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Biological soil crusts, consisting of cyanobacteria, green algae, lichens, and mosses, are important in stabilizing soils in semi-arid and arid lands. Integrity of these crusts is compromised by compressional disturbances such as foot, vehicle, or livestock traffic. Using a portable wind tunnel, we found threshold friction velocities (TFVs) of undisturbed crusts well above wind forces experienced at these sites; consequently, these soils are not vulnerable to wind erosion. However, recently disturbed soils or soils with less well-developed crusts frequently experience wind speeds that exceed the stability thresholds of the crusts. Crustal biomass is concentrated in the top 3 mm of soils. Sandblasting by wind can...
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...
We conducted a natural removal experiment, utilizing a local outbreak of sylvatic plague (Yersinia pestis) as the removal agent, to test the effects of removal of Gunnison's prairie dogs (Cynomys gunnisoni) on plant and nocturnal rodent assemblages in three grassland habitats (ponderosa, pinyon-juniper, and desert grasslands) in northern Arizona. We measured plant cover, rodent abundance, plant and rodent species richness, and plant and rodent composition at three treatment locations: active prairie dog colonies (n=15), inactive colonies (n=15), and control locations (n=15). Only the amount of plant cover differed significantly among treatments. As landscape level heterogeneity among habitat types increased, rodent...
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Biological soil crusts are regarded as an indicator of healthy landscapes. To understand the response of biological soil crusts to grazing in northern sagebrush steppe, we examined nine Artemisia-dominated sites in Wyoming where livestock have been excluded for 32–45 years. Using two common sampling methods (20 m line transects and 0.25 m2 quadrats) we determined biological soil crust cover and richness inside and outside exclosures. Total biological soil crust cover did not differ inside and outside the exclosures at any of the nine sites, regardless of monitoring method. Cover of biological soil crusts using the transect method ranged from 2% to 8% inside and 1% to 6% outside the exclosure. Cover of biological...
Harvest methods used to estimate plant biomass can be replaced by non-destructive methods, which are cost effective and allow for multiple estimates of biomass in the same location ([Catchpole and Catchpole, 1993] and [Sala and Austin, 2000]). Flombaum and Sala (2007) developed a method based on a model relating plant cover and aboveground biomass of dominant grass species of the Patagonian steppe. The study enlarged the range of cover and biomass by removing portions of individual tussock grasses and obtained significant relationships between cover and biomass data for all categories (Flombaum and Sala, 2007). Mont�s (2009) pointed out that reducing the area of a tuft could lead to an overestimation of the relationship...
The alien grass Bromus tectorum dominates stable annual-plant communities that have replaced native shrub-perennial grass communities over much of the semi-arid western United States. We conducted field competition experiments between B. tectorum and a native grass, Elymus elymoides, on two sites to determine the effects of B. tectorum competition on perennial grasses, and the role of B. tectorum competition in the stability of B. tectorum-dominated communities. B. tectorum competition acting on seedling-stage E. elymoides plants greatly reduced first-year relative growth rates and biomass which, in turn, reduced second-year survival, biomass, and flowering. However, B. tectorum competition acting on older E. elymoides...
This study determined the influence differing soil surface textures and vegetative covers have on the magnitude of wind erosion in a semi-arid environment. The study was conducted from March 2000 through late April 2000 on the Jornada Experimental Range approximately 37 km north of Las Cruces, New Mexico. Big Spring Number Eight (BSNE) samplers placed at nine locations, collected particulates in suspension and saltation at heights of 5, 10, 20, 50, and 100 cm from the following surfaces: loose sand, thick silty physical crust, flaky physical crust, weak desert pavement, and a forb/grass ground cover. BSNE samplers collected the largest amounts of sediment were collected in areas of loose sand and at sites directly...
We surveyed for pygmy rabbits, Brachylagus idahoensis, in Summer 2003 in Nevada (USA) to better determine the distribution, habitat, and soil patterns of this potentially threatened species. Pygmy rabbits and/or their sign (burrows and fecal pellets) were observed at 261 of 643 survey sites and their known distribution was extended 12 km to the south. Data on topography, soil, lithology, and hydrology were compared between sagebrush habitats where pygmy rabbits and/or their sign was present and absent. A predictive equation was produced and used as a model for characterizing habitats where pygmy rabbits were present. This model successfully explained the occurrence of pygmy rabbits and/or their sign on 56.7% of...
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...
Medium-sized kangaroo rats (Dipodomys spp. Gray) function as keystone species in the dynamics of desert bunchgrasses. We tested the hypothesis that kangaroo rat graminivory leads to reduced grass growth and inflorescence production, and that kangaroo rat grass consumption reflects their preferences for open microhabitats. We excluded kangaroo rats from grasses, and measured tiller loss, leaf and tiller growth and inflorescence production. We recorded the extent of tiller loss in grasses varying in tussock size or the extent of surrounding cover. Consumption of tillers by kangaroo rats was extensive, peaking in late summer. Grasses protected from kangaroo rat graminivory showed elevated leaf and tiller growth and...
Encroachment of the shrub Prosopis glandulosa Torr. (honey mesquite) into semi-arid grasslands is a serious concern in the south-western United States, yet little is known about the long-term dynamics of the invasion process. We used ten high-resolution aerial and satellite images taken from 1936 to 1996 to track the population dynamics and spatial pattern of all P. glandulosa greater than 2 m in diameter on a 75 ha area in southern New Mexico. Shrub cover and patch numbers increased from 1936 to the 1970s, then stabilized at 43% cover and 83 patches ha?1. Individual patches were extremely persistent: 95% of the area occupied by shrub patches in 1936 was still occupied in 1996. Recruitment into the 2 m size class...
