A Decade of Post‐Fire Succession Amplifies the Effect of Wildfire on the Surface Radiation Balance and Permafrost Thaw in Subarctic Peatlands

ABSTRACT Increasing wildfire activity is driving permafrost thaw in subarctic peatlands across the southern Northwest Territories, but the key mechanisms and progression of thaw following fire remain poorly understood. In response, 10 years (2015–2024) of near‐continuous surface (four‐component radiation, wind, and snow) and subsurface measurements (temperature, moisture, and frost tables) were examined from a burned and unburned permafrost peatland in the southern Taiga Plains ecoregion. A low‐severity wildfire in 2014 burned a portion of a peat plateau with stunted black spruce, which led to full tree mortality but left most dead trees standing. Results indicated that wildfire increased the rate of permafrost thaw (4 cm year −1 higher on average), smoothed the permafrost table topography, and led to 100% talik extent (perennially unfrozen layer above permafrost) within 8 years following the fire. Post‐fire succession during the first decade, including the gradual toppling of dead burnt trees, ultimately amplified the energy available for ground heating and permafrost thaw. In contrast, the immediate reduction in albedo and snowpack alterations following fire had either only short‐term effects or even cooling effects. This study demonstrated that summertime processes outweighed wintertime processes in driving permafrost thaw, suggesting the effects of wildfire may intensify in the future as winters shorten under current climate warming projections. Considering millions of hectares in the Northwest Territories have recently burned, findings from this study directly support projections of permafrost thaw and resulting land cover changes driven by regional wildfire disturbance coupled with ongoing climate warming.