Fireline surface level and thaw depths: Wickersham fire sites (1977 - 2009)

In June of 1971, the Wickersham fire burned 6313 ha in an open black spruce forest underlain with permafrost and provided an opportunity to study fire and fireline effects on the rate and patterns of permafrost, vegetation, and soil recovery. Because of the fire?s proximity to Fairbanks, a concentrated effort was made to control the fire and 29 bulldozers constructed 113 km of fireline which averaged 12 m in width (Viereck and Dyrness 1979). The construction of firelines with heavy machinery involves the complete removal of vegetation and the soil organic layer down to mineral soil. The removal of the organic layer and subsequent loss of thermal insulation results in an increase in permafrost depth of thaw. In addition, thermal subsidence, erosion, and formation of gullies makes the fireline surface unstable and full recovery tends to be a lengthy process. This long-term study examines fireline surface level changes and maximum depth of thaw over time on cross sections of two firelines underlain with ice rich permafrost.