Canadian Forest Service Publications
Resistance of the boreal forest to high burn rates. 2014. Héon, J.; Arseneault, D.; Parisien, M.-A. Proceedings of the National Academy of Sciences of the United States of America 111(38):13888-13893.
Issued by: Northern Forestry Centre
Catalog ID: 35706
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Boreal ecosystems and their large carbon stocks are strongly shaped by extensive wildfires. Coupling climate projections with records of area burned during the last 3 decades across the North American boreal zone suggests that area burned will increase by 30–500% by the end of the 21st century, with a cascading effect on ecosystem dynamics and on the boreal carbon balance. Fire size and the frequency of large-fire years are both expected to increase. However, how fire size and time since previous fire will influence future burn rates is poorly understood, mostly because of incomplete records of past fire overlaps. Here, we reconstruct the length of overlapping fires along a 190-km-long transect during the last 200 y in one of the most fire-prone boreal regions of North America to document how fire size and time since previous fire will influence future fire recurrence. We provide direct field evidence that extreme burn rates can be sustained by a few occasional droughts triggering immense fires. However, we also show that the most fire-prone areas of the North American boreal forest are resistant to high burn rates because of overabundant young forest stands, thereby creating a fuel-mediated negative feedback on fire activity. These findings will help refine projections of fire effect on boreal ecosystems and their large carbon stocks.
Plain Language Summary
Climate change is expected to result in increased wildfire activity – both more fires and larger fires – but estimates of the potential increase vary widely. To understand how past fires can affect the future risk of fires, the researchers studied fires for the past 200 years along 190 km of the James Bay Road in Quebec, one of the most fire-prone boreal forest areas in North America. In addition to using recent data on fires, they found fire scars and dated tree stands to reconstruct the history of fires in the area. They found that large, severe fires decrease the likelihood of subsequent fires, because there is less biomass to burn and because the young forest stands that grow after a fire are more resistant to fire. However, the type of tree that grows back can also be a factor, as jack pine burns more easily than aspen, for example. Overall, the study shows that wildfires can create a “negative feedback,” as they limit the chance of future wildfires. The study sheds light on the effects of extreme weather (most wildfires occurred during serious droughts) and the age of trees on fire risk. It provides key information for predicting wildfires, especially under climate change.