Graduation date: 1991

Ashe Juniper (Juniperus ashei) is native to the Edwards Plateau in central Texas. In the past 150 years, however, this species has rapidly increased in abundance within its range. Reduced fire frequency and increased livestock grazing, are two factors attributed to the rapid rate of juniper encroachment. While the losses associated with brush encroachment are recognized, many ranchers lack the funds necessary to implement management practices to reduce juniper densities on their property. The high cost associated with clearing brush has led to the creation of cost-share programs, which help offset the expenses incurred by participating landowners. The Leon River Restoration Project (LRRP), implemented on private lands within Coryell and Hamilton Counties, Texas, is one such cost-share program. Funding for the LRRP is received through non-programmatic sources, in the form of grants, from various state and federal organizations and agencies. The Natural Resources Conservation Service (NRCS) provides a second source of funding through the Environmental Quality Incentives Program (EQIP). Participants contracted through LRRP funds receive 85% cost-share benefits, up to a maximum of $15,000. Landowners participating in the LRRP under EQIP funds receive 50% cost-share incentives, up to a maximum of $250,000. The purpose of this study was to record changes that occurred on land enrolled in the LRRP, following juniper removal, and the economic benefits recognized by this work. Thirty landowners scheduled to participate in the LRRP were interviewed in 2003, prior to juniper control work. In 2006, 23 of the original 30 landowners participated in a second interview, following their completion of brush removal work. Changes attributed to juniper removal were recorded during these post-clearing interviews. Stocking rate changes were used as the basis for measuring economic benefits recognized by the clearing efforts. Changes in hunting or grazing lease rates resulting from juniper clearing were also used to monitor economic benefits of the brushwork. A second component of the study tested for differences in landowner satisfaction between LRRP participants enrolled under LRRP funds, and those contracted under EQIP funds. Importanceperformance matrixes were created to display satisfaction differences.

Understanding 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.

Several studies have been conducted to research the effectiveness of brush removal on hydrologic properties such as increased water yields and water quality. The Leon River Restoration Project (LRRP) is a large scale brush management program aimed at assessing the impacts of the mechanical removal of Ashe juniper (Juniperus ashei) on the quantity and quality of water, as well as wildlife habitat and livestock forage production. The objectives of this particular study are to assess the short and long term impacts of mechanical rangeland management techniques on runoff water yield and sediment loss from rainfall simulator plots. Two ecological sites were used to conduct rainfall simulation in 3 stages. Rainfall simulations were completed on Redland and Low Stony Hill sites in June 2003 prior to treatment, July 2003 after Ashe juniper was sheared from treated areas of both sites and 11 months after treatment in June 2004. Infiltration rates on both the Redland and Low Stony Hill sites increased after juniper was removed except for the treated brush plots on the Redland site, which experienced a 33% decrease. During the third simulation, infiltration rates decreased on all plots. Grass and litter biomass, as well as bare ground were influential on both sites. Percent bare ground affected infiltration rates the most on the Redland site where bare ground on the treated brush site was 23% in July 2003 and 42% in June 2004. The grass plots on the Low Stony Hill site had the greatest percentages of bare ground during the second simulation. Very few significant differences were apparent with sediment production on the Low Stony Hill site; however, the treated brush plots on the Redland site did experience a significant increase in soil loss following treatment. Sediment production increased from 24.6 kg/ha to 1,730 kg/ha in one month on the treated brush site. All other plots on the Redland site decreased in sediment discharge. Sediment production also had minor increases on the grass plots and treated brush of the Low Stony Hill. Once again, standing crop and bare ground seemed to have the greatest influence on sediment production.

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 135-141). Also available via the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 99-102). Also available on the World Wide Web.

Thesis (Ph. D., Natural Resources)--University of Idaho, May 2007. / Major professor: Lee A. Vierling. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.

Logging and forest thinning operations generate large amounts of residues in the form of small trees, branches and foliage that are usually left on the ground to decay or are burned. These resources are readily available, but it is uneconomical to remove them from the forest. The potential utilization of these resources was investigated for western juniper. This species is invading rangeland in the Interior West, altering the ecology of the land, and farmers are being encouraged to remove it. However, limited markets for the wood make removal costly. Developing uses for other parts of the stem could make removal more economically attractive. Western juniper foliage and twigs were steam distilled to obtain essential oils which were tested for their activity against subterranean termites and fungi. Residues from the steam distillation were pretreated with dilute sulfuric acid and digested with enzymes to determine their digestibility. The goal was to determine if an integrated operation involving steam distillation to remove essential oils, followed by enzymatic digestion of extraction residues was feasible. Essential oil recovery from foliage averaged 0.77% wet weight, while yields from twigs were about 0.13% wet weight. Foliage essential oil showed high antifungal and termiticidal activities at the concentrations tested. Total sugar yields from foliage extraction residues (40-55%) were higher than those obtained from branchwood residues (15-25%). The highest yields were obtained at 121°C and 1 hour pretreatment in 1% sulfuric acid. These results show that an integrated operation involving steam distillation of western juniper foliage to remove essential oil and enzymatic digestion of extraction residues is technically feasible. Additional work to determine the optimum distillation and pretreatment conditions for foliage would be needed. / Graduation date: 2012

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 97-103). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 42-44). Also available on the World Wide Web.