Climate change puts city's ash trees at greater risk from killer insect, researchers say

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This article was published 18/5/2018 (610 days ago), so information in it may no longer be current.

Winnipeg's ash tree canopy may be in more imminent danger than anticipated from an invasion of destructive insects because of significant changes to the city's climate.

A new study from the University of Waterloo takes a look at the western cities that may soon be under siege from the emerald ash borer beetle responsible for killing nearly all the ash trees in southern Ontario and in the Great Lakes states.

It was previously thought some northern regions might be spared the worst. But Kim Cuddington, associate professor in the department of biology at the University of Waterloo, led a research team that found that unlikely to be the case; their work recently appeared in the journal Biological Invasions.

"We had thought that Canada might be too cold and the winters too extreme (and) it would kill off the over-wintering larvae underneath the tree bark," Cuddington said.

"To test that hypothesis, we measured under-bark temperatures. We measured the temperatures at which larvae would be killed and then we created a map that predicted how cold the under-bark temperatures were and basically (extrapolated) about how frequently the temperatures were cold enough to kill the larvae. And if it was infrequent, we would conclude that the beetle could live in that area for long enough to kill a tree."

The Asian beetle, discovered in North America in 2002, is believed to have been shipped in untreated wooden packaging materials.

When Cuddington's team began the research around 2008, she said she wasn't even thinking about climate change. That is, until she started doing probability calculations and noticed dramatic cold-temperature differences.

"If you look at the probability of those extreme cold events over a 40-year period versus the probability over the last 20 years, it’s changed substantially," she said.

Winnipeg is among western cities in danger of losing its ash trees. City forester Martha Barwinsky said 13 have already been infected by the insect. The baker's dozen was spotted within a 1.5-kilometre radius in the Archwood neighbourhood last November and the trees have since been removed.

The city hasn't factored climate-change concerns into its strategy for fending off the emerald ash borer beetle yet, she said.

"We don’t have any hard facts about it just yet and we are working with Canadian Forest Service in their research on the cold tolerance of emerald ash borer. So there’s still a lot of unknowns," she said.

Climate change may impact the beetle's life cycle, extending it by a year or two, Barwinsky said. The bugs can live from one to six years.

The city estimates it could lose all of its estimated 356,000 ash trees if the insect infestation gets out of hand. About 200 traps are being set up in June in hopes of catching the critters.

City crews will remove infected or dead trees on public property — roughly 100,000 — but private-property owners would be responsible for getting rid of their more than 250,000 trees.

Only elm trees outnumber ash in Winnipeg.

Barwinsky recommends property owners call arborists to determine whether they should consider injecting preventative insecticides in their trees or pre-emptively remove them.

Trees Winnipeg's executive director Kerienne La France said the group expects more calls as awareness of the emerald ash borer beetle grows.

"We’d let (callers) know that treating your tree is a long-term commitment and it should be considered if the tree is really valuable to the homeowner, or if it’s in a prominent place in your landscape or if it’s just such a size that you would hate to lose it," she said. "Those are the trees that are definitely worth protecting, because any tree that isn’t treated will definitely be gone."

jessica.botelho@freepress.mb.ca

Twitter: @_jessbu