Browsing by Subject "Grasslands"
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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 Effect of anthropogenic disturbance and landscape structure on body size, demographics, and chaotic dynamics of Southern High Plains amphibians(Texas Tech University, 2002-05) Gray, Matthew JamesAmphibian populations are declining globally. Anthropogenic disturbance of landscapes surrounding wetlands may affect fitness, demographics, and dynamics of amphibian populations. Spatial positioning and relative connectedness of wetlands also may influence population demographics. Thus, I examined the effect of anthropogenic landscape use (cultivation vs. grassland) and structure on postmetamorphic body size (a fitness correlate), demographics, and dynamics of amphibians at 16 playa wetlands on the Southern High Plains (SHP) of Texas during 1999 and 2000. Amphibian populations were monitored using drift fence and pitfall traps, landscape structure was quantified using spatial analysis software, and dynamics were assessed using difference equations. Postmetamorphic body size of all amphibian species and age classes generally was greater at grassland than cropland playas, and in 1999 (i.e., a wetter year) than 2000. Abimdance of New Mexico and plains spadefoots (Spea multiplicata and S. bombifrons) generally was greater at cropland than grassland playas, and greater for barred tiger salamanders (Ambystoma tigrinum mavortium) in 1999 than 2000. Mean daily abundance of amphibians also was positively related to landscape structure indices representing geometric complexity and spatial positioning of wetlands. In general, as landscapes became more complex (e.g., numbers of edges increased) and inter-playa distance decreased, mean daily abundance of amphibians increased. Additional demographic analysis indicated that temporal niche partitioning existed in SHP amphibian populations; however, no differences existed between landuses. Lastly, biological chaos in the amphibian assemblage existed at 1 of 8 cropland and 7 of 8 grassland playas. A stochastic density-dependent Ricker function predicted chaotic dynamics most accurately. Anthropogenic disturbance surrounding wetlands affects body size, demographics, and dynamics of SHP amphibians. Spatial positioning of wetlands and landscape complexity may be as or more important than general landuse in affecting amphibian demographics. Annual differences in body size and abundance suggest rainfall may be important in influencing amphibian populations. Although spadefoot abundance was positively influenced by anthropogenic disturbance, I recommend retention and restoration of grasslands surrounding playa wetlands because landscape cultivation decreased body size and altered amphibian demographics and dynamics from an undisturbed state. These results have important implications in conservation biology, landscape ecology, and basic ecological and mathematical theory.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 Effects of simulated precipitation on nitrogen cycling and microbial processes in a grassland ecosystem at Big Bend National Park, Texas(Texas Tech University, 2003-12) Nagy, Amber MelanieVariations in the timing and magnitude of precipitation events have the potential to influence microbial dynamics and subsequent ecosystem level processes on a variety of scales leading to irreversible changes in vegetation structure and composition. According to the Hadley Climate Change Model #2, the Big Bend region of far west Texas is expected to receive 25% more precipitation in both the winter and summer months. The effects of changes in precipitation amounts and timing on nitrogen dynamics and microbial processes in the Sotol-grasslands at Big Bend National Park were studied. The objectives for this thesis were to: (1) monitor changes in soil nitrogen dynamics in response to variations in precipitation timing and amounts, (2) evaluate impacts of increased precipitation on soil microbial dynamics, and (3) examine, using a greenhouse experiment, the impacts of rainfall pH on soil nitrogen dynamics and microbial biomass production. The field experimental site was in the Sotol-grasslands along the Pine Canyon Watershed at Big Bend National Park, Dominant species plots, containing either Side-Oats grama, Sotol, or Brownspined Prickly-Pear cacti, and also community plots containing all three plant species, were established to examine the impacts of additional precipitation on soil microbial and nitrogen dynamics. Four water treatments (control, summer water only, winter water only, and summer and winter water) were applied beginning in January 2002. Winter water treatments were applied once during the winter season and summer watering took place over three different watering events. Additional water amounts were determined during the first year of the experiment by adding an additional 25% of the past 100 years precipitation averages. During the second year of the experiment, additional moisture was an additional 25%. of the previous three months' precipitation. This approach accounted for yearly precipitation variation. Plant type and season of water addition influenced the rate