Beetle versus Bear
Posted July 16, 2007
How can a tiny beetle threaten the survival of Yellowstone's famed Grizzly bears? The answer was revealed at a meeting I attended this weekend at the beautiful B Bar ranch, situated on the northern border of Yellowstone National Park. The meeting, organized by Louisa Willcox and Janet Barwick of NRDC's Livingston, MT outpost, brought together scientists and journalists for field trips and seminars exploring the relationship between Yellowstone's Grizzlies, White Bark Pine trees and mountain pine beetles.
The short story is that the Yellowstone population of Grizzly bears (which is isolated from Grizzlies in Glacier, Alaska, and Canada) depends heavily on White Bark Pine nuts to fatten up for winter. Unfortunately for the bears, White Bark Pines are being ravaged by unprecedented outbreaks of mountain pine beetles. While the beetles are endemic to Lodge Pole Pines, infestations in higher elevation White Bark Pines were rare until the last few years. Jesse Logan, a scientist who recently retired from the Forest Service, explained that the outbreaks in White Bark Pine are linked to warming temperatures, which allow the beetles to reproduce in one year, instead of two, at the elevation of 8-10 thousand feet where White Bark Pines are found. Diana Six, a scientist at the University of Montana, explained that drought also plays a role by weakening the trees' ability to defend themselves against beetle attacks.
I had read about this interaction last year when working on NRDC's report Losing Ground: Western National Parks Endangered by Climate Disruption, which includes it as an example, But reading about an ecosystem is nothing like seeing it. Friday afternoon we hiked up a steep slope in the National Forest Northeast of Yellowstone Park in search of beetles. At first glance the stand of White Bark Pines looked to be in good shape. While there were a few dead trees which had been killed by beetles in previous years, most of the White Barks appeared to be thriving. The area had never been logged (unlike Lodgepole Pine, White Bark Pine is not a commercial species) and we saw a number of trees that were more than 500 years old according to Jesse. The positive assessment didn't last too long. Louisa noticed a tree showing signs of an active beetle infestation. The tree was still green and I would have walked by it without noticing anything wrong, but Diana Six immediately pronounced it effectively dead. The telltale sign was tiny holes in the bark sprinkled with dry saw dust. With a few swipes of her hatchet Diana uncovered live beetles hollowing out the critical living tissue of the tree. From the air the next day we could easily see the red stains on the landscape indicating that entire stands of White Barks were being consumed by the beetles.
It's hard not to be depressed by this ecological tragedy, but I also saw some reasons for hope. In 1988, wildfires swept through Yellowstone, burning over one million acres. Today small White Bark Pines are regenerating the forest, finding toeholds next to boulders or fallen trees that provide a bit of protection from the desiccating heat of summer and killing cold of winter that prevails on the high alpine slopes where they find their niche. I can't help but think that these hardy organisms will find a way to survive if we just give them a chance by slowing the pace of global warming to improve the odds in their epic battle with the beetles.
Some pictures from the weekend: