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Emerald ash borer, Nova Scotia's latest invasive pest, is well-suited for our winters

The emerald ash borer has been confirmed in Bedford, the first confirmed appearance in Nova Scotia. Currently there are no regulations in place to deal with the tree-destroying beetle. - Canadian Food Inspection Agency
The emerald ash borer has been confirmed in Bedford, the first confirmed appearance in Nova Scotia. Currently there are no regulations in place to deal with the tree-destroying beetle. - Canadian Food Inspection Agency

The emerald ash borer is one tough beetle.

The presence of this invasive tree pest, which has killed millions of ash trees across North America, was confirmed for the first time in Nova Scotia last week.

The ash borer is among several tree pests that have moved into the province in the past couple of years, including the hemlock woolly adelgid (an aphid), the spruce longhorn beetle and the southern pine beetle.

But “it’s a lot tougher” than species such as the southern pine beetle that have moved north from warmer areas such as the southern United States, likely as a result of climate change, said invasive insect expert Corey Lesk.

The ash borer can withstand temperatures as low as -30 C.

“It’s from northern China and lives in China and Mongolia,” said Lesk, a researcher at Columbia University in New York, in a recent interview.

“And it goes all the way up into eastern Siberia. So yeah, it can really tolerate (the cold), it’s from a place that’s literally brutally cold.”

The emerald ash borer first appeared in Canada in about 2002, likely carried in wooden pallets on a container ship from the United States. It can spread quickly by subsequent wood movement, for example, a camper bringing an infected log into another site.

“This is a continental scale problem,” said Lesk, who recently led a study that linked warming temperatures to the movement of the southern pine beetle into northern North America.

“This is the kind of invasion that threatens to eliminate ash on the continent just because it’s not cold-limited for all practical purposes. ... There’s no solid management options here, it’s a generalist among ash trees and ash species, which are widely distributed across the continent. It’s free to spread so the only place where it couldn’t wipe out ash trees is where it’s too cold and those areas are sandwiched between the boreal forest, where there’s no ash, and the very northernmost hardwoods and mixed forests.”

The ash borer was discovered in DeWolf Park in Bedford last week. A Canadian Food Inspection Agency spokeswoman said Monday the agency is still surveying the area to determine whether the pest has become established in the area where it was found and whether it has spread.

The agency says the movement of all ash material such as logs, branches and woodchips, and all species of firewood from the affected site has been restricted.

While the ash borer has the potential to devastate the province’s three ash species, the overall impact on the forest sector will be minimal, said Peter Duinker, a professor at the School for Resource and Environmental Studies at Dalhousie University.

“Ash is an incredibly small component of the entire forest estate of Nova Scotia,” Duinker said in a recent interview, much less than one per cent of our tree population in the wild and about 2.5 per cent of the urban forest in Halifax.

“That doesn’t mean it isn’t important in some specific areas. For example, there’s quite a bit of ash on the North Mountain in the Annapolis Valley. If the emerald ash borer finds those, then we could see a fair amount of dead woodland up on the North Mountain. But for most of the rest of the province, ash is pretty much a sub-species and is in scattered distribution.”

He said the recent spread of tree pests can be traced to the skyrocketing movement of goods in the global economy, which would fall under the invasive pest category, and “irruptive" population increases of insects that are already here related to factors such as global warming.

“That’s what the mountain pine beetle in central B.C. is subject to. That’s a native species but that native species is kept in check by a couple of weeks of really cold winter nights. If you don’t have those anymore, the species becomes irruptive and can take off. If the habitat is right …. it can do a number on the forests.”

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