Browsing by Subject "Chihuahuan Desert (Tex.)"
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Item A comparison of the rodent faunas in sandhill habitats from the northern Chihuahuan Desert in Texas(2005-08) Brant, Joel G.; Phillips, Carleton J.; Jones, Clyde J.; Baker, Robert J.; Strauss, Richard E.; McIntyre, Nancy E.During the latter years of the twentieth century, scientists and naturalists began placing increasing emphasis on the importance of the world’s rich diversity of species. In keeping with this trend, biologists have increased their efforts to learn as much about the biodiversity of every environment and have demonstrated that the results of these efforts are essential to understanding how diversity is maintained in each environment. The objective of this study is to characterize the rodent communities inhabiting sand dune habitats at two protected areas in the northern Chihuahuan Desert. The sand dunes at each locality were divided into three dune habitats (cover sands, vegetated dunes, and active dunes) based on substrate stability and vegetative cover. Sampling was conducted in each of these dune habitats from November 2000 to August 2003 (Monahans Sandhills State Park) and October 2003 to February 2004 (Guadalupe Mountains National Park). Twenty-nine species of mammals were recorded from Monahans Sandhills State Park (MSSP) with Dipodomys ordii being the most abundant species. The sand dunes at Guadalupe Mountains National Park (GMNP) yielded 23 mammalian species with the most abundant species being Dipodomys merriami. Rodent diversity was significantly higher in sand dune areas than in the surrounding cover sands at both parks. Active dunes from both parks had significantly more species and were more diverse than the cover sands habitats. The habitat heterogeneity hypothesis is the most likely mechanism that accounts for these results and the maintenance of this level of biodiversity in sand dune environments.Item A comparison of the rodent faunas in sandhill habitats from the Northern Chihuahuan Desert in Texas(Texas Tech University, 2005-08) Brant, Joel G.; Phillips, Carleton J.; Jones, Clyde J.; Baker, Robert J.; Strauss, Richard E.; McIntyre, Nancy E.During the latter years of the twentieth century, scientists and naturalists began placing increasing emphasis on the importance of the world’s rich diversity of species. In keeping with this trend, biologists have increased their efforts to learn as much about the biodiversity of every environment and have demonstrated that the results of these efforts are essential to understanding how diversity is maintained in each environment. The objective of this study is to characterize the rodent communities inhabiting sand dune habitats at two protected areas in the northern Chihuahuan Desert. The sand dunes at each locality were divided into three dune habitats (cover sands, vegetated dunes, and active dunes) based on substrate stability and vegetative cover. Sampling was conducted in each of these dune habitats from November 2000 to August 2003 (Monahans Sandhills State Park) and October 2003 to February 2004 (Guadalupe Mountains National Park). Twenty-nine species of mammals were recorded from Monahans Sandhills State Park (MSSP) with Dipodomys ordii being the most abundant species. The sand dunes at Guadalupe Mountains National Park (GMNP) yielded 23 mammalian species with the most abundant species being Dipodomys merriami. Rodent diversity was significantly higher in sand dune areas than in the surrounding cover sands at both parks. Active dunes from both parks had significantly more species and were more diverse than the cover sands habitats. The habitat heterogeneity hypothesis is the most likely mechanism that accounts for these results and the maintenance of this level of biodiversity in sand dune environments.Item Biosolids and chemical fertilizer application on the Chihuahuan desert grasslands(Texas Tech University, 1998-08) Cooley, Philip EarlSewage sludge or biosolids refers to the solids removed from municipal waste water during treatment. Currently, sewage sludge is used to refer to untreated material, while biosolids refers to treated material., There are several estimates as to how much sewage sludge is currently produced or will be produced in the U.S. in the future. On average, a typical person generates 16.9 liters of sewage sludge per week (Chermisinoff, 1993). According to the U.S. Environmental Protection Agency (USEPA, 1989) approximately 6.5 million dry tons of sewage sludge are generated annually, and this is expected to increase to approximately 13 million dry tons by the year 2000. Due to the large quantities of sewage sludge generated, management of treated sewage sludge, or biosolids, is becommg increasingly important. The Marine Protection Research and Sanctuary Act of 1988 banned ocean dumping of biosolids as a disposal technique, leaving only land filling, incineration, and land application. Land filling is facing increased regulations because of ground water pollution and decreases in available land fill space. Incineration is also plagued with problems, such as air pollution, high energy input, and capital