Yellowstone's Ecology of Fear

Twelve years ago, wolves were reintroduced to Yellowstone National Park after a 70 year absence due to over hunting (and outright slaughter). Beyond the pure principle of reintroduction, an added bonus was cutting the elk population in the area, and subsequently reducing the pressure on riparian Aspen saplings. Researchers at Oregon State have been following this trend for a while now, and just published a paper on the revitalization of the Aspen population in Yellowstone:

The findings... show that a process called "the ecology of fear" is at work, a balance has been restored to an important natural ecosystem, and aspen trees are surviving elk browsing for the first time in decades.

The research, done by forestry researchers at Oregon State University, supports theories about "trophic cascades" of ecological damage that can be caused when key predators -- in this case, wolves -- are removed from an ecosystem, and show that recovery is possible when the predators are returned.

But is it this "ecology of fear", the change in the elks' behavior since the reintroduction of the wolves that's allowing the Aspen saplings to grow, or is it the fact that the elk population has been cut by 50 percent?

Probably both:

The OSU researchers say they believe there are two forces at work -- both the lower populations of elk, and their changed behavior due to fear of wolves -- but it's difficult to determine exactly which force is the most significant.

The researchers are obviously thrilled about the results.

"When I first looked at these degraded ecosystems in the mid-1990s in Yellowstone, I had doubts we would ever be able to bring the aspen back," said Robert Beschta, a professor emeritus of forestry at OSU and co-author on the study. "There were so many elk, and the stream ecosystems were in such poor shape. The level of recovery we're seeing is very encouraging."

Encouraging indeed. This study should provide more evidence that restoration of historic ecosystems is possible and that large, "top level" vertebrates like wolves are just as integral in a system than the basal organisms.