of N-mineralization, N-mineralization rates in the dominant species plots were significantly different among dates during the winter and spring, but not during the summer and warmer periods of the year. Plots with Side-Oats grama experienced the highest average rate of N-mineralization across date while Sotol plots had the lowest average rate of mineralization. Across the two years, ammonification rates were positive during the ApriI-June (2002) sample dates in all treatments and after the summer and winter watering events. For the remainder of the sampling periods, ammonification rates were negative. The negative rates are indicative of NH4+-N loss through either plant uptake and/or the process of nitrification. An increase in nitrification across plant types was found during the spring months and also early autumn months. The increase in nitrification rates does not appear to be directly related to water addition, but is a seasonal interaction for both the single species and community plots. Microbial biomass carbon production was directly related to soil moisture in that, for both plot types, plots watered in both the summer and winter contained the largest amounts of microbial biomass on average over the duration of the experiment. In the dominant species plots, vegetation type had a direct impact on the amounts of microbial biomass carbon and the levels of extractable NH4+-N and extractable NO3- -N contained within the plots. In the greenhouse experiment using soil from the Sotol-grasslands treated with water of varying pH's to simulate acid rain, it was found that water addition initially stimulated the release of immobilized or otherwise unavailable nitrogen, thereby allowing that nitrogen to become available for N-mineralization, It was also found that, like the field study at the Sotol-grasslands, nitrification is the primary contributor in N-mineralization, Microbial biomass carbon amounts were found to increase when treated with water pH 4,5, but levels of microbial biomass carbon declined initially when treated with water at pH at 3.5 and 5, The increase may be attributed to an increase in bacterial and fungal activity resulting from the changes in soil conditions, namely nitrogen and water availability, in response to acidic precipitation. Together, the field and greenhouse results suggest that alteration in precipitation patterns and amounts coupled with changes in rainfall chemistry as a result of pollution will have significant impacts on soil microbial activity and subsequently nitrogen dynamics in a complex manner within the Sotol grasslands at Big Bend National Park,.Item Fire and clipping effect on purple threeawn (Aristida purpurea) during three phenological stages(2012-05) Richarte, Leobardo; Villalobos, Carlos; Rideout-Hanzak, Sandra; Wester, David B.This study was conducted to develop strategies to improve cattle production on purple threeawn (Aristida purpurea) infested grasslands using different defoliations practices at specific phenological stages. Specific objectives included: 1) to determine prescribed fire and clipping effect on purple threeawn survival and change in basal area during three phenological stages.- 2) to evaluate the effect of burning and clipping on forage quality of purple threeawn at three phenological stages, and 3) to generate a specific equation to predict purple threeawn biomass production during three phenological stages. This study was carried out at the Texas Tech University, Native Rangeland located in Lubbock, Texas, during 2010 and 2011. In the 2010 growing season, during vegetative, reproductive and post-reproductive phenological stages, four hundred fifty purple threeawn plants were selected randomly regardless plant size, to be treated with one of the three defoliations types. During each phenological stage one hundred-fifty plants were treated; fifty plants were clipped simulating 90% utilization and fifty plants more were left untreated used as control plants. Phenological stages were: vegetative (June), reproductive (July) and post-reproductive (October). Two, four, and six months after defoliations, I collected forage samples from both treated and control plants to determine forage quality. Forage quality in this study was composed of two variables: crude protein content (CP) and in vitro dry matter digestibility (IVDMD). Basal crown area of defoliated and control plants was measured just after applied treatments. At the end of 2010 growing season we measured basal crown area again in our plants. Percent change in basal crown area was calculated. In addition, mortality was evaluated in defoliated and control plants at the beginning of the next growing season after defoliations. Finally, during each phenological stage 65 plants were randomly selected to measure variables related to biomass production, clipped and weighed to develop models to predict biomass. Experimental treatments to analyze forage quality (CP and IVDMD) were composed of three factors; 1) phenological stage (S); vegetative (V), reproductive (R), and post-reproductive (PR); 2) defoliation types (D); burning (B), clipping (CL), and control (CT); and 3) sampling time after defoliation (T) ; 2, 4, and 6 months