How returning wolves are changing Yellowstone

December 29, 2011 | By Cassandra Profita

Scientists studying the effect of wolf reintroduction in Yellowstone National Park have published a new report with updated findings.

In the 15 years since wolves returned to the park, they found, elk and coyote populations have declined, new aspen, willow and cottonwood trees are growing, and beaver colonies are on the rise.

Elk had been over-browsing young trees and preventing new recruits, according to William Ripple, a professor for Oregon State University and lead author of the study. But the presence of wolves keeps their numbers in check and prevents elk from eating too many young trees.

“Yellowstone increasingly looks like a different place,” Ripple said in an OSU news release (see the accompanying video above). “These are still the early stages of recovery, and some of this may still take decades. But trees and shrubs are starting to come back and beaver numbers are increasing. The signs are very encouraging.”

William Ripple, courtesy of Oregon State University

Young aspen trees are now recovering in Yellowstone National Park, after wolves that were re-introduced in 1995 helped to limit elk browsing that had been killing young trees. The older trees seen here date to the last time there were wolves in the park 70 years ago. 

Gray wolves were extirpated from Yellowstone in the 1920s, and by the mid-to-late 1900s their absence allowed elk to over-browse new aspen trees. Hardly any new aspen trees grew up in the wolves absence. But now, new trees are growing again.

Since wolves were reitroduced to Yellowstone in 1995-96, researchers have found:

• Wolf population increased until 2003 and elk behavior changed
• Northern range elk dropped from 15,000 in the early 90s to 6,000 last year
• Beaver colonies increased from one in 1996 to 12 in 2009, promising better fish and waterfowl habitat
• Coyote numbers decreased, promising more small mammals such as red foxes, ravens and bald eagles for other predators to eat

Of course, a lot of other changes have taken place since wolves were reintroduced to Yellowstone. The reintroduced wolves spread out into Montana and Idaho, Oregon and Washington, and have reignited fights over how to handle their attacks on livestock. Montana and Idaho reinstated wolf hunts, and Oregon and Washington hashed out new wolf management plans. Reimbursement programs have been arranged to pay ranchers for livestock lost to wolves, and wolf advocate groups have sprung up to fight for wolves in court.
The list of ways wolves are changing the landscape in the West could go on and on. What would you put on the list?

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