Aspen is making a comeback in and around Yellowstone National Park, because of predators

Yellowstone Wolf

This is the first large-scale study to show that aspen is recovering in areas around the park, as well as inside the park boundary, said Luke Painter, a wildlife ecologist at Oregon State University and lead author on the study. Wolves were reintroduced to the park in 1995. The study shows their predation on elk is a major reason for new growth of aspen, a tree that plays an important ecological role in the American West.