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

2025 forest health conditions

Temperature and weather

Temperatures were near the 30-year average in 2025, with some variation.

Spring and summer were dryer than usual in Northwest and Southern regions and Far North of Ontario.

Warmer than average temperatures were recorded in the summer and fall, dropping to below average in December. Notable weather events included:

  • a late March ice storm in Eastern and Southern Ontario
  • incidences of major thunderstorms and wind
  • tornadoes in the Northeast and Southern regions
  • a major downburst in Samuel de Champlain Provincial Park, resulting in the park’s closure for the rest of the year

The area of blowdown recorded increased from 2024 at over 6,086 hectares.

Insects, diseases and invasive species

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

  • spruce budworm defoliation declined for the third year, with most defoliation in Northeast Region
  • jack pine budworm defoliation decreased for the fifth consecutive year, with most recorded in Northwest region
  • forest tent caterpillar decreased across the north for the second consecutive year

The quarantine area for emerald ash borer expanded to include the District of Timiskaming.

The federally regulated area for hemlock woolly adelgid was expanded to include the:

  • Regional Municipality of Niagara and Haldimand County
  • City of Hamilton
  • Township of Alnwick and Haldimand

The insect was also detected in new locations outside the regulated areas in the Greater Toronto Area and Norfolk County.

No spongy moth defoliation was mapped.

No new occurrences of oak wilt were detected.

We continued to document the presence of beech bark disease in Northeast and Southern regions.

Beech leaf disease was recorded in new municipalities in districts where the disease had been previously reported.

Technicians used the ESRI Field Maps tool to record observations. This tool allowed for real time data collection and sharing to make decisions about further surveying efforts. It provided a better user experience for technicians collecting data, allowing for a more map-focused interface compared to QuickCapture used in 2024.

2024 forest health conditions

Temperature and weather

Temperatures were near or above the 30-year average in 2024.

Spring and summer were wetter than usual in the Northwest and Southern regions, respectively.

Warmer than average temperatures and below average snowfall and rain were recorded from January to March and this trend continued into spring 2024. Notable weather events included:

  • incidences of heavy rain in spring and summer
  • flash freeze and extreme heat events in winter and summer, respectively
  • tornadoes in Southern Region

Area of blowdown recorded was much less than in 2023 at just over 1,600 hectares.

Aerial surveys

For the first time, technicians used the ESRI QuickCapture tool to record forest health observations while on the landscape in preparation for aerial surveys.

This year’s monitoring challenges included limited aircraft and pilot availability for aerial surveys.

Pests, diseases and invasive species

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

We continued to document the presence of beech bark disease throughout Southern Region, which is a combination of an invasive insect (beech scale) and an invasive stem fungus.

Beech leaf disease was reported in new areas within districts where beech leaf disease was previously reported.

Emerald ash borer was detected in new areas within the quarantine area in:

  • Peterborough Bancroft and Minden Parry Sound districts in Southern Region
  • Sudbury and Sault Ste. Marie Blind River districts in Northeast Region

Hemlock woolly adelgid was confirmed in 3 new locations outside regulated areas in Aylmer Guelph district in Southern Region.

Notable elm zigzag sawfly defoliation was reported in Ontario for the first time.

No new occurrences of oak wilt were detected.

2023 forest health conditions

Temperatures were near or slightly above the 30-year average in 2023.

Above average snowfall and rain early in the year was offset with drier conditions for the remainder of the year. Notable weather events included:

  • tornadoes in the south
  • several localized incidences of heavy rain in summer and fall

Area of blowdown recorded was much less than in 2022 at just over 4,000 hectares.

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

We continued to document the presence of beech bark disease, which is a combination of an invasive insect (beech scale) and an invasive stem fungus. It continues to spread across Southern Region.

Beech leaf disease was reported in new areas within districts where beech leaf disease was previously reported.

The invasive emerald ash borer beetle was detected in new areas in:

  • the regulated area in Kemptville Kingston and Minden Parry Sound districts in Southern Region
  • Sudbury and Sault Ste. Marie Blind River districts in Northeast Region

Hemlock woolly adelgid was confirmed in three new locations in Southern Region.

The first detections of oak wilt, an invasive disease caused by a fungus, were confirmed in Canada in the Niagara Falls and Springwater areas.

2022 forest health conditions

2022 began colder than the 30-year average, but the remainder of the year was close to seasonal temperatures.

Spring was wetter than usual in the northwest with variable temperatures and precipitation across the province leading into the fall. Notable weather events include:

  • tornadoes in the south
  • several incidences of heavy rain in summer and fall

We aerially mapped more than 10,000 hectares of blowdown, mostly in Southern Region. This area was the most recorded since 2016.

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

  • jack pine budworm continued to decrease, but the affected area shifted eastward
  • spruce budworm continued, with the affected area increasing mainly in northeast
  • forest tent caterpillar increased mainly in the northeast, but was also mapped in the northwest
  • spongy moth declined in Southern and Central Ontario, with increased observations of parasites and pathogens
  • large aspen tortrix decreased and was found only in the northeast

We continued to document the presence of beech bark disease, which is a combination of an invasive insect (beech scale) and an invasive stem fungus. It continues to spread across Southern Region.

Beech leaf disease was reported in new areas in districts where beech leaf disease was previously reported.

Unreported occurrences of the invasive emerald ash borer beetle were detected in the regulated area in Bancroft, Sudbury and North Bay districts.

Hemlock woolly adelgid was confirmed in two new locations in Southern Region.

2021 forest health conditions

In 2021, warmer temperatures and a warm, dry spring may have influenced insect pest populations. Notable weather events included tornadoes in the south and increased wildfires, especially in Northwestern Ontario.

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

  • jack pine budworm continued in the northwest, but affected a smaller area than in 2020
  • spruce budworm continued in the northeast, with the affected area almost tripling the area affected in 2020
  • forest tent caterpillar was minimal and only mapped in the northeast
  • spongy moth continued to increase in Southern and Central Ontario, affecting a record-high area of the province
  • large aspen tortrix decreased and we found it mainly in the northeast

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 the Northeast Region.

In 2021, we confirmed beech leaf disease in the Peterborough District and we detected new locations of the disease in the Guelph and Aylmer districts. Researchers confirmed a nematode (worm-like pest) is causing the disease and they are investigating how the nematode spreads.

New occurrences of the invasive emerald ash borer beetle were reported in the quarantined area in Pembroke, Kemptville and Parry Sound districts.

This year’s monitoring challenges included wildfire smoke that blanketed much of the north for extended periods, which made aerial observations difficult, especially in the northwest.

Field staff continued to work safely by implementing COVID-19 protocols.

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.

Earlier reports

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