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Study: Wolves in Yellowstone have helped both trees and beavers

The Associated Press today drew our attention to a just-published paper in Biological Conservation: “Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction,” by William J. Ripple and Robert L. Beschta. Since the AP has been known to object to even the briefest unauthorized quotes from their stories, however, screw them. Check out instead the story by Cory Hatch in the Jackson Hole Daily online, “Wolves helping aspens.”

The study was launched in 1997 in an attempt to understand why aspen trees were at the time declining in Yellowstone, said study coauthor William Ripple, an ecology professor at Oregon State University.

“There was no clear scientific answer,” he said. “The topic of predators and wolves was not on my radar.”

After coring aspen trees and counting tree rings, “we found that there was a major decline … starting in the first half of the 20th century,” Ripple said. “Aspen continued its decline all the way up to our study period, in 1997. At that point, we looked at the records. We found that wolves were extirpated early on, and the last wolf was killed in 1926.”

Since wolves were returned in 1995 and ’96, Ripple and his colleagues formed a hypothesis that aspens and other plants would start growing again into tall trees.

Indeed, the percentage of aspen trees browsed in one habitat type ­­— upland areas without logs — dropped from 84 percent to 24 percent from 2006 to 2010. In 97 aspen stands, the mean height of the five tallest trees increased from 60.6 inches to 100.7 inches during the same four years.

And if you’re not too intimidated by ecological jargon, do read the study itself (it’s a PDF).

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