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A 36,200 cal yr B.P. vegetation history was developed from macrofossils and pollen from 55 packrat middens from 1287 to 1442 m elevation in the Peloncillo Mountains of southeasternmost Arizona, USA. Today, these elevations are dominated by semidesert grassland with a mixture of Chihuahuan and Sonoran Desert shrubs, including an eastern disjunct population of jojoba (Simmondsia chinensis). From 36,200 to 15,410 cal yr B.P., rocky areas just above large, pluvial lakes that occupied what are now dry playas supported Pinus edulis, Juniperus osteosperma, Juniperus cf. coahuilensis, Quercus cf. turbinella and a rich understory of summer-flowering C4 annuals and grasses, indicating abundant summer rains and mild winters....
1. Soil disturbance by animals affects the availability of water, nutrients, sediment and seeds, which are critical for the maintenance of functional ecosystems. We examined long-lived faunal structures across six vegetation communities in the northern Chihuahuan desert of New Mexico, USA, testing the proposition that disturbances in undesertified grassland differ in magnitude and effect from those in desertified grassland. 2. Vertebrate and invertebrate disturbances totalled 18.9 structures ha−1 across 18 sites. The most common were pits and mounds of American badgers (Taxidea taxus, 32%), nests of the ant Aphaenogaster cockerelli (18.8%) and mounds of kangaroo rats (Dipodomys spectabilis, 31%). 3. Desertification...
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Natural landscapes in the Southwestern United States are changing. In recent decades, rising temperatures and drought have led to drier conditions, contributed to large-scale ecological impacts, and affected many plant and animal species across the region. The current and future trajectory of climate change underscores the need for managers and conservation professionals to understand the impacts of these patterns on natural resources. In this regional assessment of the Southwest Climate Change Initiative, we evaluate changes in annual average temperatures from 1951–2006 across major habitats and large watersheds and compare these changes to the number of species of conservation concern that are found within these...
Drought and freezing are both known to limit desert plant distributions, but the interaction of these stressors is poorly understood. Drought may increase freezing tolerance in leaves while decreasing it in the xylem, potentially creating a mismatch between water supply and demand. To test this hypothesis, we subjected Larrea tridentata juveniles grown in a greenhouse under well-watered or drought conditions to minimum temperatures ranging from -8 to -24 �C. We measured survival, leaf retention, gas exchange, cell death, freezing point depression and leaf-specific xylem hydraulic conductance (k?). Drought-exposed plants exhibited smaller decreases in gas exchange after exposure to -8 �C compared to well-watered...
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These bat location estimates have been reported by Bogan and others (In press) and come in the form of a GIS shape file. Three species of nectar-feeding phyllostomid bats migrate north from Mexico into deserts of the United States (U.S.) each spring and summer to feed on blooms of columnar cacti and century plants (Agave spp). However, the habitat needs of these important desert pollinators are poorly understood. We followed the nighttime movements of two species of long-nosed bats (Leptonycteris yerbabuenae and L. nivalis) in an area of late-summer sympatry at the northern edges of their migratory ranges. We radiotracked bats in extreme southwestern New Mexico during 22 nights over two summers and acquired location...
State-and-transition models are increasingly being used to guide rangeland management. These models provide a relatively simple, management-oriented way to classify land condition (state) and to describe the factors that might cause a shift to another state (a transition). There are many formulations of state-and-transition models in the literature. The version we endorse does not adhere to any particular generalities about ecosystem dynamics, but it includes consideration of several kinds of dynamics and management response to them. In contrast to previous uses of state-and-transition models, we propose that models can, at present, be most effectively used to specify and qualitatively compare the relative benefits...
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Grasslands of the Sky Islands region once covered over 13 million acres in southeastern Arizona and adjacent portions of New Mexico, Sonora, and Chihuahua. Attempts to evaluate current ecological conditions suggest that approximately two thirds of these remain as intact or restorable grassland habitat. These grasslands provide watershed services such as flood control and aquifer recharge across the region, and continue to support dozens of species of concern. Prioritizing conservation interventions for these remaining grassland blocks has been challenging. Reliable data on condition and conservation value of grasslands in the region have not been systematically summarized. State and national boundaries further complicate...
Late Quaternary histories of two North American desert biomes—C4 grasslands and C3 shrublands—are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial–interglacial cycle. By contrast, key C3 desert shrubs appeared somewhat abruptly after 5000 cal. yr BP. Bioclimatic envelopes for select C4 and C3 species are mapped to interpret the glacial–interglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert...
