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Mining activities are a major source of land degradation in arid regions, and remediation methods developed for mesic sites may not be appropriate for arid sites. In climates where potential evapotranspiration exceeds precipitation, it might be possible to prevent the migration of contaminants away from a mine site by controlling the site water balance through vegetation, and allowing natural attenuation processes to reduce pollutant levels over time. We investigated the feasibility of remediating a nitrate-contaminated source-plume system in a desert environment using biological methods. The study site was a former uranium mill in Monument Valley, Arizona, where NO3? used in ore processing had leaked from the soil...
Plant community structure in the southwestern United States co-varies with soil surface characteristics due to their role in controlling water availability. At the University of Arizona Desert Laboratory on Tumamoc Hill, we evaluated winter and summer season dynamics of photosynthesis in a dominant shrub species, Larrea tridentata (creosotebush), across soils with contrasting development of surface and sub-surface horizons. We measured pre-dawn water potential (?pd), stomatal conductance (gs), leaf nitrogen content (%N), and determined stable carbon isotope discrimination (?). There were no differences in these parameters throughout the winter, although ? was higher and %N was lower on the clay than sandy soil early...
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There is growing recognition among ecologists that ecosystem engineers play important roles in creating habitat for other species, but the comparative and combined effects of co-existing engineers are not well known. Here, we evaluated the separate and interactive effects of two burrowing rodents, Gunnison's prairie dogs (Cynomys gunnisoni) and banner-tailed kangaroo rats (Dipodomys spectabilis), on lizards in the Chihuahuan Desert grassland (USA). We found that the mounds and burrow systems of both rodent species provided important habitat for lizards, with lizard abundance being 2 to 4-fold higher on mounds than in adjacent areas without mounds. Kangaroo rat mounds supported greater numbers of lizards than prairie...
Pinyon and juniper have been expanding into sagebrush (Artemisia tridentata) ecosystems since settlement of the Great Basin around 1860. Herbaceous understory vegetation is eliminated as stand densities increase and the potential for catastrophic fires increases. Prescribed fire is increasingly used to remove trees and promote recovery of sagebrush ecosystems. We quantified the effects of prescribed fire, vegetation type, and time following fire on soil KCl extractable nitrogen and NaHCO3 extractable phosphorus in a pinyon?juniper woodland and its associated sagebrush ecosystem immediately before and for 4 years after a spring prescribed burn. Potassium chloride extractable NH4+ and total inorganic-N increased immediately...
Biological soil crusts (biocrusts) cover up to 60–70% of the soil surface in grasslands rehabilitated during the “Grain for Green� project implemented in the hilly Loess Plateau region in 1999. As biocrusts fix nitrogen (N), they are an important part of restoring soil fertility. We measured nitrogenase activity (NA) in biocrusts from sites rehabilitated at six different time periods to estimate 1) the effects of moisture content and temperature on NA in biocrusts of different ages and 2) the potential N contribution from biocrusts to soils and plants in this region. Results show that NA in the biocrusts was mostly controlled by the species composition, as the activity of biocrusts dominated by free-living...
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Previous studies have shown that landscape structure influences animal movement and population structure. In this study, we show an indirect interaction between beetles and prairie dogs due to prairie dog ecosystem engineering. Gunnison's prairie dog (Cynomys gunnisoni Hollister) towns have more bare ground and are structurally less complex than adjacent unmodified grasslands. This results in bare ground facilitating beetle movement. Differences in landscape structure between prairie dog towns and unmodified grasslands had a significant effect on the movement of the darkling beetle, Eleodes hispilabris Say. Beetle movement tended to be more linear (pathway fractal dimension approached 1) on prairie dog habitats...
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Biological soil crusts (BSCs) are an integral part of dryland ecosystems and often included in long-term ecological monitoring programs. Estimating moss and lichen cover is fairly easy and non-destructive, but documenting cyanobacterial level of development (LOD) is more difficult. It requires sample collection for laboratory analysis, which causes soil surface disturbance. Assessing soil surface stability also requires surface disturbance. Here we present a visual technique to assess cyanobacterial LOD and soil surface stability. We define six development levels of cyanobacterially dominated soils based on soil surface darkness. We sampled chlorophyll a concentrations (the most common way of assessing cyanobacterial...
Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh-bunchgrass communities were used to analyze the influence of disturbances on invasibility after a recovery period. These communities evolved with periodic fires shifting dominance from shrubs to herbaceous species. However, fire can facilitate Bromus tectorum L. invasion of these plant communities. We evaluated the invasibility of A. tridentata ssp. wyomingensis-bunchgrass communities 4 years after prescribed fall burning at six sites by comparing burned to unburned (control) communities. These communities did not have B. tectorum present prior to introduction. B. tectorum was introduced at 1, 10, 100, 1000, and 10,000 seeds m?2 in burned and...
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Saltcedar (Tamarix spp.) is an exotic, invasive shrub of riparian corridors in the western United States that can promote soil salinization via leaf exudates as Tamarix litter accumulates on the soil surface. Tamarix stands occur in association with big sagebrush (Artemisia tridentata), greasewood (Sarcobatus vermiculatus), and cottonwood (Populus deltoides) in northern Wyoming, depending on topographic position. Revegetation of Tamarix-invaded sites can be limited by altered soil conditions. Tamarix stands in northcentral Wyoming were selected to determine the relationship of Tamarix shrubs and associated vegetation to soil salinity, pH, and nutrients. In general, salinity of surface soils (0?5 cm) was greater...
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Ecosystem engineering by animals can create new habitats and increase the heterogeneity of the habitat mosaic that in turn can increase plant and animal diversity. Prairie dogs in North America alter both the above- and below-ground structure of the landscape and create novel habitats in grassland ecosystems. The ground-dwelling arthropod community associated with Gunnison's prairie dog modified habitats is compositionally different from that found in the surrounding grassland. Individual arthropod families and species have different distributions in both active prairie dog towns and inactive towns, compared to unmodified grasslands. These different responses to ecosystem engineering increase beta (between-habitat)...
All species of the genus Phrynosoma are cryptically colored and patterned, but two species have bold black or white vertebral-line patterns on their dorsal surfaces. Phrynosoma mcallii lives on aeolian-sand substrates and often rests below shrubs. It has a black vertebral line which is hypothesized to mimic dark shadows of stems falling on the smooth, litter-free sand beneath shrubs. Phrynosoma cornutum inhabitats grasslands and arid shrub-habitats in which below-shrub sites are littered with bleached plant stems. The white middorsal stripe of this species is thought to mimic white stems of the under-shrub litter. Although crypticity in horned lizards has been extensively studied, the two examples of apparent object...
Relatively few studies have examined the ecological and biogeochemical effects of livestock grazing in southeastern Utah. In this study, we evaluated how grazing has affected soil organic carbon and nitrogen to a depth of 50 cm in grasslands located in relict and actively-grazed sites in the Canyonlands physiographic section of the Colorado Plateau. We also evaluated differences in plant ground cover and the spatial distribution of soil resources. Results show that areas used by domestic livestock have 20% less plant cover and 100% less soil organic carbon and nitrogen compared to relict sites browsed by native ungulates. In actively grazed sites, domestic livestock grazing also appears to lead to clustered, rather...
Soil P transformations and distribution studies under water limited conditions that characterize many grasslands may provide further insight into the importance of abiotic and biotic P controls within grass-dominated ecosystems. We assessed transformations between P pools across four sites spanning the shortgrass steppe, mixed grass prairie, and tallgrass prairie along a 400-mm precipitation gradient across the central Great Plains. Pedon total elemental and constituent mass balance analyses reflected a pattern of increased chemical weathering from the more arid shortgrass steppe to the more mesic tallgrass prairie. Soil surface A horizon P accumulation was likely related to increased biocycling and biological mining....
Blackbrush is a dominant shrub species in the transition zone between North American warm and cold deserts. Its seeds are dormant at dispersal and lose dormancy in response to moist chilling. Seeds from warmer low-elevation habitats have shorter chilling requirements and a higher optimum chilling temperature than those from colder habitats where winter snow regularly occurs. This ecotypic variation functions to time germination optimally in habitats with contrasting chilling regimes. Regulation of germination phenology is an important feature of the life history of this ecotonal species, which must be able to migrate elevationally through recruitment from seed in response to long-term climatic shifts in order to...
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Relatively few studies have examined the ecological and biogeochemical effects of livestock grazing in southeastern Utah. In this study, we evaluated how grazing has affected soil organic carbon and nitrogen to a depth of 50 cm in grasslands located in relict and actively-grazed sites in the Canyonlands physiographic section of the Colorado Plateau. We also evaluated differences in plant ground cover and the spatial distribution of soil resources. Results show that areas used by domestic livestock have 20% less plant cover and 100% less soil organic carbon and nitrogen compared to relict sites browsed by native ungulates. In actively grazed sites, domestic livestock grazing also appears to lead to clustered, rather...
