Projected climate change impacts on forest land cover and land use over the Willamette River Basin, Oregon, USA

Upland forests in the Pacific Northwest currently provide a host of ecosystem services. However, the regional climate is expected to warm significantly over the course of the 21st century and this factor must be accounted for in planning efforts to maintain those services. Here we couple a dynamic global vegetation model (MC2) with a landscape simulation model (Envision) to evaluate potential impacts of climate change on the vegetation cover and the disturbance regime in the Willamette River Basin, Oregon. Three CMIP5 climate model scenarios, downscaled to a 4 km spatial resolution, were employed. In our simulations, the dominant potential vegetation cover type remained forest throughout the basin, but forest type transitioned from primarily evergreen needleleaf to a mixture of broadleaf and needleleaf growth forms adapted to a warmer climate. By 2100, there was a difference (i.e., climate/vegetation disequilibrium) between potential and actual forest type for 20-50 % of the forested area. In the moderate to high climate change scenarios, the average area burned per year increased three to nine fold from the present day. Forest harvest on private land is projected to be affected late in the century because of fire altering the availability of rotation-age stands. A generally more disturbed and open forest landscape is expected, which may significantly alter the hydrologic cycle.