National Geographic's Strange Days on Planet Earth . Predators . Wolves in Yellowstone Park

Publish date: 2024-08-13
Wolves in Yellowstone Park

What do you like best about your profession?
Beschta: “The capability to do research and teach on issues that may ultimately influence how natural resources on public and private lands are managed...”

See Bob Beschta's full Q&A »

What makes you most fearful for the future?
Ripple: “I worry most about the overabundance of the human species and the concurrent diminishment of wildlife habitat...”

See Bill Ripple's full Q&A »

What makes you most hopeful for the future?
Smith: “[I'm hopeful from seeing] that we have been able to put back a little and that recovery of nature is possible if people want to do it...”

What would you recommend for students wanting to pursue a similar career?
Larsen: “Obtaining a university degree in geography, biology, botany, or a related field. Experience is also invaluable...”

See Eric Larsen's full Q&A »

Bob Beschta border
Bob Beschta

When hydrologist Bob Beschta arrived in Yellowstone in 1996, he noticed something odd with the Lamar River. The stream was over-widened, the banks were eroding and precious soil was sloughing off down river. Vegetation that used to line and safeguard the riverbanks had vanished. What was going on?

Meanwhile biologists Bill Ripple and Eric Larsen were probing into another mystery – the disappearance of aspen trees in the park. At first they considered climate change. But if that were the cause, they reasoned, aspens should be declining throughout the area. Instead they found that aspens outside the park were flourishing. Next they turned to fire to see if possibly a reduction in the number of forest fires in the park was hurting the aspens. (These are trees that in fact thrive after a burn.) But the huge fire of 1988 ultimately produced few large trees.

Checking the Yellowstone aspens border
The elimination of Yellowstone's wolves allowed the elk to browse aspens unchecked.

Finally, Ripple and Larson decided to look within the aspens themselves. Drilling cores from nearly a hundred trees and counting growth rings, they determined that most the trees were at least 70 years old. It appeared that the aspen trees had stopped regenerating around the 1930s.

One significant change happened in Yellowstone back then. All the park's resident wolves were dead. Between 1883 and 1917 more than 100,000 wolves were killed for bounty in Montana and Wyoming alone. By the 1970s they were listed as endangered in the United States.

Gray Wolf border
The disappearance of trees and streamside vegetation can be traced to missing wolves.
In an intensely controversial act performed for an entirely different set of reasons, biologist Doug Smith and his colleagues introduced 31 gray wolves from Canada to Yellowstone starting in 1995. What grabbed the headlines was the politics of predators. But the effect of these wolves on the Yellowstone ecosystem would become the more enduring story. Research suggests that the elimination of Yellowstone's wolves allowed the elk to browse aspens and willows brazenly. Though other factors may have played a role, it seems the disappearance of trees and streamside vegetation (and the accompanying loss of beaver and songbird habitats) can be traced to the missing wolves. It would appear that Yellowstone needs its top dog to keep elk on the run and its vital plant and animal diversity intact.
References
»Ripple, W. J., Larsen, E.J., Renkin, R. A., and Smith, D. W. (2001). Trophic Cascades among Wolves, Elk, and Aspen on Yellowstone National Park's Northern Range. Biological Conservation, 102, 227-334.
 
»Ripple, W. J. and Beschta, R. L. (2003). Wolf reintroduction, predation risk, and cottonwood recovery in Yellowstone National Park. Forest Ecology and Management, 184, 299-313.
 

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