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News Release

November 30, 2006

Report: Climate Change Linked to Spread of Tree Pests

Invasive pests could cause even more damage to Canadian trees as the climate warms, say University of Guelph researchers. They’ve just finished a report linking climate change to the likely spread of pests in Canadian forests and cities.

In the report, Prof. Shelley Hunt of the Department of Environmental Biology maps out areas in Canada that could be invaded by tree pests in a warmer future. She says the predictive maps can help scientists and regulators prepare for new pest invasions.

“We need to be ready for increased pressure from tree pests as the climate warms,” said Hunt. “The maps in our report help by drawing a clearer picture of where, when, and which invasive species will be able to spread because of higher temperatures.”

Hunt’s maps focus on four exotic invaders: the brown spruce longhorn beetle, the European wood wasp, the Asian gypsy moth and the Asian long-horned beetle. Using reviews of scientific literature that have tracked the species’ trends in Canada, Hunt matched each pest’s survival range to temperature models generated using two complex computer programs called the Canadian Coupled Global Circulation Model and the Hadley Circulation Model. These programs predict how high temperatures will rise, based on the expected greenhouse gas emissions in a certain number of years.

In this way, she was able to predict just how each invader might take advantage of temperature increases, mapping survival and habitat ranges for the years 2020, 2050 and 2080.

According to the models, Hunt says increasing greenhouse gases (GHGs) emitted into the atmosphere mean higher temperatures and more treed areas becoming susceptible to attack from pests. Trees normally store carbon for use for energy and growth from carbon dioxide gas in the atmosphere. But when pest damage occurs, trees are less effective carbon “sinks.” For example, when large old trees in a forest are killed by an insect pest, they are replaced with small young trees that store less carbon.

Also, some tree species store more carbon than others. Oak trees, for example, have denser wood and store more carbon than pine trees. If an insect outbreak results in one tree species dying off and being replaced by another, the carbon storage capacity of the forest could change.

The Asian gypsy moth, which feeds on oak leaves, is currently limited by Canada’s cold climate. But Hunt’s report shows that even under a low GHG emissions scenario, the climate will be warm enough for it to spread widely in every province by 2050.

Warmer temperatures don’t just increase the range over which invasive species can survive Canada’s cold winters. They also result in a longer growing season for insects, potentially allowing them to produce more generations each year and increasing their populations.

Hunt says there’s a long list of invasive species that still need more in-depth research. In addition to the mapped species, her report takes a detailed look at pests such as hemlock woolly adelgid, sudden oak death, and emerald ash borer, which recently killed trees lining city streets in Windsor, Ont. She notes that insects are not always the bad guys in forest ecosystems – many native insects have beneficial roles that are still not fully understood.

Ultimately Hunt hopes her research and maps can be used to better understand the effects of climate change on forests, and to help find measures to control invasive pests.

“Understanding which factors limit pest survival, such as natural predators in native habitats, will lead to effective measures to minimize the impacts of these invasive species,” said Hunt.

Other collaborators in this research were Profs. Gard Otis and Jonathan Newman, Department of Environmental Biology. Funding was provided by the BIOCAP Canada Foundation.