Canadian Forest Service Publications
Hydrological controls on deep burning in a northern forested peatland. 2015. Lukenbach, M.C.; Hokanson, K.J.; Moore, P.A.; Devito, K.J.; Kettridge, N.; Thompson, D.K.; Wotton, B.M.; Petrone, R.M.; Waddington, J.M. Hydrological Processes 29(18):4114-4124.
Issued by: Northern Forestry Centre
Catalog ID: 35972
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While previous boreal peatland wildfire research has generally reported average organic soil burn depths ranging from 0.05 to 0.20 m, here, we report on deep burning in a peatland in the Utikuma Complex forest fire (SWF-060, ~90 000 ha, 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 ± 0.02 m 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 >100 kg m-3) and low peat moisture (m <250%) at the peatland margin allowed for severe smouldering to propagate deep into the peat profile. We estimated that carbon release from this margin ‘hotspot’ ranged from 10 to 85 kg C m -2 (mean = 27 kg C m-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.
Plain Language Summary
Peat wildfires are receiving international attention because they are challenging to manage and their release of pollutants has far-reaching health impacts. Peatlands in the Boreal Plains are particularly vulnerable to wildfire. To better understand how hydrological processes influence severe burning during wildfire in boreal peatlands, we analyzed the extreme peat burning that occurred during the 2011 Utikuma Complex wildfire in Alberta. Extremely deep smouldering, to a depth of 50 cm and more, was observed at the transition between the peatland and the surrounding forest, while the depth of peat smouldering was limited to 10 cm at the middle of the peatland. We found that a combination of dense peat and the peat’s inability to retain water during dry periods (which often are a precursor to large wildfires) led to deep combustion at the peatland–forest interface. We estimated that 80% of the carbon emissions from the peatland during this wildfire came from the peatland-forest interface. Our findings suggest that the peatland-forest margin is a unique carbon-loss “hotspot” that may be missed if depth of burn is measured only at the centre of peatlands.