Thesis (M.S.)--Southern Oregon University, 2005. / "A thesis submitted to the Department of Biology of Southern Oregon University in partial fulfillment of the requirements for the degree of Master of Science in Environmental Education." Includes bibliographical references (p. 36-50) Also available via Internet as PDF file through Southern Oregon Digital Archives: http://soda.sou.edu. Search Bioregion Collection.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 107-118). Also available on the World Wide Web.

Since European American settlement of the Intermountain Region, dramatic changes in vegetation composition and structure have occurred in the sagebrush steppe ecosystem. Western juniper (Juniperus occidentalis spp. occidentalis Vasek), although indigenous to the Intermountain Region, has increased since the late 1800s. Considerable work has been done documenting juniper woodland expansion in the Intermountain West, however, little is known about the environmental variables that influence rates of tree establishment and structural attributes of woodlands across landscapes. Most studies of western juniper have addressed site-specific questions at limited spatial scales. Consequently, there is a lack of research on broader scale patterns of woodland development occurring across heterogeneous landscapes. In addition, changes in the amount, composition, and structure of fuels during the transition from open sagebrush steppe communities to closed juniper woodlands have profound influences on the size, intensity, frequency, and behavior of fire. However, limited data exist quantifying changes in fuels during this transition, thus, consequences to fire behavior have been difficult to predict. The major impetus for the study was to determine the influence of environmental variables on rates and structural attributes of woodland development and associated changes in fuel loading characteristics during the transition from sagebrush steppe communities to closed juniper woodlands in the High Desert and Humboldt ecological provinces. The proportion of trees greater than 150 years old relative to trees less than 150 years suggest western juniper has greatly expanded in the Owyhee Mountains and on Steens Mountain since settlement of the areas. Ninety-five percent of the trees established after the 1850s. As evidenced by the presence of western juniper in 96% of plots sampled in this study, juniper is able to encroach upon a variety of plant alliances and under a broad range of environmental conditions over diverse landscapes. Although it appears the occurrence of western juniper within the woodland belt is not spatially limited by environmental or vegetative conditions, stand structural and fuel loading characteristics do vary considerably across heterogeneous landscapes. Total juniper density, density of dominant trees comprising the primary canopy, and certain live and dead fuels biomass very substantially with site potential. Spatial variation in stand structure and fuels may have significant implications to management of juniper at the landscape scale. / Graduation date: 2005

Current research indicates that the expansion of western juniper can inhibit soil water retention, storage and prolonged releases from watersheds. This phenomenon is of great importance in eastern Oregon, as western juniper is encroaching into sagebrush/grass communities with a correlated reduction in herbaceous ground cover, resulting in reduced infiltration rates and increased soil loss. A paired watershed study for the purpose of monitoring water quality/quantity as affected by western juniper in the Camp Creek drainage, a tributary to the Crooked River, was established in 1994. Monitoring methods consisted of annual and semiannual measurements of hillslope soil movement, channel morphology, including total cross-sectional area, scour and deposition, channel discharge, depth to groundwater, and precipitation. Channel discharge was established using a 3,0 H-flume with a pressure transducer and stilling well and data logger. Changes in channel morphology were determined using 25 permanent, channel cross-section plots per watershed. Hillslope erosion processes were determined using 12 transects of 3 sediment stakes per watershed, located within gullies of subwatersheds. Data showed the two study areas to be well correlated with regards to soil movement, both within the main channels and in the subwatersheds (hillslopes). Some of the geomorphometric properties are similar (not statistically different) and differences in other parameters can be explained. Channel discharge appears to be significantly different in intensity, frequency, and duration of flow. These differences in surface discharge may be explained as further data collection of subsurface flow analysis in conjunction with sampling of springs located in each watershed are conducted. / Graduation date: 2005

Western juniper has rapidly expanded into sagebrush steppe communities in the Intermountain West during the past 120 years. This expansion has occurred across a wide range of soil types and topographic positions. These plant communities, however, are typically treated in current peer-reviewed literature generically. The focus of this research is to investigate watershed level response to Western juniper encroachment at multiple topographic positions. Data collected from plots used to measure vegetation, soil moisture, and infiltration rates show that intercanopy sites within encroached Western juniper communities generally exhibit a significant decrease in intercanopy plant density and cover, decreased infiltration rates, increased water sediment content, and lower soil moisture content. High-resolution remotely sensed imagery and Geographic Information Systems were used with these plot level measurements to characterize and model the landscape-scale response for both biotic and abiotic components of a Western juniper encroached ecosystem. These data and their analyses included an inventory of plant density, plant cover, bare ground, gap distance and cover, a plant community classification of intercanopy patches and juniper canopy cover, soil moisture estimation, solar insulation prediction, slope and aspect. From these data, models were built that accurately predicted shrub density and shrub cover throughout the watershed study area, differentiated by aspect. We propose a new model of process-based plant community dynamics associated with current state-and-transition theory. This model is developed from field measurements and spatially explicit information that characterize the relationship between the matrix mountain big sagebrush plant community and intercanopy plant community patterns occurring within a Western juniper dominated woodland at a landscape scale. Model parameters (states, transitions, and thresholds) are developed based on differences in shrub density and cover, steady-state infiltration rates, water sediment content, and percent bare ground in response to juniper competition and topographic position. Results from both analysis of variance and multivariate hierarchical cluster analysis indicate that states, transitions, and thresholds can be accurately predicted for intercanopy areas occurring within the study area. In theory, this model and the GIS-based layers produced from this research can be used together to predict states, transitions, and thresholds for any location within the extent of the study area. This is a valuable tool for assessing sites at risk and those that have exceeded the ability to self-repair. / Graduation date: 2005