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Often as a result of large-scale military maneuvers in the past, many soils in the Mojave Desert are highly vulnerable to soil compaction, particularly when wet. Previous studies indicate that natural recovery of severely compacted desert soils is extremely slow, and some researchers have suggested that subsurface compaction may not recover. Poorly sorted soils, particularly those with a loamy sand texture, are most vulnerable to soil compaction, and these soils are the most common in alluvial fans of the Mojave Desert. Recovery of compacted soil is expected to vary as a function of precipitation amounts, wetting-and-drying cycles, freeze-thaw cycles, and bioturbation, particularly root growth. Compaction recovery,...
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This research considers the applicability of different vegetation indices at 30 m resolution for mapping and monitoring desert wetland (cienega) health and spatial extent through time at Cienega Creek in southeastern Arizona, USA. Multiple stressors including the risk of decadal-scale drought, the effects of current and predicted global warming, and continued anthropogenic pressures threaten aquatic habitats in the southwest and cienegas are recognized as important sites for conservation and restoration efforts. However, cienegas present a challenge to satellite-imagery based analysis due to their small size and mixed surface cover of open water, exposed soils, and vegetation. We created time series of five well-known...
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Dune destabilization and increased mobility is a worldwide issue causing ecological, economic, and health problems for the inhabitants of areas with extensive dune fields. Dunes cover nearly a third of the Navajo Nation within the Colorado Plateau of southwestern USA. There, higher temperatures and prolonged drought beginning in 1996 have produced significant increases in dune mobility. Vegetation plays an important role in dune stabilization, but there are few studies of the plants of the aeolian surfaces of this region. We examined plant species and their attributes within a moderately vegetated dune field of the Navajo Nation to understand the types and characteristics of plants that stabilize rangeland dunes....
The intent of long-term ecological monitoring is to document changes in important properties of biological communities. At the least, a long-term monitoring system should be designed to detect long-term trends in three key attributes: soil and site stability, hydrologic function, and the biotic integrity of the system. There are four basic guidelines for developing integrated soil-vegetation monitoring systems for rangelands. These are: (1) identifying a suite of indicators which are consistently correlated with the functional status of one or more critical ecosystem processes and=or properties; (2) selecting base indicators on site specific objectives and resource concerns, and inherent soil and site characteristics;...
Microbiotic soil crusts play several important roles in many arid and semiarid ecosystems around the world. Their effects on soil hydrology, however, are poorly understood. It has been speculated that crusts (1) improve soil water availability by "sealing" the soil surface to water loss, or (2) diminish soil water by increasing the latent heat of a soil profile thereby increasing evaporation. In order to distinguish between these two opposing hypotheses, we analyzed water loss and temperature of soil profiles covered by different types of microbiotic soil crust (cyanobacteria, Psora decipiens, Placidium squamulosum) and a bare soil. We conducted experiments under growth chamber and field conditions. After watering...
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Recovery of soil properties from World War II-era military training exercises in the Mojave Desert was measured approximately 55 years following disturbance. Tracks from military vehicles were still visible, particularly in areas of desert pavement. Soil penetrability was much lower in visible tracks than outside the tracks. Soils in tracks had fewer rocks in the top 10cm of the soil profile than adjacent untracked soils. Larger particles (> 4.8mm) formed a moderately well-developed pavement outside of the tracks, while smaller, loose particles ( h 4.8mm) dominated the surface of the tracks. The time required to restore the desert pavement is likely to be measured in centuries. Based on biomass estimates, the cyanobacterial...
Thermodynamics predict that in calcareous soils where the equilibrium activity of solution orthophosphate (Pso) is controlled by any calcium-phosphate mineral, calcium oxalate (CaC2O4) precipitation will increase Pso by depressing Ca2+ ion activity in soil solution and enhancing dissolution of the P-controlling mineral. Plants and/or associated microflora capable of imparting effective levels of oxalic acid (H2C2O4) to soil solution, may significantly improve their phosphorus nutrition via this mechanism. In previous work, we presented evidence for calcium oxalate (CaC2O4) formation in the rhizosphere of vesicular-arbuscular mycorrhizal (VAM) western wheatgrass (Agropyron smithii Rydb.). Herein, we report on further...
