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Biological soil crusts provide habitat for microarthropods of various trophic groups in arid systems, but the community composition and functional role of microarthropods in these unique systems are not well characterized for many desert locations. This study examined the microarthropod community, including mites, collembolans, and tardigrades, associated with early- and late-successional stage biological soil crusts at two locations, Colorado Plateau (southeastern Utah) and Chihuahuan Desert (southern New Mexico). Most microarthropod groups were more abundant in Colorado Plateau than Chihuahuan Desert, and tardigrades were more abundant near the surface (0?10 cm) than at depth (10?30 cm). Although the microarthropod...
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Animals that modify their environment through engineering and herbivory have important impacts on ecosystems, yet the interactive roles of such species have rarely been studied. We studied the comparative and interactive effects of two burrowing herbivorous rodents, Gunnison's prairie dogs (Cynomys gunnisoni) and banner-tailed kangaroo rats (Dipodomys spectabilis), on vegetation where they co-occurred in a Chihuahuan Desert grassland. We found that their effects remained distinct and, thus, non-substitutable, where they co-occurred. The rodents differentially altered plant community structure relative to their different mound types, herbivory, and spatial scales of disturbance. Vegetation structure and plant species...
This research experimentally examined seasonal effects of fire on biological soil crusts and perennial grasses in shortgrass steppe. We predicted dormant-season fire would have greater negative effects on biological soil crusts than fire during the growing season, but less of an impact on perennial grasses than fire during the growing season. Treatments were dormant- and growing-season fires and unburned reference condition plots. Response variables included biological soil crust and grass percent ground cover, and crust nitrogen fixation and chlorophyll a content. Results indicated shortgrass steppe can recover from fire in three to 30 months, dependent on fire season. Burning during the dormant-season had little...
Recent drought across the desert Southwest US may strongly affect the physiological functioning of evergreen desert species that maintain leaves through these dry periods. In July 2002 we compared the ecophysiological performance of the open-canopied, small-leaved creosotebush (Larrea tridentata) to the dense-canopied, more broad-leaved jojoba (Simmondsia chinensis) growing on a ridge-top, east- and west-facing slopes to assess how differences in leaf habit and exposure affect these species' ability to withstand severe drought. Standardized precipitation index (SPI) from 100 years precipitation data showed July 2002 rainfall was normal, but the 12-month period ending July 2002 was of extreme aridity (SPI = ?2.71)....
In this paper, we develop a five-step approach for analysis of historical relationships among areas of endemism using a set of 22 clades (9 mammal, 7 bird, 4 reptile, 1 amphibian, and 1 cactus) drawn from the warm deserts biota of western North America. As has been suggested in previous studies of portions of this biota, our results suggest a complex biogeographic history, but with substantial support for the influence of several major vicariant events in the diversification and assembly of the aridlands biota. We discuss and demonstrate the reciprocal strengths (and weaknesses) of phylogeography and phylogenetic biogeography for defining areas of endemism, analysing vicariance and dispersal, and dealing with temporal...
The recognition and characterization of aeolian dust in soil contribute to a better understanding of landscape and ecosystem dynamics of drylands. Results of this study show that recently deposited dust, sampled in isolated, mostly high-ground settings, is chemically and mineralogically similar on varied geologic substrates over a large area (15 000 km2) in the Mojave Desert. The silt-plus-clay fraction (fines) on these isolated surfaces is closely alike in magnetic-mineral composition, in contrast to greatly dissimilar magnetic compositions of rock surfaces of vastly different lithologies, on which the fines have accumulated. The fines, thus, are predominantly deposited dust. The amounts of potential nutrients...
The desert/grassland biome transition zone in central New Mexico provides an important region for testing species differences to changing environmental conditions and various land management practices. Interactions of black grama (Bouteloua eripoda) and blue grama (Bouteloua gracilis) significantly affect the resultant plant community and its influence on system structure and function. Black grama demonstrated higher productivity, especially after wet years, and this species has increased its dominance during the 20-year period since livestock grazing was removed. While black grama can alter the previous pattern of overgrazing and desertification in this transition zone, our experiments demonstrated that it was...
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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...
Grass restoration on remote arid rangelands may require irrigation to stimulate establishment. However, irrigation on undeveloped sites is costly. Vertical irrigation tubes that direct applied moisture to subsurface zones where evaporation is reduced, and hydrogels that prevent applied moisture from infiltrating beyond plant root zones can maximize the portion of applied water available for plant uptake. The survival and growth of Bouteloua eriopoda (Torr.) Torr. transplants irrigated with either starch- or acrylic-based hydrogels contained in one of three embedded watering tube styles were evaluated in a greenhouse trial. A field trial evaluated differences in transplant survival and cover between treatments consisting...
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Climate change and invasions by non-native organisms are two factors of global change likely to alter the structure and function of arid and semi-arid ecosystems. We conducted a large-scale field experiment to determine how changes in amount of summer precipitation and invasions by an African grass (Eragrostis lehmanniana) may interact with soil texture to affect community and ecosystem processes in temperate grasslands and savannas of southern Arizona, USA. In particular, we investigated the response of soil moisture at several soil depths within seventy-two 2.7 m2 plots under six 9 m×18 m rainout shelters to a 3-fold difference in irrigation between February and November 2002, as well as to a single large pulse...
Soil surfaces dominated by cyanobacteria and cyanolichens (such as Collema sp.) are widespread in deserts of the world. The influence of these biological soil crusts on the uptake of bioessential elements is reported for the first time for six seed plants of the deserts of Utah. This sample almost doubles the number of species for which the influence of biological soil crusts on mineral uptake of associated vascular plants is known. These new case studies, and others previously published, demonstrate that cyanobacterial or cyanobacteria- Collema crusts significantly alter uptake by plants of many bioessential elements. In studies now available, these crusts always increase the N content of associated seed plants....
