Ripple effect

Restoring lost species to their natural habitats is more than a gesture, it can be vital to maintaining the biodiversity that underpins a healthy ecosystem: Take away even one species and the ripple effects can be extensive. Before the reintroduction of wolves into the park in 1995, stands of willow and aspen trees in Yellowstone National Park in the U.S. were in decline, beaver populations were shrinking, and even rivers flowed differently. The problem contributing to the park’s imbalance was the elimination of wolves decades earlier. Effectively hunted out of the park by the 1930s, wolves no longer posed a threat, and elk flourished and overgrazed the park’s saplings so that new trees struggled to grow.