Effects of Fires on Carbon Cycling
in North American Boreal Peatlands

S.C. Zoltai, L.A. Morrissey, G.P. Livingston, and W.J. de Groot

 ABSTRACT

Boreal peatlands occupy about 1.14 x106 km2 in North America. Fires can spread into peatlands, burning the biomass and, if moisture conditions permit, burning into the surface peat. Charred layers in peat sections reveal that historically bogs in the subhumid continental regions and permafrost peatlands of the subarctic regions have been the most susceptible to fires. Fire return periods were estimated from the numbers and ages of the charred peat layers. Based on average moisture conditions of the surface, about 0.5% of the peatlands (6,420 km2) can be expected to burn annually, but the surface peat layer is expected to burn only in a small portion of this area (1,160 km2). Carbon losses from above-ground combustion, in the form of CO2, CO, CH4 and non-methane hydrocarbons, is the highest in forested swamps at 2.031 Tg C yr-1. Carbon losses due to combustion of surface peat is the highest in the driest peatlands, those affected by permafrost, at 5.825 Tg C yr-1. The total estimated carbon release due to above-ground combustion is 2.918 Tg C yr-1 and 6.721 Tg C yr-1 due to below ground peat combustion. These estimates of direct carbon emissions to the atmosphere due to wildfires suggest a globally significant, but relatively small source in contrast with emissions from wildfires in uplands.

The effects of a possible climate change are expected to be most prominent in the continental and northern parts of North America. Lower water table would result in increased CO2, but decreased CH4 emissions from the peatlands. A drier climate may mean increased fire frequency and intensity, resulting in more fires in peatlands and an increased probability of the fires consuming part of the peat.