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
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
- Boucher, D., Boulanger, Y., et al. 2018. Current and projected cumulative impacts of fire, drought, and insects on timber volumes across Canada. Ecological Applications 28, 1245–1259.
- Boulanger, Y., Gauthier, S., et al. 2014. A refinement of models projecting future Canadian fire regimes using homogeneous fire regime zones. Canadian Journal of Forest Research 44, 365–376.
- Gauthier, S., Bernier, P.Y., et al. 2015. Boreal forest health and global change. Science 349, 819–822.
- Gillett, N.P., Weaver, A.J. 2004. Detecting the effect of climate change on Canadian forest fires. Geophysical Research Letters 31, L18211.
- Hanes, C.C., Wang, X., et al. 2019. Fire-regime changes in Canada over the last century. Canadian Journal of Forest Research 49, 256–269.
- Kurz, W.A., Stinson, G., et al. 2008. Risk of natural disturbances makes future contribution of Canada’s forests to the global carbon cycle highly uncertain. Proceedings of the National Academy of Sciences 105, 1551–1555.
- Price, D.T., Alfaro, R.I., et al. 2013. Anticipating the consequences of climate change for Canada’s boreal forest ecosystems. Environmental Reviews 21, 322–365.
- Asian longhorned beetle photo by Taylor Scarr, Canadian Forest Service
- Emerald ash borer photo by David Cappaert, Bugwood.org
- European gypsy moth photo by USDA APHIS PPQ, Bugwood.org
- Hemlock woolly adelgid photo by Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station, Bugwood.org
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