How does disturbance shape Canada's forests

Fire, insects and disease constantly affect Canada’s forests. They renew whole forest landscapes and shape forest composition, structure and habitat diversity over time.

These natural disturbances – and others such as drought, floods and wind storms – vary in severity, extent and frequency, and their relative importance varies from region to region and over time. The result is that Canada’s forests are all part of a dynamic landscape, one that has always been in a constant state of change.

Natural disturbances, the forces of change in Canada’s forests, are themselves being affected by climate change.

For example, climate change is expected to increase drought in some forest areas, which will in turn make forests more susceptible to insects, diseases and forest fires.

Natural disturbances bring forest renewal

Natural disturbances such as fire, insect outbreaks and disease are an important part of the natural life cycle of forests, especially Canada’s boreal forests.

Fire is a key agent of change and renewal in the boreal zone, releasing nutrients, allowing sunlight to reach the forest floor and releasing the seeds of some species from their cones. (See Why Canada’s forest need fires.)

Diseases and large insect outbreaks sometimes result in extensive stand mortality. This process releases nutrients from decaying trees and reduces competition among surviving and newly establishing trees, enabling forest renewal and succession. However, forests are less well adapted to exotic insects and diseases introduced through global trade, so these outbreaks can have negative rather than positive impacts.

Graphic displaying Canada’s forest area of 347,069,000 hectares and the proportional area affected by disturbances: 17,631,825 hectares damaged by insects; 1,405,655 hectares burned by fire; 779,577 hectares harvested.

Disturbances can have negative effects

While natural disturbances are essential to forest health and renewal, they can have a negative impact on the people, communities and businesses that reside in or rely on forests, at least in the short term. In addition to threatening human safety, property and infrastructure, natural disturbances can damage and reduce the supply of timber and so affect socio-economic well-being of communities and citizens. (See Learning to live with forest fires.)

Disturbances affect the carbon cycle

Forests play an important role in the carbon cycle, absorbing carbon as they grow and releasing it when they die and decay or burn in fires. Whether they absorb or release more carbon each year depends on many complex factors, including the impacts of natural disturbances, especially fire.

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