costs. Land application is a promising alternative to ocean dumping. Land application is defined as the spreading of biosolids on or just below the soil surface, and is becoming a widely used sludge management option. Land application is divided into four categories: agricultural use, forest lands, land reclamation, and land dedicated to sludge application. Land application is encouraged by the EPA wherever environmentally feasible (USEPA, 1989). Land application has been beneficially used on croplands, forest lands, and reclaimed mines throughout the U.S. However, land application has not been widely studied in the arid and semi-arid southwest or on native rangelands. The desert southwest, including the Trans-Pecos region of Texas, receives low and unpredictable rainfall and has high temperatures, high evaporation rates, and low organic matter contents in the soil All of these factors limit native plant growth on rangelands. Application of biosolids might ameliorate some of these conditions by providing organic matter to the soil and reducing soil water evaporation. In addition, biosolids contains several plant macro- and micro- nutrients such as nitrogen, phosphorus, copper, manganese, and zinc that can increase plant production. As long as biosolids do not cause detrimental effects in this semi-arid environment, the Trans-Pecos is an excellent area for land dedicated to sludge application for several reasons: vast acreages of available land, and few estimated number of days when biosolids can not be applied because of unfavorable weather (precipitation) (USEPA, 1989).Item Effects of biosolids and an inorganic mulch on soil-plant relationships in two Chihuahuan Desert grasslands(Texas Tech University, 2000-12) Jurado-Guerra, PedroIn-depth research is needed to understand the effects of biosolids (sewage sludge) application on plant growth in semiarid regions. The objectives of this research were to determine the effects of surface application of biosolids on soil properties and plant growth on two Chihuahuan desert grasslands sites during two years. A tobosagrass (Hilaria mutica) site with a Stellar very fine sandy loam soil and a blue grama (Bouteloua gracilis) site with a Jal fine sandy loam soil were selected on the Sierra Blanca ranch, in Texas. Biosolids at 0,18, and 34 Mg ha^-1 were applied either in the dormant or growing season to experimental plots in 1997 or 1998. An inorganic mulch (synthetic fiber-floor pads, "IM") was applied to simulate ground cover of biosolids rates. Supplemental irrigation was provided to half of the plots throughout the growing season. Afternoon soil temperature, soil-volumetric water content, and soil NO3-N were measured throughout the growing season. Plant tissue nitrogen concentration (TKN) was measured in August and October on both tobosagrass and blue grama in 1998. Standing crop was measured in October for both grasses. In general, soil temperature decreased under application of both mulches at both sites during the two years. Soil-water content was higher under application of both mulches at both sites at most sampling dates. Nitrate-nitrogen in the soil increased with application of biosolids during both seasons of application with a more pronounced effect from biosolids applied during the dormant season during the first year of application on both sites. Nitrate-nitrogen in the soil slightly increased with inorganic mulch application on both sites. The dormant application of biosolids promoted earlier improvement of soil properties compared to growing season application of biosolids during the first year of application at both sites. Tobosagrass TKN remained similar with biosolids application in August and October and decreased with IM application in October. In contrast, blue grama TKN increased with biosolids rates in October and was not affected by mulch application in any date. Standing crop of both grasses increased with application of both mulches and irrigation. Biosolids increased NO3-N in the soil and improved plant forage quality more than the inorganic mulch in both sites and years.Item Fungal functional diversity: exploring patterns and processes associated with soil fungal assemblages along an altitudinal gradient in the Chihuahuan Desert(Texas Tech University, 2002-05) Sobek, Edward AndrewSoil fungi are intimately associated with the maintenance and stability of terrestrial ecosystems through their involvement in the decomposition process. During decomposition, organic carbon is mineralized to CO2 and bound nutrients are returned to the labile soil nutrient pool for subsequent growth of plants and soil microbes. To better understand the relationship between soil fungal diversity, and factors influencing their functional ability in the decomposition of soil organic matter, this dissertation examined, (1) development of methods to determine soil fungal functional diversity, (2) seasonal trends in fungal function al diversity, and (3) the relation between soil fungal functional abilities and a suite of environmental variables that are important in ecosystem nutrient cycles. The context of this research endeavor focused on assemblages of soil fungi