Experiments were conducted to assess the influences of granivores on the seed bank in sagebrush-steppe. Rodent and/or ant exclosures were established at two distances from five harvester ant mounds. Monthly soil samples were collected from the exclosures, and from open access areas at two distances to ascertain changes in the seed bank. Seed dish experiments were conducted monthly to establish a maximum seed removal rate. Rodents were trapped monthly. More seeds were recovered from rodent exclosures than from ant exclosures. Seed banks changed temporally and spatially, with more seeds recovered in September and at 6 m from mounds. Rodents removed seeds more rapidly from seed dishes than did ants. Ants removed more...
Two native desert shrubs were evaluated for their growth potential and water and nitrogen uptake patterns over a nitrate-contaminated aquifer at a former uranium ore-processing facility in northeastern Arizona. Sarcobatus vermiculatus and Atriplex canescens are obligate and facultative phreatophytes, respectively, that dominate the local desert plant community. The main questions we addressed were: (1) Are these shrubs able to use water or nitrogen from the alluvial aquifer? (2) If so, does grazing interfere with that ability of shrubs? (3) What would be the ideal strategy to take up N from the plume and prevent its expansion and recharge using shrubs? ?18O and ?D isotope signatures from water in plant stem samples...
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Studies were conducted in the central Mojave Desert to quantify how creosote bushes (Larrea tridentata) respond to physical damage during large-scale military training exercises. Creosote bush possesses a resilient growth form that recovers from repeated physical damage via resprouts arising from meristems in stem bark below severed or crushed canopy units. At high levels of disturbance by heavy vehicles, nearly all individuals showed measurable breakage, but without additional damage each plant can regain a full canopy within 5 years under arid field conditions. Resprouts exhibited more vigorous growth and doubled the biomass accumulation stimulated by high rainfall of 1998, an El Niño year, vs. a normal year....
Climate change models envision an increase in summer precipitation in eastern California and adjacent arid regions by 2050, due to anthropogenic activities. Changes in the frequency, intensity and spatial patterns of rainfall pulses are likely to influence seedling recruitment and establishment, and ultimately community composition and dynamics. The effects of altered water availability might be complicated by the effect of adult plants on resources and conditions, potentially altering seedling recruitment success and affecting community succession. We tested the hypotheses that: (1) an experimental pulse representing a 25% increase in summer precipitation would increase photosynthesis for Artemisia tridentata and...
Differences in resource availability and quality along environmental gradients are important influences contributing to intraspecific variation in body size, which influences numerous life-history traits. Here, we examined variation in body size and sexual size dimorphism (SSD) in relation to temperature, seasonality, and precipitation among 10 populations located throughout Arizona of the western diamond-backed rattlesnake (Crotalus atrox). Specifically, in our analyses we addressed the following questions: (i) Are adult males larger in cooler, wetter areas? (ii) Does female body size respond differently to environmental variation? (iii) Is seasonality a better predictor of body size variation? (iv) Is SSD positively...
We discuss a new conceptual framework for arid and semi-arid systems that accounts for nonlinear dynamics and cross scale interactions in explaining landscape patterns and dynamics. Our framework includes a spatial and temporal hierarchy, and five key interacting components that connect scales of the hierarchy and generate threshold behaviors: (1) historical legacies that include climate, disturbance, and management regimes, (2) dynamic template of patterns in ecological variables and spatial context, (3) vertical and horizontal transport processes (fluvial, aeolian, animal), (4) rate, direction, and amount of resource redistribution between high and low resource areas, and (5) feedbacks among plants, animals, and...
Semiarid forests across the western USA and elsewhere are being thinned to reduce risk from fire, restore previous ecological conditions, and/or salvage trees from recently burned areas. Prescriptions and monitoring for thinning generally focus on biotic characteristics of vegetation, like tree density, rather than abiotic characteristics of soils and their loss, which are usually only considered in association with water erosion. Recent studies indicate that sediment transport by wind in forests is substantial and can exceed water transport, yet forest wind erosion responses to tree thinning and/or burning are unknown. We measured wind-driven horizontal dust flux, a metric related to wind erosion, with respect...
The spatial distribution of Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh within plant communities creates two distinct zones; underneath (subcanopy) and between shrub canopies (interspace). The purpose the study was to determine the influence of subcanopy and interspace zones on microsite characteristics and herbaceous vegetation. Study sites were located at the Northern Great Basin Experimental Range (NGBER) (56 km west of Burns, OR) and Baker Pass (80 km southeast of Burns, OR). At the NGBER, microsite and vegetation differences existed between subcanopy and interspace zones. Compared to the interspace, subcanopy zones were characterized by lower fluctuations in soil temperature, higher...
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We investigated the effects of winter and summer drought on a shrub/grass community of the Colorado Plateau in western North America, a winter-cold, summer-hot desert that receives both winter and summer precipitation. Summer, winter and yearlong drought treatments were imposed for 2 consecutive years using rainout shelters. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Growth for all three species was far more sensitive to winter than to summer...


map background search result map search result map Resprout characteristics of creosote bush (Larrea tridentata) when subjected to repeated vehicle damage Biological soil crusts in grazed and ungrazed Wyoming sagebrush steppe Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part II: effects on plant carbon assimilation and growth Summer and winter drought in a cold desert ecosystem (Colorado Plateau) part II: effects on plant carbon assimilation and growth Resprout characteristics of creosote bush (Larrea tridentata) when subjected to repeated vehicle damage Biological soil crusts in grazed and ungrazed Wyoming sagebrush steppe