Why Canada's forests need fires

Forest fires are part of the natural cycle of regeneration and renewal in most of Canada’s forests. They clean out the understory, remove flammable litter (decaying logs, leaves and needles) on the forest floor, reduce disease and the number of pests and open the forest canopy, allowing sunlight to trigger new growth.

Fire frequency across Canada

For most forests in Canada, the question is not if there will be a forest fire but when – and how intensely it will burn. Natural factors such as climate, physical landscape and the types of species present and human factors such as land use change and fire management policies determine how often fires return. In the boreal forest, fires recur as often as every 35 to 120 years. But in other forest types, for example those on the moist Pacific coast, fires are rare and may only happen several centuries apart.

A fire interval map shows areas in Canada where fires return roughly every 35-120 years; every 120-240 years; every 240-360 years; every 360-480 years and 480 years or more.

Canada’s forest species need fire to thrive

Nearly all plants and animals that live in Canada’s forests are adapted to fire. In fact, many depend on it. The occurrence of fires at different times and intensities across the landscape creates a variety of habitats, ranging from mature forests to recently burned sites, which is important for biodiversity.

Morel mushrooms, which sprout about a year after a forest fire, are highly sought-after gourmet delicacies.

Wood-boring beetles quickly colonize newly burned trees. Woodpeckers soon follow, feeding on the beetle larvae under the bark.

Light-loving blueberries emerge after fire, with bumper crops providing essential nutrition for black bears and other animals.

Jack pine relies on environmental triggers like the heat from fire to release seeds sealed inside its cones by sticky resin.

Forest renewal after fire in Val-Paradis, Quebec, 1997

A lightning strike near Val-Paradis, Quebec, in June 1997 started the fire that burned neighbouring stands of trembling aspen (deciduous forest) and of mixed black spruce and jack pine (coniferous forest). This burn, past fires and more recent harvesting have created a mosaic of forest types across the landscape, with stands of different ages, heights and species mixes. The area burned in 1997 shows as dark pink in the satellite image. The dates of past fires surrounding Val-Paradis are indicated.

A satellite image of the area around Val-Paradis, Quebec shows an area affected by fire in 1997, and the dates and areas of past fires in the surrounding area in 1815, 1850 and 1915.

After the fire

Over time, as the trees regenerate, the burn site will become harder to tell apart from the surrounding forest. The deciduous forest grows back more quickly than the coniferous forest.

DECIDUOUS FOREST

3 months post-fire

Trembling aspen and leafy shrubs quickly resprout from roots and burned stumps.

15 years post-fire

The loss of forest cover due to the fire is temporary, and an even-aged stand of aspen has been largely re-established to cover the burn site.

CONIFEROUS FOREST

3 months post-fire

Spruce and pine trees begin to grow from the seeds shed by their cones during the fire. They take longer to re-establish than the trembling aspen

15 years post-fire

Faster-growing jack pine forms the top of the forest canopy, while black spruce fills in the space below. Eventually, the black spruce will overtake the pine to form the upper part of the canopy.

Sources

Natural Resources Canada–Canadian Forest Service. Fire ecology.

Natural Resources Canada–Canadian Forest Service. Forest fires.

  • Fire interval map modified by David Gervais, Natural Resources Canada, from: Bernier, P.Y., Gauthier S., et al. 2016. Mapping local effects of forest properties on fire risk across Canada. Forests 7, 157; doi:10.3390/f7080157.
  • Landsat TM 5 image 1994–1997 processed by Luc Guindon and David Gervais, Natural Resources Canada.
Photo credit
  • Franck Tuot (morel mushrooms), Josée Noël, Université du Québec en Abitibi-Témiscamingue (jack pine seedling), Danielle Charron, Université du Québec à Montréal (deciduous and coniferous forests
    – fire year), David Gervais, NRCan (deciduous and coniferous forests – 15 years after).