These studies are taking place in Bonanza Creek Experimental Forest, and at the Wickersham fire site, Fairbanks, Alaska, USA. At the Wickersham Fire site active layer thickness has been measured annually since 1971 in unburned black spruce stands and in black spruce stands that were heavily and lightly burned by the 1971 Wickersham Fire. In addition the same measurements have been taken at two sites where all of the vegetation and organic laters were removed for the construction of firelines. At the Bonanza Creek Experimental Forest we are making annual measurements of thaw depth at a fireline and at an adjacent burned black spruce site and an unburned black spruce stand, a 'control', that were initiated as part of the study of the 1983 Rosie Creek Fire. In addition weekly depth of thaw measurements are made at each of the 9 LTER environmental sites in BCEF and annual thaw depths are measured at the time of maximum thaw at any of the other 27 BCEF-LTER sites that have permafrost or intermittent seasonal frost.