Eighteen Year Record of Forest Fire Effects on Ground Thermal Regimes and Permafrost in the Central Mackenzie Valley, NWT, Canada

Ground thermal conditions following a forest fire in 1994 were investigated along a hillslope transect in the discontinuous permafrost zone adjacent to a pipeline right of way in the central Mackenzie Valley, NWT, Canada. The intensity of the burn and damage to the forest and organic layer were more severe in the upper part of the slope than the bottom. Analysis of ground temperature records between 1995 and 2012 indicates that post‐fire changes to the surface altered the ground temperature regime, likely by allowing more snow to accumulate on the ground in winter (as interception by coniferous trees ceased) and decreasing albedo and evapotranspiration in summer. Active layer thickness at the affected site doubled between 1995 and 1998, before stabilising. Permafrost degradation likely occurred at the top of the slope, where burning was most severe. Towards the end of the study period, ground surface temperatures in the upper portion of the slope were lower than they were post fire (1997), whereas the surface temperatures were higher in the lower portion of the slope. In contrast, little to no change in surface temperature was observed for the Unburnt site. These changes in the burned sites are attributed to the increased re‐establishment of aspen, willow and tamarack in the upper part of the transect. Permafrost appears to be recovering at all burned sites in response to ongoing vegetation succession (except at the top of the slope), which is important for maintaining permafrost under conditions of projected climate warming in this boreal environment. Copyright © 2015 John Wiley & Sons, Ltd.