Summary:
Climate-driven shifts in temperature and drought could alter insect and disease risks across North American forests, with colder and wetter regions expected to experience some of the largest increases.
Researchers led by The University of British Columbia (UBC) analysed records from more than 1 million trees together with historical and contemporary climate data. The analysis found that warming and drought were associated with higher insect and pathogen incidence in historically cooler, wetter regions, but with lower incidence in some warmer, drier areas. Responses also differed among tree species and across insect and pathogen groups.
Under the Shared Socioeconomic Pathway 2-4.5 (SSP2-4.5) scenario, insect and pathogen incidence is projected to increase across 58% and 52% of North American forest land, respectively, over the coming decades, with the largest impacts expected at high latitudes. Species including black spruce, Rocky Mountain fir and gray willow are projected to experience particularly large increases in pest and disease pressure.
Reported in Nature Ecology & Evolution, the projections may help forest managers identify areas and tree species where closer monitoring and preventive measures could become increasingly important as climate conditions change.
— Press Release —
Farewell black spruce? How climate change and pests are reshaping North America’s forests
If global emissions continue unchecked, rising temperatures and shifting rainfall patterns could amplify tree pests and diseases across more than 80 per cent of North American forests within decades, jeopardizing critical carbon sinks, air quality and the forestry economy.
This is the key finding of a new UBC-led study published in Nature Ecology & Evolution. The researchers found that insects pose the more immediate threat, with more than 60 per cent of the areas examined projected to experience 30 per cent more insect pressure by mid-century. Species like the spongy moth, already wreaking havoc in Canadian forests, could expand significantly in eastern North America by mid-century.
Pests and diseases already damage tens of millions of hectares of North American forest annually, costing billions of dollars in economic losses.
“The forests that exist today aren’t going to be ones existing in 2040,” said senior author Dr. Jonathan Davies, professor in the departments of forest and conservation sciences and botany. “The process is happening already. I think we’ve got to put everything on the table because the status quo is no longer tenable.”
The researchers combined data from more than one million trees across the United States and parts of Canada with current and historical climate data to identify where future risks are most likely to emerge if emissions continue on their current trajectory.
“Our maps can help forest managers to identify where additional monitoring and prevention efforts should be focussed,” said Dr. Zihui Wang, a postdoctoral researcher in UBC’s department of botany and lead author of the study. “We can also project which tree species may be particularly vulnerable and which pests and pathogens could pose the biggest threat, giving us a window into the future and hopefully, a headstart on protecting our future forests.”
Climate winners and losers
Climate change is creating a complex mosaic of winners and losers rather than affecting every forest in exactly the same way, said Dr. Davies. Forests that have traditionally been cooler are more likely to experience increases in insect and disease damage as temperatures rise. In some areas that have historically been warmer, the effects may be smaller or even reversed.
Pests that may become more common as the climate warms include the woolly adelgid, which has devastated hemlock forests in parts of eastern North America, and the spongy moth.
Northern or mountain species such as gray willow, Rocky Mountain fir and black spruce are projected to face some of the greatest increases in pest and disease pressure.
However, some trees like tulip trees and American sycamores in the southeastern U.S. could see lower pest and disease pressure as conditions become less favourable for some pests and pathogens.
Read also: Spongy moth outbreaks worsen as climate change accelerates forest damage
Projections for Canada
The study projected elevated insect pressure in western B.C., but potentially fewer pathogens. The pattern is reversed in parts of eastern B.C., reflecting differences in climates and forest types between these regions. Ecologically critical tree species in B.C.’s mountains such as limber pine and whitebark pine may be especially vulnerable to the combined effects of climate change and changing pest pressure.
However, because the data focuses on the U.S., projections become less certain further north. “With more local forest health monitoring data, it might be possible for future work to refine these projections for B.C. forests,” said Dr. Wang.
Future forests
The researchers say the new maps could help governments and forest managers target monitoring and prioritize measures such as planting hardier trees, creating physical barriers to pest or pathogen spread by removing specific trees or forest sections, and maintaining tree diversity.
Dr. Davies says the findings are also a reminder that climate change affects more than weather.
“Forests are a fundamental part of our lives, but climate change is reshaping these ecosystems. This research is another early warning sign of how we’re altering the climate system and the impact it’s going to have,” said Dr. Davies.
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This research was partly funded by the Natural Sciences and Engineering Research Council of Canada.
Journal Reference:
Wang, Z., Gougherty, A.V. & Davies, T.J., ‘Spatially explicit forecasts of tree insect and disease incidence across North American forests under future climate scenarios’, Nature Ecology & Evolution (2026). DOI: 10.1038/s41559-026-03163-6
Article Source:
Press Release/Material by Alex Walls | University of British Columbia (UBC)
Featured image: Elm leafminer near Vancouver, B.C., Canada. Credit: Andy Gougherty
