How are the NWT’s forests doing? Things could be better.

NWT forests remain under strain from a drought in its fourth year, while a newly confirmed tree disease now appears established across the territory’s aspen.

Those are among findings from the territorial government’s latest forest health report, prepared by contractor SKOG Forest Health and circulated by the GNWT on Tuesday.

The report, for the 2025 year, mapped 811,000 hectares of forest health problems from insect damage to outright tree death. The amount of forest showing some form of problem was up from 654,200 hectares in 2024, but clearer skies also meant more trees could be surveyed after wildfire smoke badly limited the 2024 survey.

Drought runs through nearly every finding. Conditions have ranged from abnormally dry to severe somewhere in the NWT every month since June 2022, stressing trees and leaving them vulnerable to insects and disease. (More broadly, that drought was a sharp swing from the record wet years of 2019 to 2021, when Great Slave Lake reached its highest level on record.)

Defoliation remains the most widespread problem, affecting about 585,000 hectares in the NWT. Most of that is attributed to the aspen serpentine leaf miner, a moth whose larvae feed on aspen leaves. An estimate 333,000 hectares of aspen were affected. Drought stress and dieback were recorded on more than 123,000 hectares.

Eastern spruce budworm defoliation almost doubled to 161,225 hectares in 2025 from 85,412 hectares the year before, but that jump follows a dramatic boom and bust.

The budworm outbreak swelled to more than 1.3 million hectares in 2022 – its largest since the early 2000s – before collapsing to almost nothing by 2024, though smoke again limited that year’s study.

This year’s rebound, concentrated around Fort Liard, is still a small fraction of the earlier peak.

The longer-lasting damage comes in the white spruce the outbreak had already killed along the Arctic Red, Ramparts and Hume rivers to the north, where earlier surveys recorded mortality as high as 40 to 50 percent in the worst-hit stands. The report warns more budworm-caused tree death is anticipated in the coming years.

New disease confirmed

DNA testing has confirmed aspen running canker at seven sites across the Dehcho, South Slave and North Slave, meaning the aggressive fungus is now established throughout the range of aspen in the NWT.

First detected in the territory in 2024, near Kakisa – and unknown to science until 2020 – the disease is linked to drought and ongoing leaf-miner outbreaks.

Ground surveys were planned for 2026 to map how far it has spread.

Meanwhile, even in a drought, some forests are dying from too much water.

The forest health report recorded more than 60,000 hectares of tree death from flooding and high water tables, concentrated along the Slave River and in the Mackenzie Delta. A satellite survey of the Slave River alone identified about 35,800 hectares of drowned mature forest – a die-off that had been building for years.

Those issues could be related to earlier flooding and also to elevated groundwater levels following wildfires and associated permafrost thaw, the report asserted. Counterintuitively, wildfires burning through forests can increase the likelihood of a damaging influx of groundwater.

Other findings point to a landscape adjusting to repeated stress.

A second aspen pest, the large aspen tortrix, has expanded from about 12,000 hectares in 2024 to nearly 69,000 hectares of new defoliation this year in the hills of the Dehcho.

Black spruce decline continued across 26,000 hectares, mostly between Délı̨nę and Whatì.

Surveyors also noted heavy seed crops across the territory, like the poplar fluff that blanketed Hay River like snow at times. That’s a common sign of trees under stress putting all of their energy into reproduction.