Adria Huser, a research assistant at Thompson Rivers University, surveys the Beaver River valley in B.C.'s Glacier National Park last summer, 20 years after fire swept through the area. Environments such as this give ecologists insight into how wildfires affect the growth of new forests.Courtesy of Jill Harvey
Hannah Hoag is a Toronto-based journalist covering climate, energy and the environment.
In 2015, Ellen Whitman bushwhacked her way through a section of boreal forest in the southern Northwest Territories, near Fort Smith, and stepped into an open landscape, dotted with leafy trees. The area had once been thick with white spruce and some jack pine, but instead, Dr. Whitman saw trembling aspens surrounded by grassland.
“It was almost like a savannah,” said Dr. Whitman, who is a forest-fire research scientist at Natural Resources Canada in Edmonton. “It was a big change.”
Two fires had torn through the area less than 15 years apart. The first one burned the dense coniferous forest of older trees. The second killed off the young conifers that had sprouted after the first fire. The interval between the fires was too short for the trees to produce mature seeds and regenerate the forest on their own, allowing grasses, shrubs and deciduous trees to take root instead.
It’s a shift that threatens to recur across Canada’s boreal forest. As wildfires increase in size, severity and frequency, against a backdrop of warmer temperatures and persistent drought, the boreal is beginning to give way to birch, aspen, shrubs and grasses.
What kinds of forests are the wildfires
burning in Canada?
Wildfires have scorched more than 15.4 million hectares of land so far this year in Canada – shattering the country's past records. As large wildfires become more frequent, coniferous forests may fail to recover and give way to leafy trees, shrubs and grasslands instead. Scientists expect this shift will affect wildlife and could threaten some populations.
Canada’s land cover simplified
Needleleaf forest
Broadleaf deciduous forest
Mixed forest
Shrubland
Grassland
Lichen and moss
Other
Year-to-date areas burned
Estimates as of Aug. 24
1
2
Estimated areas burned during this wildfire season are highlighted
1
NWT
Yukon
Yellowknife
Great Slave Lake
B.C.
Alta.
Sask.
Edmonton
150 km
2
Que.
Ont.
200 km
MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCES:
NATURAL RESOURCES CANADA; CANADIAN
WILDLAND FIRE INFORMATION SYSTEM
What kinds of forests are the wildfires
burning in Canada?
Wildfires have scorched more than 15.4 million hectares of land so far this year in Canada – shattering the country's past records. As large wildfires become more frequent, coniferous forests may fail to recover and give way to leafy trees, shrubs and grasslands instead. Scientists expect this shift will affect wildlife and could threaten some populations.
Canada’s land cover simplified
Needleleaf forest
Broadleaf deciduous forest
Mixed forest
Shrubland
Grassland
Lichen and moss
Other
Year-to-date areas burned
Estimates as of Aug. 24
1
2
Estimated areas burned during this wildfire season are highlighted
1
NWT
Yukon
Yellowknife
Great Slave Lake
B.C.
Alta.
Sask.
Edmonton
150 km
2
Que.
Ont.
200 km
MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCES:
NATURAL RESOURCES CANADA; CANADIAN WILDLAND
FIRE INFORMATION SYSTEM
What kinds of forests are the wildfires burning in Canada?
Wildfires have scorched more than 15.4 million hectares of land so far this year in Canada – shattering the country's past records. As large wildfires become more frequent, coniferous forests may fail to recover and give way to leafy trees, shrubs and grasslands instead. Scientists expect this shift will affect wildlife and could threaten some populations.
Canada’s land cover simplified
Needleleaf forest
Broadleaf deciduous forest
Mixed forest
Shrubland
Grassland
Lichen and moss
Other
Year-to-date areas burned
Estimates as of Aug. 24
Yukon
Nunavut
NWT
B.C.
Alta.
N.L.
Sask.
Man.
Que.
Ont.
PEI
N.B.
N.S.
Estimated areas burned during this wildfire season are highlighted
NWT
Yukon
Yellowknife
Great Slave Lake
B.C.
