by hand-pollinated crosses in the subdioecious shrub Eurya japonica. The pollen was from male and hermaphrodite individuals, and the pollen recipients were females and hermaphrodites. Seed quality was also evaluated in terms of seed germination rate, seed germination day and seedling survival. Overall, pollen from males sired more fruits of larger size and more seeds than did pollen from hermaphrodites. The male advantage was observed when pollen recipients were females, whereas no effect was found in hermaphrodite recipients. Pollen from males also produced better quality seeds with higher germination rate and sooner germination day. Although these results could also be explained by a higher pollen load for crosses with male pollen donors, we took care to saturate the stigma regardless of the pollen donor. Therefore, these results suggest that male individuals of E. japonica have advantages in male fertility in terms of both quantity and quality. Our previous studies indicated that females exhibit higher female reproductive success compared with hermaphrodites. Thus, both the female and male functions of hermaphrodites are outperformed by females and males, respectively, raising the possibility that the subdioecious E. japonica at this study site is entering the transitional phase to dioecy along the gynodioecy–dioecy pathway. PMID:27658818

  20. Eastern Spruce Dwarf Mistletoe

    Treesearch

    F. Baker; Joseph O' Brien; R. Mathiasen; Mike Ostry

    2006-01-01

    Eastern spruce dwarf mistletoe (Arceuthobium pusillum) is a parasitic flowering plant that causes the most serious disease of black spruce (Picea mariana) throughout its range. The parasite occurs in the Canadian provinces of Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland; in the Lake States of Minnesota,...

  1. Fir dwarf mistletoe (FIDL).

    Treesearch

    Gregory M. Filip; Jerome S. Beatty; Robert L. Mathiasen

    2000-01-01

    Fir dwarf mistletoe (Arceuthobium abietinum Engelmann ex Munz) is a common and damaging parasite of white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), and California red fir (A. magnifica A. Murr.) in the western...

  2. 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…

  3. 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…

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

    USDA-ARS?s Scientific Manuscript database

    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...

  5. 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

  6. Dwarf Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Colín, P.; Klypin, A.; Valenzuela, O.; Gottlöber, Stefan

    2004-09-01

    We study properties of dark matter halos at high redshifts z=2-10 for a vast range of masses with the emphasis on dwarf halos with masses of 107-109 h-1 Msolar. We find that the density profiles of relaxed dwarf halos are well fitted by the Navarro, Frenk, & White (NFW) profile and do not have cores. We compute the halo mass function and the halo spin parameter distribution and find that the former is very well reproduced by the Sheth & Tormen model, while the latter is well fitted by a lognormal distribution with λ0=0.042 and σλ=0.63. We estimate the distribution of concentrations for halos in a mass range that covers 6 orders of magnitude, from 107 to 1013 h-1 Msolar, and find that the data are well reproduced by the model of Bullock et al. The extrapolation of our results to z=0 predicts that present-day isolated dwarf halos should have a very large median concentration of ~35. We measure the subhalo circular velocity functions for halos with masses that range from 4.6×109 to 1013 h-1 Msolar and find that they are similar when normalized to the circular velocity of the parent halo. Dwarf halos studied in this paper are many orders of magnitude smaller than well-studied cluster- and Milky Way-sized halos. Yet, in all respects the dwarfs are just downscaled versions of the large halos. They are cuspy and, as expected, more concentrated. They have the same spin parameter distribution and follow the same mass function that was measured for large halos.

  7. A distinctly disorganised dwarf

    NASA Image and Video Library

    2016-03-28

    Despite being less famous than their elliptical and spiral galactic cousins, irregular dwarf galaxies, such as the one captured in this NASA/ESA Hubble Space Telescope image, are actually one of the most common types of galaxy in the Universe. Known as UGC 4459, this dwarf galaxy is located approximately 11 million light-years away in the constellation of Ursa Major (The Great Bear), a constellation that is also home to the Pinwheel Galaxy (M101), the Owl Nebula (M97), Messier 81, Messier 82 and several other galaxies all part of the M81 group. UGC 4459’s diffused and disorganised appearance is characteristic of an irregular dwarf galaxy. Lacking a distinctive structure or shape, irregular dwarf galaxies are often chaotic in appearance, with neither a nuclear bulge — a huge, tightly packed central group of stars — nor any trace of spiral arms — regions of stars extending from the centre of the galaxy. Astronomers suspect that some irregular dwarf galaxies were once spiral or elliptical galaxies, but were later deformed by the gravitational pull of nearby objects. Rich with young blue stars and older red stars, UGC 4459 has a stellar population of several billion. Though seemingly impressive, this is small when compared to the 200 to 400 billion stars in the Milky Way! Observations with Hubble have shown that because of their low masses, star formation is very low compared to larger galaxies. Only very little of their original gas has been turned into stars. Thus, these small galaxies are interesting to study to better understand primordial environments and the star formation process.

  8. Supplementing seed banks to rehabilitate disturbed Mojave Desert shrublands: where do all the seeds go?

    USGS Publications Warehouse

    DeFalco, Lesley A.; Esque, Todd C.; Nicklas, Melissa B.; Kane, Jeffrey M.

    2012-01-01

    Revegetation of degraded arid lands often involves supplementing impoverished seed banks and improving the seedbed, yet these approaches frequently fail. To understand these failures, we tracked the fates of seeds for six shrub species that were broadcast across two contrasting surface disturbances common to the Mojave Desert—sites compacted by concentrated vehicle use and trenched sites where topsoil and subsurface soils were mixed. We evaluated seedbed treatments that enhance soil-seed contact (tackifier) and create surface roughness while reducing soil bulk density (harrowing). We also explored whether seed harvesting by granivores and seedling suppression by non-native annuals influence the success of broadcast seeding in revegetating degraded shrublands. Ten weeks after treatments, seeds readily moved off of experimental plots in untreated compacted sites, but seed movements were reduced 32% by tackifier and 55% through harrowing. Harrowing promoted seedling emergence in compacted sites, particularly for the early-colonizing species Encelia farinosa, but tackifier was largely ineffective. The inherent surface roughness of trenched sites retained three times the number of seeds than compacted sites, but soil mixing during trench development likely altered the suitability of the seedbed thus resulting in poor seedling emergence. Non-native annuals had little influence on seed fates during our study. In contrast, the prevalence of harvester ants increased seed removal on compacted sites, whereas rodent activity influenced removal on trenched sites. Future success of broadcast seeding in arid lands depends on evaluating disturbance characteristics prior to seeding and selecting appropriate species and seasons for application.

  9. Hares promote seed dispersal and seedling establishment after volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Nomura, Nanae; Tsuyuzaki, Shiro

    2015-02-01

    Although seed dispersal through animal guts (endozoochory) is a process that determines plant establishment, the behaviour of carriers mean that the seeds are not always dispersed to suitable habitats for germination. The germinable seeds of Gaultheria miqueliana were stored in the pellets of a hare (Lepus timidus ainu) on Mount Koma in northern Japan. To clarify the roles of hares in seed dispersal and germination, field censuses and laboratory experiments were conducted. The field observations were conducted on pellets and seeds in four habitats (bare ground, G. miqueliana shrub patch, Salix reinii patch, and Larix kaempferi understory), and the laboratory experiments were conducted on seed germination with different light, water potential and cold stratification treatments. The laboratory experiments confirmed that seed germination began a few weeks after the sowing of seeds, independent of cold stratification, when light was sufficient and the water potential was low. The seeds did not germinate at high water potential. The pellets were gradually degraded in situ. More seeds germinated from crushed than from intact pellets. Therefore, over the long term, seeds germinated when exposed to light due to the degradation of pellets. The pellets were proportionally dispersed among the four studied habitats. More seeds sown in the field germinated more in shaded habitats, such as in the Gaultheria patch and the Larix understory, and seeds did not germinate on bare ground, where drought often occurred. Thus, the hares had two roles in the dispersal and germination of seeds: (1) the expansion of G. miqueliana populations through seed dispersal to various habitats and (2) the facilitation of delayed seed germination to avoid risks of hazards such as drought. The relationships between small mammals represented by the hare and the shrubs that produce berries are likely to be more mutually evolved than was previously thought.

  10. Too Many Is Too Bad: Long-Term Net Negative Effects of High Density Ungulate Populations on a Dominant Mediterranean Shrub.

    PubMed

    Lecomte, Xavier; Fedriani, José M; Caldeira, Maria C; Clemente, Adelaide S; Olmi, Alessandro; Bugalho, Miguel N

    2016-01-01

    Plant-animal interactions imply costs and benefits with net balance depending on interacting species and ecological context. Ungulates, in particular, confer costs (e.g., plant leaf consumption, flower bud predation) and benefits (e.g., plant overcompensation, seed dispersal) to plants. Magnitude of costs and benefits may be altered by habitat management or ecological conditions favoring high density ungulate populations. Little is known however on whether plant costs or benefits predominate over the years, or the long-term outcomes of plant-animal interactions in habitat types sustaining high density ungulate populations. We investigated how high density ungulate populations alter plant costs and benefits by quantifying ungulate long-term effects on the shrub Cistus ladanifer (Cistaceae) individual size, seed weight and number, seed bank, and population density, through a 12-year ungulate exclusion experiment in a Mediterranean scrubland. We monitored plant size and flower buds in plants exposed or protected from ungulates and number of developed capsules and seeds consumed (potential seed dispersal) by ungulates during three reproductive seasons. We found that ungulates negatively affected shrub size and led to a dramatically decline of shrub reproductive structures and seed production, affecting the plant reproductive cycle. Number of buds was 27 times higher and number of developed seed 5 times higher in ungulate-excluded as compared to ungulate-exposed plots. After 9 years of ungulate exclusion, the C. ladanifer seed bank was 2.6 times higher in ungulate-excluded plots. The population density of C. ladanifer was 4 times higher in ungulate-excluded plots. Our long-term experiment showed that high density ungulate populations can alter plant-animal interactions by reducing plant benefits and increasing plant costs.

  11. Too Many Is Too Bad: Long-Term Net Negative Effects of High Density Ungulate Populations on a Dominant Mediterranean Shrub

    PubMed Central

    Lecomte, Xavier; Fedriani, José M.; Caldeira, Maria C.; Clemente, Adelaide S.; Olmi, Alessandro; Bugalho, Miguel N.

    2016-01-01

    Plant–animal interactions imply costs and benefits with net balance depending on interacting species and ecological context. Ungulates, in particular, confer costs (e.g., plant leaf consumption, flower bud predation) and benefits (e.g., plant overcompensation, seed dispersal) to plants. Magnitude of costs and benefits may be altered by habitat management or ecological conditions favoring high density ungulate populations. Little is known however on whether plant costs or benefits predominate over the years, or the long-term outcomes of plant-animal interactions in habitat types sustaining high density ungulate populations. We investigated how high density ungulate populations alter plant costs and benefits by quantifying ungulate long-term effects on the shrub Cistus ladanifer (Cistaceae) individual size, seed weight and number, seed bank, and population density, through a 12-year ungulate exclusion experiment in a Mediterranean scrubland. We monitored plant size and flower buds in plants exposed or protected from ungulates and number of developed capsules and seeds consumed (potential seed dispersal) by ungulates during three reproductive seasons. We found that ungulates negatively affected shrub size and led to a dramatically decline of shrub reproductive structures and seed production, affecting the plant reproductive cycle. Number of buds was 27 times higher and number of developed seed 5 times higher in ungulate-excluded as compared to ungulate-exposed plots. After 9 years of ungulate exclusion, the C. ladanifer seed bank was 2.6 times higher in ungulate-excluded plots. The population density of C. ladanifer was 4 times higher in ungulate-excluded plots. Our long-term experiment showed that high density ungulate populations can alter plant-animal interactions by reducing plant benefits and increasing plant costs. PMID:27387134

  12. Pollinating Bees Crucial to Farming Wildflower Seed for U.S. Habitat Restoration

    USDA-ARS?s Scientific Manuscript database

    Federal land managers desire seed of Great Basin perennial wildflowers, mixed with grass and shrub seed, to rehabilitate millions of acres of rangelands degraded by altered wildfire regimes, overgrazing and exotic grasses and forbs. At stake are half the nation’s sagebrush communities. Only farmed...

  13. Impacts of postfire grass seeding on vegetation recovery in southern California chaparral

    Treesearch

    Jan Beyers; C.D. Wakeman; S.G. Conard; Pete Wohlgemuth

    2002-01-01

    Postfire grass seeding as an attempt at erosion control on chaparral slopes has been a common practice for decades. Annual ryegrass (Lolium multiflorum) has been most frequently used. Critics point out that ryegrass can suppress native species and may reduce shrub seedling survival. In 1986, we began investigating the impacts of seeded ryegrass on chaparral...

  14. Effect of cattle grazing, seeded grass, and an herbicide on ponderosa pine seedling survival and growth

    Treesearch

    Philip M. McDonald; Gary O. Fiddler

    1999-01-01

    On a site of above-average quality in northern California, an early shrub-forb-grass plant community was treated by artificially seeding two forage grass species at plantation age 3, cattle grazing with and without seeded grasses, and applying a soil-active chemical (Velpar). Planted ponderosa pines were part of this community. Results for a 10-year period (1988-1997)...

  15. Seed germination biology of Intermountain populations of fourwing saltbush (Atriplex canescens: Chenopodiaceae)

    Treesearch

    Susan E. Meyer; Stephanie L. Carlson

    2007-01-01

    Fourwing saltbush (Atriplex canescens) is a widely distributed shrub of semiarid western North America. We studied viability and germinability of fourwing saltbush seeds over 10 years for collections from 23 Intermountain populations. Fruit fill averaged 53 percent, and 96 percent of filled fruits contained viable seeds even after 6 years of...

  16. 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

  17. 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.

  18. Direct seeding woody species for restoration of bottomlands

    USGS Publications Warehouse

    Twedt, D.J.; Connor, Kristina F

    2006-01-01

    I direct seeded (broadcast) seeds of 39 species of trees and shrubs using an ATV-mounted rotary spreader to initiate restoration of bottomland forest on retired agricultural sites. Four sites were planted during February, 2000, and 13 additional sites were planted during April and May, 2001. After two growing seasons, stem density of direct-seeded species varied greatly among study plots (range = 0 to 888 stems/ha) but averaged only 110 stems/ha. I recommend that future efforts at direct seeding focus on seven shrub species (Amorpha fruticosa L., Cephalanthus occidentalis L., Cornus spp., Crataegus spp., Ilex decidua Walt., Morus rubra L., and Prunus spp.) and seven tree species (Celtis laevigata Willd., Diospyros virginiana L., Fraxinus spp., Gleditsia triacanthos L., Robinia pseudoacacia L., Taxodium distichum (L.) Rich, and Ulmus spp.) that successfully established in these trials.

  19. Evolutionary and ecological correlates of early seedling morphology in East African trees and shrubs.

    PubMed

    Zanne, Amy E; Chapman, Colin A; Kitajima, Kaoru

    2005-06-01

    Seed size and cotyledon morphology are two key juvenile traits that have evolved in response to changes in plant species life-history strategies and habitat associations. Correlations of these traits with each other and with other juvenile traits were examined for 70 species of trees and shrubs in Kibale National Park, Uganda. Although species with photosynthetic cotyledons were more abundant than in other tropical floras, both univariate and multivariate analyses supported trait associations expected from the literature. Trait values varied continuously across species, yet mean trait values differed significantly among habitat association types. Species with large seeds, large seedlings, thick storage cotyledons, slow germination, large-stature adults, and dispersal by large animals were common in forest and gap habitats. An opposite suite of traits was common in open habitats (grassland and edge). Analyses incorporating phylogeny (independent contrasts and omnibus tests) confirmed that these suites of traits showed correlated evolution. Cotyledon functional morphology yielded a strong phylogenetic signal, while seed mass was labile. Nevertheless, contingent change tests found that evolutionary change from photosynthetic to reserve cotyledons was more likely when disperser and perhaps seed size of ancestral species were already large, suggesting a strong interdependency among these traits.

  20. The white dwarf luminosity function

    NASA Astrophysics Data System (ADS)

    García-Berro, Enrique; Oswalt, Terry D.

    2016-06-01

    White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for ∼ 10 Gyr. Their observed properties provide information about the history of the Galaxy, its dark matter content and a host of other interesting astrophysical problems. Examples of these include an independent determination of the past history of the local star formation rate, identification of the objects responsible for the reported microlensing events, constraints on the rate of change of the gravitational constant, and upper limits to the mass of weakly interacting massive particles. To carry on these tasks the essential observational tools are the luminosity and mass functions of white dwarfs, whereas the theoretical tools are the evolutionary sequences of white dwarf progenitors, and the corresponding white dwarf cooling sequences. In particular, the observed white dwarf luminosity function is the key manifestation of the white dwarf cooling theory, although other relevant ingredients are needed to compare theory and observations. In this review we summarize the recent attempts to empirically determine the white dwarf luminosity function for the different Galactic populations. We also discuss the biases that may affect its interpretation. Finally, we elaborate on the theoretical ingredients needed to model the white dwarf luminosity function, paying special attention to the remaining uncertainties, and we comment on some applications of the white dwarf cooling theory. Astrophysical problems for which white dwarf stars may provide useful leverage in the near future are also discussed.

  1. 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.

  2. M Dwarf Mysteries

    NASA Astrophysics Data System (ADS)

    Henry, Todd J.; Jao, Wei-Chun; Irwin, Jonathan; Dieterich, Sergio; Finch, Charlie T.; Riedel, Adric R.; Subasavage, John P.; Winters, Jennifer; RECONS Team

    2017-01-01

    During RECONS' 17-year (so far) astrometry/photometry program at the CTIO/SMARTS 0.9m, we have observed thousands of the ubiquitous red dwarfs in the solar neighborhood. During this reconnaissance, a few mysterious characters have emerged ...The Case of the Mercurial Stars: One M dwarf has been fading steadily for more than a decade, at last measure 6% fainter than when it was first observed. Another has grown brighter by 7% over 15 years. Are these brightness changes part of extremely long stellar cycles, or something else entirely?The Case of Identical Stellar Twins that Aren't: Two M dwarfs seem at first to be identical siblings traveling together through the Galaxy. They have virtually identical spectra at optical wavelengths and identical colors throughout the VRIJHK bands. Long-term astrometry indicates that they are, indeed, at the same distance via parallax measurements, and their proper motions match precisely. Yet, one of the twins is FOUR times brighter than the other. Followup work has revealed that the brighter component is a very close spectroscopic double, but no other stars are seen. So, the mystery may be half solved, but why do the close stars remain twice as bright as their widely-separated twin?The Case of the Great Kaboom!: After more than 1000 nights of observing on the reliable 0.9m telescope, with generally routine frames reading out upon the screen, one stellar system comprised of five red dwarfs flared in stunning fashion. Of the two distinct sources, the fainter one (an unresolved double) surpassed the brightness of the brighter one (an unresolved triple), increasing by more than three full magnitudes in the V filter. Which component actually flared? Is this magnificent outburst an unusual event, or in fact typical for this system and other M dwarfs?At the AAS meeting, we hope to probe the cognoscenti who study the Sun's smaller cousins to solve these intriguing M Dwarf Mysteries.This effort has been supported by the NSF through grants

  3. Effects of rodent species, seed species, and predator cues on seed fate

    USGS Publications Warehouse

    Sivy, Kelly J.; Ostoja, Steven M.; Schupp, Eugene W.; Durham, Susan

    2011-01-01

    Seed selection, removal and subsequent management by granivorous animals is thought to be a complex interaction of factors including qualities of the seeds themselves (e.g., seed size, nutritional quality) and features of the local habitat (e.g. perceived predator risk). At the same time, differential seed selection and dispersal is thought to have profound effects on seed fate and potentially vegetation dynamics. In a feeding arena, we tested whether rodent species, seed species, and indirect and direct predation cues influence seed selection and handling behaviors (e.g., scatter hoarding versus larder hoarding) of two heteromyid rodents, Ord's kangaroo rat (Dipodomys ordii) and the Great Basin pocket mouse (Perognathus parvus). The indirect cue was shrub cover, a feature of the environment. Direct cues, presented individually, were (1) control, (2) coyote (Canis latrans) vocalization, (3) coyote scent, (4) red fox (Vulpes vulpes) scent, or (5) short-eared owl (Asio flammeus) vocalization. We offered seeds of three sizes: two native grasses, Indian ricegrass (Achnatherum hymenoides) and bluebunch wheatgrass (Pseudoroegneria spicata), and the non-native cereal rye (Secale cereale), each in separate trays. Kangaroo rats preferentially harvested Indian ricegrass while pocket mice predominately harvested Indian ricegrass and cereal rye. Pocket mice were more likely to scatter hoard preferred seeds, whereas kangaroo rats mostly consumed and/or larder hoarded preferred seeds. No predator cue significantly affected seed preferences. However, both species altered seed handling behavior in response to direct predation cues by leaving more seeds available in the seed pool, though they responded to different predator cues. If these results translate to natural dynamics on the landscape, the two rodents are expected to have different impacts on seed survival and plant recruitment via their different seed selection and seed handling behaviors.

  4. Effects of rodent species, seed species, and predator cues on seed fate

    NASA Astrophysics Data System (ADS)

    Sivy, Kelly J.; Ostoja, Steven M.; Schupp, Eugene W.; Durham, Susan

    2011-07-01

    Seed selection, removal and subsequent management by granivorous animals is thought to be a complex interaction of factors including qualities of the seeds themselves (e.g., seed size, nutritional quality) and features of the local habitat (e.g. perceived predator risk). At the same time, differential seed selection and dispersal is thought to have profound effects on seed fate and potentially vegetation dynamics. In a feeding arena, we tested whether rodent species, seed species, and indirect and direct predation cues influence seed selection and handling behaviors (e.g., scatter hoarding versus larder hoarding) of two heteromyid rodents, Ord's kangaroo rat ( Dipodomys ordii) and the Great Basin pocket mouse ( Perognathus parvus). The indirect cue was shrub cover, a feature of the environment. Direct cues, presented individually, were (1) control, (2) coyote ( Canis latrans) vocalization, (3) coyote scent, (4) red fox ( Vulpes vulpes) scent, or (5) short-eared owl ( Asio flammeus) vocalization. We offered seeds of three sizes: two native grasses, Indian ricegrass ( Achnatherum hymenoides) and bluebunch wheatgrass ( Pseudoroegneria spicata), and the non-native cereal rye ( Secale cereale), each in separate trays. Kangaroo rats preferentially harvested Indian ricegrass while pocket mice predominately harvested Indian ricegrass and cereal rye. Pocket mice were more likely to scatter hoard preferred seeds, whereas kangaroo rats mostly consumed and/or larder hoarded preferred seeds. No predator cue significantly affected seed preferences. However, both species altered seed handling behavior in response to direct predation cues by leaving more seeds available in the seed pool, though they responded to different predator cues. If these results translate to natural dynamics on the landscape, the two rodents are expected to have different impacts on seed survival and plant recruitment via their different seed selection and seed handling behaviors.

  5. 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

  6. Fatty acid composition of seed oil from Fremontodendron californicum

    USDA-ARS?s Scientific Manuscript database

    The fatty acid composition of the low water-use shrub Fremontodendron californicum was examined by high temperature capillary gas chromatography. The ground seeds were extracted by supercritical fluid extraction (SFE) to obtain the oil (25.6% w/w) and for subsequent determination of the fatty acid c...

  7. Fire season and intensity affect shrub recruitment in temperate sclerophyllous woodlands.

    PubMed

    Knox, K J E; Clarke, P J

    2006-10-01

    The season in which a fire occurs may regulate plant seedling recruitment because of: (1) the interaction of season and intensity of fire and the temperature requirements for seed release, germination and growth; (2) post-fire rainfall and temperature patterns affecting germination; (3) the interaction of post-fire germination conditions and competition from surrounding vegetation; and (4) the interaction of post-fire germination conditions and seed predators and/or seedling herbivores. This study examined the effects of different fire intensities and fire seasons on the emergence and survival of shrubs representing a range of fire response syndromes from a summer rainfall cool climate region. Replicated experimental burns were conducted in two seasons (spring and autumn) in 2 consecutive years and fuel loads were increased to examine the effects of fire intensity (low intensity and moderate intensity). Post-fire watering treatments partitioned the effects of seasonal temperature from soil moisture. Higher intensity fires resulted in enhanced seedling emergence for hard-seeded species but rarely influenced survival. Spring fires enhanced seedling emergence across all functional groups. Reduced autumn recruitment was related to seasonal temperature inhibiting germination rather than a lack of soil moisture or competition. In Mediterranean-type climate regions, seedling emergence has been related to post-fire rainfall and exposure of seeds to seed predators. We think a similar model may operate in temperate summer rainfall regions where cold-induced dormancy over winter exposes seeds to predators for a longer time and subsequently results in recruitment failure. Our results support the theory that the effect of fire season is more predictable where there are strong seasonal patterns in climate. In this study seasonal temperature rather than rainfall appears to be more influential.

