Changes in forest vegetation in the Upper Wenatchee River Watershed, Washington State, USA, over 43 Years

Past land management practices have altered the character of dry, low- and mid-elevations forests on the east slopes of the Cascade Mountains in Washington State.  I investigated the effects of fire suppression and past harvest activity in the upper watershed of the Wenatchee River (9,014 ha) using an existing GIS dataset based on interpretation of 1949 and 1992 aerial photos. Patches with a Pseudotsuga menziesii (Douglas-fir) overstory appear to have declined as a result of conversion to nonforest types and by replacement by Abies grandis (grand fir) patch types. Selection cutting and fire suppression together may have allowed the less fire tolerant P. menziesii/A. grandis understory to encroach into Pinus ponderosa (ponderosa pine) stands. By 1949, previous logging had probably reduced the area covered by patches with large (>63.5 cm DBH) trees. By 1992, these patches increased in area and number, probably because medium-sized (40.64-63.5 cm DBH) trees have moved into the larger size classes. These preliminary results suggest that both fire suppression and past timber harvest have altered the structure and composition of forests in the watershed. To more accurately assess forest changes in the eastern Cascades, further work to define reference conditions on a local and regional basis is necessary.