Impact of wildfire on the thermal behavior of northern peatlands: Observations and model simulations

Wildfire represents the single largest disturbance to the ecohydrological function of northern peatlands. Alterations to peatland thermal behavior as a result of wildfire will modify the carbon balance of these important long‐term global carbon stores and regulate post‐fire ecosystem recovery. We simulate the 3‐D thermal behavior of a peatland that has been disturbed by wildfire to identify how changes in peat temperatures emerge from changes to the surface energy balance and peat thermal properties. Peat temperatures are simulated within two adjacent peatlands, one area having burned 4 years previously, the second which has been wildfire‐free for 75 years. We demonstrate that there is only a small alteration to the thermal response in Sphagnum fuscum hummocks that are not severely burnt within the wildfire. In contrast, wildfire produces important changes to the energy balance of Sphagnum hollows. A large reduction in the latent heat flux post‐fire increases surface temperatures by up to 30°C during daytime summer conditions. However, temperatures through the peat profile are insensitive to these increases in surface temperature. The low surface moisture content of near‐surface peat insulates the profile from these higher temperatures and, at depths below 0.015 m, only small differences are identifiable between burned and unburned hollow temperatures. Nevertheless, we argue that these alterations to near‐surface temperatures and evaporation rates likely substantially influence the thermal and hydrological conditions post‐wildfire, impacting the peatland recovery. Key Points Evaporation can shut down in burnt peatlands; an important negative feedback Low evaporation produces substantial increases in peat surface temperatures Second negative feedback minimizes temperature increases within the subsurface