Indicator: Forest insects

Why is this indicator important?

Forest insects often have impacts that are obvious and easy to track, making them useful indicators of forest health. While these natural disturbances are a normal part of healthy forest ecosystems, they can also affect productivity in commercial forests and have a potentially negative impact on environmental values associated with forested landscapes.

Non-native invasive species

Non-native invasive species, such as gypsy moth and emerald ash borer, remain a special concern because of their novel and uncertain ecological and socio-economic impacts.

Non-native species are often pests in urban environments, where their impacts are related to aesthetic, health and community benefits and the cost of control or tree removal, rather than to timber values.

What has changed and why?

In 2014, 20.3 million hectares (ha) of forest were damaged by insects. This is virtually unchanged from the total in 2013. While the area damaged by some insects has decreased, the area damaged by other insects has increased.

Bark beetles

Since peaking in 2007, the area affected by the mountain pine beetle in British Columbia continued to decline in 2014, shrinking by 765,000 ha to 2.2 million ha.

A spruce beetle infestation in northern British Columbia increased significantly in 2014 to 290,000 ha and has the potential for further expansion. However, it is still quite small compared to current or past areas affected by mountain pine beetle.

Forest area affected by mountain pine beetle in British Columbia, 2004-2014
Graph displaying the area disturbed in hectares by mountain pine beetle in British Columbia for each year between 2004 and 2014.
Graph data
Table displays the area affected in hectares by mountain pine beetle in British Columbia for each year between 2004 and 2014.
Year Area affected (hectares)
2004 7,021,886
2005 8,736,068
2006 9,243,408
2007 10,051,919
2008 7,841,993
2009 8,953,441
2010 6,251,586
2011 4,624,907
2012 3,016,228
2013 2,973,935
2014 2,208,687


The forest tent caterpillar outbreak that expanded so rapidly in 2013 continues to affect nearly 6 million ha of predominantly aspen forest in central and western Canada. This defoliator exhibits classic population cycles 8 to 11 years in length, with the last maximum occurring in 2006. Populations in Alberta appear to have peaked in 2013 and were on the decline in 2014, while the amount of area defoliated to the east and west was still increasing, particularly in Manitoba and Ontario.

The eastern spruce budworm outbreak in Quebec continues to increase, with 3.4 million ha undergoing moderate to severe defoliation in 2014. The abundant foliage of the host trees for spruce budworm and forest tent caterpillars sustains population increases, and the resulting defoliation decreases tree growth. If defoliation is severe or persists for several years, tree mortality can occur. Areas near the origin of the spruce budworm outbreak have now experienced seven to eight years of annual defoliation, and significant mortality is beginning to occur.

Forest area containing defoliated trees for three insects in Canada, 2004-2014
Graph displaying the area disturbed in hectares by western spruce budworm, forest tent caterpillar and eastern spruce budworm for each year between 2004 and 2014.
Graph data
Table displays the area disturbed in hectares by western spruce budworm, forest tent caterpillar and eastern spruce budworm for each year between 2004 and 2014.
Year Western spruce budworm Forest tent caterpillar Eastern spruce budworm
2004 623,735 1,578,126 750,288
2005 463,962 3,160,818 721,471
2006 776,907 5,564,624 1,105,221
2007 865,023 2,210,536 1,350,369
2008 804,711 1,557,943 876,115
2009 796,904 154,243 831,937
2010 503,014 220,651 1,510,074
2011 623,426 594,647 1,492,829
2012 456,745 729,874 1,792,062
2013 128,037 7,464,898 2,777,998
2014 44,608 5,907,787 3,533,643

What is the outlook?

The mountain pine beetle outbreak in British Columbia seems to have run its course and will likely continue its decline to historical background levels, in part because the host tree species (lodgepole pine) has been largely decimated. Populations are persisting in Alberta, but it remains unclear how far east and north the beetles will spread.

The spruce budworm outbreak in eastern Canada is expected to continue increasing in area. If recent trends continue, the outbreak will have encompassed 6 million ha in 2015 and is predicted to cover 10 million ha in 2016. Tree mortality in the core areas will also likely increase.

While the area defoliated by forest tent caterpillar in Alberta will likely decline, simultaneous growth in Manitoba and Ontario could substantially increase the total area defoliated. Previous outbreaks in Ontario have involved approximately 15 million ha, and Manitoba experienced more than 10 million ha of defoliation in 1975–1976. Although short-lived tent caterpillar outbreaks rarely result in much tree mortality, potential interactions with regional droughts could exacerbate the impact of this species.

  • The area disturbed by mountain pine beetle includes only British Columbia.
  • 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 afflicted 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.