Fire plays a significant role in forest ecosystems. An average of 9000 fires burn more than 2 million hectares each year in Canada. This is twice the average area burned in the early 1970s, and various modeling scenarios predict another doubling or more by the end of this century, because of warmer temperatures expected as a result of climate change. The growth in fire activity will have major implications for forest ecosystems, forestry activities, community protection and carbon budgets.
The effects of fire on the boreal forest have received considerable attention. However, less is known about the effects of fire on boreal peatlands. Peatland ecosystems cover 2%–3% of the earth’s land surface, but 25%–30% of the boreal forest region. It is estimated that they store 30% of the world’s terrestrial carbon, but about 64% of the estimated total global boreal forest carbon stock. These carbon reservoirs are likely to become increasingly vulnerable to fire as climate warming progresses.
Peat fire emissions
Peat fires release significant amounts of carbon dioxide and other greenhouse gases. In addition, peat fires release mercury into the atmosphere at a rate 15 times greater than upland forests, which may be a serious human health concern.
Models for predicting fuel emissions from fires are still being developed, but preliminary estimates suggest that peat fires across western Canada emit about 6 teragrams (million metric tons) of carbon annually, while fires across Canada as a whole emit about 27 teragrams. This means that peat fires are already contributing significantly to carbon emissions in Canada. Deep-burning peat fires have the potential for even higher emissions, as the carbon density of peat increases exponentially with depth.
Peat fires can also be difficult to extinguish, and severe fires in peatlands can last for months, even burning throughout the winter under the snow layer. These are often smouldering fires that create a lot of smoke from incomplete combustion and result in greater emissions of carbon monoxide.
Impacts of climate change
Because peatlands vary in their moisture conditions and fuel structure, their vulnerability to burning and rates of fuel consumption also vary. However, human impacts, such as climate change and the draining of wetlands, are increasing the overall susceptibility of peatlands to fire.
Warming temperatures will lead to more droughts, greater evapotranspiration and a subsequent lowering of the water table, which will leave peat more vulnerable to burning. In North America, over the last 50 years, there has been an increase in both very large fires (greater than 100 000 hectares) and fires occurring late in the growing season, when the water table is usually lower.
Climate change may also lead to melting of permafrost, which can in turn lead to additional peat material being consumed by fire.
If peatlands begin to burn at a greater rate or to a greater depth, as may be expected under a warming climate, fires in the boreal region could contribute to even greater carbon emissions.
Understanding and acting on the implications of peat fires
Canadian Forest Service scientists are collaborating with other peatland researchers from government agencies and universities in Canada, the U.S. and Russia to study peatland fire and understand the implications of changing fire regimes on northern peatlands and the circumboreal forest.
By studying changes in fire patterns and behaviour over time, researchers are gathering valuable information that will provide forest managers with the tools they need to manage their resources effectively. Projections of future fire regimes will allow resource managers and policy-makers to be better able to prepare for the changes ahead.
Canadian Forest Service key contact
Daniel Thompson, Forest Fire Research Scientist