Soil surface growths dominated by cyanobacteria and the lichen Collema in southeastern Utah are shown to be associated with greater tissue content of several bio-essential elements in two co-occurring seed plants (Festuca octoflora, Poaceae, and Mentzelia multiflora, Loasaceae). The elements N, P, K, Ca, Mg, and Fe were present in significantly greater concentrations in Festuca growing on soils heavily encrusted with cyanobacteria and cyanolichens than in plants on the same soil where foot traffic had destroyed the cryptobiotic crusts. With Mentzelia, N, Mg, and Fe were present in significantly greater concentrations in plants from sites with encrusted soil surfaces than on blow-sand sites. The cryptobiota appeared...
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Surface soil reclamation is used to increase the re-establishment of native vegetation following disturbance through preservation and eventual replacement of the indigenous seed reserves. Employed widely in the mining industry, soil reclamation has had variable success in re-establishing native vegetation in arid and semi-arid regions. We tested whether variable success could be due in part to a decrease of seed reserves during the reclamation process by measuring the change in abundance of germinable seed when surface soil was mechanically collected, stored in a soil pile for 4 months, and reapplied upon completion of a roadway. Overall seed reserve declines amounted to 86% of the original germinable seed in the...
Biological soil crusts of arid and semiarid lands contribute significantly to ecosystem stability by means of soil stabilization, nitrogen fixation, and improved growth and establishment of vascular plant species. In this study, we examined growth and nutrient content of Bromus tectorum, Elymus elymoides, Gaillardia pulchella, and Sphaeralcea munroana grown in soil amended with one of three levels of biological soil crust material: (1) a low-fertility sand collected near Moab, Utah; (2) sand amended with a 1-cm top layer of excised soil crust; and (3) crushed crust material. In addition, all plants were inoculated with spores of the arbuscular mycorrhizal fungus, Glomus intraradices. Plants were harvested after...
Rainfall simulation experiments were performed on 25 plots of varying microphytic crust cover in a wooded semiarid rangeland in eastern Australia. Under a rainfall intensity of 45 mm h-1, steady-state infiltration ranged from 5 mm h-1 to 41 mm h-1, but there was no effect of cover on this or any of the other soil hydrological variables measured. When disturbed plots with low cover (<15% cover) were excluded from the analyses, significant increases in time to ponding were associated with increases in crust cover. Despite some significant relationships, however, crust cover was an insignificant predictor of soil hydrological status at this site. We attribute this to the well-structured nature of the soils at the site,...
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Post-fire recovery of arid shrublands is typically slow, and planting greenhouse-raised seedlings may be a means of jump-starting this process. Recovery can be further accelerated by understanding the factors controlling post-planting survival. In fall 2007 and 2009, we outplanted seedlings of two contrasting native evergreen shrubs—fast-growing Nevada jointfir and slow-growing blackbrush—across five burned sites in the Mojave Desert. To increase soil moisture and optimize seedling survival, we experimentally applied and evaluated soil amendments and supplemental watering. We also evaluated two herbicides that reduce competitive invasive annual grasses and two types of herbivore protection. Survival of jointfir...
Recovery of soil properties from World War II-era military training exercises in the Mojave Desert was measured approximately 55 years following disturbance. Tracks from military vehicles were still visible, particularly in areas of desert pavement. Soil penetrability was much lower in visible tracks than outside the tracks. Soils in tracks had fewer rocks in the top 10cm of the soil profile than adjacent untracked soils. Larger particles (> 4.8mm) formed a moderately well-developed pavement outside of the tracks, while smaller, loose particles ( h 4.8mm) dominated the surface of the tracks. The time required to restore the desert pavement is likely to be measured in centuries. Based on biomass estimates, the cyanobacterial...
Cryptobiotic soil crusts are an important component of semiarid and arid ecosystems. An important role of these crusts is the contribution of fixed nitrogen to cold-desert ecosystems. This study examines the residual effects of various intensities and combinations of different surface disturbances (raking, scalping, and tracked vehicles) on nitrogenase activity, chlorophyll content, and chlorophyll degradation in these soil crusts. Nine months after disturbance chlorophyll content of disturbed soils was not statistically different from undisturbed controls, except in the scalped treatments, indicating recovery of this characteristic is fairly quick unless surface material is removed. Differences in chlorophyll degradation...
    map background search result map search result map Contrasting long-term survival of two outplanted Mojave Desert perennials for post-fire revegetation Contrasting long-term survival of two outplanted Mojave Desert perennials for post-fire revegetation