Peatlands are often viewed as fire resistant landscape features. However, when sufficiently dry, peatlands can experience fires that are substantial in both spatial extent and severity, and can create greater landscape connectivity for fire spread.
Burned forested bog showing lightly burned sphagnum hummocks; near Slave Lake Alberta, September 2011.
Smouldering is the typical form of combustion in peat soils. Compared to flaming combustion, smouldering is flameless and characterized by lower:
- temperature
- spread rate
- heat release rate
Models for predicting carbon emissions from peatland fires are under development. Preliminary estimates suggest that peatland fires across western Canada emit about 6 teragrams (million metric tons) of carbon each year. Overall, wildland fires across Canada emit about 27 teragrams annually. This means that peatland fires can contribute significantly to national carbon emissions. Deep-burning peatland fires have the potential for even higher emissions, as the carbon density of peat increases exponentially with depth.
Peatland ecosystems cover 25 to 30% of the boreal forest region and store about 64% of the estimated total global boreal forest carbon stock. They also:
- retain and purify fresh water
- absorb pollutants
- support biodiversity
Under current scenarios, expected increases in global temperatures have the potential to significantly alter these dominant features of the Canadian landscape.
The Canadian Forest Service is collaborating with national and international experts to better understand peatland fire and the implications of changing fire regimes.
Smouldering combustion
Detecting and effectively extinguishing smouldering combustion deep below the surface can be considerably challenging. These fires can persist for months and can even burn throughout the winter, referred to as holdover or overwinter fires, until being extinguished by sufficient precipitation or reemerging by igniting surface and above-ground fuels.
Due to incomplete combustion, large quantities of smoke are produced from carbon-rich peat soils. This smoke contains large amounts of carbon dioxide and other greenhouse gases. Additionally, peatland fires release mercury into the atmosphere at a rate 15 times greater than other types of wildland fires. Atmospheric mercury is one of several serious concerns resulting from smouldering peat. Other human health hazards include the production of:
- volatile organic compounds
- carbon monoxide
- polyaromatic hydrocarbons
Impact of warming temperatures
Peatlands differ from upland forests in moisture conditions, fuel structure, vulnerability to burning and rates of fuel consumption. Warming temperatures are increasing the frequency and severity of drought conditions.
Preferential burning in peatlands and lowland conifer compared to mixedwood uplands. Wood Buffalo National Park, June 2012
Evapotranspiration is being enhanced and peatland water tables are subsequently lowering, leaving these vast carbon reservoirs more vulnerable to fire.
In more northern regions, warmer temperatures are contributing to permafrost melting, which exposes additional peat material to increased risk of consumption during a fire.
Since 1959, an average of approximately 8,000 wildland fires burn a combined area of 2.1 million hectares each year. Fire seasons have increased in duration and are starting a week earlier and ending a week later, and are characterized by a greater number of large fires (≥200 hectares) burning significantly larger areas. Across North America, the number of very large fires (≥100000 hectares) and fires occurring late in the growing season are increasing, when peatland water tables are usually low.
If peatlands burn at a greater rate or to a greater depth, as expected under a changing climate, fires in the boreal region could contribute an even greater extent to national carbon emissions.
Peatland fire research
Additional research in this field will continue to provide forest managers with the tools needed to manage their resources effectively. Future fire regime projections enable resource managers and policymakers to be better prepared for the challenges ahead.
The development and future deployment of the Peatland subsystem within the next generation of Canada’s Fire Weather Index (FWI) System will provide a better indication of fire danger in peatlands. Peatlands have a large water holding capacity and integrate drought conditions longer than other landscape features. The Peatland Moisture Code, an indicator of water table depth relative to the surface in forested peatlands, will represent ecosystems where fire potential and the drying of fuels is controlled by slower processes than those captured by other FWI System moisture codes.
- Interactive effects of vegetation, soil moisture and bulk density on depth of burning of thick organic soils (2011)
- The Canadian model for peatlands (CaMP): A peatland carbon model for national greenhouse gas reporting (2020)
- Fire-regime changes in Canada over the last half century (2019)
- Controls on boreal peat combustion and resulting emissions of carbon and mercury (2018)
- Hydrological controls on deep burning in a northern forested peatland (2015)
- Peatland-fire interactions: A review of wildland fire feedbacks and interactions in Canadian boreal peatlands (2021)
- Peatland hydrological dynamics as a driver of landscape connectivity and fire activity in the boreal plain of Canada (2019)
- Development of a forested peatland carbon dynamics module for the Carbon Budget Model of the Canadian Forest Sector–Workshop Report (2016)