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Changes in precipitation patterns and inputs have the potential to cause major changes in productivity, composition, and diversity of terrestrial plant communities. Vegetation response to altered timing of precipitation was assessed during a 7-year experiment in an Artemisia tridentata spp. wyomingensis community in the northern Great Basin, USA. Four permanent rainout shelters excluded natural rainfall, with seasonal distribution of precipitation controlled with the use of an overhead sprinkler system. Precipitation treatments under each shelter were WINTER, SPRING, and CURRENT. The WINTER treatment received 80% of its water between October and March; in the SPRING treatment 80% of total water was applied between...
Global environmental change is altering temperature, precipitation patterns, and resource availability in aridland ecosystems. In 2006, we established a multifactor global change experiment to determine the interactive effects of nighttime warming, increased atmospheric N deposition, and more frequent occurrence of El Ni�o years on plant community dynamics in a northern Chihuahuan Desert grassland. Here we only report the results of warming and N addition from the first monsoon growing season prior to the imposition of the precipitation treatments. Our passive nighttime warming treatment increased daily minimum temperatures by 1.4?3.0 �C. Fertilization increased NO3N supply, as measured with Root Simulator Probes,...
Comparative water relations in Artemisia tridentata Nutt. subsp. wyomingensis and Kochia prostrata (L. ), credited to Romo, James T, published in 1988. Published in Journal of Arid Environments, volume 15, on pages 53 - 64, in 1988.
Landscapes in the arid and semiarid region of southwesternNorth America are influenced by summertime precipitation generated by the North American Monsoon System (NAMS). Increases in seasonal precipitation during the NAMS lead to a set of cascading effects on the ecohydrological processes occurring on the land surface, ranging from increases in ecosystem productivity and wildlife migrations to streamflow generation.While this general response has been recognized in studies ofNorthAmerican deserts, there have been relatively few coordinated efforts to quantify the interacting processes that characterize the ecohydrology of the NAMS. This special issue of the Journal of Arid Environments documents recent progress...
Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs were characterized using 32P as a nutrient tracer. Larrea tridentata's horizontal zone of influence was sparse near the plant's stem base, with a maximum probability of accessing 32P (Pmax) of 41%. However, its horizontal zone of influence extended beyond 5 m, and the distance from the stem base at which the probability of accessing 32P was half Pmax (L503 m) was significantly greater than the other three shrubs. Ambrosia dumosa's zone of influence was dense near the plant's stem base (Pmax78%), but was rare at distances >2 m (L501 m). Zones of influence for Lycium andersonii and Lycium pallidum were intermediate between those...
A portable wind tunnel was used to test the contribution of biological and physical elements to overall soil aggregation on a soil dominated by biological soil crusts in south-eastern Australia. After moderate disturbance and simulated wind erosion, 90% of surface aggregates on the loamy soil and 76% on the sandy soil were dominated by biological elements (cryptogams). Lower levels of biological bonding were observed on the severely disturbed treatment. Linear regression indicated a significant positive relationship (r2=0·72) between biological soil crust cover and dry aggregation levels greater than 0·85mm. To maintain sediment transport below an erosion control target of 5gm−1s−1 for a 65kmh−1 wind at...
We set up an automatic weather station over a playa (the flat floor of an undrained desert basin that becomes at times a shallow lake), approximately 65 km east?west by 130 km north?south, located at the U.S. Army Dugway Proving Ground (40�08?N, 113�27?W, 1124 m above mean sea level) in north-western Utah, U.S.A., in 1999. This station measured the incoming (Rsi) and outgoing (Rso) solar or shortwave radiation using two CM21 Kipp & Zonen pyranometers (one inverted), the incoming (Rli or atmospheric) and outgoing (Rlo or terrestrial) longwave radiation, using two CG1 KippZonen pyrgeometers (one inverted), and the net (Rn) radiation using a Q*7 net radiometer (Radiation Energy Balance System, REBS). We also measured...
The Artemisia tridentata spp. wyomingensis (Beetle & A. Young) S.L. Welsh alliance is the most extensive of the big sagebrush complex in the Intermountain West and is characterized by a wide range of environments and vegetation heterogeneity. The purpose of this study was to identify environmental factors driving variation in plant species composition and determine the potential for using environmental factors to explain vegetation characteristics of the A. tridentata spp. wyomingensis alliance. Seventeen environmental factors and seven vegetation response variables were measured on 107 relatively undisturbed, late seral A. tridentata spp. wyomingensis sites across southeastern Oregon and northern Nevada. Non-metric...
In this study we present a technique to discriminate between climate or human-induced dryland degradation, based on evaluations of AVHRR NDVI data and rainfall data. Since dryland areas typically have high inter-annual rainfall variations and rainfall has a dominant role in determining vegetation growth, minor biomass trends imposed by human influences are difficult to verify. By performing many linear regression calculations between different periods of accumulated precipitation and the annual NDVImax, we identify the rainfall period that is best related to the NDVImax and by this the proportion of biomass triggered by rainfall. Positive or negative deviations in biomass from this relationship, expressed in the...
map background search result map search result map The influence of soil texture and vegetation on soil moisture under rainout shelters in a semi-desert grassland The effects of precipitation timing on sagebrush steppe vegetation Potential environmental controls on nitrogenase activity in biological crusts of the northern Chihuahuan Desert Burrowing rodents increase landscape heterogeneity in a desert grassland Burrowing rodents increase landscape heterogeneity in a desert grassland The influence of soil texture and vegetation on soil moisture under rainout shelters in a semi-desert grassland The effects of precipitation timing on sagebrush steppe vegetation Potential environmental controls on nitrogenase activity in biological crusts of the northern Chihuahuan Desert