In 2015, scientist Ellen Whitman set out to visit Wood Buffalo National Park, a vast wilderness stretching across northeastern Alberta and the Northwest Territories.
At the time, the country had been subject to two major wildfires ten years apart – the most recent in 2014.
“The first fire burned a really big, mature pine forest and it grew back like pine with a little bit of aspen mixed in,” recalled Whitman, a wildfire investigation specialist at Natural Resources Canada.
“Then that second fire killed all those seedlings and all of a sudden it’s actually a grassland with a few scattered aspen trees.”
Her team’s findings, documented in a recently published paperare part of a growing body of evidence showing how changing climate and increased wildfire severity are changing the composition of North American forests.
Her research compared areas of forest with similar climate and soil conditions, but half had been set on fire twice in a short period of time, while the other half had a longer period of regrowth.
In the areas where the fire had returned more quickly, aspens rather than conifers predominated and growth under the trees was much less established. Areas of exposed mineral soil, where all organic matter had burned off, were also more common.
“If you had a major disturbance or repeated burning on top of burning or a very severe drought in the year after a fire, we can start to see these patches change to a more southerly structure in their ecosystem structure,” Whitman said.
“Almost more like a savanna in some cases.”
Scientists say such a transformation is likely to take place elsewhere in Canada’s boreal forests in the coming years.
Good fires and bad fires
Experts are quick to point out that fires are a crucial and natural aspect of a forest’s life cycle; they have allowed Canada’s boreal forests to flourish for millennia.
But there is also evidence that fires are getting bigger and more intense, changing growth after the flames die down.
“People talk about good fire and bad fire. The good fire is the fire we’ve had in the past that helped renew this landscape,” said Jennifer Baltzer, an associate professor in the department of biology at Wilfrid Laurier University. inOntario.
“The bad fires (are) what we see in light of a combination of climate warming and really effective firefighting in the past.”
Baltzer also studied how boreal forests change across North America. Black spruce dominated most sites before a fire, but tended to lose dominance in the aftermath, according to data collected for a Research Paper 2021.
In more extreme cases, areas filled with black spruce failed to regenerate at all. The findings also have troubling implications for the carbon stored beneath the forest floor, she said, potentially increasing the amount released into the atmosphere.
More than 5.1 million acres have burned across Canada so far this year, according to federal data.
The worst fire season on record was in 1995, when 7.1 million acres burned, government data showed. The country is on track to surpass that by the end of June.
“I expect what we’re seeing now will turn out to be very serious blazing fires,” said Merritt Turetsky, director of the Institute of Arctic and Alpine Research at the University of Colorado Boulder.
“We know that when a lot of organic matter — in the trees, as well as on the ground in moss and peat layers — when a large amount of it is consumed during a fire, sites don’t recover to what they were before.”
In this changing landscape, there will be “winners and losers” among not just trees, but also the birds and mammals that thrive in a new environment, Whitman said.
Bison, for example, prefer the long grasses and open spaces now found at the site of the recurring fires. On the other hand, there is evidence that woodland caribou depend on conifer bogs as maternal habitat, she said.
“If we start to lose those, it doesn’t necessarily bode well for those species because the timing of reproduction is super important for them to have a habitat where they’re less likely to encounter predators.”
Change in expectations
Researchers say there are ways to slow these changes, starting with reducing greenhouse gas emissions.
In addition, Baltzer said fire management has improved by allowing some fires to burn and increasing the number of fires in some cases prescribed burns in others, it would help reduce the number of out-of-control, large-scale fires.
“In many parts of Canada, we have a buildup of fuels in the landscape because of effective suppression,” she said.
“If you can reduce some of the fuel in the landscape, there’s the potential to help facilitate fires that aren’t as damaging.”
Going forward, Whitman suggested that different approaches will be needed depending on circumstances – and expectations. Planting more trees in burnt-out areas could help, but only up to a point, she said.
“We can certainly replant after fires, but as people have really seen this year, it takes up a huge portion of the landscape,” she said, explaining that planting trees is not realistic in some cases.
She stressed that in many cases, trees have still demonstrated the ability to reseed and regenerate.
“It’s really more a matter of whether it needs to be a forest that’s as dense or has the exact same composition as you previously expected, or should we say… maybe it’s a little bit of a changed ecosystem. “