Yellowstone’s Wolves Save Its Aspens

But the study found that an “ecology of fear” has helped to restore balance to the valley, protecting young aspen shoots from browsing elk for the first time in decades.
William J. Ripple, a professor in the university’s College of Forestry and an author of the study, said aspens were recovering in areas where it would be difficult for elk to escape a wolf attack. “We think these elk need to balance the risk of being killed versus eating in their favorite places. So it’s a trade-off between food and risk in an ecology of fear,” he said.