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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


Graph summary

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.

Graph data
Table showing the area disturbed, in hectares, by three forest insect species: forest tent caterpillar, eastern spruce budworm and jack pine budworm for each year from 2008 to 2018.
Year Eastern spruce budworm Forest tent caterpillar Jack pine budworm
2008 876,115 1,568,128 168,834
2009 831,937 154,243 205,701
2010 1,510,074 220,651 44,968
2011 1,492,829 594,647 27,765
2012 1,792,062 729,874 61,018
2013 2,777,998 7,464,898 92,176
2014 3,583,700 5,903,787 26,356
2015 5,235,854 4,841,071 24,634
2016 4,970,951 4,013,393 206,849
2017 5,519,287 2,993,477 748,880
2018 5,992,899 1,560,811 1,187,801

Forest area containing beetle-killed trees for two insects in Canada, 2008 to 2018


Graph summary

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.

Graph data
Table showing the area disturbed, in hectares, by two forest insect species: mountain pine beetle and spruce beetle, for each year from 2008 to 2018.
Year Mountain pine beetle Spruce beetle
2008 7,841,993 51,593
2009 8,953,441 63,863
2010 6,251,586 66,267
2011 4,624,907 61,774
2012 3,016,228 43,195
2013 2,973,935 26,601
2014 2,208,687 336,396
2015 1,447,954 242,344
2016 376,669 291,972
2017 332,259 506,881
2018 318,796 343,758

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
A forest tent caterpillar on an aspen leaf.
Forest tent caterpillar
Sources and information
Photo credit
  • Forest tent caterpillar stock photo by pokergecko/iStock by Getty Images.


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

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