Que.
Alta.
Sask.
Ont.
Edmonton
200 km
150 km
MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCES: NATURAL RESOURCES CANADA;
CANADIAN WILDLAND FIRE INFORMATION SYSTEM
Wildfires have burned a staggering 15.4 million hectares so far this year, an area roughly the size of lakes Superior and Michigan combined. It is by far the worst wildfire season on record in Canada, where in an average year 2.1 million hectares burn.
Historically, wildfire has been an important element in renewing the boreal. It clears out dead trees and other dry fuels and creates the conditions for fire-adapted tree species such as black spruce to distribute seeds and grow a new forest that resembles past ones. Wildfire also temporarily reshapes the forest for birds and other animals, creating open spaces for flycatchers and other insect eaters, and leaving behind dead trees that become larvae buffets for woodpeckers.
But drought and warmer temperatures because of climate change have created hot and dry conditions that are causing fires to ignite more easily, grow larger and spread faster. Those changes to the fire regime are driving long-lasting shifts in the boreal.
“Our forests are going to change,” said Jill Harvey, the Canada Research Chair in Fire Ecology at Thompson Rivers University in Kamloops, who studies repeat wildfires, historical fire regimes, drought and regeneration.
“Forests need time to recover following wildfires. They need years for trees to germinate and time for trees to grow. … With drier conditions and more wildfires, we will see change in our forests, their structure and their function.”
Subalpine fir seedlings in Glacier National Park are growing back after a 2017 wildfire. When fires burn the same area in quick succession, it can leave coniferous species like fir at a disadvantage as deciduous trees arrive and grow faster.Natalie Maslowski/Courtesy of Jill Harvey
TRU grad student Natalie Maslowski establishes a plot at Beaver Valley this past July to measure the regeneration from repeat wildfires.Nicola Costerton/Courtesy of Jill Harvey
The number of large fires (greater than 200 hectares) in the boreal doubled between 1959 and 2015, according to a recent study. These big fires have a higher likelihood of encountering areas that have burned in the past 10 to 30 years, Dr. Whitman says.
In a 2022 study of the northwestern boreal forest in Alberta, Dr. Whitman and her colleagues found that the number of reburns occurring less than 15 years apart had increased over the past 50 years.
Between 2014 and 2021, about 6 per cent of Canada’s boreal forest reburned within 30 years or less. Some years it is close to zero; in other years it is much more. In 2015, when close to four million hectares burned, the reburn rate climbed to 9 per cent, covering 357,000 hectares. The numbers will be far more dramatic by the time the 2023 fire season wraps up.
As of Aug. 18, about 10 per cent of the forest that burned this year overlapped with areas that have burned within the past 30 years, according to a preliminary analysis by Dr. Whitman and Quinn Barber, a fire science analyst at the Canadian Forest Service. Their estimates are based on satellite hot spots, the best data source currently available, and have not been peer reviewed. The total estimated reburned area for 2023: 1.5 million hectares.
Canada’s boreal forest covers about 270 million hectares, so the prematurely reburned area remains relatively small. But it is a growing trend that has accelerated more rapidly in recent years.
Bigger and more severe burns mean there are fewer unburned islands of trees left in a stand, which can influence its ability to regenerate. If the mature conifers are too far away, their heavy seeds won’t reach the burned area. Instead, they’ll be beaten out by the light, feathery seeds of aspen or grass.
Flames rise from the woods near Mistissini, Que., this past June.Cpl. Marc-Andre Leclerc/Canadian Forces via Reuters
In mid-July, as wildfires consumed northern Quebec, scientists there were surprised to see that several burned forest patches were less than 50 years old. High temperatures and dry conditions seemed to play a role.
A new analysis published on Tuesday by the World Weather Attribution Initiative found human-caused climate change made the weather conditions, including high temperatures and dry conditions, that drove the wildfires in Quebec two times more likely.
