Spatial and age class analysis of managed western juniper (Juniperus occidentalis) woodlands in central Oregon

Graduation date: 2007Juniper is a native species to Oregon and confers ecological benefits to wildlife\ud when it is at savannah and transitional densities. Its range and extent have fluctuated with climatic change, but the current range expansion is unprecedented in its extent. The range expansion has been associated with the degradation of the sagebrush steppe ecosystem in central Oregon. In the past, attempts to restore the sagebrush-steppe from western juniper aforestation were motivated by the desire to improve forage quality. Currently western juniper management is wider in scope, encompassing social, ecological, and environmental objectives. Past research in the area of western juniper management focused extensively on the causes of western juniper aforestation, its impact on understory plant communities, soil and the water budget. Researchers have also explored multiple mechanisms for removing western juniper and have quantified resulting amelioration of ecosystem function. However little work has been done identifying topographical features or environmental conditions that may influence the density of western juniper woodlands and seedling reestablishment following the application of treatment regimes. This study used spatial modeling to explore the influence that elevation and direct incident radiance have on western juniper density and multivariate, nonparametric\ud tools to identify relationships between topography, understory plant community and seedling reestablishment on managed sites. The study findings indicate that western juniper densities in central Oregon are influenced by topographical features in the landscape. The multivariate analysis revealed that seedling reestablishment is positively associated with the diversity of the understory plant community. The study also revealed that on almost all of the sites included in the study, western juniper seedling are reestablishing after treatment application. With the information generated in the study, managers have tools with which\ud to assess the risk a region has to be dominated by western juniper woodlands.\ud Managers can then efficiently allocate western juniper management resources by\ud choosing to treat that sites that have both the greatest risk and the greatest capacity to meet their objectives