Accurately assessing free-ranging animals? patterns of surface activity and refuge use is critical, yet fundamentally challenging for biologists and wildlife managers. We evaluate the accuracy of an automated technique?temperature-based activity estimation (TBAE)?in estimating surface activity and refuge use patterns of two sympatric reptiles, the western diamond-backed rattlesnake (Crotalus atrox) and the Gila monster (Heloderma suspectum) in the Sonoran Desert. TBAE derived from a comparison of body temperature to shaded air temperature was effective in estimating the overall percent surface activity for both rattlesnakes (observed surface activity 51.8%, TBAE estimated surface activity 48.2%) and Gila monsters...
A 1.6 ha plot of Atriplex canescens (fourwing saltbush) was established in a desert soil at a former uranium ore-processing plant, near Monument Valley, Arizona, to remediate nitrate and ammonium N contamination. The plants were irrigated to stimulate growth and N uptake. However, NO3? loss from the soil was unexpectedly rapid. Initially, the soil contained approximately 180 mg kg?1 NO3??N distributed at depths up to 4.6 m, but concentrations decreased to 80 mg kg?1 after 41 months. Losses occurred throughout the plot at all soil depths. NH4?N remained unchanged (ca.180 mg kg?1). Soil moisture was generally below field capacity and soil?water flux showed no net downward movement over the course of the study. A salt...
Patterns and processes involved in litter breakdown on desert river floodplains are not well understood. We used leafpacks containing Fremont cottonwood (Populus deltoides subsp. wislizenii) leaf litter to investigate the roles of weather and microclimate, flooding (immersion), and macroinvertebrates on litter organic matter (OM) and nitrogen (N) loss on a floodplain in a cool-temperate semi-arid environment (Yampa River, northwestern Colorado, USA). Total mass of N in fresh autumn litter fell by 20% over winter and spring, but in most cases there was no further N loss prior to termination of the study after 653 days exposure, including up to 20 days immersion during the spring flood pulse. Final OM mass was 10?40%...
Cyanobacterial soil crusts are a community of microorganisms living in the soil surface of different habitats worldwide. Through photosynthesis, cyanobacteria produce extracellular polysaccharides (EPS) increasing the soil carbon (C) pool as carbohydrates. The layer of polysaccharides also acts as a mechanical structure surrounding the filamentous cyanobacteria that together with the soil particles form stable aggregates in the topsoil thus decreasing C loss by erosion. Thus despite their apparent importance to the dryland system we have only a limited understanding of their role and possible applications in dryland soil environments. This review draws on these disparate sources of information in order to provide...
Soil evaporation, a critical ecohydrological process in drylands, can exhibit substantial spatio-temporal variation. Spatially, ecohydrological controls of soil evaporation may generally depend on a hierarchical structure spanning from the presence or absence of litter, through canopy patches of woody plants and intercanopy patches separating them, up to the overall vegetation mosaic characterized by density of woody plant cover in the landscape, although assessment of these factors in concert is generally lacking. Temporally, ecohydrological controls can be further complicated by not only seasonal climate, but also phenology, particularly in seasonally deciduous drylands. We experimentally assessed the interactive...
map background search result map search result map Engineering rodents create key habitat for lizards Soil salinity patterns in Tamarix invasions in the Bighorn Basin, Wyoming, USA Biogeochemical and ecological impacts of livestock grazing in semi-arid southeastern Utah, USA Visually assessing the level of development and soil surface stability of cyanobacterially dominated biological soil crusts Conservation of prairie dog ecosystem engineering may support arthropod beta and gamma diversity Prairie dog engineering indirectly affects beetle movement behavior Conservation of prairie dog ecosystem engineering may support arthropod beta and gamma diversity Prairie dog engineering indirectly affects beetle movement behavior Engineering rodents create key habitat for lizards Biogeochemical and ecological impacts of livestock grazing in semi-arid southeastern Utah, USA Visually assessing the level of development and soil surface stability of cyanobacterially dominated biological soil crusts Soil salinity patterns in Tamarix invasions in the Bighorn Basin, Wyoming, USA