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.
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.
|Year||Area affected (hectares)|
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.
|Year||Western spruce budworm||Forest tent caterpillar||Eastern spruce budworm|
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.
- National Forestry Database. Forest insects – National tables, Table 4.1, Area within which moderate to severe defoliation occurs including area of beetle-killed trees by insects and province/territory, 1975–2015. (April 13, 2016)
- 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.
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