SUSCEPTIBILITY OF PERMAFROST SOILS TO DEEP THAW AFTER FOREST-FIRES ININTERIOR ALASKA, USA, AND SOME ECOLOGIC IMPLICATIONS

Some soils with permafrost thaw deeply and become drier after forest f ires in interior Alaska, while others change little. Soils with permaf rost on the coldest and wettest landscape positions (concave to plane, lower slope positions, and north-facing midslopes) usually failed to thaw deeply after fires in the study area. Soils with permafrost on wa rmer and drier positions (convexities, crests and shoulders, and east- , west-, or south-facing midslopes) thawed deeply in some instances an d not in others, presumably as a function of fire severity or frequenc y. The driest soils (those on convex, upper slope positions, usually w ith sand and gravel at shallow depth) lack permafrost regardless of ti me since fire. Postfire vegetation changes on soils that fail to thaw are weaker than on soils that thaw deeply after fire or were dry and o riginally free of permafrost. Soils with permafrost that fail to thaw show little postfire increase in cover of the plants browsed by moose. More cover and forage for voles are present on soils with permafrost and soils that thaw deeply after fires than on those that are always d ry and permafrost free.