Hydrological controls on deep burning in a northern forested peatland

While previous boreal peatland wildfire research has generally reported average organic soil burn depths ranging from 0.05 to 0.20m, here, we report on deep burning in a peatland in the Utikuma Complex forest fire (SWF-060, ~90000ha, May 2011) in the sub-humid climate of Alberta's Boreal Plains. Deep burning was prevalent at peatland margins, where average burn depths of 0.42±0.02m were fivefold greater than in the middle of the peatland. We examined adjacent unburned sections of the peatland to characterize the hydrological and hydrophysical conditions necessary to account for the observed burn depths. Our findings suggest that the peatland margin at this site represented a smouldering hotspot due to the effect of dynamic hydrological conditions on margin peat bulk density and moisture. Specifically, the coupling of dense peat (bulk density >100kgm^-3) and low peat moisture (m -2 (mean=27kgCm^-2), accounting for ~80% of the total soil carbon loss from the peatland during the wildfire. As such, we suggest that current estimations of peatland carbon loss from wildfires that exclude (and/or miss) these 'hotspots' are likely underestimating total carbon emissions from peatland wildfires. We conclude that assessments of natural and managed peatland vulnerability to wildfire should focus on identifying dense peat on the landscape that is vulnerable to drying.