Browsing by Subject "brush management"
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Item Habitat relationships of seven breeding bird species in the Leon River Watershed investigated at local scales(Texas A&M University, 2005-02-17) Juarez Berrios, Edwin AlfredoOver the past 100?150 years Texas rangelands have dramatically changed from native open savannahs to dense woodlands. On the Edwards plateau, a major management concern is the increasing encroachment of Ashe juniper (Juniperus ashei). Preceding an anticipated brush management program, I investigated the presence, co-occurrence, and habitat relationships of 7 breeding bird species in the Leon River Watershed in central Texas, USA: black-capped vireo (Vireo atricapillus), golden-cheeked warbler (Dendroica chrysoparia), northern bobwhite (Colinus virginianus), white-eyed vireo (Vireo griseus), Bell?s vireo (Vireo bellii), painted bunting (Passerina ciris), and brown-headed cowbird (Molothrus ater). Vegetation characteristics were compared between sites occupied by each species and unoccupied sites using univariate analysis. Models for predicting species site occupancy were developed (using logistic regression) based on habitat characteristics correlated with the presence of each species. Two species of special concern, the endangered black-capped vireo and golden-cheeked warbler occupied 5.6% of sites and 13.8% of sites respectively, while the brood parasite brown-headed cowbird was the most widespread, occupying 86.8% of sites. Species co-occurrence patterns revealed significant associations between the golden-cheeked warbler and each of 5 other species. For most species, variables included in habitat models could be explained by knowledge of species known habitat associations. For example, the black-capped vireo was positively associated with increasing low-growing (<1.5 m) hardwood cover and with Low Stony Hill ecological sites. The golden-cheeked warbler was positively associated with increasing density of larger juniper trees, increasing variability in vertical vegetation structure, and decreasing midstory canopy of deciduous nonoaks (e.g., cedar elm [Ulmus crasifolia]). It also preferred Low Stony Hill and Steep Adobe ecological sites. Site occupancy seemed to be driven by variables that describe overall vegetation structure. In particular, cover of low-growing non-juniper vegetation and juniper tree density appeared to be important in determining site occupancy for several species. Although the models constructed were not very robust, resource managers can still benefit from such models because they provide a preliminary examination of important controlling variables. Managing rangelands to maintain or restore a mosaic of juniper patches and open shrublands are likely to help meet the habitat requirements of these bird communities.Item Landowner survey of a cost-share brush management program in two Texas watersheds(Texas A&M University, 2004-11-15) Narayanan, Christopher RamWith the expanding population of Texas and the resulting increase in demand for water, the scarcity of water is becoming an increasingly urgent issue and research is being conducted to find ways to improve water yield, the amount of water that is used for aquifer recharge and riparian areas (lakes, streams, etc). Rangelands provide a major catchment for both surface reservoirs and aquifers. The Edwards Aquifer Recharge Zone and the Twin Buttes Drainage Area were selected to determine the tradeoffs between brush management for increased water yield and wildlife habitat improvement. In April 2002, a mail survey of 300 randomly selected landowners was conducted in each of the two watersheds to gain information regarding their demographics, land cover, and willingness to enter into a cost-share brush removal program. A total of 131 usable questionnaires (43.7%) were returned by Edwards Aquifer area participants, and 141 usable questionnaires (47.0%) were returned by Twin Buttes area participants. Respondents were asked questions including attitudes towards brush amounts and management strategies, and certain constraints that may be included in a cost-share brush removal program. Most respondents indicated interest in enrolling at least part of their land in such a program. Reasoning behind interest varied in each study area. However, interest in various contractual agreements was neutral at best. Policy implications entail considering wildlife habitat mitigation, landowners' preferences, and potential for increasing water yield and determining if all can be managed, or if trade-offs must be considered.Item The Effect of Ashe Juniper Removal on Groundwater Recharge in the Edwards Aquifer(2011-02-22) Bazan, RobertoUnderstanding groundwater recharge rates has direct relevance for management of the Edwards Aquifer, which serves as the main source of fresh water for the city of San Antonio and surrounding communities. As population around San Antonio continues to grow, so does the demand for water and the stress placed on the aquifer. A method that is commonly believed to augment water yields is brush management. Over the last 150 years an increase in juniper density on the Edwards Plateau has coincided with decreasing streamflow. This has led many to believe that removing juniper would increase available water. Due to its karstic nature, the recharge zone of the Edwards Aquifer is assumed to be a prime location for augmenting water yields through vegetation manipulation. This study assesses the dynamics of recharge and the effects of manipulating surface vegetation. To accomplish this, a shallow cave located in the Edwards Aquifer recharge zone in San Antonio, Texas was instrumented to monitor drip recharge in response to simulated rainfall events. In 2004, simulations were conducted over the cave to measure recharge rates with a dense Ashe juniper canopy. The data and observations from the initial simulations were used to establish a baseline with the juniper in place. In February 2008 the juniper stand was cleared and the rainfall simulations were reproduced in June and July 2008, and again in early June 2009. Results from the study indicated that even though the amount of rainfall reaching the surface increased, a decrease in the amount of recharge occurred. The decrease can be possibly be explained by the elimination of stemflow, which is believed to direct higher concentrations of water to preferential flow paths near the base of the tree, and an increase in surface runoff. However, because such a large portion of the water reaching the surface is not accounted for by the budget, it is difficult to conclude that a change in recharge did not occur at a larger scale.