Whitebark pine trees on the slopes of Mount Washburn

Whitebark pine trees on the slopes of Mount Washburn in Yellowstone National Park have so far weathered the multiple attacks of mountain pine beetle, blister rust and climate change.

BILLINGS -- Whitebark pine trees have no defense against mountain pine beetles, which recently cycled through an epidemic in the West that was unprecedented in human history.

The tiny beetles, about the size of a grain of rice, have co-evolved with lodgepole pine trees, their preferred food source. Lodgepole pines grow at lower elevations and are quicker to reproduce than whitebark pine, which thrive at high elevations and take about 80 years to produce their first seeds.

Over centuries, lodgepole pine trees have developed ways to fight off the beetle attacks, such as chemicals toxic to the insect as well as ways to disrupt the beetle’s chemical communication system.

Yet when the beetles reach a stand of mid-elevation trees where there are both lodgepole and whitebark pine trees, the beetles attack the lodgepole, despite the fact that the whitebark is more defenseless.

“This was one of the eureka moments in our study,” said Phil Townsend, a professor at the University of Wisconsin, who has spent six years performing research in the Greater Yellowstone Ecosystem on pine beetles. “In these transition zones where you have both species, the whitebark pines are surviving.

“The mountain pine beetle hasn’t figured out that the whitebark pine is a better host,” he added.

“But if you move up in elevation into pure whitebark pine stands, the mountain pine beetle doesn’t know the difference and will take them all out,” he said.

The results of Townsend’s research were recently published in the Proceedings of the National Academy of Sciences.

The findings are a small victory for whitebark pine in what has otherwise been a pretty dour decade. In 2011, the trees were approved as a candidate species for listing under the Endangered Species Act, meaning they were threatened but the federal government has more pressing species to deal with first.

Whitebark pine is a high-mountain survivor, growing at elevations and in cold conditions conducive to few other tree species. Some of the trees are 1,000 years old. According to the U.S. Fish and Wildlife Service, about 44 percent of the trees are found in Wyoming, Montana, Idaho, Nevada, California, Oregon, and Washington. The rest live in British Columbia and Alberta, Canada.

Although not a commercial timber, whitebark’s seeds provide food for squirrels, birds and grizzly bears. Its canopy also helps shade snow from melting, allowing for slower spring runoff. But warmer winters have allowed mountain pine beetles to climb to elevations they previously avoided, taking a toll on the slow-growing trees. They also are threatened by white pine blister rust, an invasive and fatal disease that has devastated other stands of white pines across the United States.

Because whitebark live in such isolated “islands” high atop mountains, Townsend believes that the genetics between stands may be different. With enough searching, he said, maybe a whitebark pine could be found that has developed defenses against mountain pine beetles.

“Now we need to look more broadly at that whole range,” he said. “We’re trying to look at the genetics and find a place where whitebark pine is bucking the trend. Then we could use them as a seed source and gain more information to come up with solutions to protect this ecosystem.”

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