Western pine beetles munch eastward

Now that the mountain pine beetle has chewed through some 70,000 square miles of forest in the western States and Canada, it seems the voracious pest is expanding its palate. Beetles in Canada were recently discovered attacking jack pines (Pinus banksiana) for the first time, a break from their usual diet of lodgepole (Pinus contorta), according to a study [PDF] published this month in the journal Molecular Ecology. With this switch in taste, the beetle could be setting up to cross the continent via the vast Canadian boreal forest, putting trees on the East Coast at risk.

Up to this point, the mountain pine beetle has munched mainly on lodgepole pine-dominated forests in the western U.S. and Canada. But at the eastern edge of Canada's lodgepole range, hybrid lodgepole-jack pines may have helped the critters switch to the eastern species. Scientists from the University of Alberta who authored the new study were able to verify that purebred jack pines as far east as Alberta's Slave Lake had fallen to beetle attack.

The pine beetle's leap to jack pine has been anticipated -- indeed feared -- by biologists for a decade. High Country News contributing editor Michelle Nijhuis reported on that prediction in 2004 in her article, "Global Warming's Unlikely Harbingers".

The Great Plains have long been considered an insurmountable barrier to the mountain pine beetle, but once the beetle hits this new host (jack pines), nothing would stop it from plowing eastward into stands of eastern white pine and cruising south all the way to the loblolly pine forests of the Southeastern United States. This would add up to a supersized sweep of outbreaks, beginning in the U.S. Southwest, stretching across the southern half of Canada, and curving down the Eastern Seaboard of the United States into southern Texas. "The shortest route from Logan, Utah, to Nacogdoches, Texas," says Forest Service researcher Jesse Logan, "might be through Ontario, Canada."

But the beetle has at least two hurdles to clear before devouring eastern forests. The first is jumping between dispersed stands of jack pine, a more sporadic food supply than the expansive lodgepole forests to the west. Forestry practices in the West have resulted in widespread, even-aged lodgepole stands in which beetles -- who only munch mature trees -- thrive. The patchy distribution of jack pines may keep the beetles from going rampant.

Cold is the second barrier to the beetle's eastward march. Warming winters in lower latitudes boosted the beetle outbreak, but Canada is still cold -- for now.

As insect ecologist Allan Carroll of the University of British Columbia, who was not involved in the new study, told Discovery News, "Currently the climatic conditions over much of the northern boreal forest aren't quite suitable for these populations. We fully predict that in short order it will become good for mountain pine beetles -- certainly within the next 30 to 50 years."

Though the mountain pine beetle outbreak -- the worst in 125 years of record keeping -- is devastating enough to seem like an alien scourge, the rice-sized bug is actually native to the West, where cold winters have historically kept it in check. Once the beetle jumps the jack pine gap, though, it will invade new territory and "therefore should be considered an invasive species and managed as such," scientists warn in the new paper. Canada's ability to fight the beetle -- an ongoing struggle in the West -- could determine the fate of eastern forests.

The University of Alberta scientists conclude their paper on a sobering note:

When we factor in climate change, the vulnerability of ecosystems such as the boreal forest to disturbance is further increased, putting an extremely important ecosystem in jeopardy.

Nathan Rice is an intern for High Country News.

Photo of beetle kill in Manning Park, British Columbia, Canada, courtesy Flickr user Tim Gage.