Article from Jim Robbins in The New York Times
Hiking along the small, purling Blacktail Deer Creek, Douglas W. Smith, a wolf biologist, makes his way through a lush curtain of willows.
Nearly absent for decades, willows have roared back to life in Yellowstone, and the reason, Smith believes, is that 10 years after wolves were introduced to Yellowstone, the park is full of them.
He says the wolves have changed the park's ecology in many ways; for one, they have scared the elk to high ground and away from browsing on every willow shoot by rivers and streams.
"Wolves have caused a trophic cascade," he said.
"Wolves are at the top of it all here. They change the conditions for everyone else, including willows."
The last 10 years in Yellowstone have rewritten the book on wolf biology. Wildlife biologists and ecologists are stunned by the changes they have seen.
It is a rare chance to understand in detail how the effects of an "apex predator" ripple through an ecosystem. Much of what has taken place is recounted in the recently released book "Decade of the Wolf: Returning the Wild to Yellowstone," by Smith and Gary Ferguson.
In 1995, 14 wolves from Canada were brought into the park by truck and sleigh in the dead of winter, held in a cage for 10 weeks and released. Seventeen were added in 1996. Now, about 130 wolves in 13 packs roam the park.
Yellowstone, says Smith, is full.
Over the next 10 years, elk numbers dropped considerably. One of the world's largest elk herds, which feeds on rich grasses on the northern range of the park, dropped from 19,000 in 1994 to about 11,000. Wolf reintroduction has been cited as the culprit by hunters, but Smith says the cause is more complex.
Data recently released after three years of study by the Park Service, the U.S. Geological Survey, and the University of Minnesota found that 53 per cent of elk deaths were caused by grizzly bears that eat calves. Just 13 per cent were linked to wolves and 11 per cent to coyotes. Drought also played a role. The study is continuing.
Scientists do say that wolf predation has been significant enough to redistribute the elk. That in turn has affected vegetation and a variety of wildlife.
The elk had not seen wolves since the 1920s when they disappeared from the park. Over the last 10 years, as they have been hunted by wolf packs, they have grown more vigilant.
They move more than they used to, and spend most of their time in places that afford a 360-degree view, said Smith. They do not spend time in places where they do not feel secure - near a rise or a bluff, places that could conceal wolves.
In those places, willow thickets and cottonwoods have bounced back. Aspen stands are also being rejuvenated. Until recently, the only cottonwood trees in the park were 70 to 100 years old. Now large numbers of saplings are sprouting.
William Ripple, a professor of botany at Oregon State University, calls the process the "ecology of fear," which has allowed the vegetation to thrive as a result of behavioural changes in the newly skittish and peripatetic elk.
Though the changes now are on a fairly small scale, the effects of the wolves will spread, and in 30 years, according to Smith, Yellowstone will look very different.
Not everyone is convinced. "Wolves have a role to play," said Robert Crabtree, a canid biologist who has researched wolves and coyotes in the park since the late 1980s. "But the research has ignored climate change and flooding, which have also had an effect on vegetation. Their work isn't wrong, but it's incomplete."
Where willows and cottonwoods have returned, they stabilize the banks of streams and provide shade, which lowers the water temperature and makes the habitat better for trout, resulting in more and bigger fish. Songbirds like the yellow warbler and Lincoln sparrow have increased where new vegetation stands are thriving.
Willow and aspen have brought beaver back to the streams and rivers on the northern range. In 1996, there was one beaver dam on the northern range; now there are 10.
© 2005 The Chronicle-Herald - Halifax. All rights reserved.
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