EFFECTS OF FIRE ON LANDSCAPE HETEROGENEITY IN YELLOWSTONE-NATIONAL-PARK, WYOMING

A map of burn severity resulting from the 1988 fires that occurred in Yellowstone National Park (YNP) was derived from Landsat Thematic Mapp er (TM) imagery and used to assess the isolation of burned areas, the heterogeneity that resulted from fires burning under moderate and seve re burning conditions, and the relationship between heterogeneity and fire size. The majority of severely burned areas were within close pro ximity (50 to 200 m) to unburned or lightly burned areas, suggesting t hat few burned sites are very far from potential sources of propagules for plant reestablishment. Fires that occurred under moderate burning conditions early during the 1988 fire season resulted in a lower prop ortion of crown fire than fires that occurred under severe burning con ditions later in the season. Increased dominance and contagion of burn severity classes and a decrease in the edge: area ratio for later fir es indicated a slightly more aggregated burn pattern compared to early fires. The proportion of burned area in different burn severity class es varied as a function of daily fire size. When daily area burned was relatively low, the proportion of burned area in each burn severity c lass varied widely. When daily burned area exceeded 1250 ha, the burne d area contained about 50% crown fire, 30% severe surface burn, and 20 % light surface burn. Understanding the effect of fire on landscape he terogeneity is important because the kinds, amounts, and spatial distr ibution of burned and unburned areas may influence the reestablishment of plant species on burned sites.