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How does disturbance shape Canada's forests?

Canada’s forests are periodically affected by natural disturbances such as fire, insects and drought. These disturbances can impact and renew entire forest landscapes and, over time, will influence forest composition, structure and biodiversity.

Natural disturbances vary in severity, extent and frequency. All together, these characteristics define the natural disturbance regime of a particular region. Natural disturbances constantly change Canada’s forests and are part of a dynamic landscape.

Alien invasive insects are a threat to Canada's forests

Emerald ash borer, a small, shiny green beetle, situated on a green leaf.Emerald ash borer
Asian longhorned beetle, a large black beetle with white spots and very long antennae, sitting on a decomposing leaf.Asian longhorned beetle
European gypsy moth, a cream-coloured moth with light brown stripes, situated on a tree trunk.European gypsy moth
Hemlock twig with about 100 hemlock woolly adelgid egg sacs, which resemble tiny cotton balls, situated at the base of the needles.Hemlock woolly adelgid

Natural disturbances vary from one region to another

Natural disturbance regimes vary from one region to another within Canada. For example, spruce budworm outbreaks are most prevalent in the balsam fir forests of eastern Canada while wildfires burned more areas annually in the boreal forest and the taiga in central Canada. Some disturbances are specific to a particular tree species (e.g. mountain pine beetle affects only pine species) while others can affect the whole landscape (e.g. fires) thus resulting in specific ecological dynamics. Disturbance severity can strongly vary, with some being stand-replacing (e.g. crown fires) and others causing only partial mortality (e.g. surface fires).

Disturbances have important ecological and socio-economic impacts

Extensive stand mortality caused by natural disturbances can have important impacts on forests by enhancing forest renewal and succession through the release of nutrients from affected trees and the reduction of competition among surviving and newly establishing trees.

Conversely, natural disturbances may have negative impacts on forest ecosystems or the people, communities and businesses who rely on forests. Exotic or non-native insects and diseases introduced through global trade (e.g. emerald ash borer, Asian longhorned beetle) can have serious negative impacts because Canada’s native forests may not be adapted to them. Also, fire poses threats to human safety, property and infrastructure. Natural disturbances can also temporarily reduce the supply of timber, with socio-economic impacts on communities and citizens.

Disturbances affect the carbon cycle

Forests play an important role in the carbon cycle as they absorb carbon as they grow and release it when they die, decay or burn. The impacts of natural disturbances are among the many complex factors that determine whether forests absorb or release more carbon each year.

Natural disturbances are affected by climate change

Virtually all natural disturbances are affected by climate or weather conditions. Therefore, any change in climate regimes can result in important changes to disturbance dynamics. For instance, rising temperatures over the last three decades have increased fire activity in Canada, especially in Western Canada. Future changes in precipitation may result in drought or floods and cause changes in the severity and frequency of insect and disease outbreaks. Impacts on Canada’s forest and the forest sector could be significant, notably by causing timber supply shortages across the harvesting land base.

Sources and information
Photo credits
  • Asian longhorned beetle photo by Taylor Scarr, Canadian Forest Service
  • Emerald ash borer photo by David Cappaert,
  • European gypsy moth photo by USDA APHIS PPQ,
  • Hemlock woolly adelgid photo by Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station,


Table of contents — The State of Canada's Forests Report

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