  8. Seed Germination

    USDA-ARS?s Scientific Manuscript database

    Initiation of seed germination is a critical decision for plants. It is important for seed populations under natural conditions to spread the timing of germination of individual seeds to maximize the probability of species survival. Therefore, seeds have evolved the multiple layers of mechanisms tha...

  9. 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. Crown Copyright © 2010. Published by Elsevier Ltd. All rights reserved.

  10. White Dwarf Mass Distribution

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Koester, D.; Romero, A. D.; Ourique, G.; Pelisoli, I.

    2017-03-01

    We present the mass distribution for all S/N ≥ 15 DA white dwarfs detected in the Sloan Digital Sky Survey up to Data Release 12 in 2015, fitted with Koester models for ML2/α=0.8 (Teff≥ 10000 K), and for DBs with S/N ≥ 10, fitted with ML2/α=1.25, for Teff >16 000 K. These mass distributions are for logg≥6.5 stars, i.e., excluding the Extremely Low Mass white dwarfs. We also present the mass distributions corrected by volume with the 1/Vmax approach, for stars brighter than g=19. Both distributions have a maximum at M=0.624 M ⊙ but very distinct shapes.

  11. Collapsing white dwarfs

    NASA Technical Reports Server (NTRS)

    Baron, E.; Cooperstein, J.; Kahana, S.; Nomoto, K.

    1987-01-01

    The results of the hydrodynamic collapse of an accreting C + O white dwarf are presented. Collapse is induced by electron captures in the iron core behind a conductive deflagration front. The shock wave produced by the hydrodynamic bounce of the iron core stalls at about 115 km, and thus a neutron star formed in such a model would be formed as an optically quiet event.

  12. Brown Dwarf Microlensing Diagram

    NASA Image and Video Library

    2016-11-10

    For the first time, two space-based telescopes have teamed up with ground-based observatories to observe a microlensing event, a magnification of the light of a distant star due to the gravitational effects of an unseen object in the foreground. In this case, the cause of the microlensing event was a brown dwarf, dubbed OGLE-2015-BLG-1319, orbiting a star. In terms of mass, brown dwarfs fall somewhere between the size of the largest planets and the smallest stars. Curiously, scientists have found that, for stars roughly the mass of our sun, less than 1 percent have a brown dwarf orbiting within 3 AU (1 AU is the distance between Earth and the sun). This newly discovered brown dwarf may fall in that distance range. This microlensing event was observed by ground-based telescopes looking for these uncommon events, and subsequently seen by NASA's Spitzer and Swift space telescopes. As the diagram shows, Spitzer and Swift offer additional vantage points for viewing this chance alignment. While Swift orbits close to Earth, and saw (blue diamonds) essentially the same change in light that the ground-based telescopes measured (grey markers), Spitzer's location much farther away from Earth gave it a very different perspective on the event (red circles). In particular, Spitzer's vantage point resulted in a time lag in the microlensing event it observed, compared to what was seen by Swift and the ground-based telescope. This offset allowed astronomers to determine the distance to OGLE-2015-BLG-1319 as well as its mass: around 30-65 times that of Jupiter. http://photojournal.jpl.nasa.gov/catalog/PIA21077

  13. 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.

  14. 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

  15. 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.

  16. Convection in White Dwarfs

    NASA Astrophysics Data System (ADS)

    Provencal, Judith L.; Shipman, H.; Dalessio, J.; M, M.

    2012-01-01

    Convection is one of the largest sources of theoretical uncertainty in our understanding of stellar physics. Current studies of convective energy transport are based on the mixing length theory. Originally intended to depict turbulent flows in engineering situations, MLT enjoys moderate success in describing stellar convection. However, problems arising from MLT's incompleteness are apparent in studies ranging from determinations of the ages of massive stars, to understanding the structure F and early A stars, to predicting the pulsation periods of solar stars, to understanding the atmosphere of Titan. As an example for white dwarfs, Bergeron et al. (1995) show that model parameters such as flux, line profiles, energy distribution, color indices, and equivalent widths are extremely sensitive to the assumed MLT parameterization. The authors find systematic uncertainties ranging from 25% for effective temperatures to 11% for mass and radius. The WET is engaged in a long term project to empirically determine the physical properties of convection in the atmospheres of pulsating white dwarfs. The technique, outlined by Montgomery et al. (2010), uses information from nonlinear (non-sinusoidal) pulse shapes of the target star to empirically probe the physical properties of its convection zone. Approximately two thirds of all white dwarfs show nonlinear characteristics in their light curves. We present current results from WET targets in 2008-2011.

  17. 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.

  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. Tall shrub layer biomass in conifer plantations in northeastern Minnesota.

    Treesearch

    Lewis F. Ohmann

    1982-01-01

    Provides estimates of biomass (pounds/acre) for tall shrub species in 53 conifer plantations in northeastern Minnesota. The estimates are analyzed by plantation age and silvicultural practices used to establish and release the plantations.

  20. 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...

  1. Proceedings: Wildland Shrub and Arid Land Restoration Symposium

    Treesearch

    Bruce A. Roundy; E. Durant McArthur; Jennifer S. Haley; David K. Mann

    1995-01-01

    Includes 62 papers dealing with wildland shrubs and restoration of arid lands. The key topics include: overview, restoration and revegetation, ecology, genetic integrity, management options, and field trip.Individual papers from this publication

  2. 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...

  3. 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.

  4. Shrubs of California's chaparral, timberland, and wood land: area, ownership, and stand characteristics.

    Treesearch

    Charles L. Boisinger

    1988-01-01

    A statewide inventory of shrubs in chaparral and on timberland and woodland in California is presented, and the relevance of shrubs to resource management is discussed. Shrub types (excluding coastal sage and Great Basin and desert shrubs) cover about 10 million acres, 73 percent of which is chaparral. Chamise is the most widespread type in chaparral (51 percent of...

  5. Estimation of shrub leaf biomass available to white-tailed deer.

    Treesearch

    Lynn L. Rogers; Ronald E. McRoberts

    1992-01-01

    Describes an objective method for using shrub height to estimate leaf biomass within reach of deer. The method can be used in conjunction with surveys of shrub height, shrub density, and shrub species composition to evaluate deer habitat over large areas and to predict trends in forage availability with further forest growth.

  6. A multifaceted view on the impacts of shrub encroachment.

    PubMed

    Maestre, Fernando T; Eldridge, David J; Soliveres, Santiago

    2016-07-01

    Shrub encroachment, a global phenomenon with management implications, is examined in two papers in the current issue of Applied Vegetation Science. Barbosa da Silva et al. show that encroachment simplifies herbaceous community, and Pittarello et al. illustrate how pastoral practices can restore encroached grasslands. While detrimental effects of shrub encroachment on grassland vegetation are often reported, we argue for a more holistic view when assessing this land cover change.

  7. 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.

  8. A multifaceted view on the impacts of shrub encroachment

    PubMed Central

    Maestre, Fernando T.; Eldridge, David J.; Soliveres, Santiago

    2017-01-01

    Shrub encroachment, a global phenomenon with management implications, is examined in two papers in the current issue of Applied Vegetation Science. Barbosa da Silva et al. show that encroachment simplifies herbaceous community, and Pittarello et al. illustrate how pastoral practices can restore encroached grasslands. While detrimental effects of shrub encroachment on grassland vegetation are often reported, we argue for a more holistic view when assessing this land cover change. PMID:28239276

  9. 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.

  10. 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

  11. 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.

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

    PubMed

    Liang, Eryuan; Eckstein, Dieter

    2009-09-01

    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. 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. 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. 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.

  13. NGEE Arctic Plant Traits: Shrub Transects, Kougarok Road Mile Marker 64, Seward Peninsula, Alaska, 2016

    DOE Data Explorer

    Peter Thornton; Colleen Iversen; Stan Wullschleger; Verity Salmon; Mark Lara

    2017-03-01

    Transect data is from point center quarter surveys for shrub density performed in July 2016 at the Kougarok hill slope located at Kougarok Road, Mile Marker 64. For each sample point along the transects, moving averages for shrub density and shrub basal area are provided along with GPS coordinates, average shrub height and active layer depth. The individual height, basal area, and species of surveyed shrubs are also included. Data upload will be completed January 2017.

  14. Shrubs, streamflow, and the paradox of scale

    NASA Astrophysics Data System (ADS)

    Wilcox, Bradford P.; Owens, M. Keith; Dugas, William A.; Ueckert, Darrell N.; Hart, Charles R.

    2006-10-01

    In this paper, we examine the linkage between woody plants and the water budget for three important woody plant communities in Texas, USA: saltcedar (Tamarix chinensis, Tamarix ramosissima), Ashe juniper (Juniperus ashei Buchholz), and mesquite (Prosopis glandulosa Torr. var. glandulosa). In most cases, these species are found in distinct physiographic and soil settings. Saltcedar is restricted to stream channels and floodplains; Ashe juniper is found mostly on karst limestone outcrops with shallow soils; and mesquite is found on deep soils. Because of these differences, changes in woody plant cover in each community will have a different effect on the water budget. For each type, we review the available literature and explicitly report the scale of observation (tree, stand, catchment, or landscape). A simple framework called the shrub-streamflow framework, which recognizes differences in response due to differences in physiographic setting, climate, and potential for deep drainage or subsurface flow, enables us to generalize the results. The fundamental premise of the framework is simple: for shrublands to be hydrologically sensitive to changes in woody plant cover, soil water or groundwater must be accessible to deep-rooting plants but too deep for shallow-rooting ones. Such a situation exists if groundwater is close to the surface (within 3-5 m and/or if deep drainage occurs (because of either high precipitation input or bypass flow in the soil). We argue that on an area basis, conversion of saltcedar stands to herbaceous plants in riparian regions has a much greater potential for increasing water yield than does conversion of woodlands to grasslands in upland regions where deep drainage does not occur. On upland sites where deep drainage does occur, conversion from woody to herbaceous vegetation may result in a savings of 40-80 mm year-1 of water. But such savings have been observed only up to the small-catchment scale, and until further work is done it is

  15. 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.

  16. Limber Pine Dwarf Mistletoe (FIDL)

    Treesearch

    Jane E. Taylor; Robert L. Mathiason

    1999-01-01

    Limber pine dwarf mistletoe (Arceuthobium cyanocarpum (A. Nelson ex Rydberg) Coulter & Nelson) is a damaging parasite of limber pine (Pinus flexilis James), whitebark pine (P. albicaulis Engelm.), Rocky Mountain bristlecone pine (P. aristata Engelm.) and Great Basin bristlecone pine (P. longaeva D.K. Bailey). Limber pine dwarf mistletoe occurs in the Rocky...

  17. An archetypal dwarf galaxy

    NASA Image and Video Library

    2013-01-07

    The constellation of Ursa Major (The Great Bear) is home to Messier 101, the Pinwheel Galaxy. One of the biggest and brightest spiral galaxies in the night sky, Messier 101 is also the subject of one of Hubble's most famous images (heic0602). Like the Milky Way, Messier 101 is not alone, with smaller dwarf galaxies in its neighbourhood. NGC 5477, one of these dwarf galaxies in the Messier 101 group, is the subject of this image from the NASA/ESA Hubble Space Telescope. Without obvious structure, but with visible signs of ongoing starbirth, NGC 5477 looks much like an archetypal dwarf irregular galaxy. The bright nebulae that extend across much of the galaxy are clouds of glowing hydrogen gas in which new stars are forming. These glow pinkish red in real life, although the selection of green and infrared filters through which this image was taken makes them appear almost white. The observations were taken as part of a project to measure accurate distances to a range of galaxies within about 30 million light-years from Earth, by studying the brightness of red giant stars. In addition to NGC 5477, the image includes numerous galaxies in the background, including some that are visible right through NGC 5477. This serves as a reminder that galaxies, far from being solid, opaque objects, are actually largely made up of the empty space between their stars. This image is a combination of exposures taken through green and infrared filters using Hubble's Advanced Camera for Surveys. The field of view is approximately 3.3 by 3.3 arcminutes. 

  18. Tidal Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Houck, James R.; Higdon, Sarah

    2004-09-01

    Tidal Dwarf Galaxies (TDG's) are formed from material stripped from the disks of spiral galaxies, which are undergoing tidal interactions with a nearby companion. These galaxies provide important clues to our understanding of galaxy formation, evolution and cosmic recycling. Using the IRS we will measure the star formation activity in 6 TDG candidates. We will measure the ionization state ( [NeII] 12.8 um, [NeIII] 15.6 um and [NeV] 14.3um and [OIV] 25.9 um), the density in the ionized gas ([SIII] 18.7um/33.5um), the PAH fractions at 5.5-9um and 11-12.2um and possibly (optimistic here!) molecular hydrogen emission form PDRs at H2 (S0) 28um and H2 (S1) at 17um. In addition to the IRS observations we will map both the Guitar and Stephan's Quintet with IRAC. This will enable us to compare the PAH fraction in the dwarf galaxy to that of its parent. Similarly we will compare our observation of the proposed TDG at the southern tip of NGC 4038 with the GT observations of the central region of the Antennae. This program compliments two existing GT programmes: 1) the high-Z program - these observations enable us to observe in fine detail the nearby/present day analogs of galaxy formation in the early universe. 2) Blue Compact Dwarf programme - On first inpsection BCD's and TDG's appear the same: BCDs are similar in size to TDG's, but TDG's may not have a large dark matter halo component (affecting the long term stability of an object) and BCD's typically have a much lower metallicity. We will be able to compare the star formation activity in terms of the ionization state and PAH fraction in the two galaxy types.

  19. Do changes in grazing pressure and the degree of shrub encroachment alter the effects of individual shrubs on understorey plant communities and soil function?

    PubMed Central

    Soliveres, Santiago; Eldridge, David J.

    2015-01-01

    Summary Shrub canopies in semi-arid environments often produce positive effects on soil fertility, and on the richness and biomass of understorey plant communities. However, both positive and negative effects of shrub encroachment on plant and soil attributes have been reported at the landscape-level. The contrasting results between patch- and landscape-level effects in shrublands could be caused by differences in the degree of shrub encroachment or grazing pressure, both of which are likely to reduce the ability of individual shrubs to ameliorate their understorey environment. We examined how grazing and shrub encroachment (measured as landscape-level shrub cover) influence patch-level effects of shrubs on plant density, biomass and similarity in species composition between shrub understories and open areas, and on soil stability, nutrient cycling, and infiltration in two semi-arid Australian woodlands. Individual shrubs had consistently positive effects on all plant and soil variables (average increase of 23% for all variables). These positive patch-level effects persisted with increasing shrub cover up to our maximum of 50% cover. Heavy grazing negatively affected most of the variables studied (average decline of 11%). It also altered, for some variables, how individual shrubs affected their sub-canopy environment with increasing shrub cover. Thus for species density, biomass and soil infiltration, the positive effect of individual shrubs with increasing shrub cover diminished under heavy grazing. Synthesis Our study refines predictions of the effects of woody encroachment on ecosystem structure and functioning by showing that heavy grazing, rather than differences in shrub cover, explains the contrasting effects on ecosystem structure and function between individual shrubs and those in dense aggregations. We also discuss how species-specific traits of the encroaching species, such as their height or its ability to fix N, might influence the relationship between

  20. 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.

  1. 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

  2. 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.

  3. White Dwarf Calibration

    NASA Astrophysics Data System (ADS)

    Colina, Luis

    1994-01-01

    As a result of last November calibration workshop, all parties agreed that the HST should be switched to the WD basis for absolute fluxes. This proposal implements that decision. A measurement of the absolute sensitivity of the FOS detectors will be performed using theoretical pure hydrogen model atmosphere calculations for three white dwarfs. The high resolution gratings will be used in the 1 arcsec aperture. A four stage peakup of the standard star provides centering in the aperture. Observations are requested for fall 94 with repeated observations about two months after.

  4. 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

  5. Hybrid dwarfness in crosses between wheat (Triticum aestivum L.) and rye (Secale cereale L.): a new look at an old phenomenon.

    PubMed

    Tikhenko, N; Rutten, T; Tsvetkova, N; Voylokov, A; Börner, A

    2015-03-01

    The existence of hybrid dwarfs from intraspecific crosses in wheat (Triticum aestivum) was described 100 years ago, and the genetics underlying hybrid dwarfness are well understood. In this study, we report a dwarf phenotype in interspecific hybrids between wheat and rye (Secale cereale). We identified two rye lines that produce hybrid dwarfs with wheat and have none of the hitherto known hybrid dwarfing genes. Genetic analyses revealed that both rye lines carry a single allelic gene responsible for the dwarf phenotype. This gene was designated Hdw-R1 (Hybrid dwarf-R1). Application of gibberellic acid (GA3 ) to both intraspecific (wheat-wheat) and interspecific (wheat-rye) hybrids showed that hybrid dwarfness cannot be overcome by treatment with this phytohormone. Histological analysis of shoot apices showed that wheat-rye hybrids with the dwarf phenotype at 21 and 45 days after germination failed to develop further. Shoot apices of dwarf plants did not elongate, did not form new primordia and had a dome-shaped appearance in the seed. The possible relationship between hybrid dwarfness and the genes responsible for the transition from vegetative to generative growth stage is discussed.

  6. Permafrost response to increasing Arctic shrub abundance depends on the relative influence of shrubs on local soil cooling versus large-scale climate warming

    NASA Astrophysics Data System (ADS)

    Lawrence, David M.; Swenson, Sean C.

    2011-10-01

    Deciduous shrub abundance is increasing across the Arctic in response to climatic warming. In a recent field manipulation experiment in which shrubs were removed from a plot and compared to a control plot with shrubs, Blok et al (2010 Glob. Change Biol. 16 1296-305) found that shrubs protect the ground through shading, resulting in a ~ 9% shallower active layer thickness (ALT) under shrubs compared to grassy-tundra, which led them to argue that continued Arctic shrub expansion could mitigate future permafrost thaw. We utilize the Community Land Model (CLM4) coupled to the Community Atmosphere Model (CAM4) to evaluate this hypothesis. CLM4 simulates shallower ALT (~- 11 cm) under shrubs, consistent with the field manipulation study. However, in an idealized pan-Arctic + 20% shrub area experiment, atmospheric heating, driven mainly by surface albedo changes related to protrusion of shrub stems above the spring snowpack, leads to soil warming and deeper ALT (~+ 10 cm). Therefore, if climate feedbacks are considered, shrub expansion may actually increase rather than decrease permafrost vulnerability. When we account for blowing-snow redistribution from grassy-tundra to shrubs, shifts in snowpack distribution in low versus high shrub area simulations counter the climate warming impact, resulting in a grid cell mean ALT that is unchanged. These results reinforce the need to consider vegetation dynamics and blowing-snow processes in the permafrost thaw model projections.

  7. Facilitating the afforestation of Mediterranean polluted soils by nurse shrubs.

    PubMed

    Domínguez, María T; Pérez-Ramos, Ignacio M; Murillo, José M; Marañón, Teodoro

    2015-09-15

    The revegetation of polluted sites and abandoned agricultural soils is critical to reduce soil losses and to control the spread of soil pollution in the Mediterranean region, which is currently exposed to the greatest soil erosion risk in Europe. However, events of massive plant mortality usually occur during the first years after planting, mainly due to the adverse conditions of high irradiance and drought stress. Here, we evaluated the usefulness of considering the positive plant-plant interactions (facilitation effect) in the afforestation of polluted agricultural sites, using pre-existing shrubs as nurse plants. We used nurse shrubs as planting microsites for acorns of Quercus ilex (Holm oak) along a gradient of soil pollution in southwestern Spain, and monitored seedling growth, survival, and chemical composition during three consecutive years. Seedling survival greatly increased (from 20% to more than 50%) when acorns were sown under shrub, in comparison to the open, unprotected matrix. Facilitation of seedling growth by shrubs increased along the gradient of soil pollution, in agreement with the stress gradient hypothesis that predicts higher intensity of the facilitation effects with increasing abiotic stress. Although the accumulation of trace elements in seedling leaves was higher underneath shrub, the shading conditions provided by the shrub canopy allowed seedlings to cope with the toxicity provoked by the concurrence of low pH and high trace element concentrations in the most polluted sites. Our results show that the use of shrubs as nurse plants is a promising tool for the cost-effective afforestation of polluted lands under Mediterranean conditions. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. Arctic shrub growth trajectories differ across soil moisture levels.

    PubMed

    Ackerman, Daniel; Griffin, Daniel; Hobbie, Sarah E; Finlay, Jacques C

    2017-10-01

    The circumpolar expansion of woody deciduous shrubs in arctic tundra alters key ecosystem properties including carbon balance and hydrology. However, landscape-scale patterns and drivers of shrub expansion remain poorly understood, inhibiting accurate incorporation of shrub effects into climate models. Here, we use dendroecology to elucidate the role of soil moisture in modifying the relationship between climate and growth for a dominant deciduous shrub, Salix pulchra, on the North Slope of Alaska, USA. We improve upon previous modeling approaches by using ecological theory to guide model selection for the relationship between climate and shrub growth. Finally, we present novel dendroecology-based estimates of shrub biomass change under a future climate regime, made possible by recently developed shrub allometry models. We find that S. pulchra growth has responded positively to mean June temperature over the past 2.5 decades at both a dry upland tundra site and an adjacent mesic riparian site. For the upland site, including a negative second-order term in the climate-growth model significantly improved explanatory power, matching theoretical predictions of diminishing growth returns to increasing temperature. A first-order linear model fit best at the riparian site, indicating consistent growth increases in response to sustained warming, possibly due to lack of temperature-induced moisture limitation in mesic habitats. These contrasting results indicate that S. pulchra in mesic habitats may respond positively to a wider range of temperature increase than S. pulchra in dry habitats. Lastly, we estimate that a 2°C increase in current mean June temperature will yield a 19% increase in aboveground S. pulchra biomass at the upland site and a 36% increase at the riparian site. Our method of biomass estimation provides an important link toward incorporating dendroecology data into coupled vegetation and climate models. © 2017 John Wiley & Sons Ltd.

  9. Water storage capacity, stemflow and water funneling in Mediterranean shrubs

    NASA Astrophysics Data System (ADS)

    Garcia-Estringana, P.; Alonso-Blázquez, N.; Alegre, J.

    2010-08-01

    SummaryTo predict water losses and other hydrological and ecological features of a given vegetation, its water storage capacity and stemflow need to be accurately determined. Vast areas of the Mediterranean region are occupied by shrublands yet there is scarce data available on their rainwater interception capacity. In this study, simulated rainfall tests were conducted in controlled conditions on nine Mediterranean shrubs of varying anatomic and morphological features to determine water storage capacity, stemflow and the funneling ratio. After assessing correlations between these hydrological variables and the biometric characteristics of the shrubs, we compared two methods of determining storage capacity: rainfall simulation and immersion. Mean water storage capacity was 1.02 mm (0.35-3.24 mm), stemflow was 16% (3.8-26.4%) and the funneling ratio was 104 (30-260). Per unit biomass, mean storage capacity was 0.66 ml g -1 and ranged from 0.23 ml g -1 for Cistus ladanifer to 2.26 ml g -1 for Lavandula latifolia. Despite their small size, shrubs may generate high water losses to the atmosphere when they form dense communities and this can have a significant impact in regions where water is scarce. When considered the whole shrubs in absolute terms (ml per plant), water storage capacity and stemflow were correlated to biomass and the dendrometric characteristics of the shrubs, yet in relative terms (expressed per surface area unit or as %), anatomic features such as pubescence, branch rigidity or leaf insertion angle emerged as determining factors. The use of a simple procedure to assess storage capacity was inefficient. The immersion method underestimated storage capacity to a different extent for each species. Some shrubs returned high stemflow values typical of their adaptation to the semiarid climate. In contrast, other shrubs seem to have structures that promote stemflow yet have developed other drought-adaptation mechanisms. In this report, we discuss the

  10. Direct seeding

    Treesearch

    Richard M. Godman; G. A. Mattson

    1992-01-01

    At present, direct seeding of hardwoods in the Lake States is more of a supplemental than a primary means of artificial regeneration. Direct seeding may be used to augment a poor seed crop or increase the proportion of a preferred species. In the future, it will no doubt play a bigger role-in anticipation of this we need to collect and store the amounts of seed needed...

