William Ripple

Scientists say in a new study that the return of gray wolves has dramatically altered the landscape in portions of Yellowstone National Park, by curbing foraging elk herds that prevented new aspen, willow and cottonwood trees from taking root.

Study author William Ripple from Oregon State University said tree stands are expanding in areas where for decades dense elk populations prevented new growth.

Wolves were reintroduced to Yellowstone in 1995 and 1996 after being killed off early last century. About 100 now roam the park and elk numbers have dropped sharply.