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Wildlife in Yellowstone National Park is undergoing dramatic shifts with consequences that are beginning to return the landscape to conditions not seen in nearly a century, according to a series of new studies.
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In the park’s northeast section, elk have decreased in number in their historic winter range in the Lamar Valley and are now more numerous outside the park. This change in elk numbers and distribution can be traced back to the reintroduction of wolves in 1995-96. Scientists have hypothesized that wolves affect both the numbers and the behavior of elk, thereby reducing the impact of browsing on vegetation, a concept known as a “trophic cascade.”
Rising grizzly bear numbers are also taking their toll on elk. As a result, lush vegetation is growing back in many but not all areas.
“Without wolves, this would not have happened,” said Luke Painter, an instructor at Oregon State University and lead author of three recent papers that describe the results of his fieldwork monitoring vegetation growth patterns in the park. “Wolves caused a fundamental change, but certainly they are interacting with other factors such as bears, climate, fire and human activity.”
Bison have also played an important role in the changes in vegetation in northern Yellowstone. Their numbers have increased four-fold as elk have decreased. In places where bison congregate, they browse on aspen, cottonwood and willow, compensating in part for the decline in elk. However, bison cannot reach as high as elk to browse, allowing more trees to escape and grow to maturity.
Bison and Aspen trees in Yellowstone National Park image via Shutterstock.
Read more at Oregon State University.
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