  11. Habitability of planets around red dwarf stars.

    PubMed

    Heath, M J; Doyle, L R; Joshi, M M; Haberle, R M

    1999-08-01

    Recent models indicate that relatively moderate climates could exist on Earth-sized planets in synchronous rotation around red dwarf stars. Investigation of the global water cycle, availability of photosynthetically active radiation in red dwarf sunlight, and the biological implications of stellar flares, which can be frequent for red dwarfs, suggests that higher plant habitability of red dwarf planets may be possible.

  12. 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

  13. 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

  14. 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

  15. [Soil moisture dynamics under artificial Caragana microphylla shrub].

    PubMed

    Alamusa; Jiang, Deming; Fan, Shixiang; Luo, Yongming

    2002-12-01

    Applying the methods of deducing time series from vegetation space alignment, we analyzed the spatial and temporal variation features of soil moisture under artificial Caragana microphylla shrubs built in 1984, 1987, 1995, 1999. The results showed that affected by mechanical composition of mobile sandy dunes, the soil of sandy land was mainly composed of sandy particle, and the particles of > 0.01 mm were accounted for 97%. The withered moisture was 1.55%. The field waterhold capacity was 5.5%, and the available moisture storage was 3.95%. With the increase of the dominance of fix-sand vegetation, the moisture content of soil under artificial Caragana microphylla shrubs was decreased. The soil moisture of vegetation built in 1984 was lower than that built in 1999. The soil moisture conditions of four stages vegetation were continued depressing from April to June in a year, the lowest point presenced in June, and then gradually increased from July to October. The vertical change of soil moisture showed the tendency of increasing with soil depth. The soil moisture decreased by the degrees of early built vegetation (1984, 1987). Especially in 70 cm soil depth, the moisture content of soil decreased obviously. Caragana microphylla shrubs absorbed water and aggravated the shortage of soil moisture content near the root system, which affected the component of vegetation in Caragana microphylla shrubs. The species of herbaceous plants and annual plants increased during the growth of Caragana microphylla shrub.

  16. 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.

  17. Shrubs and Runoff in Semiarid Landscapes: Whats the Linkage?

    NASA Astrophysics Data System (ADS)

    Wilcox, B. P.; Owens, M. K.; Knight, R.; Lyons, R. K.

    2001-12-01

    Here we examine linkage between streamflow and shrub cover in semiarid landscapes with a focus on the extensive Texas rangelands covered by mesquite and juniper. The conclusions drawn are consistent with results from field studies and with our understanding of runoff processes from rangelands. Whether and how shrub control will affect streamflow depends on shrub characteristics, precipitation, soils, and geology. Precipitation is perhaps the most fundamental of these factors: there is little if any real potential for increasing streamflow where annual precipitation is below about 500 mm. For areas in which precipitation is sufficient, an excellent indicator that there is potential for increasing streamflow through shrub control is that base flow is an important component of streamflow. Another key indicator is shallow soils underlain by fractured parent material; under such conditions, increased streamflows are possible mainly because water that would otherwise be lost through interception by the canopy instead moves into the soil and quickly travels beyond the root zone. Conversely, where soils are deep there is little evidence that streamflow can be significantly increased by reducing brush cover. Results from a 10 year small watershed study where juniper was selectively removed in the Edwards plateau region of Texas will be summarized in this presentation. In assessing the potential for shrub control to increase streamflow, the runoff generation process should be explicitly identified. Areas in which Horton overland flow is the primary runoff mechanism offer little potential for increasing streamflow via vegetation management.

  18. 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.

  19. Throwing Icebergs at White Dwarfs

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-08-01

    Where do the metals come from that pollute the atmospheres of many white dwarfs? Close-in asteroids may not be the only culprits! A new study shows that distant planet-size and icy objects could share some of the blame.Pollution ProblemsArtists impression of rocky debris lying close around a white dwarf star. [NASA/ESA/STScI/G. Bacon]When a low- to intermediate-mass star reaches the end of its life, its outer layers are blown off, leaving behind its compact core. The strong gravity of this white dwarf causes elements heavier than hydrogen and helium to rapidly sink to its center in a process known as sedimentation, leaving an atmosphere that should be free of metallic elements.Therefore its perhaps surprising that roughly 2550% of all white dwarfs are observed to have atmospheric pollution by heavy elements. The short timescales for sedimentation suggest that these elements were added to the white dwarf recently but how did they get there?Bringing Ice InwardIn the generally accepted theory, pre-existing rocky bodies or an orbiting asteroid belt survive the stars evolution, later accreting onto the final white dwarf. But this scenario doesnt explain a few observations that suggest white dwarfs might be accreting larger planetary-size bodies and bodies with ices and volatile materials.Dynamical evolution of a Neptune-like planet (a) and a Kuiper belt analog object (b) in wide binary star systems. Both have large eccentricity excitations during the white dwarf phase. [Stephan et al. 2017]How might you get large or icy objects which would begin on very wide orbits close enough to a white dwarf to become disrupted and accrete? Led by Alexander Stephan, a team of scientists at UCLA now suggest that the key is for the white dwarf to be in a binary system.Influence of a CompanionIn the authors model, the white-dwarf progenitor is orbited by both a distant stellar companion (a common occurrence) and a number of large potential polluters, which could have masses between that

  20. 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.

  1. The brown dwarf kinematics project

    NASA Astrophysics Data System (ADS)

    Faherty, Jackie K.

    2010-10-01

    Brown dwarfs are a recent addition to the plethora of objects studied in Astronomy. With theoretical masses between 13 and 75 MJupiter , they lack sustained stable Hydrogen burning so they never join the stellar main sequence. They have physical properties similar to both planets and low-mass stars so studies of their population inform on both. The distances and kinematics of brown dwarfs provide key statistical constraints on their ages, moving group membership, absolute brightnesses, evolutionary trends, and multiplicity. Yet, until my thesis, fundamental measurements of parallax and proper motion were made for only a relatively small fraction of the known population. To address this deficiency, I initiated the Brown Dwarf Kinematics (BDKP). Over the past four years I have re-imaged the majority of spectroscopically confirmed field brown dwarfs (or ultracool dwarfs---UCDs) and created the largest proper motion catalog for ultracool dwarfs to date. Using new astrometric information I examined population characteristics such as ages calculated from velocity dispersions and correlations between kinematics and colors. Using proper motions, I identified several new wide co-moving companions and investigated binding energy (and hence formation) limitations as well as the frequency of hierarchical companions. Concurrently over the past four years I have been conducting a parallax survey of 84 UCDs including those showing spectral signatures of youth, metal-poor brown dwarfs, and those within 20 pc of the Sun. Using absolute magnitude relations in J,H, and K, I identified overluminous binary candidates and investigated known flux-reversal binaries. Using current evolutionary models, I compared the MK vs J-K color magnitude diagram to model predictions and found that the low-surface gravity dwarfs are significantly red-ward and underluminous of predictions and a handful of late-type T dwarfs may require thicker clouds to account for their scatter.

  2. Seed arrival in tropical forest tree fall gaps.

    PubMed

    Puerta-Pińero, Carolina; Muller-Landau, Helene C; Calderón, Osvaldo; Wright, S Joseph

    2013-07-01

    Tree deaths open gaps in closed-canopy forests, which allow light to reach the forest floor and promote seed germination and seedling establishment. Gap dependence of regeneration is an important axis of life history variation among forest plant species, and many studies have evaluated how plant species differ in seedling and sapling performance in gaps. However, relatively little is known about how seed arrival in gaps compares with seed arrival in the understory, even though seed dispersal by wind and animals is expected to be altered in gaps. We documented seed arrival for the first seven years after gap formation in the moist tropical forests of Barro Colorado Island (BCI), Panama, and evaluated how the amount and functional composition of arriving seeds compared with understory sites. On average, in the first three years after gap formation, 72% fewer seeds arrived in gaps than in the understory (207 vs. 740 seeds x m(-2) x yr(-1)). The reduction in number of arriving seeds fell disproportionately on animal-dispersed species, which suffered an 86% reduction in total seed number, while wind-dispersed species experienced only a 47% reduction, and explosively dispersed species showed increased seed numbers arriving. The increase in explosively dispersed seeds consisted entirely of the seeds of several shrub species, a result consistent with greater in situ seed production by explosively dispersed shrubs that survived gap formation or recruited immediately thereafter. Lianas did relatively better in seed arrival into gaps than did trees, suffering less of a reduction in seed arrival compared with understory sites. This result could in large part be explained by the greater predominance of wind dispersal among lianas: there were no significant differences between lianas and trees when controlling for dispersal syndromes. Our results show that seed arrival in gaps is very different from seed arrival in the understory in both total seeds arriving and functional

  3. Sowing the Seeds of Planets? (Artist's Concept)

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Planet Clumps and Crystals around Brown Dwarfs

    This artist's concept shows microscopic crystals in the dusty disk surrounding a brown dwarf, or 'failed star.' The crystals, made up of a green mineral found on Earth called olivine, are thought to help seed the formation of planets.

    NASA's Spitzer Space Telescope detected the tiny crystals circling around five brown dwarfs, the cooler and smaller cousins of stars. Though crystallized minerals have been seen in space before -- in comets and around other stars -- the discovery represents the first time the little gem-like particles have been spotted around confirmed brown dwarfs.

    Astronomers believe planets form out of disks of dust that circle young brown dwarfs and stars. Over time, the various minerals making up the disks crystallize and begin to clump together. Eventually, the clumps collide and stick, building up mass like snowmen until planets are born.

    About the Graph: Planet Clumps and Crystals around Brown Dwarfs The graph of data from NASA's Spitzer Space Telescope shows the spectra (middle four lines) of dusty disks around four brown dwarfs, or 'failed stars,' located 520 light-years away in the Chamaeleon constellation. The data suggest that the dust in these disks is crystallizing and clumping together in what may be the birth of planets.

    Spectra are created by breaking light apart into its basic components, like a prism turning sunlight into a rainbow. Their bumps represent the 'fingerprints' or signatures of different minerals.

    Here, the light green vertical bands highlight the spectral fingerprints of crystals made up primarily of a green silicate mineral found on Earth called olivine. As the graph illustrates, three of the four brown dwarfs possess these microscopic gem-like particles. For comparison, the spectra of dust between stars (top) and the comet Hale-Bopp (bottom) are shown. The comet has the tiny

  4. Sowing the Seeds of Planets? (Artist's Concept)

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Planet Clumps and Crystals around Brown Dwarfs

    This artist's concept shows microscopic crystals in the dusty disk surrounding a brown dwarf, or 'failed star.' The crystals, made up of a green mineral found on Earth called olivine, are thought to help seed the formation of planets.

    NASA's Spitzer Space Telescope detected the tiny crystals circling around five brown dwarfs, the cooler and smaller cousins of stars. Though crystallized minerals have been seen in space before -- in comets and around other stars -- the discovery represents the first time the little gem-like particles have been spotted around confirmed brown dwarfs.

    Astronomers believe planets form out of disks of dust that circle young brown dwarfs and stars. Over time, the various minerals making up the disks crystallize and begin to clump together. Eventually, the clumps collide and stick, building up mass like snowmen until planets are born.

    About the Graph: Planet Clumps and Crystals around Brown Dwarfs The graph of data from NASA's Spitzer Space Telescope shows the spectra (middle four lines) of dusty disks around four brown dwarfs, or 'failed stars,' located 520 light-years away in the Chamaeleon constellation. The data suggest that the dust in these disks is crystallizing and clumping together in what may be the birth of planets.

    Spectra are created by breaking light apart into its basic components, like a prism turning sunlight into a rainbow. Their bumps represent the 'fingerprints' or signatures of different minerals.

    Here, the light green vertical bands highlight the spectral fingerprints of crystals made up primarily of a green silicate mineral found on Earth called olivine. As the graph illustrates, three of the four brown dwarfs possess these microscopic gem-like particles. For comparison, the spectra of dust between stars (top) and the comet Hale-Bopp (bottom) are shown. The comet has the tiny

  5. Imaging planets around white dwarfs

    NASA Astrophysics Data System (ADS)

    Burleigh, Matt; Clarke, Fraser; Hodgkin, Simon

    White dwarfs should retain planetary systems in wide orbits (>≅5AU). Evolutionary models for Jovian planets show that infra-red imaging of suitable nearby white dwarfs should allow us to resolve and detect companions >≅5 Mtiny JUP. We have instigated programmes with both the 8m Gemini North (using NIRI), Gemini South (using Flamingos) and with the NAOMI Adaptive Optics system on the 4.2m William Herschel Telescope to search for such objects, which will share the large proper motions of their white dwarf hosts.

  6. 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.

  7. PHL 5038: a spatially resolved white dwarf + brown dwarf binary

    NASA Astrophysics Data System (ADS)

    Steele, P. R.; Burleigh, M. R.; Farihi, J.; Gänsicke, B. T.; Jameson, R. F.; Dobbie, P. D.; Barstow, M. A.

    2009-06-01

    A near-infrared excess is detected at the white dwarf PHL 5038 in UKIDSS photometry, consistent with the presence of a cool, substellar companion. We have obtained H- and K-grism spectra and images of PHL 5038 using NIRI on Gemini North. The target is spatially and spectrally resolved into two components: an 8000 K DA white dwarf, and a likely L8 brown dwarf companion, separated by 0.94 arcsec. The spectral type of the secondary was determined using standard spectral indices for late L and T dwarfs. The projected orbital separation of the binary is 55 AU, so it becomes only the second known wide WD+dL binary to be found after GD 165AB. This object could potentially be used as a benchmark for testing substellar evolutionary models at intermediate to older ages.

  8. 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.

  9. Tidal Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Duc, P.-A.; Mirabel, I. F.; Brinks, E.

    The life and evolution of galaxies are dramatically affected by environmental effects. Interactions with the intergalactic medium and collisions with companions cause major perturbations in the morphology and contents of galaxies: in particular stars and gas clouds may be gravitationally pulled out from their parent galaxies during tidal encounters, forming rings, tails and bridges. This debris of collisions lies at the origin of a new generation of small galaxies, the so-called "tidal dwarf galaxies" (TDGs). The authors have carried out multi-wavelength observations of some 20 TDGs. These systems are made of two stellar components: young stars, formed from the recent collapse of expelled H I clouds, and an older stellar population, tidally pulled out from the disks of their interacting parent galaxies. In the observed TDGs, the current star formation episode is fuelled by a large reservoir of H I gas and is younger than 10 Myr.

  10. 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

  11. Demographic patterns of the shrub Ceanothus megacarpus in an old stand of chaparral in the Santa Monica Mountains

    USGS Publications Warehouse

    Montygierd-Loyba, T. M.; Keeley, J.E.; DeVries, J.J.

    1986-01-01

    Wildfires have had a major influence on the structural and functional adaptations that have evolved in Mediterranean-type ecosystems. Some chaparral shrubs sprout after fires while others produce serotinous cones or seeds refractory to germination until they are cued by a fire. Ceanothus megacarpus is a sclerophylous shrub commonly found in California in either pure of mixed stands which does not survive fires but whose seeds germinate following a fire. Because in recent decades man-made fires have become frequent, few older stands remain, and they have been described as "decadent" or "senescent." Since data on older chaparral stands are scarce, a stand of chaparral in the Santa Monica Mountains of southern California, which last burned in 1929 was studied in an effort to elucidate the survivorship patterns and community structure of Ceanothus megacarpus as it ages. Ceanothus is responsible for 68 percent of the basal coverage at this mixed stand, and one-eighth of the Ceanothus were found to be dead. Over 130 such dead individuals were cut at ground level and aged by ring counts to establish the survivorship curve for this species in this chaparral community in the absence of fires.

  12. Variability in leaf morphology and photosynthetic responses of arctic woody shrubs to warming and shifts in snow induced thermal insulation

    NASA Astrophysics Data System (ADS)

    Flower, C. E.; Pereyra, G.; Welker, J. M.; Trumbore, S.; Gonzalez-Meler, M. A.

    2013-12-01

    Permafrost warming in the climate sensitive Arctic tundra has been linked to shifts in vegetation, from tussock dominated to tussock/shrub systems. This vegetation shift has the potential to not only impact the abiotic conditions, but also the energy balance and biogeochemical cycling of these systems; as plant assimilation, respiration, C allocation, and rooting depth may differ between plant functional groups. We assessed leaf morphology and constructed light response curves at ambient (400 ppm) and elevated (800 ppm) CO2 concentrations to assess photosynthetic responses of dwarf birch and diamond-leaf willow to a natural and induced simulated warming experiment at the Toolik Field Station in Alaska. Results indicate a positive correlation between summer soil thaw depth and leaf surface area indicating hydrological responses of both species. Additionally, leaf area was higher in warmed plots relative to non warmed plots in both the snow addition and the control treatments. Furthermore, we found that diamond-leaf willow exhibits elevated assimilation rates relative to dwarf birch. Both species exhibited similar photosynthetic responses to elevated CO2 increasing assimilation by ~34%. These responses highlight the forcing imposed by woody vegetation in arctic regions with the potential to increase net primary production in addition to positive feedbacks on winter snow depth, soil temperature, and moisture.

  13. Flaring Red Dwarf Star (Illustration)

    NASA Image and Video Library

    2017-06-06

    This illustration shows a red dwarf star orbited by a hypothetical exoplanet. Red dwarfs tend to be magnetically active, displaying gigantic arcing prominences and a wealth of dark sunspots. Red dwarfs also erupt with intense flares that could strip a nearby planet's atmosphere over time, or make the surface inhospitable to life as we know it. By mining data from the Galaxy Evolution Explorer (GALEX) spacecraft, a team of astronomers identified dozens of flares at a range of durations and strengths. The team measured events with less total energy than many previously detected flares from red dwarfs. This is important because, although individually less energetic and therefore less hostile to life, smaller flares might be much more frequent and add up over time to produce a cumulative effect on an orbiting planet. https://photojournal.jpl.nasa.gov/catalog/PIA21473

  14. White Dwarfs in Astrometric Binaries?

    NASA Astrophysics Data System (ADS)

    Oliversen, N. A.; Evans, N. R.; Feibelman, W. A.; Kamper, K. W.

    1993-12-01

    Lippincott (1978, Space Sci Rev, 22, 153) compiled a list of astrometric binaries with unseen companions typically within 20 pc of the sun. Red companions have been observed in a number of these systems (e.g. McCarthy, D. W. 1983, IAU Coll. # 76, p. 107). Unseen, low mass companions could also be white dwarfs. We have obtained IUE observations of stars on the list which have primaries with spectral types M1 or earlier (white dwarf companions of cooler primaries could be detected from the ground), and are brighter than 10 mag, which do not have known red companions. Preliminary reductions (comparison with standard stars of appropriate spectral types) indicate that there are no white dwarfs in the sample. Further processing is being done to determine limits on possible white dwarf temperatures.

  15. Rotation Velocities of White Dwarfs

    NASA Astrophysics Data System (ADS)

    Karl, C.; Napiwotzki, R.; Heber, U.; Dreizler, S.; Koester, D.; Reid, I. N.

    White dwarfs are the compact remnants of low and intermediate mass stars (M < 8Msolar). Due to the conservation of angular momentum white dwarfs should be very fast rotators, if a significant fraction of the angular momentum of the progenitor stars were preserved. The existence of sharp NLTE cores of the hydrogen Hα line in high resolution spectra (obtained at the Keck observatory) of DA white dwarfs allowed us to determine (projected) rotational velocities v sin i for white dwarfs. Among those of our targets lying close to the ZZ Ceti instability many show evidence for extra broadening similar to rotation, whereas stars at higher temperatures (and therefore younger ones) rotate more slowly or not at all. Our result based on a large sample is in accordance with previous results presented by Koester et al. (1998). We discuss possible explanations for this astonishing result.

  16. Gaia photometry for white dwarfs

    NASA Astrophysics Data System (ADS)

    Carrasco, J. M.; Catalán, S.; Jordi, C.; Tremblay, P.-E.; Napiwotzki, R.; Luri, X.; Robin, A. C.; Kowalski, P. M.

    2014-05-01

    Context. White dwarfs can be used to study the structure and evolution of the Galaxy by analysing their luminosity function and initial mass function. Among them, the very cool white dwarfs provide the information for the early ages of each population. Because white dwarfs are intrinsically faint only the nearby (~ 20 pc) sample is reasonably complete. The Gaia space mission will drastically increase the sample of known white dwarfs through its 5-6 years survey of the whole sky up to magnitude V = 20-25. Aims: We provide a characterisation of Gaia photometry for white dwarfs to better prepare for the analysis of the scientific output of the mission. Transformations between some of the most common photometric systems and Gaia passbands are derived. We also give estimates of the number of white dwarfs of the different galactic populations that will be observed. Methods: Using synthetic spectral energy distributions and the most recent Gaia transmission curves, we computed colours of three different types of white dwarfs (pure hydrogen, pure helium, and mixed composition with H/He = 0.1). With these colours we derived transformations to other common photometric systems (Johnson-Cousins, Sloan Digital Sky Survey, and 2MASS). We also present numbers of white dwarfs predicted to be observed by Gaia. Results: We provide relationships and colour-colour diagrams among different photometric systems to allow the prediction and/or study of the Gaia white dwarf colours. We also include estimates of the number of sources expected in every galactic population and with a maximum parallax error. Gaia will increase the sample of known white dwarfs tenfold to about 200 000. Gaia will be able to observe thousands of very cool white dwarfs for the first time, which will greatly improve our understanding of these stars and early phases of star formation in our Galaxy. Tables 6 and 7 are available in electronic form at http://www.aanda.orgFull Tables 3-5 are available at the CDS via

  17. Brown Dwarf Weather (Artist's Concept)

    NASA Image and Video Library

    2017-08-17

    This artist's concept animation shows a brown dwarf with bands of clouds, thought to resemble those seen on Neptune and the other outer planets in the solar system. By using NASA's Spitzer Space Telescope, astronomers have found that the varying glow of brown dwarfs over time can be explained by bands of patchy clouds rotating at different speeds. Videos are available at https://photojournal.jpl.nasa.gov/catalog/PIA21752

  18. Seed germination of Sierra Nevada postfire chaparral species

    USGS Publications Warehouse

    Keeley, Jon E.; McGinnis, Thomas W.; Bollens, Kim A.

    2005-01-01

    The California chaparral community has a rich flora of species with different mechanisms for cuing germination to postfire conditions. Here we report further germination experiments that elucidate the response of several widespread shrub species whose germination response was not clear and include other species from the Sierra Nevada, which have not previously been included in germination studies. The shrubs Adenostoma fasciculatum and Eriodictyon crassifolium and the postfire annualMentzelia dispersa exhibited highly significant germination in response to smoke treatments, with some enhanced germination in response to heating as well. The shrubs Fremontodendron californicum and Malacothamnus fremontii were stimulated only by heat-shock treatments. Seeds buried in the soil for one year exhibited substantially higher germination for controls and most treatments. In the case of two postfire annuals, Mimulus bolanderi and M. gracilipes, germination of fresh seed was significantly greater with smoke or heating but after soil storage, over two-thirds of the control seeds germinated and treatment effects were not significant. These two annuals are generally restricted to postfire conditions and it is suggested that control germination of soil-stored seed may be a light-response (which was not tested here) as previously reported for another chaparral species in that genus.

  19. Fire cue effects on seed germination of six species of northwestern Patagonian grasslands

    NASA Astrophysics Data System (ADS)

    Gonzalez, S. L.; Ghermandi, L.

    2012-09-01

    Postfire recruitment of seedlings has been attributed to a stimulation of germination by fire-related cues. The germination response to heat shock (80 °C - 5 min), smoke (60 min), the combination of both factors and no heat no smoke (control) was studied in six native species (two dominant grasses, two dominant shrubs and two annual fugitive herbs) of northwestern Patagonian grasslands. Seeds of the grasses Festuca pallescens and Stipa speciosa and the shrub Senecio bracteolatus (Asteraceae) germinated when they were exposed to heat shock, whereas seeds of the other shrub, Mulinum spinosum (Apiaceae), were killed by this fire cue. In grasses, probably the glume of caryopsis protected embryos from heat. Possibly, the seed size could explain the different responses of the two shrubs. Heat combined with smoke reduced seed germination for S. speciosa and S. bracteolatus. The heat could have scarified seeds and the longer exposure to smoke could have been toxic for embryos. The same treatment increased germination of the annual fugitive herb Boopis gracilis (Calyceraceae). We concluded that fire differentially affects the seedling recruitment of the studied species in the northwestern Patagonian grasslands.

