Resiliency in the face of fire: How northern forests adapt to wildfire

What are some of the main drivers of the record-breaking 2023 fire season in Canada?

The 2023 fire season in Canada was hugely impactful for Canadians and it drew a lot of international attention. That level of interest does reflect how severe and dramatic that fire season was.

We broke our records for area burned nationally - around 15 million hectares - whereas our previous record was around half that. So, what created that situation? The short story is extreme temperatures and drought. In 2023, for most of the fire season (May to October), the temperature in Canada was over 2.2 degrees Celsius warmer than the recent average. We also had very little rain and snowfall in certain regions leading up to the fire season and that created a volatile situation. I think a lot of long-standing fire practitioners as well as researchers were honestly shocked how the 2023 fire season played out. Although the fire behavior and activity did respond to temperature and moisture conditions the way we'd expect, it was very dramatic.

How is it looking for Canada’s 2024 wildland fire season?

So far, the 2024 fire season is not looking to be as extreme as last year. It’s nice to have a somewhat more normal year - people need a break, and ecosystems need a break. That said, it's only July, and already around two million hectares have burned. Until quite recently, 1.96 million was about our average for a total fire season, and we're only about halfway through this year’s season. While this year is nothing on the scale of last year, I think we're probably still in for an above-average wildfire season.

It's also worth noting that this year we had holdover fires from last year. This is something that Canada and Arctic ecosystems have experienced for many years, and it happens naturally, but it means that we already have fire on the landscape very early in the season, which tends to contribute to these above-average years.

Your research looks into how forests respond to fire. What are some trends that you are seeing?

One thing I really like to reinforce is that forests are super resilient. We still see strong post-fire recovery happening naturally in most of our northern forests.

That said, during our more extreme fire seasons in the last few years, we are starting to see signs that there may be shifting ecological impacts in response. In northern forests, we expect this self-replacement paradigm where what was there before fire is what eventually grows back afterward. However, in severely or more frequently and repeatedly burned areas, fire can lead to a loss of organic matter in the soil or a loss of seed sources from trees. That causes shifts where we don't necessarily see that forest coming back the same way.

In some cases, we see changes in the tree species that make up the forest. Often, we see more broadleaf trees like birch or Aspen growing back instead of what was there before. In Eastern Canada and a bit in the Northwest Territories, we're seeing pine trees making a gain at the expense of spruce trees that are a more sensitive to frequent fire. The forest that grows back may not resemble the forest lost in the fire, but the balance of tree species has always been shifting and in some cases a rebalancing of species can be beneficial. In severe situations, areas can undergo regeneration failures and may not resemble a forest anymore. What’s concerning is the rate and extent of fire that we're currently experiencing, and if that will affect the overall ability of the forests to regenerate.

How long does forest regeneration take after wildfire?

Forest regeneration varies by the ecosystem and by the type of fire. Generally, we see seedling establishment within the first 10 years after a fire. The transition from seedlings to mature trees resembling what the forest looked like before can take 50 years or more. However, there's always forests in different stages of regeneration on the landscape and what we hope to see is a balance with older, mature forests in some places to compensate for that alternate habitat that's introduced when fire comes. With more fire happening, we have concerns about the proportion of these areas that are at a very young successional stage because they can be very vulnerable and could point to a possible habitat shift or impacts on species that are dependent on mature forests.

What are the implications for these ecosystem shifts?

The amount of habitat that's in an early stage of regrowth is increasing. Additionally, with more severe and frequent burning, we're seeing a higher proportion of forests undergoing surprising shifts. These forests that are undergoing changes have implications for fire management, for people using the land and who live in these areas, and for animals that rely on these habitats.

