Setting the Landscape Context for Paired Watershed Studies in Western Oregon

Abstract

Paired watershed studies provide valuable scientific understanding of the effects of disturbance on aquatic resources. Recently, the Watersheds Research Cooperative (WRC) in western Oregon initiated three paired watershed studies in order to investigate the effects of contemporary timber management practices on aquatic ecosystems. I use geographic information system (GIS) tools, combined with principal components and cluster analyses, to develop a landscape classification of forested headwater basins in order to support these paired watershed studies. Spatial and statistical analyses were applied to landform, geologic texture, forest cover, and climate variables that describe the biophysical and climatic setting of forested headwater catchments (300 – 58,000 km2) in western Oregon. Cluster analysis isolated 5 groups that account for major differences in environmental conditions across the landscape, but have a large ratio of among to within group dissimilarity. The first and second principal component axes correlate most strongly to differences in slope and elevation, and the percent coniferous tree cover and past harvest, respectively. Ultimately, results from clustering and principal components analysis are combined to identify areas on the landscape that are best represented by WRC study sites. Results show that the WRC sites are environmentally similar to the majority of forested areas in western Oregon, with notable exceptions. These results provide a landscape context for interpreting and extrapolating the findings of paired watershed studies and are useful for prioritizing site locations for future paired watershed studies in the region. Partners including the Bureau of Land Management, Oregon Department of Forestry, and private landowners will use this information to better understand the broader implications of contemporary timber harvest techniques on watershed processes and aquatic biota.