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.

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.