If you're an animal that depends on old growth forests, such as a woodland caribou, your habitat availability may be decreasing, and competition with other species may increase. For example, moose can actually benefit from having more early successional forests on the landscape. With more moose, there could be more wolves which then translates to issues for caribou. From another perspective, some species could benefit from having more newly burned landscapes. One example is different species of woodpecker that need these dead trees to have a food source and to reproduce successfully. When we work in recently burned sites, we can always see Black-backed woodpeckers. Similarly, we find that bison seem to enjoy hanging out in these severely burned areas, possibly due to more grasses and less fly harassment in these areas. So, there's always winners and losers.

From a human perspective, there are impacts for those that rely on the forest for food, wellbeing or lifestyle. For example, people can use the forest for timber, foraging and hunting. It can also affect how people emotionally connect to these landscapes. It can be painful to see something undergo such a dramatic change.

In terms of fire management, one positive implication is that when we see more broadleaf tree regrowth like aspen or more shrubby and grassy ground cover, that can actually lower fire activity because these species, in the event of a fire, are a less volatile fuel than a dense conifer forest. As we see more landscapes shift in this way, there could actually be a reduction in fire activity.

The future question is if we see a shift where there’s an increase in tree species that lower fire risks, do we actually see less fire happening? Or has the temperature and the weather become so severe that we lose the benefit of that negative feedback?

What could be the impact of more frequent and intense Arctic fires on the boreal forest?

Trees have a lot of inertia. So even though our climate may be rapidly changing, mature trees are resilient and long lived. They can survive a climate that's not 100% their ideal for a long time, so in a way, mature trees could be holding that ecosystem in place despite other changes. When a disturbance like fire removes those mature trees, it could actually open up that landscape to undergo a big change. So it's possible that fire increasing in the future could facilitate ecosystem transitions.

There are variable responses in how the tree line is affected by fire. In some cases, having a fire disturbance might remove competition and allow seedlings to come in and advance the tree line or expand it northward. In other cases, the fire just knocks the tree line back and we don't really see the trees benefiting much from that disturbance. That can be due to a lot of reasons such as insects and animals that eat tree seeds or climate conditions not being ideal for seedlings.

Another major implication of more fire in the north is increasing carbon dioxide and methane emissions. In northern forests, we have a lot of areas with very deep organic soils or peatland, and they store a lot of carbon for many years. When it burns, it can release substantial greenhouse gas emissions. Often peatlands or thick organic soils protect permafrost in the north, and when fire burns and reduces the thickness of that organic insulating layer, permafrost thaw might accelerate and release more greenhouse gases.

How have northern forests adapted to fire?

In northern ecosystems, fire was more frequent in the past or at least affected a more expansive area of Canada. Some of that is due to natural climactic conditions and also Indigenous Peoples’ cultural burning. Tree species have made amazing adaptations to these conditions.

Northern forests are more conifer-dominated, and dense trees grow really closely together with species like black spruce and jack pine, in a structure that promotes high intensity, crown fires which burn all the way up forest canopies. One example of an adaptation to fire is the black spruce, which carries all its cones in a ball up at the top of the tree, creating a seed source even if the tree is dead. Similarly, jack pine and lodgepole pine have serotinous cones that are sealed and actually require heat to open. Fires are essentially expected in northern forest ecosystems, and trees have adapted to have a seed source to reestablish themselves in those conditions.

That said, we're getting concerned because forests have these adaptations to a certain fire regime and characteristics of fire. But if we see more intense and frequent fires, when forests are pushed beyond the bounds of that adaptation, that's when we start seeing changes to what’s growing back and ecological transitions. And that points to a real fire regime shift.

What is your involvement in CAFF's ArcticFIRE project?

The main activity we are working on now is a summary of recent understandings around fire ecology and ecological changes associated with the intense climate change that's been happening in the north. We’re looking at how that's translating to changes to our ecosystems as well as changes in how we might manage fire. There’s also some interest in consolidating datasets across international boundaries to gain a more comprehensive, circumpolar or at least cross-boundary understanding in a lot of these places around what has been happening for fire activity and how that relates to changing Arctic climates.