Increased variability in precipitation, including frequency of drought, is predicted for many arid and semiarid regions globally. The ability of soils to retain water can increase resilience by buffering vegetation communities against precipitation extremes. Little is known, however, about water retention by carbonate-cemented soil horizons, which occur extensively in arid and semiarid ecosystems. It has been speculated that they may significantly modify vertical and temporal distribution of plant-available water (PAW). To investigate this hypothesis, PAW was monitored at three sites in a mixed shrub-grass community in southern New Mexico, USA, across soils with differing degrees of carbonate horizon development:...
Past research has shown that the most important areas for active sand movement in the northern part of the Chihuahuan Desert are mesquite-dominated desert ecosystems possessing sandy soil texture. The most active sand movement in the mesquite-dominated ecosystems has been shown to take place on elongated bare soil patches referred to as streets . Aerodynamic properties of mesquite streets eroded by wind should be included in explaining how mesquite streets are more emissive sand sources than surrounding desert land. To understand the effects of wind properties, we measured them at two flat mesquite sites having highly similar soil textures but very different configurations of mesquite. The differences in wind properties...
The Chihuahuan desert of New Mexico, USA, has changed in historical times from semiarid grassland to desert shrublands dominated by Larrea tridentata and Prosopis glandulosa. Similar displacement of perennial grasslands by shrubs typifies desertification in many regions. Such structural vegetation change could alter average values of net primary productivity, as well as spatial and temporal patterns of production. We investigated patterns of aboveground plant biomass and net primary production in five ecosystem types of the Jornada Basin Long-Term Ecological Research (LTER) site. Comparisons of shrub-dominated desertified systems and remnant grass-dominated systems allowed us to test the prediction that shrublands...
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Resumen ejecutivo El objetivo del presente Plan Maestro de la Alianza Regional para la Conservación de Pastizales del Desierto Chihuahuense es brindar un marco de cooperación para la acción regional para los estados que integran el Desierto Chihuahuense. Como concepto rector de este documento se ha tomado el del desarrollo sustentable, es decir, se invita a explorar y abordar las vertientes sociales y económicas de toda actividad que tenga que ver con el manejo y uso de los pastizales como ecosistema natural y viceversa. Este documento está dividido en dos partes fundamentales. La primera ofrece una perspectiva continental y nacional sobre el Desierto Chihuahuense, su importancia ambiental, económica y social;...
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RESUMEN En México y EUA, los pastizales del Desierto Chihuahuense han experimentado un gran deterioro desde mediados de 1800's. Ello se ha debido principalmente deficientes prácticas ganaderas, al cambio climático, la supresión del fuego, a la fragmentación de hábitat y cambio de uso de suelo. En conjunto, se ha provocado un incremento en los escurrimientos y la erosión, una disminución de la diversidad biológica y pérdida en las concentraciones de aves, incremento en la invasión de especies no nativas y una disminución en la cantidad de forraje para animales domésticos y silvestres. La Estrategia para la Conservación de los Pastizales de Desierto Chihuahuense (ECOPAD) ofrece un esquema de cooperación para enfrentar...
Using 18 years of census data from permanent quadrats, we examined the interactions between spatially coexisting but temporally segregated winter and summer ephemeral plant communities in the Chihuahuan Desert. The ability of winter and summer annuals to achieve nearly complete temporal segregation by partitioning the bimodal annual rainfall permits the coexistence of a diverse flora of annual (and perennial) plants in this unproductive arid environment. Despite the differences in their biogeographical affinities and temporal segregation, long-term data indicated that at the scales of both the entire 20-ha study site and small 0.25-m2 sample quadrats, abundances of plants were never high in two successive growing...
Biological soil crusts are key mediators of carbon and nitrogen inputs for arid land soils and often represent a dominant portion of the soil surface cover in arid lands. Free-living soil nematode communities reflect their environment and have been used as biological indicators of soil condition. In this study, we test the hypothesis that nematode communities are successionally more mature beneath well-developed, late-successional stage crusts than immature, early-successional stage crusts. We identified and enumerated nematodes by genus from beneath early- and late-stage crusts from both the Colorado Plateau, Utah (cool, winter rain desert) and Chihuahuan Desert, New Mexico (hot, summer rain desert) at 0?10 and...