associated with an environmental gradient in the Chihuahuan Desert, specifically, the Pine Canyon Watershed in Big Bend National Park. The Pine Canyon Watershed contains five distinct vegetation zones along an altitudinal gradient and contains the majority of vegetation types that are found in the Chihuahuan Desert. Soil samples were collected within each of these zones over a three-year period. Sampling coincided with seasonal changes in temperature and precipitation. Functional diversity was determined for fungal assemblages from each vegetation zone, using the Soil FungiLog procedure developed from this research.Item The effect of daily temperature variability on microbial and plant processes in a Chihuahuan Desert ecosystem(2012-05) van Gestel, Natasja; Zak, John; Tissue, David T.; Strauss, Richard E.; Scwhilk, Dylan W.; Cox, Stephen B.Worldwide, the daily temperature range of air (DTRair = Tmax – Tmin) has decreased by 0.07 °C per decade, with a 43% stronger decline for arid and semiarid regions. Although the daily temperature range of soil (DTRsoil) has not been widely measured, it is reasonable to assume that it has decreased at a similar rate and magnitude as DTRair. The role of temperature on plant and soil processes has been extensively studied, but the role of temperature variability on these processes has been largely ignored. In arid systems where DTRsoil is characteristically high, projected additional reductions in DTRsoil may have significant impacts on ecosystem functioning. My dissertation focuses on elucidating the role of high temperature variability on microbial and plant processes in an arid ecosystem, both intra- (i.e. seasonal) and inter-annually. Using a passive temperature manipulation experiment that successfully reduced DTRsoil in a Chihuahuan Desert soil at Big Bend National Park, my field study evaluated the biomass and activity responses of microorganisms in response to year-round reductions in DTRsoil, and subsequent changes to soil nutrient levels. In addition, changes to leaf-level physiology, leaf N content and leaf xylem water status of the dominant and representative plant species of arid landscapes, Larrea tridentata (creosotebush), were measured in response to reduced DTRsoil. To better link below-ground processes to plant responses, I conducted all measurements on the same day. High temperature variability was an important stressor to microbial growth as soil microbial biomass C and N increased in response to reductions in DTRsoil. Reduced DTRsoil benefited both dormant and active microbial populations through increased biomass C and N relative to control plots in both dry (spring) and wet (summer) seasons. In contrast, microbial activity, measured as CO2 evolution from soil in inter-shrub spaces, was more sensitive to soil water content and less sensitive to temperature variability than microbial biomass. Therefore, reductions in DTRsoil generated the largest effects on CO2 evolution in summer, which is the wettest season in Big Bend National Park. Increased microbial biomass reduced soil exchangeable N, most likely because extra N was required for biomass construction. However, soil exchangeable N levels did not always decrease in response to increased microbial biomass, suggesting that mineralization of N from a more stable pool of soil organic matter functioned to replenish depleting levels of soil exchangeable N. Although, I observed changes to belowground dynamics, including soil nutrient status and soil CO2 efflux rates, reductions in leaf [N] in Larrea tridentata did not alter photosynthetic rates in response to reductions in DTRsoil. Lastly, I compared different multiple regression models that utilized daily insolation and air temperature data to predict daily maximum and minimum soil temperatures at two soil depths (0 and 15 cm). Using a weighted average of current and past insolation (to incorporate a “heat” storage effect) in combination with air temperature provided the best fit for observed daily maximum and minimum soil temperature near the soil surface. An analytical solution can then be applied to use the predicted soil surface temperature data to estimate daily maximum and minimum soil temperatures deeper into the soil profile. In summary, my research generated three major findings. First, deserts dominated by Larrea may function temporarily as a source of C, resulting in a positive feedback to rising global temperatures. This imbalance will be sustained as long as the C and energy source (i.e. soil organic matter) continue to fuel higher levels of microbial activity. Second, if additional N incorporated into microbial biomass (labile pool) was derived from a more stable pool, this could increase volatile losses of N and further limit N in this N-limited system, and in turn, affect future primary productivity. Third, my dissertation produced promising results for predicting the soil thermal environment from above-surface conditions in a desert system. Using the same variables, this approach could be used in other arid systems with limited soil temperature data. Predicting future soil thermal regime is necessary to anticipate impacts on ecosystem function.