Abstract
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.
Highlights
Permafrost vulnerability to climate change may be underestimated unless effects of wildfire are considered
We hypothesized that a perturbed soil thermal regime on the top of peat plateaus increases the vulnerability to complete thaw at peat plateau edges, and predicted accelerated rates of thermokarst bog expansion within historical fire scars compared to unburned areas (Fig. 2)
Differences in soil thermal regimes were considered to be primarily due to differences in fire histories among sites, since sites all had similar peat depths, and current or pre-fire tree densities, and since the variability in mean annual air temperatures between −0.8 and −3.1 °C among unburned sites did not explain any of the variability in their active layer depth or talik coverage (p > 0.5, linear regressions) (Supplementary Table 1)
Summary
Permafrost vulnerability to climate change may be underestimated unless effects of wildfire are considered. 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. Potential impacts from wildfire on soil thermal regimes in our study region are required to act through other mechanisms given the greater peat depths. We hypothesized that a perturbed soil thermal regime on the top of peat plateaus increases the vulnerability to complete thaw at peat plateau edges, and predicted accelerated rates of thermokarst bog expansion within historical fire scars compared to unburned areas (Fig. 2). Combining field measurements and remote sensing approaches allowed us to estimate an area of thermokarst bog development directly caused by wildfire over the last 30 years, and its relative contribution to overall thermokarst bog development in the study region
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