Canadian Forest Service Publications
Wildfire as a major driver of recent permafrost thaw in boreal peatlands. 2018. Gibson, C.M.; Chasmer, L.E.; Thompson, D.K.; Quinton, W.L.; Flannigan, M.D.; Nature Communications 9(2018):3041.
Issued by: Northern Forestry Centre
Catalog ID: 39829
CFS Availability: PDF (download)
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Permafrost vulnerability to climate change may be underestimated unless effects of wildfire are considered. Here we assess impacts of wildfire on soil thermal regime and rate of thermokarst bog expansion resulting from complete permafrost thaw in western Canadian permafrost peatlands. Effects of wildfire on permafrost peatlands last for 30 years and include a warmer and deeper active layer, and spatial expansion of continuously thawed soil layers (taliks). These impacts on the soil thermal regime are associated with a tripled rate of thermokarst bog expansion along permafrost edges. Our results suggest that wildfire is directly responsible for 2200 ± 1500 km2 (95% CI) of thermokarst bog development in the study region over the last 30 years, representing ~25% of all thermokarst bog expansion during this period. With increasing fire frequency under a warming climate, this study emphasizes the need to consider wildfires when projecting future circumpolar permafrost thaw.
Plain Language Summary
Peatlands in the northern boreal forest often contain large expanses of permafrost terrain, where permanently frozen ice-cored mounds form and trees grow in otherwise wet areas. The presence of trees on permafrost wetlands increases wildfire risk; severe wildfire can lead to the thaw of the ice-cored mounds, returning the ecosystem to a wetter state and releasing methane, an important greenhouse gas, into the atmosphere from the previously frozen soil at a dramatic rate. Thawing of permafrost mounds is expected to increase in response to climate change, but it is not known how much wildfire will accelerate this process. In this study we examined several permafrost peatlands in northern Alberta and the southern Northwest Territories that had last burned between 2 and 49 years earlier. Fire had an affect on the amount of thawing and permafrost for as long as 30 years afterwards, at which point thaw rates in burned areas were equal to those in non-burned areas. We estimate that wildfire is directly responsible for 25% of all permafrost thaw in the region, accounting for about 2200 km2 of thawed area, or slightly less than half the area of Prince Edward Island. Our findings can be used to predict future carbon emissions from the boreal forest.