after defoliations. Additionally, treatments for mortality and change in basal area analyses were composed of two factors: 1) phenological stage (PS); vegetative (V), reproductive (R), and post-reproductive (PR); and defoliation types (D); burning (B), clipping (CL), and control (CT). We used multiple linear regression to predict biomass production at each phenological stage. Analysis of variance, test of normality and heterogeneous variances were performed on forage quality, basal area change and mortality data. Significant differences between treatments were concluded using Fisher’s LSD test at P<0.05 level. Mortality and change in basal area results might be affected by an above and uniform rain distribution during the 2010 growing season. Threeawn plant mortality and basal area change were significantly affected by phenological stage. This suggests that threeawn mortality in response to severe defoliations depends on plants phenology. Burning during reproductive stage was the treatment combination that promotes the highest plants mortality as well as negative basal area change. Threeawn plants exhibited fire resistant during vegetative and post-reproductive stage at least in a in a short term study. Forage quality of unmanaged threeawn plants is low for cattle production during most of the growing season, during the vegetative stage forage quality can be classified as median levels; once it changes to reproductive it is classified as poor. As result, there is a necessity to increase threeawn forage quality using management tools such as clipping and fire. CP content and IVDMD were significantly affected by an interaction between defoliation type and sampling time at each phenological stage. Clipping and burning treatments proved efficient for increasing threeawn forage quality during each phenological stage, particularity 2 and 4 months after defoliations. Clipping and control treatments stimulated regrowth which in most cases possessed similar forage quality. However, burning plants tend to promote higher forage quality levels. Our forage quality data suggest that fire applied during post-reproductive stage, and deferment during the winter with grazing started at the beginning of the next growing season is the best choice to generate the highest forage quality for cattle in threeawn grasslands, although this advantage is lost in a short period of time, usually no more than 4 months. We generated efficient models to predict threeawn biomass at each phenological stage. These models might be used to calculate fine fuel densities to applied prescribed fires.Item Post-fire successional effects on breeding grassland birds in mesquite savanna habitats of the Texas rolling plains(Texas A&M University, 2007-04-25) Lee, Stephanie L.North American grasslands and grassland birds have declined drastically due to habitat degradation by fire suppression (i.e., woody encroachment), fragmentation, and conversion to croplands. A better understanding is needed of the relationships among disturbance regimes (e.g., fire), resultant vegetation changes, and grassland bird communities to effectively manage remaining grasslands and grassland birds. I assessed the relationship between post-fire succession, and mean relative abundance and nesting ecology of breeding grassland birds (i.e., nest-site selection and nest success) in mesquite-dominated rangeland of the Texas Rolling Plains, where prescribed fire is used as a tool to manage shrub encroachment. Brush cover, grass cover, and visual obstruction generally increased with post-fire succession, and bare ground decreased with post-fire succession. Species richness, grasshopper sparrows (Ammodramus savannarum), Cassin??????s sparrows (Aimophila cassinii), and dickcissels (Spiza americana) responded positively to post-fire succession, and lark sparrows (Chondestes grammacus) responded negatively to post-fire succession.; abundance of these avian groups was low on the control sites. During 2004??????2005, 90 grassland bird nests were monitored. I found conflicting results for vegetation parameters important to nest site selection and probability of nest success. For all species except lark sparrows, nest-site location was positively associated with visual obstruction and with grass or forb cover. However, the probability of nest success increased with lower visual obstruction, bare ground cover, or grass cover. Grassland bird abundance, nest-site location, and nest success had differing associations with vegetation variables. These results suggest that to effectively manage remaining grasslands for sustainable breeding grassland bird populations, managers should engage in practices that keep habitat in multiple vegetative successional stages.Item A review of the impacts of invasive grasses on herpetofauna(2015-08) Wright, Ian Michael; Gilbert, Lawrence E.; Leibold, Mathew ASpecies invasions pose one of the greatest threats to the maintenance and stability of biodiversity in ecosystems across the globe (Vitousek 1990). Plant species in particular are uniquely predisposed to successfully invade and establish themselves in novel habitats. In the United States alone invasive plants are responsible for nearly 35 billion