  20. Planets around nearby M dwarfs

    NASA Astrophysics Data System (ADS)

    Jones, Hugh; Tuomi, M., Anglada-Escude, G., Feng, F., Butler, R.P., Vogt, S.

    2017-01-01

    Our current view of exoplanets is one derived primarily from Solar-like stars with a strong focus on understanding our Solar System. Our knowledge about the properties of exoplanets around the dominant stellar population by number, the so called low-mass stars or M dwarfs is much more cursory. Based on combining radial velocities of nearby M dwarfs obtained with HARPS, UVES and HIRES datea we find many new M dwarf planets. By computing the estimated detection probability function the occurrence rate of planets less than 10 Earth masses around nearby M dwarfs is found to be around two planet per star. The mass of radial velocity M dwarf planets is relatively much lower than the expected mass dependency based on stellar mass and thus it is inferred that planet formation efficiency around low mass stars is relatively impaired. Techniques to overcome the practical issue of obtaining good quality radial velocity data for M dwarfs are considered: (1) the wavelength sensitivity of radial velocity signals, (2) the combination of radial velocity data from different experiments for robust detection of small amplitude signals and (3) optimum selection of targets.

  1. Revealing Massive Black Holes in Dwarf Galaxies with X-rays

    NASA Astrophysics Data System (ADS)

    Reines, A.

    2014-07-01

    Supermassive black holes (BHs) live at the heart of essentially all massive galaxies, power AGN, and are thought to be important agents in the evolution of their hosts. However, the origin of these monster BHs is largely unknown. While direct observations of the first ``seeds" of supermassive BHs in the infant Universe are unobtainable with current telescopes, finding and studying dwarf galaxies hosting massive BHs today can provide valuable constraints on the masses, host galaxies, and formation mechanism of supermassive BH seeds. We have recently completed the first systematic search for AGN in dwarf galaxies using optical spectroscopy, increasing the number of known dwarfs with massive BHs by more than an order of magnitude (Reines et al. 2013). However, this optical search is biased towards BHs radiating at high fractions of their Eddington limit in galaxies with little on-going star formation. Alternative search techniques and diagnostics at other wavelengths are necessary to make further progress. I will discuss our efforts to find and study massive BHs in dwarf galaxies using observations at X-ray wavelengths. These observations are more sensitive to weakly accreting massive BHs and are already beginning to reveal massive BHs hidden at optical wavelengths in star-forming dwarf galaxies.

  2. Cold temperature increases winter fruit removal rate of a bird-dispersed shrub.

    SciTech Connect

    Charles Kwit; Douglas J. Levey; Cathryn H. Greenberg; Scott F. Pearson; John P. McCarty; Sarah Sargent

    2004-01-10

    Kwit, C., D. J. Levey; C. H. Greenberg, S. F. Pearson, J.P. McCarty, and S. Sargent. Cold temperature increases winter fruit removal rate of a bird-dispersed shrub. Oecologia. 139:30-34. Abstract: We tested the hypothesis that winter removal rates of fruits of wax myrtle, Myrica cerifera, are higher in colder winters. Over a 9-year period, we monitored M. cerifera fruit crops in 13 0.1-ha study plots in South Carolina, U.S.A. Peak ripeness occurred in November, whereas peak removal occurred in the coldest months, December and January. Mean time to fruit removal within study plots was positively correlated with mean winter temperatures, thereby supporting our hypothesis. This result, combined with the generally low availability of winter arthropods, suggests that fruit abundance may play a role in determining winter survivorship and distribution of permanent resident and short-distance migrant birds. From the plant's perspective, it demonstrates inter-annual variation in the temporal component of seed dispersal, with possible consequences for post-dispersal seed and seedling ecology.

  3. Seed germination and life history syndromes in the California chaparral

    USGS Publications Warehouse

    Keeley, J.E.

    1991-01-01

    Syndromes are life history responses that are correlated to environmental regimes and are shared by a group of species (Stebbins, 1974). In the California chaparral there are two syndromes contrasted by the timing of seedling recruitment relative to wildfires. One syndrome, here called the fire-recruiter or refractory seed syndrome, includes species (both resprouting and non-resprouting) which share the feature that the timing of seedling establishment is specialized to the first rainy season after fire. Included are woody, suffrutescent and annual life forms but no geophytes have this syndrome. These species are linked by the characteristic that their seeds have a dormancy which is readily broken by environmental stimuli such as intense heat shock or chemicals leached from charred wood. Such seeds are referred to as “refractory” and dormancy, in some cases, is due to seed coat impermeability (such seeds are commonly called hardseeded), but in other cases the mechanism is unknown. Seeds of some may require cold stratification and/or light in addition to fire related stimuli. In the absence of fire related cues, a portion or all of a species’ seed pool remains dormant. Most have locally dispersed seeds that persist in the soil seed bank until the site burns. Dispersal of propagules is largely during spring and summer which facilitates the avoidance of flowering and fruiting during the summer and fall drought. Within a life form (e.g., shrub, suffrutescent, etc.), the seeds of these species have less mass than those of species with non-refractory seeds and this possibly reflects the environmental favorableness of the postfire environment for seedling establishment. Regardless of when fire occurs, germination is normally delayed until late winter or early spring. In the absence of fire, or other disturbance, opportunities for population expansion are largely lacking for species with this syndrome. The other syndrome, here called the fire-resister or non

  4. [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.

  5. Environmental indices for common Michigan trees and shrubs.

    Treesearch

    Gary J. Brand

    1985-01-01

    Plants are indicators of environmental factors like moisture, nutrients, heat, and light. Semi-quantitative indices for these four factors were developed for 90 Michigan trees and shrubs. The indices and a tally of species present provide a simple evaluation of the environment of a forest stand and a useful management aid.

  6. Foliar uptake of fog in coastal California shrub species.

    PubMed

    Emery, Nathan C

    2016-11-01

    Understanding plant water uptake is important in ecosystems that experience periodic drought. In many Mediterranean-type climates like coastal California, plants are subject to significant drought and wildfire disturbance. During the dry summer months, coastal shrub species are often exposed to leaf wetting from overnight fog events. This study sought to determine whether foliar uptake of fog occurs in shrub species and how this uptake affects physiology and fuel condition. In a controlled greenhouse experiment, dominant California shrub species were exposed to isotopically labeled fog water and plant responses were measured. Potted plants were covered at the base to prevent root uptake. The deuterium label was detected in the leaves of four out of five species and in the stems of two of the species. While there was a minimal effect of foliar water uptake on live fuel moisture, several species had lower xylem tension and greater photosynthetic rates after overnight fog treatments, especially Salvia leucophylla. Coastal fog may provide a moisture source for many species during the summer drought, but the utilization of this water source may vary based on foliar morphology, phenology and plant water balance. From this study, it appears that drought-deciduous species (Artemisia californica and Salvia leucophylla) benefit more from overnight fog events than evergreen species (Adenostoma fasciculatum, Baccharis pilularis and Ceanothus megacarpus). This differential response to fog exposure among California shrub species may affect species distributions and physiological tolerances under future climate scenarios.

  7. Micropropagation of the endangered shrub pondberry (Lindera melissifolia [Walt.] Blume)

    Treesearch

    Tracy S. Hawkins; Nathan M. Schiff; Emile s. Gardiner; Theodore Leininger; Margaret S. Devall; A. Dan Wilson; Paul Hamel; Deborah D. McCown; Kristina Connor

    2007-01-01

    A micropropagation protocol using shoot cultures is described for Lindera melissifolia, a federally listed endangered shrub endemic to the southeastern United States. Stock plants were harvested from native L. melissifolia populations growing in the lower Mississippi Alluvial Valley. In vitro proliferation was on woody plant medium...

  8. Rooting cuttings of shrub species for plantings in California wildlands

    Treesearch

    Eamor C. Nord; J. R. Goodin

    1970-01-01

    Selected shrub species are being studied in southern California for their possible fuel volume or slow burning characteristics. In propagation tests, five species-fourwing, Gardner's, Nuttall's, and allscale saltbushes; and creeping sage - rooted successfully from green tip and ripewood stem cuttings taken in spring and fall and placed under intermittent mist...

  9. Effect of global climate change on rare trees and shrubs

    Treesearch

    Margaret S. Devall

    2008-01-01

    In the past, climate has fluctuated with periodsof cooler, warmer, drier or wetter weather thanat present. Plants have been able to adapt,but widespread, rapid warming could be disastrousfor rare trees and shrubs – i.e. thosenative species that are among an area’s most

  10. Recent emissions research in southwestern shrub and grassland fuels

    Treesearch

    David R. Weise; Wayne Miller; David R. Cocker; Heejung Jung; Seyedehsan Hosseini; Marko Princevac; Robert J. Yokelson; Ian Burling; Sheryl Akagi; Shawn Urbanski; WeiMin Hao

    2015-01-01

    While it is currently challenging to use prescribed burning in chaparral and other southwestern shrub fuel types due to many constraints, any such activities require smoke management planning. Information on fuels and emissions from chaparral were limited and based on older sampling systems. The DoD SERDP program funded a project to measure fuels and smoke emissions in...

  11. Herbicides for shrub and weed tree control in western Oregon.

    Treesearch

    H. Gratkowski

    1978-01-01

    Herbicides were tested on 16 common shrubs and weed trees during the past 24 years. The woody plants included snowbrush ceanothus, deerbrush ceanothus, mountain whitethorn, varnishleaf ceanothus, sprouting and nonsprouting forms of greenleaf manzanita, hairy manzanita, hoary manzanita, golden chinkapin, golden evergreenchinkapin, Saskatoon serviceberry, Pacific madrone...

  12. 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.

  13. Biodiversity, ecology, and microelement composition of Kyzylkum Desert shrubs (Uzbekistan)

    Treesearch

    Lyuba A. Kapustina

    2001-01-01

    Geobotanic research and large-scale mapping with the help of Geographical Information System (GIS) permit us to find out the present state of Kyzylkum Desert shrublands, regularities of plant communities distribution, and chemical composition of the main dominant shrubs. Zonal vegetation types were formed on the basis of Old Xerophilous and Old Mediterranean floras in...

  14. 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.

  15. 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...

  16. Experimental and numerical modeling of shrub crown fire initiation

    Treesearch

    Watcharapong Tachajapong; Jesse Lozano; Shakar Mahalingam; Xiangyang Zhou; David Weise

    2009-01-01

    The transition of fire from dry surface fuels to wet shrub crown fuels was studied using laboratory experiments and a simple physical model to gain a better understanding of the transition process. In the experiments, we investigated the effects of varying vertical distances between surface and crown fuels (crown base height), and of the wind speed on crown fire...

  17. Biomass Estimation for some Shrubs from Northeastern Minnesota

    Treesearch

    David F. Grigal; Lewis F. Ohmann

    1977-01-01

    Biomass prediction equations were developed for 23 northeastern Minnesota shrub species. The allowmetric function was used to predict leaf, current annual woody twig, stem, and total woody biomass (dry grass), using stem diameter class estimated to the nearest 0.25 cm class at 15 cm above ground level as the independent variable.

  18. Managing lntermountain rangelands - salt-desert shrub ranges

    Treesearch

    James P. Blaisdell; Ralph C. Holmgren

    1984-01-01

    This guide for range managers and users is a distillation of the most important research findings over the past 50 years. The research provides a strong scientific basis for planning and decisionmaking in the management of the saltdesert shrub rangelands of the Great Basin and lntermountain areas, which cover some 40 million acres. Much of the research...

  19. Common shrubs of chaparral and associated ecosystems of southern California

    Treesearch

    C. Eugene. Conrad

    1987-01-01

    This Guide presents taxonomic keys based on vegetative features of 132 southern California shrub and subshrub species found in an area bounded by the southern part of the coast ranges, the north and east sides of the transverse and peninsular ranges, and Mexico. The keys are supported with instructions and an extensive glossary. Species discussion includes a brief...

  20. [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.

  1. 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…

  2. 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...

  3. The Shrub Sciences Laboratory at 25 Years: Retrospective and prospective

    Treesearch

    E. Durant McArthur

    2001-01-01

    The Shrub Sciences Laboratory celebrated its 25th anniversary with the symposium documented by these proceedings and a ceremony honoring people instrumental in its establishment: Mr. A. Perry Plummer represented Forest Service Research and Development and Dr. Howard C. Stutz represented Brigham Young University. The laboratory came into being because of the research...

  4. Supplementing seed banks to rehabilitate disturbed Mojave Desert shrublands: Where do all the seeds go?

    USGS Publications Warehouse

    DeFalco, L.A.; Esque, T.C.; Nicklas, M.B.; Kane, J.M.

    2012-01-01

    Revegetation of degraded arid lands often involves supplementing impoverished seed banks and improving the seedbed, yet these approaches frequently fail. To understand these failures, we tracked the fates of seeds for six shrub species that were broadcast across two contrasting surface disturbances common to the Mojave Desert-sites compacted by concentrated vehicle use and trenched sites where topsoil and subsurface soils were mixed. We evaluated seedbed treatments that enhance soil-seed contact (tackifier) and create surface roughness while reducing soil bulk density (harrowing). We also explored whether seed harvesting by granivores and seedling suppression by non-native annuals influence the success of broadcast seeding in revegetating degraded shrublands. Ten weeks after treatments, seeds readily moved off of experimental plots in untreated compacted sites, but seed movements were reduced 32% by tackifier and 55% through harrowing. Harrowing promoted seedling emergence in compacted sites, particularly for the early-colonizing species Encelia farinosa, but tackifier was largely ineffective. The inherent surface roughness of trenched sites retained three times the number of seeds than compacted sites, but soil mixing during trench development likely altered the suitability of the seedbed thus resulting in poor seedling emergence. Non-native annuals had little influence on seed fates during our study. In contrast, the prevalence of harvester ants increased seed removal on compacted sites, whereas rodent activity influenced removal on trenched sites. Future success of broadcast seeding in arid lands depends on evaluating disturbance characteristics prior to seeding and selecting appropriate species and seasons for application. ?? 2010 Society for Ecological Restoration International.

  5. Shrubs as ecosystem engineers across an environmental gradient: effects on species richness and exotic plant invasion.

    PubMed

    Kleinhesselink, Andrew R; Magnoli, Susan M; Cushman, J Hall

    2014-08-01

    Ecosystem-engineering plants modify the physical environment and can increase species diversity and exotic species invasion. At the individual level, the effects of ecosystem engineers on other plants often become more positive in stressful environments. In this study, we investigated whether the community-level effects of ecosystem engineers also become stronger in more stressful environments. Using comparative and experimental approaches, we assessed the ability of a native shrub (Ericameria ericoides) to act as an ecosystem engineer across a stress gradient in a coastal dune in northern California, USA. We found increased coarse organic matter and lower wind speeds within shrub patches. Growth of a dominant invasive grass (Bromus diandrus) was facilitated both by aboveground shrub biomass and by growing in soil taken from shrub patches. Experimental removal of shrubs negatively affected species most associated with shrubs and positively affected species most often found outside of shrubs. Counter to the stress-gradient hypothesis, the effects of shrubs on the physical environment and individual plant growth did not increase across the established stress gradient at this site. At the community level, shrub patches increased beta diversity, and contained greater rarified richness and exotic plant cover than shrub-free patches. Shrub effects on rarified richness increased with environmental stress, but effects on exotic cover and beta diversity did not. Our study provides evidence for the community-level effects of shrubs as ecosystem engineers in this system, but shows that these effects do not necessarily become stronger in more stressful environments.

  6. Production of deerbrush and mountain whitethorn related to shrub volume and overstory crown closure

    Treesearch

    John G. Kie

    1985-01-01

    Annual production by deerbrush (Ceanothus integerrimus) and mountain whitethorn shrubs (C. cordulatus) in the south-central Sierra Nevada of California was related to shrub volume, volume squared, and overstory crown closure by regression models. production increased as shrub volume and volume squared increased, and decreased as...

  7. Simple methods for raising tree and shrub seedlings in Afghanistan [Dari version

    Treesearch

    R. Kasten Dumroese; Thomas D. Landis; Tara Luna; George Hernandez

    2008-01-01

    Growing trees and shrubs in nurseries is rewarding. You may wish to grow trees and shrubs for many reasons: 1) reforestation; 2) land stabilization; 3) fire wood (energy); 4) improving water quality; 5) urban landscapes; 6) providing shade; 7) producing fruits or nuts. If you enjoy growing plants, you are more likely to produce better trees and shrubs (Figure 1.1). In...

  8. Vegetation Trends in a 31-Year-Old Ponderosa Pine Plantation: Effect of Different Shrub Densities

    Treesearch

    Philip M. McDonald; Celeste S. Abbott

    1997-01-01

    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....

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

    USDA-ARS?s Scientific Manuscript database

    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...

  10. [Dynamics of allozyme heterozygosity in Siberian dwarf pine Pinus pumila (Pall.) Regel populations of the Russian Far East: comparison of embryos and maternal plants].

    PubMed

    Politov, D V; Belokon', M M; Belokon', Iu S

    2006-10-01

    Siberian dwarf pine, or Japanese stone pine, Pinus pumila (Pall.) Regel is widespread in eastern Siberia and the Russian Far East; the species is bird-dispersed and has a unique spreading or shrub living form. A mixed mating system (predominant outcrossing with self-pollination and matings of close relatives) leads to the formation of partly inbred progenies in P. pumila, as in the majority of other conifers. The question arises as to whether inbred individuals persist in the reproductive part of a population, which can have negative genetic consequences. The ADH, FDH, FEST, GDH, GOT, IDH, LAP, MNR, MDH, PEPCA, 6-PGD, PGI, PGM, SKDH, and SOD isozyme systems were analyzed to study the dynamics of heterozygosity in four P. pumila natural populations from the Pacific region, optimal for the species. Samples were collected in northern Koryakia, southern Kamchatka (two samples), and the Kunashir Island (Kurils). Wright's fixation index was used to estimate the level of inbreeding in embryos from dormant seeds resulting from free pollination and in maternal plants. A substantial level of inbreeding (F(IS) = 0.124-0.342) was observed in the embryo samples but not in three out of the four adult samples. The inbreeding level at the reproductive age was high only in the sample from Koryakia, which was explained by a relatively young age of plants in the population frequently affected by fires. A general increase in heterozygosity, characteristic of other conifers as well, was attributed to elimination of inbred progenies and by balancing selection for heterozygotes, which is a key factor maintaining allozyme polymorphism in populations.

  11. Nitrogen oxide pullution may spark seeds` growth

    SciTech Connect

    Malakoff, D.A.

    1997-05-23

    Could a common air pollutant be fooling the seeds of some wild plants into germinating when conditions are deadly to the seedlings? That`s the provocative question raised by a finding reported in this issue. Two ecologists have learned that the seeds of a common California wildflower can be prompted to germinate by exposure to nitrogen oxides, gases produced by both natural wildfires and motor vehicles and power plants. Botanists have long recognized that many plants inhabiting fire-prone areas, such as the and forests of the Southwest and the shrub-choked hillsides of southern California, grow best on freshly burned-over land. Scorched soils are often rich in nutrients, such as nitrogen and phosphorus released from burned vegetation, and they are free of shrubs that can otherwise shade sun-loving seedlings. For many of these phoenix like plants, a fire`s searing heat is what prompts them to rise from the ashes. Heat cracks the hard, outer coat of seeds that can lie dormant in the soil for decades. This allows water to seep in, spurring growth.

  12. Dwarf elliptical galaxies

    NASA Technical Reports Server (NTRS)

    Ferguson, Henry C.; Binggeli, Bruno

    1994-01-01

    Dwarf elliptical (dE) galaxies, with blue absolute magnitudes typically fainter than M(sub B) = -16, are the most numerous type of galaxy in the nearby universe. Tremendous advances have been made over the past several years in delineating the properties of both Local Group satellite dE's and the large dE populations of nearby clusters. We review some of these advances, with particular attention to how well currently availiable data can constrain (a) models for the formation of dE's, (b) the physical and evolutionary connections between different types of galaxies that overlap in the same portion of the mass-spectrum of galaxies, (c) the contribution of dE's to the galaxy luminosity functions in clusters and the field, (d) the star-forming histories of dE's and their possible contribution to faint galaxy counts, and (e) the clustering properties of dE's. In addressing these issues, we highlight the extent to which selection effects temper these constraints, and outline areas where new data would be particularly valuable.

  13. First-year establishment, biomass and seed production of early vs. late seral natives in two medusahead (Taeniatherum caput-meducae) invaded soils

    Treesearch

    Shauna M. Uselman; Keirith A. Snyder; Elizabeth A. Leger; Sara E. Duke

    2014-01-01

    Re-seeding efforts to restore or rehabilitate Great Basin rangelands invaded by exotic annual grasses are expensive and have generally achieved limited success. There is a need to identify new strategies to improve restoration outcomes. We tested the performance of a native early seral seed mix (annual forbs, early seral grasses and shrubs) with that of a native late...

  14. Grass-Shrub Associations over a Precipitation Gradient and Their Implications for Restoration in the Great Basin, USA.

    PubMed

    Holthuijzen, Maike F; Veblen, Kari E

    2015-01-01

    As environmental stress increases positive (facilitative) plant interactions often predominate. Plant-plant associations (or lack thereof) can indicate whether certain plant species favor particular types of microsites (e.g., shrub canopies or plant-free interspaces) and can provide valuable insights into whether "nurse plants" will contribute to seeding or planting success during ecological restoration. It can be difficult, however, to anticipate how relationships between nurse plants and plants used for restoration may change over large-ranging, regional stress gradients. We investigated associations between the shrub, Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), and three common native grasses (Poa secunda, Elymus elymoides, and Pseudoroegneria spicata), representing short-, medium-, and deep-rooted growth forms, respectively, across an annual rainfall gradient (220-350 mm) in the Great Basin, USA. We hypothesized that positive shrub-grass relationships would become more frequent at lower rainfall levels, as indicated by greater cover of grasses in shrub canopies than vegetation-free interspaces. We sampled aerial cover, density, height, basal width, grazing status, and reproductive status of perennial grasses in canopies and interspaces of 25-33 sagebrush individuals at 32 sites along a rainfall gradient. We found that aerial cover of the shallow rooted grass, P. secunda, was higher in sagebrush canopy than interspace microsites at lower levels of rainfall. Cover and density of the medium-rooted grass, E. elymoides were higher in sagebrush canopies than interspaces at all but the highest rainfall levels. Neither annual rainfall nor sagebrush canopy microsite significantly affected P. spicata cover. E. elymoides and P. spicata plants were taller, narrower, and less likely to be grazed in shrub canopy microsites than interspaces. Our results suggest that exploring sagebrush canopy microsites for restoration of native perennial grasses might

  15. Grass-Shrub Associations over a Precipitation Gradient and Their Implications for Restoration in the Great Basin, USA

    PubMed Central

    Holthuijzen, Maike F.; Veblen, Kari E.

    2015-01-01

    As environmental stress increases positive (facilitative) plant interactions often predominate. Plant-plant associations (or lack thereof) can indicate whether certain plant species favor particular types of microsites (e.g., shrub canopies or plant-free interspaces) and can provide valuable insights into whether “nurse plants” will contribute to seeding or planting success during ecological restoration. It can be difficult, however, to anticipate how relationships between nurse plants and plants used for restoration may change over large-ranging, regional stress gradients. We investigated associations between the shrub, Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), and three common native grasses (Poa secunda, Elymus elymoides, and Pseudoroegneria spicata), representing short-, medium-, and deep-rooted growth forms, respectively, across an annual rainfall gradient (220–350 mm) in the Great Basin, USA. We hypothesized that positive shrub-grass relationships would become more frequent at lower rainfall levels, as indicated by greater cover of grasses in shrub canopies than vegetation-free interspaces. We sampled aerial cover, density, height, basal width, grazing status, and reproductive status of perennial grasses in canopies and interspaces of 25–33 sagebrush individuals at 32 sites along a rainfall gradient. We found that aerial cover of the shallow rooted grass, P. secunda, was higher in sagebrush canopy than interspace microsites at lower levels of rainfall. Cover and density of the medium-rooted grass, E. elymoides were higher in sagebrush canopies than interspaces at all but the highest rainfall levels. Neither annual rainfall nor sagebrush canopy microsite significantly affected P. spicata cover. E. elymoides and P. spicata plants were taller, narrower, and less likely to be grazed in shrub canopy microsites than interspaces. Our results suggest that exploring sagebrush canopy microsites for restoration of native perennial grasses

  16. 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.

