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The Boreal Forest
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See the Boreal
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Fire
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Fire |
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Friend of the Boreal Forest
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Boreal landscape, post fire Photo: Evan Ferrari
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Only 2–3% of natural forest fires in the boreal exceed 200 hectares in size, but large fires can range into the tens of thousands of hectares. These large fires account for more than 95% of the 1.3 million hectares of boreal forest that burns on average each year across Canada. |
For thousands of years the boreal forest and all life within it have in some way been shaped by fire. Whether obvious or subtle in form, boreal forest species have adapted to or, in many cases, come to rely on the presence of natural wildfire. In the heart of the boreal forest, natural fire frequency ranges on average from every 50 to every 200 years.
Re-growth after fire, Photo: Evan Ferrari
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For intact boreal forests, fire is renewing. It breaks rock, releasing minerals into the soil and enriching it. Fire kills pathogens and bacteria within and around burnt areas; smoke from fire can travel long distances, thus killing pathogens over a large area. A natural disturbance, fire clears accumulated leaf and needle litter from the forest floor, exposing a mineral and soil bed which is receptive to seed implantation and growth (blackened soils and wood absorb heat from the sun, creating favourable growing conditions). |
Fire destroys fire-sensitive, shade-tolerant hardwood seedlings thereby allowing the re-establishment of a conifer forest, including, for example, black spruce. Under the right conditions, mature spruce forests are host to a variety of lichens, providing an important food source for woodland caribou. Finally, fire allows nutrients that are normally locked up in leaf litter and woody debris to be recycled back into the soil.
Black spruce and jack pine, in particular, are well adapted to fire. Black spruce cones tend to sit high on the tree to ensure the best chance of seed survival after a fire. Their semi-waxen seal often breaks open after a fire, resulting in reseeding of the burned area.
Jack pine are thin-barked and highly resinous — biologists have described these trees as “roman candles” that can literally explode into flame. Jack pine cones open only under high heat (50 ° C or more), and seedlings need the open conditions of a post-fire landscape to thrive.
Fire in the boreal forest does not destroy everything in its path. It is estimated that, on average, islands of live trees cover close to 25% of a burnt boreal area, and live and mildly scorched trees can make up as much as 50% of such areas. These islands and peninsulas of unburned or mildly scorched trees form a refuge for wildlife and a seed source for the regenerating forest, while standing dead trees left behind by fires can become important feeding and nesting sites for insect eaters (e.g., three-toed and black backed woodpeckers) and cavity nesters (e.g., northern flying squirrel, boreal owl and common goldeneye).
While clearcutting also serves to open up large forest areas, it does not resemble natural fire in most other aspects. Most clearcuts, for example, do not include dense islands of live trees, the patchiness and rough edges of burned areas and rarely leave intact internal forest areas. Most significantly, in contrast to fires, clearcuts leave behind a network of roads. Scientists have found that road density is inversely proportional to ecological health — the more roads there are, the more fragmented and stressed the forest becomes.
Fire is an important evolutionary mechanism. We must recognize the important ecological differences between fire and forestry and ensure that the majority of forests remain shaped by fire and other natural forces, just as they have been for centuries.
For more information, please see our Forests, Fires and Logging: Setting the Record Straight fact sheet.
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