Researchers at McGill University have confirmed that aspen play a key role in forest fire prevention and mitigation across Canada. Planting these trees near communities can reduce both the likelihood and severity of fires and limit how far they spread, the researchers said. 

“Aspen is not a 100 per cent effective fire deterrent, but compared with other species, it is a better choice to plant around communities or critical infrastructure,” said Flavie Pelletier, lead author and recent PhD graduate in Natural Resource Sciences. 

While individual aspen trees burn easily due to traits like thin bark, large aspen stands have the opposite effect, with bigger patches linked to lower fire severity. This study, which found that aspen trees are much more common at fire perimeters than within burned areas, was the first to demonstrate the pattern on a national scale. 

The team had expected aspen stands to burn more severely in spring, when trees are drier due to the lack of leaves. However, researchers did not observe any significant link between the season and fire severity or the proportion of aspen along the perimeters, Pelletier said. 

“This is the strongest indicator that aspen serves as a fire barrier,” she said. “The bigger the aspen patch, the lower in severity the fire tends to be. Even with higher fire weather, as during the historic 2023 fire season, aspen’s ability to slow fire progression appears stable.” 

“Fire weather” refers to the conditions that cause wildfires to start, spread or change behaviour. 

Pelletier said that the team used previously unavailable remote-sensing data to do a large-scale analysis of how fires and aspen interact. 

The researchers developed an algorithmic tool that creates near-real-time maps of forest stand disturbances, such as wildfires, using remote-sensing data from NASA’s Landsat and the European Space Agency Sentinel-2. These fire maps can be cross-referenced with other datasets, like the newly available maps of dominant tree species from the Canadian Forest Service, to inform new analysis, such as the one on aspen. 

Pelletier said the Canadian Forest Service may adopt the tool as a second data stream to complement its coarse daily fire maps, enabling faster and more precise information on wildfires. 

Because some forestry companies remove aspen to promote commercially valuable conifers, the findings could also influence forest management practices. 

“There is value in retaining aspen for biodiversity, but also because mixed stands that include aspen may be less likely to be entirely lost in a fire,” Pelletier said. 

“Populus tremuloides as a natural fire barrier in Canada’s boreal forest under a changing climate,” by Flavie Pelletier (McGill), Jeffrey A. Cardille (McGill) and Joanne White (Canadian Forest Service), was published in Forest Ecology and Management. 

The study was funded by the Natural Sciences and Engineering Research Council of Canada and the Canadian Forest Service of Natural Resources Canada.