Effect of wildfire and fireline construction on the annual depth of thaw in a black spruce permafrost forest in interior Alaska: a 36-year record of recovery

Maximum thaw depths were measured annually in an unburned stand, a heavily burned stand, and a fireline in and adjacent to the 1971 Wickersham fire. Maximum thaw in the unburned black spruce stand ranged from 36 to 52 cm. In the burned stand, thaw increased each year to a maximum depth of 302 cm in 1995. In 1996, the entire layer of seasonal frost remained, creating a new active layer depth at 78 cm. An unfrozen soil zone (talik) remained between the two frozen layers until 2006 when the entire profile remained frozen. Permafrost returned to the burned site by the formation of a layer of seasonal frost that remained frozen through subsequent years. The fireline displayed a similar pattern with a maximum thaw of 266 cm in 1995 and the establishment of a continuous frozen layer at 69 cm, but the upper frozen layer became discontinuous after several years.