dollars in economic and environmental damage. Grasslands are among the most productive ecosystems in the US and their biodiversity is threatened by continual introduction of alien grass species. These invasive grasses have a variety of direct and indirect effects on native grassland communities and have the ability to alter fire regimes, displace native species, and simplify grassland food webs. Little is known about the impacts invasive grasses have to amphibians and reptiles but there is evidence to suggest that these and other small organisms suffer direct mortality, impoverished prey sources, and reduced reproductive opportunities as a consequence of grass invasions. Here I summarize the current literature surrounding invasive grass impacts on herpetofauna and suggest topics of further research.Item Soil nitrogen in a Tobosa grass community as affected by burning, grazing, and clipping(Texas Tech University, 1973-08) Sharrow, Steven HaroldNot availableItem Understanding functional connectivity in shortgrass and mixedgrass prairies using the swift fox as a model organism(2012-08) Schwalm, Doni; Grabowski, Timothy B.; Cronin, Matthew A.; Gripson, Phillip S.; McIntyre, Nancy E.; Waits, Lisette P.Habitat fragmentation and loss are the greatest sources of biodiversity loss today. The negative relationship between these phenomena and myriad ecological processes are well-documented. Chief amongst these impacts is the disruption of dispersal regimes, resulting in isolated or semi-isolated groups. Reduced dispersal in turn negatively influences gene flow between groups of individuals, resulting in reduced genetic diversity, increasing risk of inbreeding depression and, ultimately, heightened extinction risk. Thus, maintaining functional connectivity in ecosystems is high on the list of conservation priorities. The Great Plains is a vast ecosystem characterized by habitat fragmentation natural and anthropogenic in origin. Remnant shortgrass and mixedgrass prairies, in which this study occurs, have been reduced to < 50% of their previous extensive geographic area, largely due to agricultural development. Anthropogenic impacts on connectivity are predicted to increase, resulting in loss of up to 50% of remnant native grasslands. Thus, understanding these factors’ influence on grassland connectivity is critical for conservation and management in both contemporary and future time scales. Here, I employed a landscape genetics approach to address a series of objectives, which include assessing current and historic genetic diversity and structure in swift fox populations, relating gene flow and genetic structure patterns to landscape influences, and providing insight into conservation needs for the species. In addition, I used the swift fox as a model species to elucidate connectivity patterns across two focal areas in the shortgrass and mixedgrass prairies, ultimately presenting functional connectivity maps for these regions. Finally, I developed a new method for studying connectivity networks in fragmented populations with empirically derived cost metrics, and demonstrated its utility for identifying movement corridors using least-cost path modeling; this analysis was conducted in a fragmented swift fox population wherein genetic diversity appears to be linked to inter-population movement; thus identification of movement corridors is a critical conservation need locally.Item Understanding nitrogen and microbial dynamics associated with two degraded grassland systems in Big Bend National Park(Texas Tech University, 2004-12) Resinger, Jennifer SueDesertification is responsible for diminishing land productivity in the Chihuahuan Desert and over much of the southwestern United States. Current research indicates that the ongoing degradative loss of land productivity globally will increase as the human population continues to grow and as these systems undergo climatic changes (i.e., precipitation,temperature). The ongoing effects of desertification of formally productive grasslands, as evidenced by nitrogen dynamics and microbial processes in the Dog Canyon and Airport sites at Big Bend National Park were determined in this investigation. The objectives for this thesis were to: (1) determine seasonal patterns in soil nitrogen (extractable NH4-N and extractable NO3-N) and N-mineralization in intact versus fragmented Tabossa grass {HHaria mutica) areas in Big Bend N.P., and (2) examine the relationship between grassland fragmentation dynamics and seasonal variations in microbial biomass dynamics. The field experimental sites were located in the northernmost part of Big Bend National Park. The Dog Canyon and Airport sites were established to examine and compare microbial and nitrogen dynamics in vegetated versus bare soil areas of desertified grasslands. Soils in both sites are classified as Chalkdraw with Tabossa grass as the dominant plant species. Soils were collected from both sites during February, April, June, August, October, and December 2003, and February, April, and June 2004. Upon collection, soil samples were analyzed for soil moisture, microbial biomass, available and extractable nitrogen, net N-mineralization, soil organic matter and soil pH.