Forests in northern Ontario could be growing less resilient to fire, scientist says

"Short-interval fires" have scientists with Natural Resources Canada concerned.

A new study has shown that the increase in forest fire activity means that forests are becoming less resilient to fire.

Daniel Thompson is a Forest Fire Research Scientist with Natural Resources Canada. He said that in the past, boreal forests could go anywhere from 75 to 200 years between fires. The interval now is shortening, Thompson said, to as little as 10 years between fires.

"Basically what happens is that once these fires we typically think of as being really large, and sort of wanting to burn that older forest which is maybe full of spruce, but only when these fires get really large during these really dry periods are they able to burn into younger forest which typically has more aspen, more willow," Thompson said. "More of that sort of really leafy green stuff that normally doesn't burn."

The young forest typically is more resistant to the fires because of their leafy nature. They even form a natural firebreak.

However, in 2014, when the team compiled its research, forest fires were eating into these younger areas. Thompson said scientists noticed "quite dramatic ecological effects."

Thompson said it's worrying, especially for fire managers.

"Normally, [fire managers] would rely on younger forests to provide a really natural firebreak and that's part of that fire management process," Thompson said. "You allow some areas to burn naturally away from communities, with the expectation that they'll be less able to burn in the future.

"What we're seeing here is that when it is dry enough, those sort of traditional natural firebreaks are less robust than we thought." 

They're also seeing the near-complete loss of spruce and pine in these forests. 

Good news in the battle against climate change, Thompson said, as spruce and pine tend to be more flammable, but are replaced with grasses, and more leafy vegetation.

"But really, this is a big, natural process," Thompson said.

"This is really about helping the planning process for that future forest," Thompson said. "And really helping understand what our expected forest looks like in the future."

"That way,  we can better plan around community protection and knowing when it is too dry to rely on these young forests as barriers to fire."