  17. Genome-Scale Transcriptome Analysis of the Desert Shrub Artemisia sphaerocephala

    PubMed Central

    Zhang, Lijing; Hu, Xiaowei; Miao, Xiumei; Chen, Xiaolong; Nan, Shuzhen; Fu, Hua

    2016-01-01

    Background Artemisia sphaerocephala, a semi-shrub belonging to the Artemisia genus of the Compositae family, is an important pioneer plant that inhabits moving and semi-stable sand dunes in the deserts and steppes of northwest and north-central China. It is very resilient in extreme environments. Additionally, its seeds have excellent nutritional value, and the abundant lipids and polysaccharides in the seeds make this plant a potential valuable source of bio-energy. However, partly due to the scarcity of genetic information, the genetic mechanisms controlling the traits and environmental adaptation capacity of A. sphaerocephala are unknown. Results Here, we present the first in-depth transcriptomic analysis of A. sphaerocephala. To maximize the representation of conditional transcripts, mRNA was obtained from 17 samples, including living tissues of desert-growing A. sphaerocephala, seeds germinated in the laboratory, and calli subjected to no stress (control) and high and low temperature, high and low osmotic, and salt stresses. De novo transcriptome assembly performed using an Illumina HiSeq 2500 platform resulted in the generation of 68,373 unigenes. We analyzed the key genes involved in the unsaturated fatty acid synthesis pathway and identified 26 A. sphaerocephala fad2 genes, which is the largest fad2 gene family reported to date. Furthermore, a set of genes responsible for resistance to extreme temperatures, salt, drought and a combination of stresses was identified. Conclusion The present work provides abundant genomic information for functional dissection of the important traits of A. sphaerocephala and contributes to the current understanding of molecular adaptive mechanisms of A. sphaerocephala in the desert environment. Identification of the key genes in the unsaturated fatty acid synthesis pathway could increase understanding of the biological regulatory mechanisms of fatty acid composition traits in plants and facilitate genetic manipulation of the

  18. Effects of flowering phenology and synchrony on the reproductive success of a long-flowering shrub.

    PubMed

    Rodríguez-Pérez, Javier; Traveset, Anna

    2016-02-02

    Flowering phenology and synchrony with biotic and abiotic resources are crucial traits determining the reproductive success in insect-pollinated plants. In seasonal climates, plants flowering for long periods should assure reproductive success when resources are more predictable. In this work, we evaluated the relationship between flowering phenology and synchrony and reproductive success in Hypericum balearicum, a shrub flowering all year round but mainly during spring and summer. We studied two contrasting localities (differing mostly in rainfall) during 3 years, and at different biological scales spanning from localities to individual flowers and fruits. We first monitored (monthly) flowering phenology and reproductive success (fruit and seed set) of plants, and assessed whether in the locality with higher rainfall plants had longer flowering phenology and synchrony and relatively higher reproductive success within or outside the flowering peak. Secondly, we censused pollinators on H. balearicum individuals and measured reproductive success along the flowering peak of each locality to test for an association between (i) richness and abundance of pollinators and (ii) fruit and seed set, and seed weight. We found that most flowers (∼90 %) and the highest fruit set (∼70 %) were produced during the flowering peak of each locality. Contrary to expectations, plants in the locality with lower rainfall showed more relaxed flowering phenology and synchrony and set more fruits outside the flowering peak. During the flowering peak of each locality, the reproductive success of early-flowering individuals depended on a combination of both pollinator richness and abundance and rainfall; by contrast, reproductive success of late-flowering individuals was most dependent on rainfall. Plant species flowering for long periods in seasonal climates, thus, appear to be ideal organisms to understand how flowering phenology and synchrony match with biotic and abiotic resources, and

  19. Genome-Scale Transcriptome Analysis of the Desert Shrub Artemisia sphaerocephala.

    PubMed

    Zhang, Lijing; Hu, Xiaowei; Miao, Xiumei; Chen, Xiaolong; Nan, Shuzhen; Fu, Hua

    2016-01-01

    Artemisia sphaerocephala, a semi-shrub belonging to the Artemisia genus of the Compositae family, is an important pioneer plant that inhabits moving and semi-stable sand dunes in the deserts and steppes of northwest and north-central China. It is very resilient in extreme environments. Additionally, its seeds have excellent nutritional value, and the abundant lipids and polysaccharides in the seeds make this plant a potential valuable source of bio-energy. However, partly due to the scarcity of genetic information, the genetic mechanisms controlling the traits and environmental adaptation capacity of A. sphaerocephala are unknown. Here, we present the first in-depth transcriptomic analysis of A. sphaerocephala. To maximize the representation of conditional transcripts, mRNA was obtained from 17 samples, including living tissues of desert-growing A. sphaerocephala, seeds germinated in the laboratory, and calli subjected to no stress (control) and high and low temperature, high and low osmotic, and salt stresses. De novo transcriptome assembly performed using an Illumina HiSeq 2500 platform resulted in the generation of 68,373 unigenes. We analyzed the key genes involved in the unsaturated fatty acid synthesis pathway and identified 26 A. sphaerocephala fad2 genes, which is the largest fad2 gene family reported to date. Furthermore, a set of genes responsible for resistance to extreme temperatures, salt, drought and a combination of stresses was identified. The present work provides abundant genomic information for functional dissection of the important traits of A. sphaerocephala and contributes to the current understanding of molecular adaptive mechanisms of A. sphaerocephala in the desert environment. Identification of the key genes in the unsaturated fatty acid synthesis pathway could increase understanding of the biological regulatory mechanisms of fatty acid composition traits in plants and facilitate genetic manipulation of the fatty acid composition of oil

  20. Effects of flowering phenology and synchrony on the reproductive success of a long-flowering shrub

    PubMed Central

    Rodríguez-Pérez, Javier; Traveset, Anna

    2016-01-01

    Flowering phenology and synchrony with biotic and abiotic resources are crucial traits determining the reproductive success in insect-pollinated plants. In seasonal climates, plants flowering for long periods should assure reproductive success when resources are more predictable. In this work, we evaluated the relationship between flowering phenology and synchrony and reproductive success in Hypericum balearicum, a shrub flowering all year round but mainly during spring and summer. We studied two contrasting localities (differing mostly in rainfall) during 3 years, and at different biological scales spanning from localities to individual flowers and fruits. We first monitored (monthly) flowering phenology and reproductive success (fruit and seed set) of plants, and assessed whether in the locality with higher rainfall plants had longer flowering phenology and synchrony and relatively higher reproductive success within or outside the flowering peak. Secondly, we censused pollinators on H. balearicum individuals and measured reproductive success along the flowering peak of each locality to test for an association between (i) richness and abundance of pollinators and (ii) fruit and seed set, and seed weight. We found that most flowers (∼90 %) and the highest fruit set (∼70 %) were produced during the flowering peak of each locality. Contrary to expectations, plants in the locality with lower rainfall showed more relaxed flowering phenology and synchrony and set more fruits outside the flowering peak. During the flowering peak of each locality, the reproductive success of early-flowering individuals depended on a combination of both pollinator richness and abundance and rainfall; by contrast, reproductive success of late-flowering individuals was most dependent on rainfall. Plant species flowering for long periods in seasonal climates, thus, appear to be ideal organisms to understand how flowering phenology and synchrony match with biotic and abiotic resources, and

  1. The late-M dwarfs

    NASA Astrophysics Data System (ADS)

    Bessell, M. S.

    1991-02-01

    Far-red spectra and VRIJHK photometry have been obtained for a sample of late-M dwarfs selected on the basis of large reduced red magnitudes from the LHS Catalog. Half of the stars in the three faintest 1 mag bins are late-M stars, the other red stars are metallic-hydride subdwarfs. Relations between various colors for the late-M dwarfs are investigated. Of all the colors I - K most reliably correlates with spectral type. FeH bands near 9900 A are clearly seen in the spectra of all dwarf stars later than M5. Two stars cooler than VB10, and similar in temperature to LHS2924 have been identified; both have H-alpha in emission and appear variable in magnitude and R - I color; one is a flare star. The other stars are of earlier spectral type and resemble W359 and VB8. The observed MI, I - K main sequence is in good agreement with the IG theoretical main sequence of Stringfellow, and the faintest stars could be about 0.09 solar mass red dwarfs or lower mass brown dwarfs.

  2. White dwarf kinematics versus mass

    NASA Astrophysics Data System (ADS)

    Wegg, Christopher; Phinney, E. Sterl

    2012-10-01

    We investigated the relationship between the kinematics and mass of young (<3 × 108 yr) white dwarfs using proper motions. Our sample is taken from the colour-selected catalogues of the Sloan Digital Sky Survey and the Palomar-Green Survey, both of which have spectroscopic temperature and gravity determinations. We find that the dispersion decreases with increasing white dwarf mass. This can be explained as a result of less scattering by objects in the Galactic disc during the shorter lifetime of their more massive progenitors. A direct result of this is that white dwarfs with high mass have a reduced scale height, and hence their local density is enhanced over their less massive counterparts. In addition, we have investigated whether the kinematics of the highest mass white dwarfs (>0.95 M⊙) are consistent with the expected relative contributions of single star evolution and mergers. We find that the kinematics are consistent with the majority of high-mass white dwarfs being formed through single star evolution.

  3. Distinguishing CDM dwarfs from SIDM dwarfs in baryonic simulations

    NASA Astrophysics Data System (ADS)

    Strickland, Emily; Fitts, Alex B.; Boylan-Kolchin, Michael

    2017-06-01

    Dwarf galaxies in the nearby Universe are the most dark-matter-dominated systems known. They are therefore natural probes of the nature of dark matter, which remains unknown. Our collaboration has performed several high-resolution cosmological zoom-in simulations of isolated dwarf galaxies. We simulate each galaxy in standard cold dark matter (ΛCDM) as well as self-interacting dark matter (SIDM, with a cross section of σ/m ~ 1 cm2/g), both with and without baryons, in order to identify distinguishing characteristics between the two. The simulations are run using GIZMO, a meshless-finite-mass hydrodynamical code, and are part of the Feedback in Realistic Environments (FIRE) project. By analyzing both the global properties and inner structure of the dwarfs in varying dark matter prescriptions, we provide a side-by-side comparison of isolated, dark-matter-dominated galaxies at the mass scale where differences in the two models of dark matter are thought to be the most obvious. We find that the edge of classical dwarfs and ultra-faint dwarfs (at stellar masses of ~105 solar masses) provides the clearest window for distinguishing between the two theories. At these low masses, our SIDM galaxies have a cored inner density profile, while their CDM counterparts have “cuspy” centers. The SIDM versions of each galaxy also have measurably lower stellar velocity dispersions than their CDM counterparts. Future observations of ultra faint dwarfs with JWST and 30-m telescopes will be able to discern whether such alternate theories of dark matter are viable.

  4. Shrub morpho-types as indicator for the water flow energy - Tivoli travertine case (Central Italy)

    NASA Astrophysics Data System (ADS)

    Erthal, Marcelle Marques; Capezzuoli, Enrico; Mancini, Alessandro; Claes, Hannes; Soete, Jeroen; Swennen, Rudy

    2017-01-01

    Travertines from Tivoli area (Central Italy) possess abundant shrub-like fabrics that are laterally continuous over hundreds of square meters. They occur dominantly in horizontal layers with aggradational and progradational stacking patterns. Their fabrics and morphologies are remarkably similar to the shrubs lithotypes reported in literature for the Pre-Salt reservoirs, offshore Brazil and Angola, with huge oil accumulations. Petrographic and micro-computer tomography analyses allowed the identification of six shrub morpho-types (i.e., narrow dendriform, wide dendriform, fili dendriform, arborescent, arbustiform and pustular). Dendriform shrubs are the most common lithotype in Tivoli area, and three different subtypes could be distinguished according to the arrangement of their branches. The shrubs consist largely of peloidal micritic aggregates engulfed in spar calcite, ranging in average from 1 to 3 cm in height. The shrubs are interpreted to have developed in very shallow extensive waterlogged slightly inclined flat areas, changing laterally into a slope system with crusts as the main lithotype. Changes in the hydrodynamic conditions with episodes of stagnancy influenced the shrub morpho-types making them very variegated. Shrub morphologies likely reflect specific (micro-) environments that are controlled by water flow rates, evaporation and microbial activity. The latter processes influenced shrub fabric and morphology. Under high flow conditions, CO2 degassing is the main process leading to carbonate precipitation. Consequently, denser and tightly packed morphologies will precipitate, composing mainly the crust lithotype. In this scenario microbes are less dominant. Dendriform shrubs, with narrow, wide and fili morphologies are interpreted to occur in moderate to low energy water flows. Narrow dendriform shrubs reflect faster flowing conditions, with decreasing impact of flow on the morphological aspects from wide dendriform shrubs to fili dendriform shrubs

  5. Effects of a warmer climate on seed germination in the subarctic

    PubMed Central

    Milbau, Ann; Graae, Bente Jessen; Shevtsova, Anna; Nijs, Ivan

    2009-01-01

    Background and Aims In a future warmer subarctic climate, the soil temperatures experienced by dispersed seeds are likely to increase during summer but may decrease during winter due to expected changes in snow depth, duration and quality. Because little is known about the dormancy-breaking and germination requirements of subarctic species, how warming may influence the timing and level of germination in these species was examined. Methods Under controlled conditions, how colder winter and warmer summer soil temperatures influenced germination was tested in 23 subarctic species. The cold stratification and warm incubation temperatures were derived from real soil temperature measurements in subarctic tundra and the temperatures were gradually changed over time to simulate different months of the year. Key Results Moderate summer warming (+2·5 °C) substantially accelerated germination in all but four species but did not affect germination percentages. Optimum germination temperatures (20/10°C) further decreased germination time and increased germination percentages in three species. Colder winter soil temperatures delayed the germination in ten species and decreased the germination percentage in four species, whereas the opposite was found in Silene acaulis. In most species, the combined effect of a reduced snow cover and summer warming resulted in earlier germination and thus a longer first growing season, which improves the chance of seedling survival. In particular the recruitment of (dwarf) shrubs (Vaccinium myrtillus, V. vitis-idaea, Betula nana), trees (Alnus incana, Betula pubescens) and grasses (Calamagrostis lapponica, C. purpurea) is likely to benefit from a warmer subarctic climate. Conclusions Seedling establishment is expected to improve in a future warmer subarctic climate, mainly by considerably earlier germination. The magnitudes of the responses are species-specific, which should be taken into account when modelling population growth and migration

  6. Mid-infrared Colors of Dwarf Galaxies: Young Starbursts Mimicking Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Hainline, Kevin N.; Reines, Amy E.; Greene, Jenny E.; Stern, Daniel

    2016-12-01

    Searching for active galactic nuclei (AGNs) in dwarf galaxies is important for our understanding of the seed black holes that formed in the early universe. Here, we test infrared selection methods for AGN activity at low galaxy masses. Our parent sample consists of ˜18,000 nearby dwarf galaxies (M * < 3 × 109 M ⊙, z < 0.055) in the Sloan Digital Sky Survey with significant detections in the first three bands of the AllWISE data release from the Wide-field Infrared Survey Explorer (WISE). First, we demonstrate that the majority of optically selected AGNs in dwarf galaxies are not selected as AGNs using WISE infrared color diagnostics and that the infrared emission is dominated by the host galaxies. We then investigate the infrared properties of optically selected star-forming dwarf galaxies, finding that the galaxies with the reddest infrared colors are the most compact, with blue optical colors, young stellar ages, and large specific star formation rates. These results indicate that great care must be taken when selecting AGNs in dwarf galaxies using infrared colors, as star-forming dwarf galaxies are capable of heating dust in such a way that mimics the infrared colors of more luminous AGNs. In particular, a simple W1-W2 color cut alone should not be used to select AGNs in dwarf galaxies. With these complications in mind, we present a sample of 41 dwarf galaxies that fall in the WISE infrared color space typically occupied by more luminous AGNs and that are worthy of follow-up observations.

  7. Brown dwarfs from decaying accreting triple systems

    NASA Astrophysics Data System (ADS)

    Umbreit, S.; Burkert, A.; Henning, Th.; Mikkola, S.; Spurzem, R.

    We investigate the dynamical decay of non-hierarchical accreting triple systems and its implications on the ejection model as Brown Dwarf formation scenario. We analyse the end states of these systems and determine the fraction of Brown Dwarfs formed as well as the semi-major axis distribution of the formed Brown Dwarf binaries. Furthermore we estimate how destructive such triple interactions can be to disks surrounding the Brown Dwarfs.

  8. Uncoupling the effects of seed predation and seed dispersal by granivorous ants on plant population dynamics.

    PubMed

    Arnan, Xavier; Molowny-Horas, Roberto; Rodrigo, Anselm; Retana, Javier

    2012-01-01

    Secondary seed dispersal is an important plant-animal interaction, which is central to understanding plant population and community dynamics. Very little information is still available on the effects of dispersal on plant demography and, particularly, for ant-seed dispersal interactions. As many other interactions, seed dispersal by animals involves costs (seed predation) and benefits (seed dispersal), the balance of which determines the outcome of the interaction. Separate quantification of each of them is essential in order to understand the effects of this interaction. To address this issue, we have successfully separated and analyzed the costs and benefits of seed dispersal by seed-harvesting ants on the plant population dynamics of three shrub species with different traits. To that aim a stochastic, spatially-explicit individually-based simulation model has been implemented based on actual data sets. The results from our simulation model agree with theoretical models of plant response dependent on seed dispersal, for one plant species, and ant-mediated seed predation, for another one. In these cases, model predictions were close to the observed values at field. Nonetheless, these ecological processes did not affect in anyway a third species, for which the model predictions were far from the observed values. This indicates that the balance between costs and benefits associated to secondary seed dispersal is clearly related to specific traits. This study is one of the first works that analyze tradeoffs of secondary seed dispersal on plant population dynamics, by disentangling the effects of related costs and benefits. We suggest analyzing the effects of interactions on population dynamics as opposed to merely analyzing the partners and their interaction strength.

  9. Uncoupling the Effects of Seed Predation and Seed Dispersal by Granivorous Ants on Plant Population Dynamics

    PubMed Central

    Arnan, Xavier; Molowny-Horas, Roberto; Rodrigo, Anselm; Retana, Javier

    2012-01-01

    Secondary seed dispersal is an important plant-animal interaction, which is central to understanding plant population and community dynamics. Very little information is still available on the effects of dispersal on plant demography and, particularly, for ant-seed dispersal interactions. As many other interactions, seed dispersal by animals involves costs (seed predation) and benefits (seed dispersal), the balance of which determines the outcome of the interaction. Separate quantification of each of them is essential in order to understand the effects of this interaction. To address this issue, we have successfully separated and analyzed the costs and benefits of seed dispersal by seed-harvesting ants on the plant population dynamics of three shrub species with different traits. To that aim a stochastic, spatially-explicit individually-based simulation model has been implemented based on actual data sets. The results from our simulation model agree with theoretical models of plant response dependent on seed dispersal, for one plant species, and ant-mediated seed predation, for another one. In these cases, model predictions were close to the observed values at field. Nonetheless, these ecological processes did not affect in anyway a third species, for which the model predictions were far from the observed values. This indicates that the balance between costs and benefits associated to secondary seed dispersal is clearly related to specific traits. This study is one of the first works that analyze tradeoffs of secondary seed dispersal on plant population dynamics, by disentangling the effects of related costs and benefits. We suggest analyzing the effects of interactions on population dynamics as opposed to merely analyzing the partners and their interaction strength. PMID:22880125

  10. Seed dispersal limitations shift over time in tropical forest restoration.

    PubMed

    Reid, J Leighton; Holl, Karen D; Zahawi, Rakan A

    2015-06-01

    Past studies have shown that tropical forest regeneration on degraded farmlands is initially limited by lack of seed dispersal, but few studies have tracked changes in abundance and composition of seed rain past the first few years after land abandonment. We measured seed rain for 12 months in 10 6-9-year-old restoration sites and five mature, reference forests in southern Costa Rica in order to learn (1) if seed rain limitation persists past the first few years of regeneration; (2) how restoration treatments influence seed community structure and composition; and (3) whether seed rain limitation is contingent on landscape context. Each restoration site contained three 0.25-ha treatment plots: (1) a naturally regenerating control, (2) tree islands, and (3) a mixed-species tree plantation. Sites spanned a deforestation gradient with 9-89% forest area within 500 m around the treatment plots. Contrary to previous studies, we found that tree seeds were abundant and ubiquitous across all treatment plots (585.1 ± 142.0 seeds · m(-2) · yr(-1) [mean ± SE]), indicating that lack of seed rain ceased to limit forest regeneration within the first decade of recovery. Pioneer trees and shrubs comprised the vast majority of seeds, but compositional differences between restoration sites and reference forests were driven by rarer, large-seeded species. Large, animal-dispersed tree seeds were more abundant in tree islands (4.6 ± 2.9 seeds · m(-2) · yr(-1)) and plantations (5.8 ± 3.0 seeds · m(-2) · yr(-1)) than control plots (0.2 ± 0.1 seeds · m(-2) · yr(-1)), contributing to greater tree species richness in actively restored plots. Planted tree species accounted for < 1% of seeds. We found little evidence for landscape forest cover effects on seed rain, consistent with previous studies. We conclude that seed rain limitation shifted from an initial, complete lack of tree seeds to a specific limitation on large-seeded, mature forest species over the first decade

  11. Induced abnormality in Mir- and earth grown super dwarf wheat

    NASA Astrophysics Data System (ADS)

    Bubenheim, D. L.; Stieber, J.; Campbell, W. F.; Salisbury, F. B.; Levinski, M.; Sytchev, V.; Pdolsky, I.; Chernova, L.

    Super-dwarf wheat grown on the Mir space station using the Svet ``Greenhouse'' exhibited morphological, metabolic and reproductive abnormalities compared with Earth-grown wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of `Super-Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen gains, however, contained only one nuclei, while normal viable pollen is tri-nucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was the presence of a high level of atmospheric ethylene (1,200 ppb). Ground studies conducted by exposing `Super-Dwarf' wheat to ethylene just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples.

  12. Induced abnormality in Mir- and Earth grown Super Dwarf wheat

    NASA Technical Reports Server (NTRS)

    Bubenheim, D. L.; Stieber, J.; Campbell, W. F.; Salisbury, F. B.; Levinski, M.; Sytchev, V.; Podolsky, I.; Chernova, L.; Pdolsky, I.

    2003-01-01

    Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with Earth-grown wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super-Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen gains, however, contained only one nuclei, while normal viable pollen is tri-nucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was the presence of a high level of atmospheric ethylene (1,200 ppb). Ground studies conducted by exposing 'Super-Dwarf' wheat to ethylene just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples. c2002 Published by Elsevier Science Ltd on behalf of COSPAR.

  13. Induced abnormality in Mir- and Earth grown Super Dwarf wheat

    NASA Technical Reports Server (NTRS)

    Bubenheim, D. L.; Stieber, J.; Campbell, W. F.; Salisbury, F. B.; Levinski, M.; Sytchev, V.; Podolsky, I.; Chernova, L.; Pdolsky, I.

    2003-01-01

    Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with Earth-grown wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super-Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen gains, however, contained only one nuclei, while normal viable pollen is tri-nucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was the presence of a high level of atmospheric ethylene (1,200 ppb). Ground studies conducted by exposing 'Super-Dwarf' wheat to ethylene just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples. c2002 Published by Elsevier Science Ltd on behalf of COSPAR.

  14. The Dusty Accretion of Polluted White Dwarfs

    NASA Astrophysics Data System (ADS)

    Bonsor, A.; Farihi, J.; Wyatt, M. C.; van Lieshout, R.

    2017-03-01

    Infrared observations of polluted white dwarfs provide key insights into the accretion processes in action. The standard model for the observed infrared excesses is a flat, opaque, dust disc. The infrared observations are inconsistent with the presence of such a disc around all polluted white dwarfs. We discuss potential explanations for the absence of an infrared excess for many polluted white dwarfs.

