Landscape dynamics in aspen and western juniper woodlands on the Owyhee Plateau, Idaho /by Eva K. Strand.

A century of altered fire regimes has affected the landscape vegetation dynamics in the Intermountain West. Suppression of wildfires has resulted in increases in woody plant cover in these semi-arid ecosystems, which has resulted in land cover changes affecting biogeochemical cycling, landscape composition, and habitat diversity. Recent developments in remote sensing technology, computational power, and a rapid development of analysis techniques have enabled us to quantify such changes at the landscape scale. Wavelet analysis is a powerful image analysis technique that is here applied in a novel fashion to fine scale remote sensing imagery to automatically detect the location and crown diameter of individual western juniper plants (Juniperus occidentalis ssp. occidentalis) expanding into sagebrush (Artemisia spp.) steppe at multiple scales. The produced marked point pattern of historical and current spatial juniper distribution was compared regionally and changes in foliar cover and above ground biomass were estimated across a 330,000 ha area on the Owyhee Plateau, Idaho. The above ground carbon accumulation rate from 1946 to 1998 was estimate to be 3.3 gCm{esc}p-2{esc}syr{esc}p-1{esc}s and 10.0 gCm{esc}p-2{esc}syr{esc}p-1{esc}s employing the wavelet and conventional texture analysis methods, respectively, with an additional 25% rise in belowground carbon accumulation in root stock. This research further demonstrates that estimates of carbon accumulation rates as a result of woody encroachment are highly dependent on the spatial and temporal scales of analysis. Conifer species, western juniper and Douglas-fir (Pseudotsuga menziesii) on the Owyhee Plateau, have further expanded into the biologically important quaking aspen (Populus tremuloides) habitats resulting in conifer dominance and occasional loss of aspen clones. Classification of remotely sensed imagery combined with spatially explicit modeling of aspen successional stages indicate that, in the absence of management activity, loss of seral aspen stands will continue to occur over the next centuries as a result of conifer expansion. Spatially explicit modeling results using the Tool for Exploratory Landscape Analyses (TELSA) show that a return to historic fire regimes that burn 12-14% of the modeled landscape per decade would minimize aspen loss by keeping the majority of aspen stands in early and mid seral woodland stages where conifers are subdominant. Furthermore, conifer dominance and aspen loss could be prevented by implementation of prescribed burning programs treating aspen and young conifer woodlands according to historic fire occurrence probabilities.Thesis (Ph. D., Natural Resources)--University of Idaho, May 2007