Area of forest disturbed by fire, insects, disease and harvesting
Why is this indicator important?
Forests are constantly exposed to and modified by natural disturbances such as fire, insects and diseases. Natural disturbances are an essential part of the process of forest renewal.
As well, forests are disturbed by industrial activities such as logging, road construction, oil and gas ventures and other human activities.
Foresters study both natural and human disturbances to gain a better understanding of how forest ecosystems change. They also look increasingly to natural events for insights into planning forest harvesting, working to ensure that their practices facilitate natural regeneration and recovery of ecosystem productivity following harvest.
What has changed?
Fires
In 2011, 4608 forest fires were reported across Canada, approximately two-thirds of the previous 10-year average (2001–2010). The area burned in 2011 (2.6 million hectares) was also 15% lower than the 10-year average.
The 2010 fire season was exceptionally severe, with twice the average annual area burned. Above-average dry conditions continued into the fall, with the drought code (a national index reflecting the dryness of the deep forest layers) indicating extreme conditions throughout much of western Canada and the territories. However, under La Niña’s influence, overwinter snowfall and precipitation were unusually high in much of Canada. As a result, spring arrived late in 2011 and drought conditions greatly lessened across the country, except in British Columbia, Alberta and the Yukon.
Still, despite it being a below-average year for fire activity, 2011 saw several examples of extreme fire behaviour. The most notable examples were in Alberta and Ontario.
- Strong, dry winds gusting up to 70 kilometres/hour, combined with a lack of precipitation, created severe conditions across most of northern Alberta during the May 14–15 weekend. These events led to the Slave Lake Fire, which burned into the community, destroying over 400 homes and causing $700 million in insurable losses; and the Richardson Fires, which grew to over 500 000 hectares in size, ultimately accounting for about 20% of the total area burned in Canada during 2011.
- During Ontario’s 2011 fire season, 1334 fires burned 635 373 hectares—the most area in that province ever burned in one year (the 10-year average is 1109 fires burning 76 837 hectares). Most fires were triggered by lightning events as storms tracked north and south of the province. In July alone, 650 fires burned 558 000 hectares.
Insects
In 2010, about 12.7 million hectares of forest contained beetle-killed trees or were defoliated by other insects—a decrease from 15.2 million hectares the year before.
From 1998 to 2011, the mountain pine beetle killed more than 710 million cubic metres of pine in British Columbia, which represents more than 50% of the province’s commercial pine inventory.
Since the mountain pine beetle invaded northern Alberta in 2001, about 1.3 million hectares of forest have been affected in that province. Alberta’s efforts to control the beetle, along with weather unfavourable to the insect’s survival, have significantly reduced beetle populations in southern and central Alberta. Still, their populations continue to increase and spread in northwestern Alberta and northeastern British Columbia, moving north towards the border with the Northwest Territories. Future north- and eastward expansion of the beetle will depend on a range of factors: its ability to survive the winter; its development during the summer; its interactions with native and new host trees; the distribution of susceptible host trees; and the effectiveness of control efforts.
Outbreaks by some insects are cyclical, with peak populations occurring periodically in particular regions of the country. For example, outbreaks of spruce budworm recur at approximately 35- to 40-year intervals in eastern Canada. The last extensive outbreak covered more than 50 million hectares in the 1970s and then declined to fewer than 1 million hectares in the late 1990s. Since that time, there has been resurgence and then decline of populations in different regions throughout the extensive range of spruce budworm in Canada.
Invasive pests are a particular concern for forest managers because of uncertainty about how new species might affect the existing ecosystem. For example, since it was first detected in Windsor, Ontario, in 2002, the emerald ash borer has killed millions of ash trees in parts of Ontario and Quebec. It continues to spread into new areas, having considerable economic and ecological impacts.
Diseases
As agents of disturbance in forest ecosystems, forest diseases (or pathogens) are major drivers of diversity, shaping forest structure and function. Pathogens also play a major role in decomposition and carbon cycling in Canada’s forests.
Native forest pathogens have evolved to exist in equilibrium with natural forest communities. However, they can become very destructive when the natural equilibrium is altered by forest management activities, climate change, fire or insects.
Across Canada, for example, Armillaria root disease is known to affect 203 million hectares of forest currently, infecting almost all tree species with long-term persistence. Surveys of Douglas-fir in British Columbia and spruce and balsam fir in Ontario have shown that Armillaria infection increases steadily in those species with stand age, whether after planting in harvested stands or after disturbance in natural stands. Another example is Annosus root and butt rot, now infecting an increased number of forest stands and established in regions not previously exposed to the disease.
Several alien invasive forest pathogens are also prominent in Canadian forests, in some cases threatening the survival of certain tree species. For example, white pine blister rust has destroyed extensive stands of white pine since being introduced into Canada in the early 1900s. Another introduced pathogen, the European race of the fungus that is causing Scleroderris canker in the forests of Ontario, Quebec and New Brunswick, has now become a considerable problem in Newfoundland. There it has breached a quarantine zone on the Avalon Peninsula and is threatening the native red pine stands on the island.
Environment-related factors such as drought, air pollution, extreme temperatures and nutrient deficiencies can cause disease directly or predispose trees to damage by disease-causing organisms. For example, ongoing aspen dieback and decline in western Canada and northern Ontario has been attributed to the combined effects of insect defoliation, pathogens and thaw-freeze events.
Since 2009, milder and more humid spring weather has favoured the development of many foliar diseases in Quebec, such as brown-spot needle blight and needle cast of white pine, shoot and needle blight of balsam fir, and anthracnose of maple and oak. Similar phenomena have been observed in Ontario, where ink spot of aspen affected more than 1800 hectares of forest in northern Ontario in 2009; and in southern New Brunswick, where stands show red pine affected by Sirococcus shoot blight. These foliar diseases do not typically threaten the survival of affected trees, but can reduce plant growth.
Harvesting
Provincial and territorial regulations govern harvesting of Canada’s forests.
By law, all harvested areas in Canada must be reforested. In addition, many forest management practices are designed to mimic natural disturbances such as fire. These approaches have the advantage of preserving the natural attributes of Canada’s forests and their ability to adapt to change while also considering economic and social factors.
In 2010, approximately 688 000 hectares of forest were harvested on provincial/territorial, federal and private lands, accounting for roughly 0.18% of all forest and other wooded land in Canada.
| Cause of disturbance | Hectares (millions) | Percentage change from previous year |
|---|---|---|
| Area burned (2011) | 2.6 | -14.6 |
| Area defoliated by major insectsa | ||
| Forest tent caterpillar (2010) | 0.2 | 43.1 |
| Mountain pine beetle (2011) | 4.6 | -26.4 |
| Spruce budworm (2010) | 1.5 | 53.2 |
| Area affected by pathogens | ||
| Armillaria root diseaseb | 203.0 | 0.0 |
| Area harvested (2010) | 0.7 | 12.2 |
a Area includes moderate to severe defoliation.
b Area affected remains constant year to year, but disease intensity changes.
Sources: Canadian Interagency Forest Fire Centre, National Forestry Database and British Columbia Ministry of Forests, Lands and Natural Resource Operations
Area of forest disturbed annually by fire, insects (three species) and harvesting, 2000-2011
Sources: Canadian Interagency Forest Fire Centre, National Forestry Database and British Columbia Ministry of Forests, Lands and Natural Resource Operations
Long description (includes data table)
For additional data, visit the National Forestry Database.