  15. 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.

  16. How, Now, Brown Dwarfs?

    NASA Astrophysics Data System (ADS)

    Brecher, Kenneth

    2009-01-01

    The vocabulary of astronomy is riddled with colorful names for stars, from red giants to blue stragglers. Objects with masses between roughly .01 and .1 solar masses are called "brown dwarfs". Do they - could they - ever actually appear brown? Color is not a one-dimensional physical parameter like wavelength. It is a complex, psychophysical phenomenon involving not only three degrees of freedom - hue (often incorrectly equated with "color"), saturation and brightness - but also observational context. The perceptual nature of color has been known since Newton wrote in his "Opticks” in 1704: "For the Rays to speak properly are not coloured. In them there is nothing else than a certain Power and disposition to stir up a Sensation of this or that Colour.” To most observers, the 2000 or so naked eye stars observable from the northern hemisphere all appear white, with the half dozen exceptions which look reddish/orange like Betelgeuse, Arcturus and Antares. But what color would Betelgeuse (effective temperature 3600 K) appear at a distance of, say, 100 times the Earth-Sun separation? Not red. In fact, it has a temperature about 40% higher than that of an ordinary incandescent light bulb. It would appear white (or yellowish)! Can a very cool radiating (emissive) object ever appear brown? What is brown anyway? It is not a primary or even secondary color. In this presentation, we will explore the nature and meaning of "brown” by the use of several physical and computer demonstrations developed as part of "Project LITE- Light Inquiry Through Experiments", an educational materials development project. These demonstrations show that an isolated thermally radiating object will never appear brown. Hence the term "Brown Dwarf” is as nonsensical as the phrase "How, Now, Brown Cow?". Project LITE is supported by the NSF through DUE Grant # 0715975.

  17. Pondberry (Lindera   melissifolia, Lauraceae) seed and seedling dispersers and predators

    Treesearch

    Andreza M. Martins; Fernanda M. Abilio; Plinio Gonçalves de Oliveira; Raquel Partelli Feltrin; Fernanda Scheffer Alves de Lima; Priscilla de O. Antonelli; Daniela Teixeira Vilela; Carl G. Smith III; Collin Tidwell; Paul Hamel; Margaret Devall; Kristina Connor; Theodor Leininger; Nathan Schiff; A. Dan Wilson

    2015-01-01

    Pondberry (Lindera melissifolia(Walter) Blume) is an endangered dioecious, clonal shrub that grows in periodically flooded forests of the southeastern United States. The probability of survival of dispersed pondberry seeds and new germinants is unknown, but few seedlings are noted in the forest. This study was undertaken to: (1) identify herbivores...

  18. Potential roles of fish, birds, and water in swamp privet (Forestiera acuminata) seed dispersal

    Treesearch

    Susan B. Adams; Paul B. Hamel; Kristina Connor; Bryce Burke; Emile S. Gardiner; David Wise

    2007-01-01

    Forestiera acuminata (swamp privet) is a common wetland shrub/small tree native to the southeastern United States. We examined several possible dispersal avenues for the plant. We tested germination of seeds exposed to various treatments, including passage through Ictalurus punctatus (Channel Catfi sh) guts, and conducted other...

  19. Germination response of Apocynum venetum seeds to temperature and water potential

    USDA-ARS?s Scientific Manuscript database

    Apocynum venetum (commonly known as luobuma or rafuma) is a shrub that is native to Eurasia. It is economically important for sand fixation, forage production, honey production, medicine, fiber and fuel. Rapid and uniform seed germination is critical for successful crop establishment and vegetation ...

  20. Seeds in the Organic Layers and Soil of Four Beech-Birch-Maple Stands

    Treesearch

    Raymond E. Graber; Donald F. Thompson

    1978-01-01

    Forest floor samples were collected in northern hardwood stands 5, 38, 95, and 200+ years old. The seeds contained in these samples were germinated in a greenhouse. Thirty-five species of herbs, shrubs, and trees were identified. The largest number of species, 23, were from the 5-year-old stand. The oldest stand had the fewest species, 17. Rubus and...

  1. Brown Dwarf Weather (Artist's Concept)

    NASA Image and Video Library

    2017-06-06

    This artist's concept shows what the weather might look like on cool star-like bodies known as brown dwarfs. These giant balls of gas start out life like stars, but lack the mass to sustain nuclear fusion at their cores, and instead, fade and cool with time. Observations from NASA's Spitzer Space Telescope suggest that most brown dwarfs are roiling with one or more planet-size storms akin to Jupiter's "Great Red Spot." https://photojournal.jpl.nasa.gov/catalog/PIA21475

  2. 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

  3. 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.

  4. The effect of polyethylene glycol on intake of Mediterranean shrubs by sheep and goats.

    PubMed

    Rogosic, J; Pfister, J A; Provenza, F D; Pavlicevic, J

    2008-12-01

    Poor nutritional quality and increased content of secondary compounds can reduce consumption of Mediterranean shrubs by herbivores. In 2 sequential trials, we examined the effect of polyethylene glycol (PEG) and number of shrub species offered on daily intake of Mediterranean shrubs by 12 sheep and 12 goats. The PEG (25 g) was fed to experimental animals with barley. In trial 1 (6 shrubs), goats ate more (P = 0.0008) daily total shrub biomass than did sheep (60.7 vs. 45.9 +/- 2.6 g/kg of BW). There was a trend (P = 0.08) toward a positive PEG effect on total shrub intake, with PEG-supplemented animals consuming more total shrubs than controls (56.7 vs. 50.0 +/- 2.6 g/kg of BW). Trial 2 (using 3 shrubs) was a continuation of trial 1, except that animals were given less barley and treatment animals were given more PEG (50 g). Both sheep and goats showed a numerical decrease in total shrub intake from trial 1 to trial 2. Sheep receiving PEG ate more (P = 0.002) total shrubs than did controls, but no PEG effect was found for goats. Thus, PEG had a greater influence on sheep than goats when only 3 shrubs were offered, a result that may be related to the fact that fewer shrubs with complementary secondary compounds were offered and that goats appear to have a greater ability to consume and detoxify secondary compounds from Mediterranean shrubs. Overall, as the number and diversity of shrubs offered increased, supplemental PEG had less effect on increasing intake for both goats and sheep.

  5. Adapting to alcohol: Dwarf hamster (Phodopus campbelli) ethanol consumption, sensitivity, and hoard fermentation.

    PubMed

    Lupfer, Gwen; Murphy, Eric S; Merculieff, Zoe; Radcliffe, Kori; Duddleston, Khrystyne N

    2015-06-01

    Ethanol consumption and sensitivity in many species are influenced by the frequency with which ethanol is encountered in their niches. In Experiment 1, dwarf hamsters (Phodopus campbelli) with ad libitum access to food and water consumed high amounts of unsweetened alcohol solutions. Their consumption of 15%, but not 30%, ethanol was reduced when they were fed a high-fat diet; a high carbohydrate diet did not affect ethanol consumption. In Experiment 2, intraperitoneal injections of ethanol caused significant dose-related motor impairment. Much larger doses administered orally, however, had no effect. In Experiment 3, ryegrass seeds, a common food source for wild dwarf hamsters, supported ethanol fermentation. Results of these experiments suggest that dwarf hamsters may have adapted to consume foods in which ethanol production naturally occurs.

  6. Induced Abnormality In Mir- and Earth-Grown Super Dwarf Wheat

    NASA Technical Reports Server (NTRS)

    Bubenheim, David L.; Stieber, Joseph; Campbell, William F.; Salisbury, Frank B.; Levinski, Margarita; Sytchev, Vladimir; Podolsky, Igor; Chernova, Lola; Ivanova, Irene; Kliss, Mark (Technical Monitor)

    1998-01-01

    Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with normal wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen grains however, contain only one nucleus, while normal viable pollen is trinucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was identified - a high level of atmospheric ethylene (1200 ppb). Ground studies conducted exposing "Super-dwarf" wheat to ethylene at just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples.

  7. Induced Abnormality In Mir- and Earth-Grown Super Dwarf Wheat

    NASA Technical Reports Server (NTRS)

    Bubenheim, David L.; Stieber, Joseph; Campbell, William F.; Salisbury, Frank B.; Levinski, Margarita; Sytchev, Vladimir; Podolsky, Igor; Chernova, Lola; Ivanova, Irene; Kliss, Mark (Technical Monitor)

    1998-01-01

    Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with normal wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen grains however, contain only one nucleus, while normal viable pollen is trinucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was identified - a high level of atmospheric ethylene (1200 ppb). Ground studies conducted exposing "Super-dwarf" wheat to ethylene at just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples.

  8. Four new triterpenes from the endemic relict shrub Tetraena mongolica.

    PubMed

    Tang, Sheng-An; Ding, Lin-Lin; Zhai, Hui-Yuan; Qin, Nan; Duan, Hong-Quan

    2012-01-01

    A chemical investigation of the endemic relict shrub Tetraena mongolica led to the isolation of four new triterpenes: 11α,12α:13β,28-diepoxyoleanane-3β-yl trans-caffeate (1), 3β-hydroxy-11α,12α-epoxyoleanane-28-al (2), olean-11-en-28-al-3β-yl trans-caffeate (3), and 28-acetoxy-olean-12-en-3β-yl trans-caffeate (4). Their structures were elucidated by extensive spectroscopic methods.

  9. 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.

  10. Estimating live fuels for shrubs and herbs with BIOPAK.

    Treesearch

    Joseph E. Means; Olga N Krankina; Hao Jiang; Hongyan. Li

    1996-01-01

    This paper describes use of BIOPAK to calculate size classes of live fuels for shrubs and herbs. A library of equations to estimate such fuels in the Pacific Northwest and northern Rocky Mountains is presented and used in an example. These methods can be used in other regions if the user first enters fuel size-class equations for a given region into a new library by...

  11. 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.

  12. Soil microbial diversity in the vicinity of desert shrubs.

    PubMed

    Saul-Tcherkas, Vered; Unc, Adrian; Steinberger, Yosef

    2013-04-01

    Water and nutrient availability are the major limiting factors of biological activity in arid and semiarid ecosystems. Therefore, perennial plants have developed different ecophysiological adaptations to cope with harsh conditions. The chemical profile of the root exudates varies among plant species and this can induce variability in associated microbial populations. We examined the influence of two shrubs species, Artemisia sieberi and Noaea mucronata, on soil microbial diversity. Soil samples were collected monthly, from December 2006 to November 2007, near canopies of both shrubs (0-10-cm depth). Samples were used for abiotic tests and determination of soil bacterial diversity. No significant differences were found in the abiotic variables (soil moisture, total organic matter, and total soluble nitrogen (TSN)) between soil samples collected from under the two shrubs during the study period. No obvious differences in the Shannon-Weaver index, evenness values, or total phylogenetic distances were found for the soil microbial communities. However, detailed denaturing gradient gel electrophoresis (DGGE) clustering as well as taxonomic diversity analyses indicated clear shifts in the soil microbial community composition. These shifts were governed by seasonal variability in water availability and, significantly, by plant species type.

  13. 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.

    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.

  14. Seed proteomics.

    PubMed

    Miernyk, Ján A; Hajduch, Martin

    2011-04-01

    Seeds comprise a protective covering, a small embryonic plant, and a nutrient-storage organ. Seeds are protein-rich, and have been the subject of many mass spectrometry-based analyses. Seed storage proteins (SSP), which are transient depots for reduced nitrogen, have been studied for decades by cell biologists, and many of the complicated aspects of their processing, assembly, and compartmentation are now well understood. Unfortunately, the abundance and complexity of the SSP requires that they be avoided or removed prior to gel-based analysis of non-SSP. While much of the extant data from MS-based proteomic analysis of seeds is descriptive, it has nevertheless provided a preliminary metabolic picture explaining much of their biology. Contemporary studies are moving more toward analysis of protein interactions and posttranslational modifications, and functions of metabolic networks. Many aspects of the biology of seeds make then an attractive platform for heterologous protein expression. Herein we present a broad review of the results from the proteomic studies of seeds, and speculate on a potential future research directions. Copyright © 2010 Elsevier B.V. All rights reserved.

  15. 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

  16. 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...

  17. 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...

  18. 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)

  19. Chapter 6. Dwarf mistletoe surveys

    Treesearch

    J.A. Muir; B. Moody

    2002-01-01

    Dwarf mistletoe surveys are conducted for a variety of vegetation management objectives. Various survey and sampling techniques are used either at a broad, landscape scale in forest planning or program review, or at an individual, stand, site level for specific project implementation. Standard and special surveys provide data to map mistletoe distributions and quantify...

  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. 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)

  2. Post-dispersal predation of Acacia farnesiana seeds by Stator vachelliae (Bruchidae) in Central America.

    PubMed

    Traveset, Anna

    1990-10-01

    Post-dispersal seed predation by the bruchid beetle Stator vachelliae was investigated in Santa Rosa National Park, Costa Rica. This insect finds the seeds of the leguminous Acacia farnesiana in the feces of horses, deer, and ctenosaur lizards, the current major dispersers. Patterns of oviposition and pre-adult survival of beetles in the seeds were investigated in a series of experiments using fresh horse dung. S. vachelliae never minded into the dung balls, attacking only those seeds located on the surface. Fresh horse dung did not attract insects more readily than dry dung. The proportion of seeds attacked was not related to their density in a defecation, and was similar in three areas with different densities of the host plant. In a fourth area with no fruiting A. farnesiana shrubs all seeds survived insect predation. Bruchids attacked a greater proportion of seeds at 1 m than at 5 m from the edge of the shrub's crown. Seeds were mainly removed from horse dung by rodents with similar intensity in all areas and at both distances; this seed removal interfered with bruchid oviposition and probably with bruchid survival. S. vachelliae oviposited less frequently on seeds in dung fully exposed to sun. When oviposition on a dung pile was high, the distribution of eggs on the seeds was clumped, suggesting that some seeds were preferred to others. By the end of the dry season, bruchids stopped attacking the seeds. The results show that the fate of both seeds and bruchids is greatly influenced by the location and time of defecation.

  3. Rehabilitating downy brome (Bromus tectorum)-invaded scrublands using imazapic and seeding with native shrubs

    Treesearch

    Suzanne M. Owen; Carolyn Hull Sieg; Catherine A. Gehring

    2011-01-01

    Rehabilitation of downy brome-infested shrublands is challenging once this invasive grass dominates native communities. The effectiveness of imazapic herbicide in reducing downy brome cover has been variable, and there is uncertainty about the impacts of imazapic on native species. We used a before-after-control-impact (BACI) field experiment and greenhouse studies to...

  4. Improving cattle nutrition on the Great Plains with shrubs and fecal seeding of fourwing saltbush

    USDA-ARS?s Scientific Manuscript database

    Two in vitro trials were conducted for estimates of dietary percentage of fourwing saltbush (Atriplex canescens; FS) or winterfat (Krascheninnikovia lanata; WF) to improve diet digestibility when cattle graze mature cool-season grass. Three in vitro trials were conducted to estimate the percentage ...

  5. Investigation into seed collection practices and shrub manipulations to improve sustainable seed yield in wildland stands of bitterbrush (Purshia tridentata)

    Treesearch

    F. Leland Roberts

    2007-01-01

    The Great Basin is a series of unique ecosystems. Starting at the western edge of the Sierra Nevada mountain range in California it stretches east to the Wasatch Mountains of Utah. In the north it starts in central Oregon and Idaho and stretches south through out most of Nevada. In all the Great Basin is found in five states of the western U.S. The Great Basin supports...

  6. Three New Eclipsing White-dwarf-M-dwarf Binaries Discovered in a Search for Transiting Planets around M-dwarfs

    NASA Astrophysics Data System (ADS)

    Law, Nicholas M.; Kraus, Adam L.; Street, Rachel; Fulton, Benjamin J.; Hillenbrand, Lynne A.; Shporer, Avi; Lister, Tim; Baranec, Christoph; Bloom, Joshua S.; Bui, Khanh; Burse, Mahesh P.; Cenko, S. Bradley; Das, H. K.; Davis, Jack. T. C.; Dekany, Richard G.; Filippenko, Alexei V.; Kasliwal, Mansi M.; Kulkarni, S. R.; Nugent, Peter; Ofek, Eran O.; Poznanski, Dovi; Quimby, Robert M.; Ramaprakash, A. N.; Riddle, Reed; Silverman, Jeffrey M.; Sivanandam, Suresh; Tendulkar, Shriharsh P.

    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 × 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 ⊙ (0.01 AU). The M-dwarfs have masses of approximately 0.35 M ⊙, and the white dwarfs have hydrogen-rich atmospheres with temperatures of around 8000 K and have masses of approximately 0.5 M ⊙. 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 ⊙ (95% confidence) in one of the systems. Accounting for our detection efficiency and geometric factors, we estimate that 0.08%^{+0.10%}_{-0.05%} (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 relatively large orbital radii. Similar eclipsing

  7. 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

  8. A greener Greenland? Climatic potential and long-term constraints on future expansions of trees and shrubs

    PubMed Central

    Normand, Signe; Randin, Christophe; Ohlemüller, Ralf; Bay, Christian; Høye, Toke T.; Kjær, Erik D.; Körner, Christian; Lischke, Heike; Maiorano, Luigi; Paulsen, Jens; Pearman, Peter B.; Psomas, Achilleas; Treier, Urs A.; Zimmermann, Niklaus E.; Svenning, Jens-Christian

    2013-01-01

    Warming-induced expansion of trees and shrubs into tundra vegetation will strongly impact Arctic ecosystems. Today, a small subset of the boreal woody flora found during certain Plio-Pleistocene warm periods inhabits Greenland. Whether the twenty-first century warming will induce a re-colonization of a rich woody flora depends on the roles of climate and migration limitations in shaping species ranges. Using potential treeline and climatic niche modelling, we project shifts in areas climatically suitable for tree growth and 56 Greenlandic, North American and European tree and shrub species from the Last Glacial Maximum through the present and into the future. In combination with observed tree plantings, our modelling highlights that a majority of the non-native species find climatically suitable conditions in certain parts of Greenland today, even in areas harbouring no native trees. Analyses of analogous climates indicate that these conditions are widespread outside Greenland, thus increasing the likelihood of woody invasions. Nonetheless, we find a substantial migration lag for Greenland's current and future woody flora. In conclusion, the projected climatic scope for future expansions is strongly limited by dispersal, soil development and other disequilibrium dynamics, with plantings and unintentional seed dispersal by humans having potentially large impacts on spread rates. PMID:23836785

  9. A greener Greenland? Climatic potential and long-term constraints on future expansions of trees and shrubs.

    PubMed

    Normand, Signe; Randin, Christophe; Ohlemüller, Ralf; Bay, Christian; Høye, Toke T; Kjær, Erik D; Körner, Christian; Lischke, Heike; Maiorano, Luigi; Paulsen, Jens; Pearman, Peter B; Psomas, Achilleas; Treier, Urs A; Zimmermann, Niklaus E; Svenning, Jens-Christian

    2013-08-19

    Warming-induced expansion of trees and shrubs into tundra vegetation will strongly impact Arctic ecosystems. Today, a small subset of the boreal woody flora found during certain Plio-Pleistocene warm periods inhabits Greenland. Whether the twenty-first century warming will induce a re-colonization of a rich woody flora depends on the roles of climate and migration limitations in shaping species ranges. Using potential treeline and climatic niche modelling, we project shifts in areas climatically suitable for tree growth and 56 Greenlandic, North American and European tree and shrub species from the Last Glacial Maximum through the present and into the future. In combination with observed tree plantings, our modelling highlights that a majority of the non-native species find climatically suitable conditions in certain parts of Greenland today, even in areas harbouring no native trees. Analyses of analogous climates indicate that these conditions are widespread outside Greenland, thus increasing the likelihood of woody invasions. Nonetheless, we find a substantial migration lag for Greenland's current and future woody flora. In conclusion, the projected climatic scope for future expansions is strongly limited by dispersal, soil development and other disequilibrium dynamics, with plantings and unintentional seed dispersal by humans having potentially large impacts on spread rates.

  10. Spatio-temporal patterns of ptarmigan occupancy relative to shrub cover in the Arctic

    USGS Publications Warehouse

    Schmutz, Joel A.

    2014-01-01

    Rock and willow ptarmigan are abundant herbivores that require shrub habitats in arctic and alpine areas. Shrub expansion is likely to increase winter habitat availability for ptarmigan, which in turn influence shrub architecture and growth through browsing. Despite their ecological role in the Arctic, the distribution and movement patterns of ptarmigan are not well known, particularly in northern Alaska where shrub expansion is occurring. We used multi-season occupancy models to test whether ptarmigan occupancy varied within and among years, and the degree to which colonization and extinction probabilities were related to shrub cover and latitude. Aerial surveys were conducted from March to May in 2011 and April to May 2012 in a 21,230 km2 area in northeastern Alaska. In areas with at least 30 % shrub cover, the probability of colonization by ptarmigan was >0.90, indicating that moderate to extensive patches of shrubs (typically associated with riparian areas) had a high probability of becoming occupied by ptarmigan. Occupancy increased throughout the spring in both years, providing evidence that ptarmigan migrated from southern wintering areas to breeding areas north of the Brooks Range. Occupancy was higher in the moderate snow year than the high snow year, and this was likely due to higher shrub cover in the moderate snow year. Ptarmigan distribution and migration in the Arctic are linked to expanding shrub communities on a wide geographic scale, and these relationships may be shaping ptarmigan population dynamics, as well as rates and patterns of shrub expansion.

  11. 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.

  12. 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.

  13. Shrub sensitivity to recent warming across Arctic Alaska from dendrochronological and remote sensing records

    NASA Astrophysics Data System (ADS)

    Andreu-Hayles, Laia; Gaglioti, Benjamin V.; D'Arrigo, Rosanne; Anchukaitis, Kevin J.; Goetz, Scott

    2017-04-01

    Shrub expansion into Arctic and alpine tundra ecosystems has been documented during the last several decades based on repeat aerial photography, remote sensing, and ground-truthed estimates of vegetation cover. Today, summer temperatures limit the northern limit of Arctic shrubs, and warmer summers have been shown to have higher NDVI in shrub tundra zones. Although global warming has been considered the main driver of shrub expansion, soil types, shrub species and non-linear responses can moderate how sensitive shrub growth is to climate warming. Here, we assess the sensitivity of shrub growth to inter-annual climate variability using a newly generated network of 18 shrub ring-width chronologies in the tundra regions of the North Slope of Alaska. We then test whether the dendroclimatic patterns we observe at individual sites are representative of the broader region using remotely sensed productivity data (NDVI). The common period of both satellite and shrub ring data from all sites was 1982 to 2010. Instrumental daily data from Toolik Lake and interpolated products was compared to detrended growth rates of Salix spp. (willow) and Alnus sp. (alder), located on and to the west of the Dalton Highway ( 68-70°N 148°W). Whereas summer temperatures were found to enhance shrub growth, warm temperatures outside the core of the growing season have the inverse effect in some chronologies. All tundra shrub chronologies shared a common strong positive response to summer temperatures despite growing in heterogeneous site conditions and belonging to different species. In this work we will discuss shrub climate sensitive across Alaska and how NDVI data compared to the shrub ring-width network.

  14. Heterozygote excess through life history stages in Cestrum miradorense Francey (Solanaceae), an endemic shrub in a fragmented cloud forest habitat.

    PubMed

    Reyes-Zepeda, F; González-Astorga, J; Montaña, C

    2013-01-01

    Comparisons of genetic diversity and population genetic structure among different life history stages provide important information on the effect of the different forces and micro-evolutionary processes that mould diversity and genetic structure after fragmentation. Here we assessed genetic diversity and population genetic structure using 32 allozymic loci in adults, seeds, seedlings and juveniles of eight populations of the micro-endemic shrub Cestrum miradorense in a highly fragmented cloud forest in central-eastern Mexico. We expected that due to its long history or rarity, this species may have endured the negative effects of fragmentation and would show moderate to high levels of genetic diversity. High genetic diversity (H(e) = 0.445 ± 0.03), heterozygote excess (F(IT) = -0.478 ± 0.034, F(IS) = -0.578 ± 0.023) and low population differentiation (F(ST) = 0.064 ± 0.011) were found. Seeds had higher genetic diversity (H(e) = 0.467 ± 0.05) than the later stages (overall mean for adults, seedlings and juveniles H(e) = 0.438 ± 0.08). High gene flow was observed despite the fact that the fragmentation process began more than 100 years ago. We conclude that the high genetic diversity was the result of natural selection, which favours heterozygote excess in all stages, coupled with a combination of a reproductive system and seed/pollen dispersal mechanisms that favour gene flow.

