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Environment | Flora and Fauna

Researchers Say Wolves Help Plants By Eating Deer, Elk

A wolf in Yellowstone National Park.

A wolf in Yellowstone National Park.

Yellowstone National Park

Researchers at Oregon State University say they have more evidence wolves help keep deer and elk populations in check, to the benefit of many plant species.

An analysis of 42 past studies from across North America, Asia, and Europe suggests that wolves play a key role in limiting the size of elk, deer and moose populations.

The paper, published by Oregon State University researchers in the European Journal of Wildlife Research, found that relatively pristine areas where wolves had been exterminated had six times as many grazing herbivores as the study areas where wolves were still present.

Bill Ripple, an ecologist at Oregon State University and one of the paper’s authors, studies trophic cascades: the links between predators, prey populations like deer and elk, and the plants those prey species snack on.

“When you remove wolves, the herbivore populations erupt in the absence of their native predator. At that point they can cause adverse ecological affects by eating themselves out of house and home,” says Ripple.

Ripple is best known for decades of research and tree ring studies in Yellowstone National Park that connected the extermination of wolves there led to an abrupt decline in Aspen trees. Ripple says without wolves, elk populations grew and lingered longer along unprotected stream banks, eating young aspen shoots and saplings and disrupting the ecosystem.

Ripple’s team also studied cottonwood and big leaf maple trees in Olympic National Park, along the Hoh, Queets, and Quinault rivers. Wolves were extirpated from the park in the 1920s.

“What we found was very similar to Yellowstone,” Ripple says. “After the wolves were killed these trees declined along those three rivers.”

The new study didn’t involve original fieldwork but instead synthesized data on deer, elk, moose, and caribou populations gathered in past studies in northern forests ranging from Sweden to South Dakota.

(An Oregon State University-produced video on Ripple’s research findings.)

Ripple says he wants policy makers to consider the effects that wolves and their prey have on plant communities when they set targets for wolf recovery and when they limit wolf populations through hunts, as the state of Idaho has done.

Ripple says it’s not yet clear how many wolves it takes per square mile to be ecologically effective, and to have a positive impact on plant populations, but he thinks more research should be done to identify that minimum density.

The state of Idaho recently reinstated wolf hunts, allowing 378 wolves to be killed in 2011 and the first part of 2012. Wildlife managers there say one of their goals is to help boost deer and elk populations.

Mike Meckler, a spokesman for the Idaho Department of Fish and Game, says he had no comment on OSU study’s conclusions.

John Stephenson, a biologist with the U.S. Fish and Wildlife Service in Oregon, says it is tricky to take research done in relatively pristine areas and apply it to the mix of rural and wild landscapes that elk and deer occupy Oregon and Idaho.

A ballooning elk herd on the Zumwalt Prairie in Wallowa County is overeating rare native grasses. But Stephenson says in most areas, Oregon’s elk herds are considered to be a manageable size.

“We face a lot of scrutiny that having wolves back is going to reduce the elk population such that there won’t be a harvestable surplus. That is the concern we hear most from the public,” Stephenson says.