What Is the Boreal Forest?

The boreal forest is one of the largest biomes on Earth, representing nearly one third of the world’s forested area. It stretches across the cold regions of the Northern Hemisphere, from Canada and Russia to northern Europe. During winter, temperatures can drop to a bone-chilling −50 °C, colder than your home freezer! Summers are relatively warm, with long days of sunlight that help plants to grow quickly during the short growing season. This harsh, vast environment is home to well-known animals like beaver, moose, bears, and caribou. Most of the trees here are conifers, like black spruce and jack pine. Their secret? Needles and cones specially adapted to withstand extreme cold. These conifers cover 80% of Canada’s forests, forming the backbone of this unique ecosystem.

Boreal forests are also vital for people. For thousands of years, Indigenous Peoples have lived in and cared for these forests, relying on them for food, medicine, and cultural traditions; and these groups still play a key role in forest protection today. Beyond their cultural and social importance, boreal forests represent a major economic resource. About one-third of the world’s timber and a quarter of its paper come from them. They are also critical for limiting climate change: thanks to the trees that live there, the boreal forests act like a gigantic vacuum cleaner for greenhouse gases, notably those that humans release into the atmosphere.

The Regeneration of Forests After Fires

Canada’s boreal forests are like giant, ever-changing mosaics constantly reshaped by natural disturbances. Insects, storms, and diseases modify small patches, while crown fires—fires that spread through the tops of the trees high above the ground—can transform thousands of hectares in days. Some areas burn completely, but some patches of forest are usually spared by the fire. Fire is based on three essential ingredients: heat, fuel, and oxygen, known as the “fire triangle” (Figure 1). In the boreal forest, dry needles, fallen branches, and dense underbrush provide plenty of fuel, while warm, dry conditions during summer create the heat. Oxygen, of course, is everywhere. Most fires are triggered by lightning during spring and summer thunderstorms, but human actions—like discarded cigarettes or campfires—can also play a role in starting fires.

After they start, fires spread across vegetation, sometimes even in the soil, and can burn large areas if there is enough fuel and the climate conditions stay the same. Although fires burn trees, human-built structures and soils are also at risk (Figure 2). In 2023, a single fire in eastern Canada burned more than 460,000 hectares (4,600 km²)—an area six times larger than New York City! While it may seem disastrous, fire is part of the forest’s natural renewal. For millennia, fire has cleared land, allowing new plants to grow.

In fact, black spruce and jack pine trees have developed an extraordinary strategy to take advantage of the heat generated by fires. Their cones, which contain seeds, are coated with a very sticky resin that melts under intense heat, allowing the cones to open when a fire burns a forest. With the ground cleared of competing vegetation and bathed in sunlight (because shade-giving trees are gone), their seeds find the perfect environment to grow.

Fires also recycle nutrients back into the soil, making it more fertile. The mix of burned and unburned areas creates a patchwork of young and old forests, providing diverse habitats for a wide variety of wildlife. Some animals thrive in recently burned areas, while others prefer mature forests. This fire–regrowth cycle keeps boreal forests diverse and resilient.

When Forest Fires Become Too Frequent or Too Severe

Although the boreal forest is well adapted to fires, a delicate balance exists, based on the necessary time for forests to recover. Black spruce and jack pine trees typically require 50–100 years to produce enough seeds to regenerate the forest at the same density as before a fire [2]. In eastern Canada, fires occur in general every 80–150 years (Figure 3), giving trees most of the time they need to grow, mature, and produce seeds before the next fire.

But what happens if another fire, particularly a severe one, occurs too soon after the last fire—before the trees produce seed-containing cones? After the first fire, the conifers will begin to regenerate. But if a second fire occurs too soon, young conifers may not have enough time to reach maturity and begin to produce seeds. Without a sufficient seed bank, the forest may experience regeneration failure. Thus, when fires become too frequent, the forest may turn into an open woodland dominated by grasses, shrubs, and lichens, with only a few scattered trees (Figure 3) [3]. This shift from dense, closed forest, to open, more barren land changes the entire ecosystem, with no possibility to return to its initial state. Wildlife habitats are altered, carbon storage capacity is reduced, and the timber industry loses its raw materials.

What Does the Future Hold for Boreal Forests?