  15. Dwarf mutations in grass pea (Lathyrus sativus L.): origin, morphology, inheritance and linkage studies.

    PubMed

    Talukdar, Dibyendu

    2009-08-01

    Induction of mutation has been used to create additional genetic variability in grass pea (Lathyrus sativus L.). During the ongoing investigations on different induced-morphological mutants, the author detected three types of dwarf mutants in grass pea. One mutant, designated as dwf1 type was earlier identified in colchicine-induced C2 generation of grass pea variety BioR-231 while the other two, designated as dwf2 and dwf3 were isolated in 250 Gy and 300 Gy gamma ray irradiated M2 progeny of variety 'BioR-231' and 'Hooghly Local', respectively. As compared to their parental varieties (controls), all the three mutants manifested stunted, erect and determinate stem, early maturity and tolerance to pod shattering habit. The mutants differed from each other, as well as with controls, in number of primary branches, nature of stipules and internodes, length of peduncle, leaflet and seed coat colour, seed yield and seed neurotoxin content. The three dwarf mutants were monogenically recessive and bred true in successive generations. F2 segregation pattern obtained from the crosses involving the three mutants indicated that dwarf mutation in grass pea was controlled by two independent non-allelic genes, assigned as df1 (for dwf1 type), df2 (for dwf2 type) and df3 (for dwf3 type), with the df1 locus being multiple allelic. Primary trisomic analyses revealed the presence of df1/df2 locus on the extra chromosome of trisomic type I, whereas df3 was located on the extra chromosome of type III. Linkage studies involving five other phenotypic markers suggested linked association of df1/df2 locus with lfc (leaflet colour) and wgn (winged internode) and df3 locus with cbl (seed coat colour). Both the loci; however, assorted independently with flower colour and stipule character. The dwarf types can be utilized as valuable tools for further cytogenetic research and breeding of grass pea.

  16. Effects of experimental hypogravity on peroxidase and cell wall constituents in the dwarf marigold

    NASA Technical Reports Server (NTRS)

    Siegel, S.; Speitel, T.; Shiraki, D.; Fukumoto, J.

    1978-01-01

    Dwarf Marigolds grown from seed under experimental hypogravity are modified in lignin content, hemicellulose composition, and peroxidase activity. The two conditions used, clinostats and flotation, induced changes differing in magnitude but qualitatively similar. Most responses on clinostats required corrections for vertical axis rotational effects, thus limiting the value of these instruments in free-fall simulation. These findings extend earlier observations suggesting that increased peroxidase and decreased lignin are characteristic of growth under experimental hypogravity.

  17. Effects of experimental hypogravity on peroxidase and cell wall constituents in the dwarf marigold

    NASA Technical Reports Server (NTRS)

    Siegel, S.; Speitel, T.; Shiraki, D.; Fukumoto, J.

    1977-01-01

    Dwarf marigolds grown from seed under experimental hypogravity are modified in lignin content, hemicellulose composition and peroxidase activity. The two conditions used, clinostats and flotation, induced changes differing in magnitude but qualitatively similar. Most responses on clinostats required correction for vertical axis rotational effects, thus limiting the value of these instruments in free-fall simulation. These findings extend earlier observations suggesting that increased peroxidase and decreased lignin are characteristic of growth under experimental hypogravity.

  18. [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.

  19. 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.

  20. Adaptive responses reveal contemporary and future ecotypes in a desert shrub

    USGS Publications Warehouse

    Richardson, Bryce A.; Kitchen, Stanley G.; Pendleton, Rosemary L.; Pendleton, Burton K.; Germino, Matthew J.; Rehfeldt, Gerald E.; Meyer, Susan E.

    2014-01-01

    Interacting threats to ecosystem function, including climate change, wildfire, and invasive species necessitate native plant restoration in desert ecosystems. However, native plant restoration efforts often remain unguided by ecological genetic information. Given that many ecosystems are in flux from climate change, restoration plans need to account for both contemporary and future climates when choosing seed sources. In this study we analyze vegetative responses, including mortality, growth, and carbon isotope ratios in two blackbrush (Coleogyne ramosissima) common gardens that included 26 populations from a range-wide collection. This shrub occupies ecotones between the warm and cold deserts of Mojave and Colorado Plateau ecoregions in western North America. The variation observed in the vegetative responses of blackbrush populations was principally explained by grouping populations by ecoregions and by regression with site-specific climate variables. Aridity weighted by winter minimum temperatures best explained vegetative responses; Colorado Plateau sites were usually colder and drier than Mojave sites. The relationship between climate and vegetative response was mapped within the boundaries of the species–climate space projected for the contemporary climate and for the decade surrounding 2060. The mapped ecological genetic pattern showed that genetic variation could be classified into cool-adapted and warm-adapted ecotypes, with populations often separated by steep clines. These transitions are predicted to occur in both the Mojave Desert and Colorado Plateau ecoregions. While under contemporary conditions the warm-adapted ecotype occupies the majority of climate space, climate projections predict that the cool-adapted ecotype could prevail as the dominant ecotype as the climate space of blackbrush expands into higher elevations and latitudes. This study provides the framework for delineating climate change-responsive seed transfer guidelines, which are

  1. Adaptive responses reveal contemporary and future ecotypes in a desert shrub.

    PubMed

    Richardson, Bryce A; Kitchen, Stanley G; Pendleton, Rosemary L; Pendleton, Burton K; Germino, Matthew J; Rehfeldt, Gerald E; Meyer, Susan E

    2014-03-01

    Interacting threats to ecosystem function, including climate change, wildfire, and invasive species necessitate native plant restoration in desert ecosystems. However, native plant restoration efforts often remain unguided by ecological genetic information. Given that many ecosystems are in flux from climate change, restoration plans need to account for both contemporary and future climates when choosing seed sources. In this study we analyze vegetative responses, including mortality, growth, and carbon isotope ratios in two blackbrush (Coleogyne ramosissima) common gardens that included 26 populations from a range-wide collection. This shrub occupies ecotones between the warm and cold deserts of Mojave and Colorado Plateau ecoregions in western North America. The variation observed in the vegetative responses of blackbrush populations was principally explained by grouping populations by ecoregions and by regression with site-specific climate variables. Aridity weighted by winter minimum temperatures best explained vegetative responses; Colorado Plateau sites were usually colder and drier than Mojave sites. The relationship between climate and vegetative response was mapped within the boundaries of the species-climate space projected for the contemporary climate and for the decade surrounding 2060. The mapped ecological genetic pattern showed that genetic variation could be classified into cool-adapted and warm-adapted ecotypes, with populations often separated by steep dines. These transitions are predicted to occur in both the Mojave Desert and Colorado Plateau ecoregions. While under contemporary conditions the warm-adapted ecotype occupies the majority of climate space, climate projections predict that the cool-adapted ecotype could prevail as the dominant ecotype as the climate space of blackbrush expands into higher elevations and latitudes. This study provides the framework for delineating climate change-responsive seed transfer guidelines, which are needed

  2. 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

  3. Spatial patterns of soil moisture as affected by shrubs, in different climatic conditions.

    PubMed

    Pariente, Sarah

    2002-02-01

    Abstract. At three study sites, representing Mediterranean, semi-arid and mildly-arid climatic conditions, the effect of shrubs on the spatial patterns of soil moisture was studied. At each site soil moisture was measured, on hillslopes, at the vicinity of 8 shrubs. For each shrub the measurements have been taken at 3 microenvironments, i.e. under the shrub (US), at the margins of shrub (MS) and between shrubs (BS). At the microenvironments US and MS the measurements were taken at 3 directions: upslope, downslope and sideslope of the shrubs. At all sampling points soil samples were taken from 3 depths: 0-2, 2-5 and 5-10 cm. In addition, rock fragments cover percentage near the shrubs was determined. A soil moisture pattern was found, around each shrub, which is composed of a radial gradient and a downslope gradient. The radial gradient is expressed by soil moisture decreasing from the US microenvironment, in all directions, through the MS towards the BS microenvironment. The US microenvironment has a 'spatial advantage' of higher soil moisture content due to (1) relatively higher infiltration rate, (2) capture overland flow from the BS area upslope that shrub and (3) low evaporation rate because of the shading effect. The downslope gradient is expressed by decreasing soil moisture from the upslope direction of each shrub (MS and US microenvironments) towards the downslope direction of that shrub (MS and US microenvironments, respectively). This gradient is controlled by the relatively high content of rock fragments near the shrubs at their upslope direction. Such rock fragments spatial distribution is attributed to (1) the detachment and transport of rock fragments by sheep and goats trampling and (2) the effect of shrub on the continuity of overland flow and sediment transport. The effect of rock fragments is similar to that of shrubs regarding increasing infiltration and decreasing evaporation rate. The relatively high soil moisture at the upslope direction of

  4. Sex-specific reproductive components and pollination ecology in the subdioecious shrub Fuchsia microphylla.

    PubMed

    Cuevas, E; Jiménez, R; Lopezaraiza-Mikel, M

    2014-11-01

    In subdioecious populations, functional female, male and hermaphrodite individuals coexist. Subdioecy may be a transitional state towards dioecy or a breakdown of dioecy, although lability in sex expression may maintain subdioecy as a stable condition. To better understand the ecological aspects involved in sex ratio dynamics and breeding system evolution, we studied the pollination and female fitness components of female and hermaphrodite individuals of the subdioecious shrub Fuchsia microphylla. In two natural populations at the Trans-Mexican Volcanic Belt we estimated female frequency and several reproductive components of female and hermaphrodite plants under natural pollination and experimental pollination treatments. Average female frequency was 42%, and on average, 42.5% of hermaphrodites produced fruits. Female plants showed a 17-fold female fertility advantage over hermaphrodites through increased fruit production, as the number of seeds and germination rates did not differ between morphs. Hermaphrodite flowers were larger, with similar nectar production and concentration to female flowers, and pollinators did not show consistent morph preferences. Some hermaphrodites produced fruits autonomously, and female flowers excluded from pollinators produced fruits putatively by apomixis. Fruit production in hermaphrodites, but not in females, was related to height, suggesting increased investment of hermaphrodites in the female function at higher resource status. For sex ratios to be at equilibrium, the female fertility advantage should be reduced about eightfold. However, it may be that hermaphrodites are maintained by producing fruits at no cost to the male function at higher resource status, as the gender plasticity hypothesis proposes.

  5. The neotropical shrub Lupinus elegans, fromtemperate forests, may not adapt to climate change.

    PubMed

    Soto-Correa, J C; Sáenz-Romero, C; Lindig-Cisneros, R; de la Barrera, E

    2013-05-01

    Considering that their distribution is limited to altitudinal gradients along mountains that are likely to become warmer and drier, climate change poses an increased threat to temperate forest species from tropical regions. We studied whether the understorey shrub Lupinus elegans, endemic to temperate forests of west-central Mexico, will be able to withstand the projected temperature increase under seven climate change scenarios. Seeds were collected along an altitudinal gradient and grown in a shade-house over 7 months before determining their temperature tolerance as electrolyte leakage. The plants from colder sites tolerated lower temperatures, i.e. the temperature at which half of the maximum electrolyte leakage occurred (LT50), ranged from −6.4 ± 0.7 to −2.4 ± 0.3 °C. In contrast, no pattern was found for tolerance to high temperature (LT50 average 42.8 ± 0.3 °C). The climate change scenarios considered here consistently estimated an increase in air temperature during the present century that was higher for the maximum air temperature than for the mean or minimum. In particular, the anomaly from the normal maximum air temperature at the study region ranged from 2.8 °C by 2030 to 5.8 °C by 2090. In this respect, the inability of L. elegans to adapt to increasingly higher temperatures found here, in addition to a possible inhibition of reproduction caused by warmer winters, may limit its future distribution.

  6. An examination of the function of male flowers in an andromonoecious shrub Capparis spinosa.

    PubMed

    Zhang, Tao; Tan, Dun-Yan

    2009-03-01

    The pollen donor and pollinator attractor hypotheses are explanations for the functions of the male flowers of andromonoecious plants. We tested these two hypotheses in the andromonoecious shrub Capparis spinosa L. (Capparaceae) and confirmed that pollen production and cumulative volume and sugar concentration of nectar do not differ between male and perfect flowers. However, male flowers produced larger anthers, larger pollen grains and smaller ovaries than perfect flowers. Observations on pollinators indicated that two major pollinators (Xylocopa valga Gerst and Proxylocopa sinensis Wu) did not discriminate between flower morphs and that they transferred pollen grains a similar distance. However, there were more seeds per fruit following hand pollination with pollen from male flowers than from perfect flowers. Individuals of C. spinosa with a larger floral display (i.e. bearing more flowers) received more pollen grains on the stigma of perfect flowers. Female reproductive success probably is not limited by pollen. These results indicate that male flowers of C. spinosa save resources for female function and that they primarily serve to attract pollinators as pollen donors.

  7. Flower size and longevity influence florivory in the large-flowered shrub Cistus ladanifer

    NASA Astrophysics Data System (ADS)

    Teixido, Alberto L.; Méndez, Marcos; Valladares, Fernando

    2011-09-01

    Plants with larger and longer-lived flowers receive more pollinator visits and increase reproductive success, though may also suffer more from antagonistic interactions with animals. Florivores can reduce fruit and seed production, so selection on flower size, floral longevity and/or number of flowers may thus be determined by the relative effects of both pollinators and florivores. In this study flowers of Cistus ladanifer, a large-flowered Mediterranean shrub, were monitored to evaluate the effects of flower size, floral longevity and number of flowers on levels of florivory in four populations. Number of flowers was variable but did not differ among populations. Both flower size and floral longevity of C. ladanifer showed broad variation and significantly differed among populations. Overall, 7% of flowers suffered attack by florivores, which were mainly ants picking the stamens and beetles consuming petals and pollen. Within-populations, larger and longer-lived flowers tended to be affected by florivores more frequently. The low overall incidence of florivores and its lack of between-population variation suggest that florivory may not influence intraspecific variation of these floral traits. However, moderate florivory levels on the largest and longest-lived flowers open the possibility of exerting selection towards smaller and shorter-lived flowers in some of the populations studied.

  8. RADIAL VELOCITY VARIABILITY OF FIELD BROWN DWARFS

    SciTech Connect

    Prato, L.; Mace, G. N.; Rice, E. L.; McLean, I. S.; Kirkpatrick, J. Davy; Burgasser, A. J.; Kim, Sungsoo S.

    2015-07-20

    We present paper six of the NIRSPEC Brown Dwarf Spectroscopic Survey, an analysis of multi-epoch, high-resolution (R ∼ 20,000) spectra of 25 field dwarf systems (3 late-type M dwarfs, 16 L dwarfs, and 6 T dwarfs) taken with the NIRSPEC infrared spectrograph at the W. M. Keck Observatory. With a radial velocity (RV) precision of ∼2 km s{sup −1}, we are sensitive to brown dwarf companions in orbits with periods of a few years or less given a mass ratio of 0.5 or greater. We do not detect any spectroscopic binary brown dwarfs in the sample. Given our target properties, and the frequency and cadence of observations, we use a Monte Carlo simulation to determine the detection probability of our sample. Even with a null detection result, our 1σ upper limit for very low mass binary frequency is 18%. Our targets included seven known, wide brown dwarf binary systems. No significant RV variability was measured in our multi-epoch observations of these systems, even for those pairs for which our data spanned a significant fraction of the orbital period. Specialized techniques are required to reach the high precisions sensitive to motion in orbits of very low-mass systems. For eight objects, including six T dwarfs, we present the first published high-resolution spectra, many with high signal to noise, that will provide valuable comparison data for models of brown dwarf atmospheres.

  9. Mutational effects of space flight on Zea mays seeds

    NASA Technical Reports Server (NTRS)

    Mei, M.; Qiu, Y.; He, Y.; Bucker, H.; Yang, C. H.

    1994-01-01

    The growth and development of more than 500 Zea mays seeds flown on Long Duration Exposure Facility (LDEF) were studied. Somatic mutations, including white-yellow stripes on leaves, dwarfing, change of leaf sheath color or seedling color were observed in plants developed from these seeds. When the frequency of white-yellow formation was used as the endpoint and compared with data from ground based studies, the dose to which maize seeds might be exposed during the flight was estimated to be equivalent to 635 cGy of gamma rays. Seeds from one particular holder gave a high mutation frequency and a wide mutation spectrum. White-yellow stripes on leaves were also found in some of the inbred progenies from plants displayed somatic mutation. Electron microscopy studies showed that the damage of chloroplast development in the white-yellow stripe on leaves was similar between seeds flown on LDEF and that irradiated by accelerated heavy ions on ground.

  10. Mutational effects of space flight on Zea mays seeds

    NASA Technical Reports Server (NTRS)

    Mei, M.; Qiu, Y.; He, Y.; Bucker, H.; Yang, C. H.

    1994-01-01

    The growth and development of more than 500 Zea mays seeds flown on Long Duration Exposure Facility (LDEF) were studied. Somatic mutations, including white-yellow stripes on leaves, dwarfing, change of leaf sheath color or seedling color were observed in plants developed from these seeds. When the frequency of white-yellow formation was used as the endpoint and compared with data from ground based studies, the dose to which maize seeds might be exposed during the flight was estimated to be equivalent to 635 cGy of gamma rays. Seeds from one particular holder gave a high mutation frequency and a wide mutation spectrum. White-yellow stripes on leaves were also found in some of the inbred progenies from plants displayed somatic mutation. Electron microscopy studies showed that the damage of chloroplast development in the white-yellow stripe on leaves was similar between seeds flown on LDEF and that irradiated by accelerated heavy ions on ground.

  11. Mutational effects of space flight on Zea mays seeds

    NASA Astrophysics Data System (ADS)

    Mei, M.; Qiu, Y.; He, Y.; Bucker, H.; Yang, C. H.

    1994-10-01

    The growth and development of more than 500 Zea mays seeds flown on LDEF were studied. Somatic mutations, including white-yellow stripes on leaves, dwarfing, change of leaf sheath color or seedling color were observed in plants developed from these seeds. When the frequency of white-yellow formation was used as the endpoint and compared with data from ground based studies, the dose to which maize seeds might be exposed during the flight was estimated to be equivalent to 635 cGy of gamma rays. Seeds from one particular holder gave a high mutation frequency and a wide mutation spectrum. White-yellow stripes on leaves were also found in some of the inbred progenies from plants displayed somatic mutation. Electron microscopy studies showed that the damage of chroloplast development in the white-yellow stripe on leaves was similar between seeds flown on LDEF and that irradiated by accelerated heavy ions on ground.

  12. [Contribution of soil seed bank to the regeneration of damaged vegetation on floodplain].

    PubMed

    Wang, Zeng-ru; Xu, Hai-liang; Yin, Lin-ke; Li, Ji-mei; Zhang, Zhan-jiang; Li, Yuan

    2008-12-01

    A field germination experiment of soil seed bank was carried out on two typical floodplains in the lower reaches of Tarim River, and a comparison was made between the soil seed banks and corresponding seedling banks on the two floodplains, aimed to assess the contribution of soil seed bank to the regeneration of damaged vegetation. The results showed that there were 12 plant species in the soil seed banks, and the life forms were mainly perennial herbs and shrubs. The soil seed banks had a density of 282.5 seeds m(-2) and 173.2 seeds x m(-2), and the seeds in top soil (0-2 cm) accounted for 76.9% and 71.0% of the total, respectively. The soil seed banks had significant effects on the seedlings species composition and density, and 84.7% and 99.4% of the seedlings on the two floodplains were emerged from corresponding soil seed banks. The similarity coefficient between soil seed bank and seedling bank of the two floodplains was 0.72 and 0.63, respectively, and there existed significant positive correlation between seedling density and soil seed bank density, illustrating that soil seed bank made important contribution to the natural regeneration of vegetation.

  13. Ethnobotanical survey of medicinally important shrubs and trees of Himalayan region of Azad Jammu and Kashmir, Pakistan.

    PubMed

    Rashid, Sofia; Ahmad, Mushtaq; Zafar, Muhammad; Sultana, Shazia; Ayub, Muhammad; Khan, Mir Ajab; Yaseen, Ghulam

    2015-05-26

    Present study was commenced with an aim to document the indigenous knowledge of medicinally important shrubs and trees of Himalayan region of Azad Jammu and Kashmir, Pakistan. This is the first contribution to the quantitative ethnobotany of this region, as no reported data focusing on shrubs and trees from the area have been published. Study reported the ethnobotanical significance of medicinal plants for the treatment of various diseases. Study was conducted during 2012-2014 following standard ethnobotanical methods. The ethnomedicinal data was collected through informed consent semi- structured interviews of 160 key informants. Documented data was analyzed by using quantitative indices of informant consensus factor (ICF), fidelity level (FL), use value (UV) and relative frequency citation (RFC). A total of 73 shrub and tree species belonging to 56 genera and 37 families were reported to be used ethnomedicinally for the treatment of various ailments. Medicinal plant diversity showed that Rosaceae was dominating family with (9 spp.) followed by Moraceae (7 spp.), Euphorbiaceae, Mimosaceae, Pinaceae, Rhamnaceae (4 spp. each), Oleaceae (3 spp.), Apocynaceae, Caesalpinaceae, Ebenaceae, Fagaceae, Lythraceae, Papilionaceae, Acanthaceae, Verbenaceae (2 spp. each) while remaining 22 families were represented by one species each. Leaves (23%) were highly utilized plant parts, followed by fruits (22%), bark (18%), seeds (10%), roots (9%), flowers (8%), whole plant and aerial parts (4% each) and stem (2%). Modes of preparation fall into 14 categories including powder (33 reports) followed by decoction (29 reports), paste (22 reports), juice (18 reports), infusion (12 reports), raw (8 reports), extract and latex (5 reports each), gum and oil (4 reports each), fresh part and pulp (2 reports each), chewed and cooked (1 report each). The highest FIC was recorded for Gastro-intestinal disorders (0.58) followed by nail, skin and hair disorders (0.44). Maximum fidelity level (FL

  14. Shrub encroachment can reverse desertification in semi-arid Mediterranean grasslands.

    PubMed

    Maestre, Fernando T; Bowker, Matthew A; Puche, María D; Belén Hinojosa, M; Martínez, Isabel; García-Palacios, Pablo; Castillo, Andrea P; Soliveres, Santiago; Luzuriaga, Arántzazu L; Sánchez, Ana M; Carreira, José A; Gallardo, Antonio; Escudero, Adrián

    2009-09-01

    The worldwide phenomenon of shrub encroachment in grass-dominated dryland ecosystems is commonly associated with desertification. Studies of the purported desertification effects associated with shrub encroachment are often restricted to relatively few study areas, and document a narrow range of possible impacts upon biota and ecosystem processes. We conducted a study in degraded Mediterranean grasslands dominated by Stipa tenacissima to simultaneously evaluate the effects of shrub encroachment on the structure and composition of multiple biotic community components, and on various indicators of ecosystem function. Shrub encroachment enhanced vascular plant richness, biomass of fungi, actinomycetes and other bacteria, and was linked with greater soil fertility and N mineralization rates. While shrub encroachment may be a widespread phenomenon in drylands, an interpretation that this is an expression of desertification is not universal. Our results suggest that shrub establishment may be an important step in the reversal of desertification processes in the Mediterranean region.

  15. A Multi-species Assessment of Post-dispersal Seed Predation in the Central Chilean Andes

    PubMed Central

    MUÑOZ, ALEJANDRO A.; CAVIERES, LOHENGRIN A.