Some areas near Lebel-sur-Quévillon had also burned in 2018, 2010 or 1995. “Although very young stands are known to be less flammable, when it’s dry, it’s dry for everyone!” Yan Boulanger, a forest ecologist at the Canadian Forest Service, posted to X, the social-media site formerly known as Twitter.
Areas that had recently been logged and replanted were also on fire. Victor Danneyrolles, a forest ecologist at the University of Quebec at Chicoutimi, and his colleagues found that by early August, an estimated 1.5 million hectares of managed forest had burned in Quebec. Of that, 45 per cent contained black spruce that was less than 50 years old, planted after clear-cutting.
“We are almost sure they won’t regenerate,” Dr. Danneyrolles said. Based on tree-planting figures from the Quebec government, he calculated that it would take more than 13 years to replant. “It is frustrating because we have been saying for years to the government that there is too much logging in those forests. Now, we are like, ‘We told you.’ ”
If these areas are left alone, jack pine, aspen and white birch might take hold instead. The forest might also shift to lichen woodlands, with sparse black spruce – or no trees at all – and lichens, shrubs, grasses and mosses.
This past June, research assistants Sarah McIntyre and Courtenay Campbell assess regeneration in the Churn Creek Protected Area, where a team established 30 plots to monitor growth over the next 20 years.Courtesy of Jill Harvey
Out west, Dr. Harvey projects the future will bring dry grasslands expanding into the montane forests of central B.C. with repeated drought and wildfire.
“It’s not just the wildfires we have to think about. It is the climate conditions we have to think about following the wildfires,” she said. She is setting up a research project to study sites in B.C. that burned 30 to 50 years ago, to see how repeat wildfires and drought after wildfire are connected to forest regeneration failure, and whether the trees’ cells record the response.
When tree species shift within a forest, so do the animals that live there. Diana Stralberg, a landscape ecologist at the Canadian Forest Service, and her colleagues used a computer model of Alberta’s boreal forests to see how severe climate change – a temperature increase of 4.3 C by 2100 – would affect bird populations there. (According to the Climate Action Tracker, the world is on track for 2.7 C warming by 2100.)
As the region warmed and wildfires became larger and more frequent, Alberta’s forests became younger. Deciduous trees dominated in one-third to one-half of the forest, and up to almost a quarter of the forest became treeless.
Yellow warblers are a species that might find new territory in the changing boreal forests.Melissa Tait/The Globe and Mail
In their projections, the boreal chickadee, Canada jay, white-winged crossbill and other birds associated with old coniferous forests declined. Others, including the red-eyed vireo and the American redstart, among others, would benefit from the shift to more aspen-dominated forests, with the abundance of some, such as the savannah sparrow and the house wren, doubling as grasslands migrated northward into the ghost forests. “You would see a loss of a lot of species that are kind of the cornerstone boreal forest species,” Dr. Stralberg says.
Reburns attract different mammals, too. In Dr. Whitman’s experience in the Northwest Territories, the reburned areas wooed wood bison. The open fields are full of high-protein grasses and windy, which stymies harassing bugs.
This year, with more than 200,000 people across Canada having evacuated their homes and communities that lie within or adjacent to the boreal, solutions seem urgent and daunting. But there are some: Rethink how we harvest forests and limit the logging of older trees in some ecosystems so that mature seeds are available to regrow a forest after it burns. Introduce prescribed burning to rebalance the fire regime and boost fire resilience in a future with more wildfire activity. Conserve moisture-rich peatlands in Alberta to buffer the boreal from fires. We might also have to adapt and begin planting drought-resilient tree species.
“It’s not like we’re losing the boreal tomorrow, but it is an indicator, and we can expect that to continue to expand and be persistent,” Dr. Whitman said.
The future of trees: More from The Globe and Mail
The federal government wants to plant two billion trees by 2031, but will likely fail without a new approach, according to an audit earlier this year. On this episode of The Decibel, reporter Matt McClearn explains how success or failure could affect other climate goals. Subscribe for more episodes.
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