Indicator: Forest insects
In 2018, 16.9 million hectares (ha) of forests were affected by insects. This is a 3.5% increase over 2017.
- Forest pest insects kill trees by eating the tree’s leaves or needles, or by feeding under the bark and so disrupting a tree’s ability to transfer nutrients and water.
- Most trees can tolerate some insect damage, but years of repeated feeding can weaken or even kill trees. Tree mortality can also happen when many insects feed at the same time, during an “outbreak”.
- Insect feeding and tree mortality can be detected from the air and used to measure changes in the population of insect pests.
- The area defoliated by spruce budworm continued to increase in Quebec, while Ontario and Manitoba experienced outbreaks of jack pine budworm. Budworms kill trees through years of repeated defoliation, but spruce budworm outbreaks are prolonged events, while jack pine budworm outbreaks are shorter, more frequent events.
- Forest tent caterpillar continued its decline across Canada. This species rarely kills trees but can impact the health of some hardwood species and is a nuisance when outbreaks occur near inhabited areas.
- Spruce beetle is increasing in prevalence in western Canada, while mountain pine beetle continues to decline. Both species are bark beetles that can kill large numbers of trees very quickly.
The indicator shows the area impacted by native forest insects. However, invasive alien insects also impacted forests in Canada in 2018. For example, the emerald ash borer expanded its range throughout the Maritimes and the hemlock woolly adelgid spread from the United States into Nova Scotia and Ontario.
Forest area containing defoliated trees for three insects in Canada, 2008 to 2018
This graph shows the trends in forest area, in hectares (ha), defoliated by three forest insects from 2008 to 2018. The insects are: (1) eastern spruce budworm, (2) forest tent caterpillar and (3) jack pine budworm.
The forest area disturbed by forest tent caterpillar was less than 2 million ha between 2008 and 2012, then increased to 7.5 million ha in 2013. Since then, the area disturbed by forest tent caterpillar decreased each year to 1.5 million ha in 2018.
The forest area defoliated by the eastern spruce budworm rose from a low of 900,000 ha in 2008 to almost 6 million ha in 2018.
Defoliation caused by jack pine budworm increased from a low of 24,000 ha in 2015 to almost 1.2 million ha in 2018.
|Year||Eastern spruce budworm||Forest tent caterpillar||Jack pine budworm|
Forest area containing beetle-killed trees for two insects in Canada, 2008 to 2018
This graph shows trends in the forest area of beetle-killed trees by two beetle species from 2008 to 2018. The insects are: (1) mountain pine beetle and (2) spruce beetle.
The forest area disturbed by mountain pine beetle has decreased each year from a peak of 8.9 million hectares (ha) in 2009, to a low of 300,000 ha in 2018. During this period, the forest area defoliated by spruce beetle expanded from 26,000 ha in 2015 to over 500,000 ha in 2017.
|Year||Mountain pine beetle||Spruce beetle|
Why is this indicator important?
- In Canada, forest insects can reduce timber supplies in all forests and affect carbon stocks in native forests. In urban forests, insects can impact ecosystem services and property values.
- Outbreaks of native insects are an expected and normal part of life in most Canadian forests. However, scientists predict that climate change could alter the location, frequency and intensity of outbreaks of native and invasive alien species, including species that have not been important defoliators in the past. Monitoring the changes in damage caused by all forest insects allows managers to predict impacts on overall forest health.
What is the outlook?
- Spruce beetle is killing significant volumes of spruce trees in regions that were previously impacted by mountain pine beetle, potentially exacerbating wood fibre supply issues in British Columbia.
- Outbreaks of jack pine budworm and spruce budworm are expected to increase across Canada, affecting significant areas of the boreal forest, including areas in northern Canada where outbreaks of budworms have rarely been seen.
- Invasive species will continue to threaten forests with the spread of emerald ash borer and hemlock woolly adelgid in the east.
What reporting frameworks does this indicator support?
- Montréal Process: 3.a
Sources and information
- Bleiker, K., Boisvenue, C., et al. 2019. Risk Assessment of the Threat of Mountain Pine Beetle to Canada's Boreal and Eastern Pine Forests. Natural Resources Canada and Canadian Council of Forest Ministers Forest Pest Working Group. Pacific Forestry Centre, Victoria, British Columbia.
- Canadian Food Inspection Agency. Emerald ash borer - Agrilus planipennis.
- Canadian Food Inspection Agency. Hemlock woolly adelgid – Adelges tsugae (Annand).
- Emilson, C., Bullas-Appleton, E., et al. 2018. Hemlock Woolly Adelgid Management Plan for Canada. Natural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre, Sault Ste. Marie, Ontario. Information Report GLC-X-21.
- National Forestry Database. Forest insects, Table 4.1, Area of moderate to severe defoliation (including beetle-killed trees) by insects. (accessed April 14, 2020).
- Forest area disturbed by defoliators includes only areas with tree mortality and moderate to severe defoliation. Defoliation does not always imply mortality. For example, stands with moderate defoliation often recover and may not lose much growth.
- Defoliation is mapped on an insect species basis, and a given area may be affected by more than one species at a time. This may result in double or triple counting in areas affected by more than one species, exaggerating the extent of the total area defoliated.
- Defoliation caused by exotic species is not mapped.
- Forest tent caterpillar stock photo by pokergecko/iStock by Getty Images.
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