    2006-01-01

    • Background and Aims Post-dispersal seed predation in alpine communities has received little attention despite evidence that seeds removed by granivores can decrease plant recruitment into ecosystems. Moreover, few studies have assessed the effects of removal of seeds of a range of species after dispersal on the seeds remaining in ecosystems. A comparison was made of the magnitude of seed removal by ants and birds of nine different shrubby-, herbaceous- and cushion-plant species in the central Chilean Andes in order to assess the interactions between birds, ants and wind, and the types of seeds. • Methods A total of 324 soil-covered plates, each containing 50 seeds of one species, were placed in the field at an altitude of 2700 m and assigned to one of four treatments: control, exclusion of ants, birds, and both. The design also allowed the effects of wind to be assessed. Seed removal from plates was monitored over 20 d. • Key Results Mean accumulative seed removal by granivores averaged over all nine species combined was 25 %. However, large differences between species were evident, with limited seed removal (3–11 %) in three herbaceous species (Alstroemeria pallida, Sisyrinchium arenarium, Pozoa coriacea), moderate (18–33 %) in five species, including a shrub (Chuquiraga oppositifolia), two herbs (Taraxacum officinale, Rhodophiala rhodolirion), and two cushion-plants (Laretia acaulis, Azorella monantha), and substantial (78 %) in the shrub Anarthrophyllum cumingii. The magnitudes of losses caused by birds compared with ants did not differ for the majority of species, although removal by birds was greater than by ants in A. cumingii, and smaller for C. oppositifolia. • Conclusions Post-dispersal seed removal is shown to be an important cause of decreased potential plant species recruitment into alpine ecosystems. The substantial differences in the magnitude of seed losses to ants and birds demonstrate the need for evaluation of seed removal

  16. Short-term effects of experimental fires on a Mojave Desert seed bank

    USGS Publications Warehouse

    Esque, Todd C.; Young, James A.; Tracy, C. Richard

    2010-01-01

    A Mojave Desert shrub community was experimentally burned to understand changes in seed bank of desert annual plant species in response to wildfire. Seed mortality ranged from 55 to 80%, and fire caused significant losses of native and alien annual seeds. Schismus arabicus, Schismus barbatus, Bromus madritensis, Bromus tectorum, Erodium cicutarium and Plantago spp. made up >95% of the seed bank. Bromus spp. and Plantago spp. had proportionately greater mortality of seeds than did Schismus spp. and E. cicutarium. Schismus spp. can be lodged into soil cracks thus avoiding lethal temperatures. E. cicutarium has a self-drilling mechanism that places the seeds at greater depth in the soil. Greater seed mortality occurred beneath shrub canopies than interspaces for most species (Plantago, spp., Bromus spp., and E. cicutarium), but microsite had little effect on Schismus spp. Fire reduced the perennial Ambrosia dumosa densities under canopies. Fire reduced the mean number of species found in samples by about one species per plot and no species was extirpated on experimental plots. The relative abundances of common species did not change dramatically as a result of fire or microsite, however; seed densities varied by treatment and affected interpretations of species compositions.

  17. 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.

  18. ``From seed-to-seed'' experiment with wheat plants under space-flight conditions

    NASA Astrophysics Data System (ADS)

    Mashinsky, A.; Ivanova, I.; Derendyaeva, T.; Nechitailo, G.; Salisbury, F.

    1994-11-01

    An important goal with plant experiments in microgravity is to achieve a complete life cycle, the ``seed-to-seed experiment''. Some Soviet attempts to reach this goal are described, notably an experiment with the tiny mustard, Arabidopsis thaliana, in the Phyton 3 device on Salyut 7. Normal seeds were produced although yields were reduced and development was delayed. Several other experiments have shown abnormalities in plants grown in space. In recent work, plants of wheat (Triticum aestivum) were studied on the ground and then in a preliminary experiment in space. Biometric indices of vegetative space plants were 2 to 2.5 times lower than those of controls, levels of chlorophyll a and b were reduced (no change in the ratio of the two pigments), carotenoids were reduced, there was a serious imbalance in major minerals, and membrane lipids were reduced (no obvious change in lipid patterns). Following the preliminary studies, an attempt was made with the Svetoblock-M growth unit to grow a super-dwarf wheat cultivar through a life cycle. The experiment lasted 167 d on Mir. Growth halted from about day 40 to day 100, when new shoots appeared. Three heads had appeared in the boot (surrounded by leaves) when plants were returned to earth. One head was sterile, but 28 seeds matured on earth, and most of these have since produced normal plants and seeds. In principle, a seed-to-seed experiment with wheat should be successful in microgravity.

  19. "From seed-to-seed" experiment with wheat plants under space-flight conditions.

    PubMed

    Mashinsky, A; Ivanova, I; Derendyaeva, T; Nechitailo, G; Salisbury, F

    1994-11-01

    An important goal with plant experiments in microgravity is to achieve a complete life cycle, the "seed-to-seed experiment." Some Soviet attempts to reach this goal are described, notably an experiment with the tiny mustard, Arabidopsis thaliana, in the Phyton 3 device on Salyut 7. Normal seeds were produced although yields were reduced and development was delayed. Several other experiments have shown abnormalities in plants grown in space. In recent work, plants of wheat (Triticum aestivum) were studied on the ground and then in a preliminary experiment in space. Biometric indices of vegetative space plants were 2 to 2.5 times lower than those of controls, levels of chlorophyll a and b were reduced (no change in the ratio of the two pigments), carotenoids were reduced, there was a serious imbalance in major minerals, and membrane lipids were reduced (no obvious change in lipid patterns). Following the preliminary studies, an attempt was made with the Svetoblock-M growth unit to grow a super-dwarf wheat cultivar through a life cycle. The experiment lasted 167 d on Mir. Growth halted from about day 40 to day 100, when new shoots appeared. Three heads had appeared in the boot (surrounded by leaves) when plants were returned to earth. One head was sterile, but 28 seeds matured on earth, and most of these have since produced normal plants and seeds. In principle, a seed-to-seed experiment with wheat should be successful in microgravity.

  20. Analysis of genetic diversity and population structure within Florida coconut (Cocos nucifera L.) germplasm using microsatellite DNA, with special emphasis on the Fiji Dwarf cultivar.

    PubMed

    Meerow, Alan W; Wisser, Randall J; Brown, J Steven; Kuhn, David N; Schnell, Raymond J; Broschat, Timothy K

    2003-02-01

    Using 15 simple sequence repeat (SSR) microsatellite DNA loci, we analyzed genetic variation within Cocos nucifera germplasm collections at two locations in south Florida, representing eight cultivars. The loci were also used in a parentage analysis of progeny of the 'Fiji Dwarf' variety at both locations. A total of 67 alleles were detected, with eight the highest number at any one locus. These loci identified 83 of the 110 individual palms. Gene diversity of the 15 loci ranged from 0.778 to 0.223, with a mean of 0.574. 'Fiji Dwarf', 'Malayan Dwarf', 'Green Niño' and 'Red Spicata' cultivars resolve as distinct clusters in a neighbor joining tree using modified Rogers distance, while the tall varieties form two aggregates. The highest gene diversity was found in the tall cultivars (H = 0.583 cumulatively), and the lowest in the 'Malayan Dwarf' (H = 0.202). After the tall coconuts, the 'Fiji Dwarf' was most genetically diverse (H = 0.436), and had the largest number of unique alleles. Genetic identity is highest among the 'Malayan Dwarf' phenotypes, and between the tall varieties. The 'Red Malayan Dwarf' is genetically distinct from the 'Green' and 'Yellow Malayan Dwarf' phenotypes, which cannot be distinguished with the SSR loci used. Off-type 'Malayan Dwarf' phenotypes (putative hybrids with talls) can be identified genotypically. Parentage analyses of 30 'Fiji Dwarf' progeny propagated from five adults surrounded by other cultivars estimate that only 20% of the progeny were out-crossed to the other varieties, while 40-46% were possible selfs. This suggests that a seed-production orchard of the variety maintained at reasonable distance from other varieties, will likely yield only 'Fiji Dwarf' genotypes. Our data are discussed in the context of hypotheses of coconut dissemination around the world.

  1. 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%.

  2. Discovery of an Ultracool White Dwarf Companion

    NASA Astrophysics Data System (ADS)

    Farihi, J.

    2004-08-01

    The discovery of a low-luminosity common proper-motion companion to the white dwarf GD 392 at a wide separation of 46" is reported. BVRI photometry suggests a low temperature (Teff~4000 K), while JHK data strongly indicate suppressed flux at all near-infrared wavelengths. Thus, GD 392B is one of the few white dwarfs to show significant collision-induced absorption due to the presence of photospheric H2 and the first ultracool white dwarf detected as a companion to another star. Models fail to explain GD 392B as a normal-mass white dwarf. If correct, the cool companion may be explained as a low-mass white dwarf or unresolved double degenerate. The similarities of GD 392B to known ultracool degenerates are discussed, including some possible implications for the faint end of the white dwarf luminosity function.

  3. White dwarfs and the interstellar medium

    NASA Technical Reports Server (NTRS)

    Dupree, A. K.; Raymond, J. C.

    1983-01-01

    Radiation emanating from hot (T greater than 40,000 K) white dwarfs can create large volumes of ionized material containing substantial column densities of highly ionized species, in particular Si IV and C IV. The ions N V and O VI can also be produced by hot, hydrogen-rich white dwarfs. These ionization spheres may be detectable around the nearby dwarfs. The relatively high space motions of these stars coupled with long recombination times in the interstellar medium suggest that a white dwarf leaves a region of ionized material - a fossil Stroemgren trail - that marks its progress through the galaxy. White dwarfs create a patchy substrate of ionized gas in the galactic plane and lead to extended ionized regions out of the plane. The spatial frequency of hot white dwarfs indicates that they contribute a radiative energy comparable to that provided by nondegenerate stars and by supernovae and capable of affecting the ionization balance of the interstellar medium.

  4. 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.

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

    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.

  6. 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.

  7. Hydraulic lift through transpiration suppression in shrubs from two arid ecosystems: patterns and control mechanisms.

    PubMed

    Prieto, Iván; Martínez-Tillería, Karina; Martínez-Manchego, Luis; Montecinos, Sonia; Pugnaire, Francisco I; Squeo, Francisco A

    2010-08-01

    Hydraulic lift (HL) is the passive movement of water through the roots from deep wet to dry shallow soil layers when stomata are closed. HL has been shown in different ecosystems and species, and it depends on plant physiology and soil properties. In this study we explored HL patterns in several arid land shrubs, and developed a simple model to simulate the temporal evolution and magnitude of HL during a soil drying cycle under relatively stable climatic conditions. This model was then used to evaluate the influence of soil texture on the quantity of water lifted by shrubs in different soil types. We conducted transpiration suppression experiments during spring 2005 in Chile and spring 2008 in Spain on five shrub species that performed HL, Flourensia thurifera, Senna cumingii and Pleocarphus revolutus (Chile), Retama sphaerocarpa and Artemisia barrelieri (Spain). Shrubs were covered with a black, opaque plastic fabric for a period of 48-72 h, and soil water potential was recorded at different depths under the shrubs. While the shrubs remained covered, water potential continuously increased in shallow soil layers until the cover was removed. The model output indicated that the amount of water lifted by shrubs is heavily dependent on soil texture, as shrubs growing in loamy soils redistributed up to 3.6 times more water than shrubs growing on sandy soils. This could be an important consideration for species growing in soils with different textures, as their ability to perform HL would be context dependent.

  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. Influence of shrub encroachment on the soil microbial community composition of remnant hill prairies.

    PubMed

    Yannarell, Anthony C; Menning, Sarah E; Beck, Alyssa M

    2014-05-01

    Hill prairies are remnant grasslands perched on the bluffs of major river valleys, and because their steep slopes make them unsuitable for traditional row crop agriculture, they have some of the lowest levels of anthropogenic disturbance of any prairie ecosystems in the Midwestern USA. However, many decades of fire suppression have allowed for shrub encroachment from the surrounding forests. While shrub encroachment of grasslands can modify soil respiration rates and nutrient storage, it is not known whether shrubs also alter the community composition of soil microorganisms. We conducted transect sampling of nine different hill prairie remnants showing varying degrees of shrub encroachment, and we used DNA-based community profiling (automated ribosomal intergenic spacer analysis) to characterize the composition of bacterial and fungal communities in the open prairie habitat, the shrub-encroached border, and the surrounding forest. While both bacterial and fungal communities showed statistically significant variation across these habitats, their predominant patterns were different. Bacterial communities of forest soils were distinct from those of the open prairie and the shrub-encroached areas, while fungal communities of the open prairie were distinct from those of the forest and the shrub-encroached border. Shrub encroachment significantly altered the community composition of soil fungal communities. Furthermore, fungal communities of heavily encroached prairie remnants more closely resembled those of the surrounding forest than those of lightly encroached prairies. Thus, shrub encroachment can cause soil fungi to shift from a "grassland" community to a "woody" community, with potential consequences for soil processes and plant-microbe interactions.

  10. 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.

  11. 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

    Growing evidence indicates an expansion of canopy-forming woody shrubs up mountain slopes and northward into Arctic tundra. The correlation between warming and greening has been used to link climate change with shrub expansion; however, the exact mechanisms driving observed increases in canopy-forming shrubs are probably more complex. Shrub expansion that results in a change in canopy cover may modify the ecology of tundra ecosystems by changing understory plant composition, soil thermal dynamics, surface albedo, nutrient turnover times and carbon storage. We surveyed the abundance of all tundra willow species (Salix spp.) growing at three sites in the Yukon Territory: the mountains of the Kluane Region, the Richardson Mountains, and on Qikiqtaruk - Herschel Island in the Beaufort Sea. At the two mountainous sites, we collected sections from the largest stem of willow shrubs at shrub line (the maximum elevation at which canopy-forming shrubs grow) and below shrub line (at approximately 50% shrub cover) in a total of 16 valleys. At the coastal site we collected samples from each of the 4 vegetation types: the alluvial fan, ridges, tussock tundra and disturbed terrain. Shrub stems were thin-sectioned using a microtome, photographed with a microscope and ring widths were measured from the digital images. We compared age distributions of willow individuals at and below shrub line and found younger populations at higher elevations, particularly on warm, south-facing aspects. Younger willows at shrub line and a lack of significant mortality in the field surveys indicate that shrubs have advanced up slope at the mountainous sites. Photographic and long-term plot data indicate increases in cover and height of willow shrub patches at the coastal site. We compared growth rings to regional weather data, and found positive correlations between annual growth and summer temperatures. Our results indicate that willows grew most in years with a warm June and July. This evidence of

  12. Demise of spiny hopsage shrubs following summer wildfire: an authentic record

    SciTech Connect

    Rickard, W.H.; McShane, M.C.

    1984-01-01

    Spiny hopsage, Grayia spinosa, shrubs growing in a plant community dominated by greasewood, Sarcobatus vermiculatus, shrubs were destroyed by a summer wildfire. In the first season after the burn, greasewood shrubs sprouted, and by April of the second spring season, greasewood had restored about one-half of its preburn canopy cover. Spiny hopsage shrubs did not sprout and their demise is attributed to stressed growing conditions imposed by an alkaline-sodic rooting substrate. The demise of spiny hopsage would likely have gone unnoticed were it not for the existence of a permanently marked study plot. 11 references, 1 table.

  13. 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.

  14. Greater effect of increasing shrub height on winter versus summer soil temperature

    NASA Astrophysics Data System (ADS)

    Paradis, Mélissa; Lévesque, Esther; Boudreau, Stéphane

    2016-08-01

    Shrub expansion is increasingly observed in arctic and subarctic environments. The development of shrub structure may significantly impact the abiotic environment at the local scale. Our objective was to reconstruct the development of the vertical structure of Betula glandulosa Michx. and to evaluate its effects on winter and summer soil temperature and on snow depth. Stratified sampling of the shrub revealed that shrub biomass distribution followed a similar pattern in stands of contrasting heights. Woody biomass was maximal in the lower stratum and relatively stable in the intermediate strata, while the foliar biomass tracked the vertical development of the shrub structure. Dendrochronological analysis revealed that shrub stands are relatively young; most of the dominant stems started their development after 1990. Shrub height was positively associated with both the dominant stem age and its vertical growth rate. Temperature differences among sites were greater during winter (ca 10 °C) than during summer (ca 2 °C), while the sum of freezing degree-days varied from 680 °C to 2125 °C. Shrub height was the most plausible variable explaining snow depth, winter ground level temperature and the sum of freezing degree-days. However, woody biomass in the 30-40 cm strata best explained summer ground level temperature. Our results suggest that the development of a shrub structure will have far-reaching consequences on the abiotic environment of subarctic ecosystems.

  15. 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.

  16. Establishing a missing link: warm summers and winter snow cover promote shrub expansion into alpine tundra in Scandinavia.

    PubMed

    Hallinger, Martin; Manthey, Michael; Wilmking, Martin

    2010-06-01

    *Shrub expansion in alpine and arctic areas is a process with possibly profound implications for ecosystem functioning. The recent shrub expansion has been mainly documented by remote sensing techniques, but the drivers for this process largely remain hypotheses. *Here, we outline a dendrochronological method, adapted to shrubs, to address these hypotheses and then present a mechanism for the current shrub expansion by linking recent climate change to shrub growth performance in northern Sweden. *A pronounced increase in radial and vertical growth during recent decades along an elevational gradient from treeline to shrubline indicates an ongoing shrub expansion. Age distribution of the shrub population indicates the new colonization of shrubs at high elevations. *Shrub growth is correlated with warm summers and winter snow cover and suggests the potential for large-scale ecosystem changes if climate change continues as projected.

  17. Project SEED.

    ERIC Educational Resources Information Center

    Chemical and Engineering News, 1986

    1986-01-01

    Reports on Project SEED (Summer Educational Experience for the Disadvantaged) a project in which high school students from low-income families work in summer jobs in a variety of academic, industrial, and government research labs. The program introduces the students to career possibilities in chemistry and to the advantages of higher education.…

  18. Helium runaways in white dwarfs

    NASA Technical Reports Server (NTRS)

    Taam, R. E.

    1979-01-01

    The long term evolution of an accreting carbon white dwarf was studied from the onset of accretion to the ignition of helium. The variations in the details of the helium shell flash examined with respect to variations in mass accretion rate. For intermediate rates the helium flash is potentially explosive whereas for high rates the shell flash is relatively weak. The results are discussed in the context of the long term evolution of novae.

  19. Brown Dwarf HIP 79124 B

    NASA Image and Video Library

    2017-01-30

    This image shows brown dwarf HIP 79124 B, located 23 times as far from its host star as Earth is from the sun. The vortex coronagraph, an instrument at the W.M. Keck Observatory, was used to suppress light from the much brighter host star, allowing its dim companion to be imaged for the first time. http://photojournal.jpl.nasa.gov/catalog/PIA21417

  20. 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.

  1. 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.

  2. Are All Magnetic White Dwarf Stars Massive?

    NASA Astrophysics Data System (ADS)

    Nitta, A.; Kepler, S. O.; Kulebi, B.; Koester, D.; Kleinman, S. J.; Winget, D. E.; Castanheira, B. G.; Corsico, A. H.

    2017-03-01

    We obtained follow-up spectra on 25 white dwarf stars identified in our white dwarf catalog of Sloan Digital Sky Survey (SDSS) as massive or magnetic. We identified over 300 magnetic white dwarf stars from SDSS with some uncertainties due to the low S/N of the spectra. With much higher S/N Gemini data, our sample should be able to help us confirm accuracy of our determinations. We present here our results so far from the follow up observations.

  3. 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.

  4. Post-fire seeding on Wyoming big sagebrush ecological sites: regression analyses of seeded nonnative and native species densities.

    PubMed

    Eiswerth, Mark E; Krauter, Karl; Swanson, Sherman R; Zielinski, Mike

    2009-02-01

    Since the mid-1980s, sagebrush rangelands in the Great Basin of the United States have experienced more frequent and larger wildfires. These fires affect livestock forage, the sagebrush/grasses/forbs mosaic that is important for many wildlife species (e.g., the greater sage grouse (Centrocercus urophasianus)), post-fire flammability and fire frequency. When a sagebrush, especially a Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis (Beetle & A. Young)), dominated area largely devoid of herbaceous perennials burns, it often transitions to an annual dominated and highly flammable plant community that thereafter excludes sagebrush and native perennials. Considerable effort is devoted to revegetating rangeland following fire, but to date there has been very little analysis of the factors that lead to the success of this revegetation. This paper utilizes a revegetation monitoring dataset to examine the densities of three key types of vegetation, specifically nonnative seeded grasses, nonnative seeded forbs, and native Wyoming big sagebrush, at several points in time following seeding. We find that unlike forbs, increasing the seeding rates for grasses does not appear to increase their density (at least for the sites and seeding rates we examined). Also, seeding Wyoming big sagebrush increases its density with time since fire. Seeding of grasses and forbs is less successful at locations that were dominated primarily by annual grasses (cheatgrass (Bromus tectorum L.)), and devoid of shrubs, prior to wildfire. This supports the hypothesis of a "closing window of opportunity" for seeding at locations that burned sagebrush for the first time in recent history.

  5. 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.

  6. Long-term effects of seeding after wildfire on vegetation in Great Basin shrubland ecosystems

    USGS Publications Warehouse

    Knutson, Kevin C.; Pyke, David A.; Wirth, Troy A.; Arkle, Robert S.; Pilliod, David S.; Brooks, Matthew L.; Chambers, Jeanne C.; Grace, James B.

    2014-01-01

    1. Invasive annual grasses alter fire regimes in shrubland ecosystems of the western USA, threatening ecosystem function and fragmenting habitats necessary for shrub-obligate species such as greater sage-grouse. Post-fire stabilization and rehabilitation treatments have been administered to stabilize soils, reduce invasive species spread and restore or establish sustainable ecosystems in which native species are well represented. Long-term effectiveness of these treatments has rarely been evaluated. 2. We studied vegetation at 88 sites where aerial or drill seeding was implemented following fires between 1990 and 2003 in Great Basin (USA) shrublands. We examined sites on loamy soils that burned only once since 1970 to eliminate confounding effects of recurrent fire and to assess soils most conducive to establishment of seeded species. We evaluated whether seeding provided greater cover of perennial seeded species than burned–unseeded and unburned–unseeded sites, while also accounting for environmental variation. 3. Post-fire seeding of native perennial grasses generally did not increase cover relative to burned–unseeded areas. Native perennial grass cover did, however, increase after drill seeding when competitive non-natives were not included in mixes. Seeding non-native perennial grasses and the shrub Bassia prostrata resulted in more vegetative cover in aerial and drill seeding, with non-native perennial grass cover increasing with annual precipitation. Seeding native shrubs, particularly Artemisia tridentata, did not increase shrub cover or density in burned areas. Cover of undesirable, non-native annual grasses was lower in drill seeded relative to unseeded areas, but only at higher elevations. 4. Synthesis and applications. Management objectives are more likely to be met in high-elevation or precipitation locations where establishment of perennial grasses occurred. On lower and drier sites, management objectives are unlikely to be met with seeding alone

  7. Landscape heterogeneity controls growth variability of alder, willow, and birch shrubs in response to observed increases in temperature and snow

    NASA Astrophysics Data System (ADS)

    Tape, K. D.; Hallinger, M.; Buras, A.; Wilmking, M.

    2013-12-01

    Over the last decade, evidence has emerged for a circumarctic trend of increasing shrub cover in tundra regions. On the Alaskan tundra, repeat photography has shown spatial differences in shrub patch dynamics: since 1950, most patches expanded while some remained stable. In this study we explore the underpinnings of this landscape heterogeneity by sampling the three dominant shrubs of the Alaskan tundra--alder, willow and birch--and creating shrub ring width chronologies to determine the influence of climate variability on shrub growth. Shrubs of expanding patches of all three species grew at higher rates than shrubs of stable patches. Alder and willow shrubs in expanding patches exhibited mainly positive growth trends, while their counterparts in stable patches exhibited mainly negative growth trends. Birch shrub growth declined in expanding and stable patches. Alder and willow shrub growth rates and responses to climate were controlled more by soil characteristics than by their genus; expanding alder and willow shrubs showed significant positive correlations with spring and summer temperatures, whereas alder and willow shrubs of stable patches were negatively influenced by winter precipitation. The widely-scattered stable shrub patches sampled here are considered ';moist tussock tundra,' which covers 13.4% of the low arctic landscape. In moist tussock tundra, and presumably also wet tussock tundra, the negative influence of deeper snow on shrubs outweighed the positive influence of deeper snow on ground temperature and nutrient stocks articulated by the snow-shrub-microbe hypothesis. Thus, while shrubs of expanding patches have generally profited from warmer summers, shrubs of stable patches have suffered from increased soil moisture resulting from increased snowmelt water. These results underscore the spatial and temporal complexity in shrub-climate dynamics, which will require considerable finesse to appropriately integrate into modeling efforts.

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

    PubMed

    Cabral, Juliano Sa