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​Abstract: Climate change predictions include warming and drying trends, which are expected to be particularly pronounced in the southwestern United States. In this region, grassland dynamics are tightly linked to available moisture, yet it has proven difficult to resolve what aspects of climate drive vegetation change. In part, this is because it is unclear how heterogeneity in soils affects plant responses to climate. Here, we combine climate and soil properties with a mechanistic soil water model to explain temporal fluctuations in perennial grass cover, quantify where and the degree to which incorporating soil water dynamics enhances our ability to understand temporal patterns, and explore the potential consequences...
Categories: Data, Publication; Types: Citation, Map Service, OGC WFS Layer, OGC WMS Layer, OGC WMS Service; Tags: 2012, AZ-02, AZ-03, AZ-04, Academics & scientific researchers, All tags...
In many ecosystems, seasonal shifts in temperature and precipitation induce pulses of primary productivity that vary in phenology, abundance, and nutritional quality. Variation in these resource pulses could strongly influence community composition and ecosystem function, because these pervasive bottom-up forces play a primary role in determining the biomass, life cycles, and interactions of organisms across trophic levels. The focus of this research is to understand how consumers across trophic levels alter resource use and assimilation over seasonal and interannual timescales in response to climatically driven changes in pulses of primary productivity. We measured the carbon isotope ratios (delta(13)C) of plant,...
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This report is volume 2 of a two-volume ecological assessment of grassland ecosystems in the Southwestern United States. Broad-scale assessments are syntheses of current scientific knowledge, including a description of uncertainties and assumptions, to provide a characterization and comprehensive description of ecological, social, and economic components within an assessment area. Volume 1 of this assessment focused on the ecology, types, conditions, and management practices of Southwestern grasslands. Volume 2 (this volume) describes wildlife and fish species, their habitat requirements, and species-specific management concerns, in Southwestern grasslands. This assessment is regional in scale and pertains primarily...
Question: How do patterns in colonization and patch expansion of an invasive woody plant (Larrea tridentata, Zygo-phyllaceae) differ between two grassland ecosystems at a biome transition zone? Location: Semi-arid/arid transition zone in central New Mexico. Methods: Frequency of occurrence, height, and surface area of saplings (n = 134) and patches of adult plants (n = 247) of the invasive shrub, L. tridentata, were measured within a mosaic of ecosystems dominated either by the Chihuahuan Desert species, Bouteloua eriopoda (Poaceae), or the shortgrass steppe species, B. gracilis, located within 1 km of the L. tridentata-dominated ecosystem. Distances between L. tridentata patches and patch area were used to estimate...
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We used the acetylene reduction assay to analyse soil nitrogenase activity at the Jornada Long-Term Ecological Research site (northern Chihuahuan Desert, New Mexico, U.S.A.). A three-day irrigation and fertilization experiment showed that water and carbon (glucose) enhanced nitrogenase activity, while NH4NO3 reduced activity. Micronutrient (Mo, Fe, Co) and phosphorus fertilization had no significant effect. A survey of Jornada Basin soils did not reveal an inverse relationship between nitrogenase activity and the ratio of available nitrogen (N) to phosphorus (P), as hypothesized; however, the highest rates of nitrogenase activity were detected in tarbush floodplain soils with a low ratio of available N to P. These...


map background search result map search result map Potential environmental controls on nitrogenase activity in biological crusts of the northern Chihuahuan Desert Sustaining the Grassland Sea Assessment of Grassland Ecosystem Conditions in the Southwestern United States: Wildlife and Fish, Volume 2 Managing Changing Landscapes in the Southwestern United States Estrategia para la Conservación de los Pastizales del Desierto Chihuahuense (ECOPAD) Plan Maestro de la Alianza Regional para la Conservación de los Pastizales del Desierto Chihuahuense 2011-2016 Radio telemetry data on nighttime movements of two species of migratory nectar-feeding bats (Leptonycteris) in Hidalgo County, New Mexico, late-summer 2004 and 2005 Publication and Report: Ecosystem Water Balance in a Desert Grassland Potential environmental controls on nitrogenase activity in biological crusts of the northern Chihuahuan Desert Radio telemetry data on nighttime movements of two species of migratory nectar-feeding bats (Leptonycteris) in Hidalgo County, New Mexico, late-summer 2004 and 2005 Sustaining the Grassland Sea Estrategia para la Conservación de los Pastizales del Desierto Chihuahuense (ECOPAD) Plan Maestro de la Alianza Regional para la Conservación de los Pastizales del Desierto Chihuahuense 2011-2016 Managing Changing Landscapes in the Southwestern United States Assessment of Grassland Ecosystem Conditions in the Southwestern United States: Wildlife and Fish, Volume 2 Publication and Report: Ecosystem Water Balance in a Desert Grassland