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Indicator: Forest insects

In 2017, 15.6 million hectares (ha) of forests were affected by insects in Canada, which is within 1% of the previous year’s value.

  • The spruce budworm in Quebec has become the dominant forest pest in Canada in terms of the area impacted.
  • The area impacted by mountain pine beetle is at its lowest value within the past 10 years.
  • Forest tent caterpillar continues to be an important defoliator of broadleaf forests in Quebec, Ontario and the Prairie provinces.
  • Western spruce budworm populations in British Columbia have reached the bottom of their outbreak cycle.
  • Forest insects are agents of ecological disturbance because their feeding affects the health of trees.
  • There are thousands of species of tree-feeding insects but only a few have a significant impact on forest health.
  • Other disturbance agents such as drought, fire, storms, or invasive insect species can trigger outbreaks or worsen their impact.

Forest area containing defoliated trees for four insects in Canada, 2007–2017


Graph summary

The area disturbed by forest tent caterpillar remained fairly low until 2012, after which it peaked in 2013; since then, it has been steadily decreasing, however still not reaching pre-2012 levels. The area disturbed by mountain pine beetle was at its highest in 2007, and has been decreasing steadily aside from a slight increase in 2009. The area disturbed by eastern spruce budworm was relatively low in 2007, but has been steadily increasing since. The area disturbed by western spruce budworm was stable and relatively low until 2013, after which it has been steadily decreasing.

Graph data
Table below displays the area disturbed (in hectares) by western spruce budworm, mountain pine beetle, forest tent caterpillar and eastern spruce budworm for each year between 2007 and 2017.
Year Forest tent caterpillar Mountain pine beetle Eastern spruce budworm Western spruce budworm
2007 2,210,536 10,051,919 1,350,369 865,023
2008 1,568,128 7,841,993 876,115 804,711
2009 154,243 8,953,441 831,937 796,904
2010 220,651 6,251,586 1,510,074 503,014
2011 594,647 4,624,907 1,492,829 623,426
2012 729,874 3,016,228 1,792,062 456,745
2013 7,464,898 2,973,935 2,777,998 128,037
2014 5,903,787 2,208,687 3,583,700 44,608
2015 4,841,071 1,447,954 5,235,854 9,135
2016 4,013,393 376,669 4,970,951 3,426
2017 2,793,777 332,259 5,519,287 704

Why is this indicator important?

  • Insect outbreaks are second only to wildfires in the impact they have on Canada’s timber supply and carbon stocks.
  • Prolonged or intense outbreaks of defoliators can cause tree mortality, but more typically forests respond through reduced growth and vigor. This stress can be the trigger that causes bark beetle populations to increase to epidemic levels and impact large areas of forests. Monitoring trends in both insect groups allows researchers and forest managers to assess overall forest health.

What is the outlook?

  • The spruce budworm epidemic in Quebec remains a threat to forests, and areas defoliated are expected to continue increasing. Spruce budworm populations are down in New Brunswick for the first time since 2014. This is a positive sign for Early Intervention Strategy research, which aims to suppress growing populations early in the outbreak cycle to levels that can be held in check by natural mortality factors.
  • Forest tent caterpillar populations increased only slightly in 2017 in Ontario. However, it is expected that this cyclical species will undergo a significant outbreak over the next few years, though the exact locations are still uncertain.
  • The expansion of mountain pine beetle populations in western Alberta as well as their eastward spread in the boreal forest, a novel habitat for this insect, remain a concern. Forest health specialists are investigating the potential effect of extremely cold weather in February 2019 on mountain pine beetle mortality and these general trends of their population expansion.

Click on the image to see a larger version.

  • Image 1
  • Image 2

What reporting frameworks does this indicator support?

Sources and information
  • National Forestry Database. Forest insects, Table 4.1 Area of moderate to severe defoliation (including beetle-killed trees) by insects. (accessed April 9, 2019).
    • 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.
Photo credits
  • Photo of mature forest tent caterpillar. Natural Resources Canada—Canadian Forest Service.
  • Photo of spruce budworm courtesy of Véronique Martel.


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

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