Influences of Fire and Climate Change on Patterns of Carbon Emissions in Boreal Peatlands

L.A. Morrissey, G.P. Livingston and S.C. Zoltai

Abstract

    Wildfires in boreal peatlands worldwide contribute approximately 29 Tg of carbon to the atmosphere each year. Susceptibility of peatlands to wildfires is largely based on the moisture content of the surface biomass and near-surface peat. Peatlands in which the water table seasonally falls well below the surface are most susceptible to burning. Nearly 94% of all carbon emissions due to wildfires are from fires in subarctic permafrost bogs (66%) and forested swamps (27%). Combustion of aboveground biomass (surface fires), however, accounts for only 30% of the total carbon emissions. Incomplete combustion within the near-surface peat (0-20cm depth) is the source of 70% of carbon emissions due to wildfires, even though the areal extent of peat fires is only 18% that of surface fires. Normalized over the surface area burned, direct carbon emissions due to peatland wildfires is estimated to be 1.5 Kg-C m^-2 yr^-1. Atmospheric loading of CO₂ due to wildfires is estimated at 25.2 Tg-C yr^-1. Emissions of CO, CH₄ and NMHC are estimated at 3.0, 0.3 and 0.27 Tg-C yr^-1 respectively. No estimates of emissions due to the indirect effects of peatland fertilization as a result of wildfires is possible at this time, although limited observations suggest they may far exceed direct emissions.

    The contribution of trace gases to the atmosphere due to peatland fires worldwide is approximately one-fifth the contribution from wildfires in all boreal and temperate forests, although relatively small in contrast to biogenic contributions due to decomposition in these wetlands. Any climatic change over the next century that would reduce the moisture content of the surface peats is expected to increase the the frequency, extent, and intensity of fires and thus emissions of carbon to the atmosphere. Such change is expected to result in a significant loss of carbon presently stored as peat.