Abstract
The potential of high severity wildfires to increase global terrestrial carbon emissions and exacerbate future climatic warming is of international concern. Nowhere is this more prevalent than within high latitude regions where peatlands have, over millennia, accumulated legacy carbon stocks comparable to all human CO2 emissions since the beginning of the industrial revolution. Drying increases rates of peat decomposition and associated atmospheric and aquatic carbon emissions. The degree to which severe wildfires enhance drying under future climates and induce instability in peatland ecological communities and carbon stocks is unknown. Here we show that high burn severities increased post-fire evapotranspiration by 410% within a feather moss peatland by burning through the protective capping layer that restricts evaporative drying in response to low severity burns. High burn severities projected under future climates will therefore leave peatlands that dominate dry sub-humid regions across the boreal, on the edge of their climatic envelopes, more vulnerable to intense post-fire drying, inducing high rates of carbon loss to the atmosphere that amplify the direct combustion emissions.
Highlights
Peatlands have persisted across the globe for millennia, accumulating and storing atmospheric carbon
Measurements were conducted in three areas of assumed pre-fire feather moss peat: i) low burn severity plots with a burn depth less than 0.05 m and residual feather moss visible; ii) moderate burn severity where the depth of burn was greater than 0.05 m, consistent with burns projected under future climates[8]; and iii) high burn severity in which the peat had been burned down to underlying mineral soil, with burn depths up to 1.0 m13
There was no significant difference in daily ET between the low severity Sphagnum plots and either the moderate burn severity (ET = 3.12 ± 0.38 mm d−1, t = 0.22, p = 0.82) or high burn severity plots (ET = 2.76 ± 0.38 mm d−1, t = −0.711, p = 0.50)
Summary
Peatlands have persisted across the globe for millennia, accumulating and storing atmospheric carbon. An increased forest canopy (fuel load) combined with reduced peat moisture contents will increase peatland wildfire severities[8] This forms peat profiles that are more sensitive to drying[9] and so further exacerbating the climate driven impacts. With such potential vulnerabilities, there is an immediate need to stress-test[10] the core feedback mechanisms within peatlands to ascertain their capability to maintain their regulating function under future extreme conditions. Measurements were conducted within a zone of Sphagnum moss peat, burned at a low severity, that more weakly restricts the supply of water to the evaporating surface[12]. Post-fire ET is calculated based upon: i) the average daily ET of the remnant burned surface cover (assumed equal to low burn severity feather moss if part of the pre-fire feather moss layer is retained or moderate burn severity peat if the feather moss layer is entirely combusted), and ii) the proportion of the post-fire peatland surface composed of these different peatland units under varying burn severity distributions
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