Forest health monitoring

Collecting information on the health of our forests is important because it helps to:

  • plan forest and pest management activities
  • design research projects, invasive species strategies, and climate change programs
  • evaluate forest sustainability and biodiversity

Forest health monitoring includes:

  • mapping areas to document how much area is affected and how severe the damage is
  • collecting insect and disease samples to track where they occur, how abundant they are, and any changes to tree species affected
  • surveying for specific forest pests, particularly invasive species or pests that affect biodiversity
  • conducting or supporting science projects related to forest health
  • collecting information from long term plots used to assess forest ecosystem health

Each report includes:

  • a summary of forest health conditions
  • amount of area disturbed
  • photos and maps
  • descriptions of damage caused by individual pests, diseases, and weather events across the province

Sometimes, we also include information about future trends/outlook on major pests such as spruce budworm or forest tent caterpillar.

Forest health conditions annual report summaries

2020 forest health conditions

In 2020, Ontario did not have many noteworthy weather events that affected forest health. However, the warmer winter and warm dry spring may have influenced insect pest populations, especially in the south.

Major pests and areas where tree leaves or needles were eaten:

We continued to monitor beech bark disease, which is a combination of an invasive insect (beech scale) and an invasive stem fungus. We recorded new locations in Southern Region.

In 2020, we made few detections of beech leaf disease beyond locations confirmed in previous years. To date, we have only found symptoms of beech leaf disease in Aylmer and Guelph districts and at one location in Aurora District. Researchers are working to determine if the sole causal agent is a nematode or if it is part of a disease complex.

New occurrences of the invasive emerald ash borer beetle were reported in Parry Sound District, which is in the quarantined zone.

Asian long-horned beetle was declared eradicated from the Toronto and Vaughan area by the Canadian Food Inspection Agency.

In 2020, only major disturbances and pests were monitored due to field work limitations related to COVID-19.

2019 forest health conditions

In 2019, Ontario had very few noteworthy weather events affecting forest health.

Areas where tree leaves/needles were eaten:

For the third consecutive year, area with leaves eaten by large aspen tortrix decreased.

A cool, damp spring followed by hot temperatures in early and mid summer were perfect conditions for brown spot needle blight. Over 6,000 hectares of damage were recorded—a record high for the province—primarily in the south.

In 2019, beech leaf disease, now thought to be associated with a nematode, was confirmed in Aurora and Guelph districts prompting work to monitor and understand the effects of beech leaf disease in forests already affected by beech bark disease.

Beech bark disease, which is a combination of an invasive insect (beech scale) and an invasive stem fungus, continued to be monitored with new locations recorded in Southern Region.

The invasive emerald ash borer beetle was found in three central Ontario districts. No new finds of Asian long-horned beetle were reported in 2019. Several other insects and diseases affected forests across the province, but damage was localized.

2018 forest health conditions

In 2018, the main weather-related issue affecting forest health was the hot, dry summer. It led to drought conditions in Southern Ontario, fires in central and northern Ontario, and storms that increased the area of trees that were blown down.

Areas where tree leaves/needles were eaten by:

For the third consecutive year, areas with tree leaves/needles eaten by large aspen tortrix were recorded in the northeast, with a slight decrease in areas affected relative to 2017. In the south, cedar leaves were eaten by leaf miners, with the affected area increasing in 2018

Based on a survey done every two years, the northern extent of ash decline and death from emerald ash borer was recorded in 2018. Traps installed in the northwest to detect whether the invasive emerald ash borer beetle was spreading from Thunder Bay did not capture any beetles. Traps put out for mountain pine beetle in the northwest and for walnut twig beetle, which is the vector of thousand cankers disease, in the south also came up empty. Several other insects and diseases affected forests across the province, but the damage was localized.

The occurrence of beech leaf disease, a disease first found in southwestern Ontario in 2017, increased in 2018 near Aylmer. This finding prompted work with partners, including the United States, to discover causes of the disease.

2017 forest health conditions

In 2017, the main weather-related issues affecting forest health were a wet, cool spring, and above average precipitation in the eastern part of the province, which led to increased leaf and needle diseases. Areas where tree leaves/needles were eaten by forest tent caterpillar, spruce budworm, and jack pine budworm all increased over previous year. Areas with forest tent caterpillar decreased in the northwest but increased in the northeast and south.

The province partnered with the Canadian Forest Service to test biological control of the invasive emerald ash borer. Several other insects affected forests across the province but damage was minimal and localized.

Wet, cool conditions resulted in more area affected by leaf damaging diseases, particularly in the south. Beech bark disease continued to spread in southern Ontario and monitoring staff began installing traps to monitor nitulid beetles, which can carry oak wilt, an invasive disease.

2016 forest health conditions

In 2016, the main weather-related issues affecting forest health were blowdown, freezing rain, and drought. Areas where tree leaves/needles were eaten by forest tent caterpillar increased while those that lost leaves because of spruce budworm and jack pine budworm decreased.

In northwestern Ontario, whitespotted sawyer beetle damage increased in areas damaged by snow in 2012. Several other insects affected forests across the province but damage was minimal and localized.

Warm and dry conditions resulted in less area affected by leaf damaging diseases, particularly in the south. Invasive emerald ash borer continued to spread and was found in Northwestern Ontario for the first time in Thunder Bay.

Earlier reports

Please contact us for earlier reports or if you need accessible formats or communications supports