The return of wolves to Yellowstone National Park has caused significant ecosystem recovery by curbing populations of elk that for decades had over-browsedyoung aspen and willow trees, according to a new study. In an analysis conducted by Oregon State University, researchers found that tree stands and shrubs have recovered along some streams, improving habitat for beaver and fish and providing more food sources for birds and bears. In the 15 years since wolves were reintroduced to Yellowstone after being killed off last century, northern elk populations have decreased from more than 15,000 to about 6,000, according to the study published in Biological Conservation. By 2006, some aspen trees had grown tall enough that they were no longer susceptible to browsing by elk. As a result, along four streams in the Lamar River basin, less than 20 percent of the tallest young aspen sprouts were being browsed last year compared with 100 percent in 1998.
U.S. Fish & Wildlife