DIATOM ASSEMBLAGES OF STREAMS INFLUENCED BY WILDFIRE

The Greater Yellowstone Area ecosystem experienced major wildfires in 1988, resulting in a substantial number of catchments being burned. We studied diatom assemblage structure at 14 sites over 5 years in catch ments ranging from 0 to over 90% burned. Coefficients of variation for selected physical measures provided a good assessment of the degree o f disturbance experienced by the various sites and correlated highly w ith percentage of catchment burned. Principal components analysis quan titatively estimated the degree of temporal change in diatom assemblag es at a site. The more extensively burned catchments showed the greate st amount of structural change in diatom taxa among years. Navicula pe rmitis Hust. and Nitzschia inconspicua Grun. were predominant in the h eavily disturbed systems, whereas Achnanthes minutissima Kuetz., A. la nceolata (Breb.) Grun., Rhoicosphenia curvata (Kuetz.) Grun. ex Rabh., and Diatoma hiemale var. mesodon (Ehr.) Grun. were common in less dis turbed streams. The results demonstrate that recovery trajectories of lotic diatom assemblages following major landscape-scale disturbances are a function of disturbance intensity resulting from differences in catchment characteristics.