COMPARING THE PRESCRIBED NATURAL FIRE PROGRAM WITH PRESETTLEMENT FIRES IN THE SELWAY-BITTERROOT WILDERNESS

The severity and extent of recent fires (1979-1990) were compared with that of presettlement fires (pre-1935) by eight major forest types in the Selway-Bitterroot Wilderness (SBW) in Idaho and Montana. Presettl ement fire intervals were determined for estimating area burned. Prese ttlement annual area burned for the entire SBW was 4,290 ha by stand r eplacement fire and 4,310 ha by nonlethal understory fire. All recent period fires>4 ha were mapped using a GIS system. Area burned was dete rmined by the fire severity classes: crowning, lethal surface, nonleth al surface, and no burning. Annual area burned averaged 2,780 ha by st and replacement and 2,270 by understory fire. Area burned during prese ttlement was 1.7 times that during the recent period. During the prese ttlement period, area burned by stand replacement and nonlethal unders tory fire was 1.5 and 1.9 times greater respectively than during the r ecent period.