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.