Over the past century, global temperatures have risen by approximately 1.5 °C, mainly due to human-driven greenhouse gas emissions. If current trends continue, the increase in temperature could reach +1.8 °C to +4.3 °C by 2100 [4]. But climate change is not the same all over the world. The northern regions, including the boreal forests, are warming almost twice as fast as the global average, and could see temperatures rise by as much as +8 °C by the end of the 21st century. This warming has profound implications for fire activity. More frequent droughts will probably happen, along with longer fire seasons, creating the perfect conditions for fires to ignite and spread. The 2023 fire season—with record-breaking fires across Canada—could be a glimpse into a future marked by increasingly intense fires [5].

Future boreal forests could be radically different from the ones we know today. Rather than a dense, conifer-dominated landscape, open environments with grasses, shrubs, or deciduous trees like birch and aspen, which regenerate quickly after a fire, could become the new norm. This shift would have wide-reaching consequences—not only would wildlife habitats change, but the forest’s ability to store carbon would also be reduced. With fewer conifers to store carbon, the boreal forest could become a net emitter of greenhouse gases because of more frequent and intense fires, speeding up climate change even more. Additionally, changes could disrupt the forest industry, leading to major economic losses, since coniferous trees like black spruce and jack pine are essential for timber production. The increasing frequency and intensity of fires could also threaten human settlements, infrastructure, and air quality, making this an urgent security and health issue.

How Can We Preserve Boreal Forest Resilience?

While we cannot stop or control fires entirely, some strategies can reduce their negative impacts on vital forest ecosystems. The first step, which is not easy, is tackling the root cause—climate change. By reducing greenhouse gas emissions and transitioning to renewable energy, we can limit global warming and help prevent the conditions that make fires more extreme. Another key strategy is leaving behind patches of mature trees or seed sources during logging operations. This retention can help preserve seeds, maintain the local climate, and support ecosystems, all of which increase the likelihood of successful regeneration after fire. Without such measures, the combination of logging and repeated fires may trigger irreversible regeneration failures in the future.

Everyone can play a role in fire prevention. Simple actions, such as following fire safety rules when camping, properly disposing of cigarettes, and respecting fire bans, can help reduce the likelihood of human-caused fires. It is also essential to raise awareness about the risks fires pose, as well as the broader issue of climate change. The more people understand these threats, the more we can come together to implement effective solutions!

Finally, supporting scientific research on fires and forest resilience is crucial. Some researchers are working to understand fires, to see how they affect ecosystems, and, most importantly, how to minimize their damage. By studying forest regeneration after fires and how well fire management strategies work, new tools can be developed to help manage this natural process in the face of rising risks. The challenge lies in finding the right balance between respecting the role of fire in these ecosystems and managing them so they do not become too frequent or severe. One thing is certain: the boreal forest needs crown fires—but not too often!

Glossary

Boreal Forest: ↑ A vast forest found in northern regions of the planet, dominated by coniferous trees like black spruce and jack pine. It plays a key role in carbon storage and wildlife habitats.

Conifers: ↑ Trees and shrubs that produce cones and have needle- or scale-like leaves, typically adapted to cold climates. The two main conifer species in northern forests of North America are black spruce and jack pine.

Crown Fire: ↑ An intense fire that spreads through the canopy of a forest. Crown fires are the most dangerous type of fire, as they can spread quickly and are often uncontrollable.

Seed Bank: ↑ Seeds stored in the soil or in cones, waiting for the right conditions to germinate and grow into new plants.

Regeneration Failure: ↑ When a forest cannot regrow after a disturbance because too few seedlings survive to replace the previous trees.

Carbon Storage: ↑ The process by which forests, oceans, and soils absorb and store carbon dioxide from the atmosphere, helping to slow down climate change.

Fire Season: ↑ The period of the year when weather conditions such as dryness and high temperatures make fires more likely to occur.

Deciduous: ↑ Trees that lose their leaves each autumn and regrow them in spring, unlike conifers that keep needles year-round.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

This project received financial support from the Ministère des Ressources naturelles et des Forêts (project CO-3323-2326-REX-2206-75). This article is a contribution of the Cold Forests International Research Network, funded by the Fonds de recherche du Quèbec - Nature et technologie (FRQNT) and the Centre National de la Recherche Scientifique (CNRS).

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