Wolves help aspen growth in Yellowstone park

RETURNING wolves to America’s most famous national park has started to restore its lost ecological balance, say scientists.

For the first time in 50 years, young aspen trees are growing again in the northern part of Yellowstone National Park. The recovery of the aspen, a golden deciduous hardwood tree regarded as a vital component of the forest landscape, is thanks to what researchers call “the ecology of fear.”

With wolves around, elk are less willing to venture into areas where for decades they had browsed freely on the young tree shoots. As a result, more of the trees are surviving, which experts believe will have positive knock-on effects throughout the ecosystem.

Wolves were eradicated from Yellowstone in the 1920s, but reintroduced in 1995. After the disappearance of the last wolf packs, aspen and cottonwood trees went into long-term decline, to the point of virtual extinction in some areas.

The loss of trees and shrubs had a major ripple effect throughout the ecosystem, say scientists. There was greater water erosion, a loss of beaver dams, and a breakdown of food webs. Birds, insects, fish and plants were all affected.

After the reintroduction of wolves, elk populations began to fall, dropping by half in the past 10 years alone. Those that remained tended to avoid browsing in areas where they felt most in danger.

The trend, identified by researchers at Oregon State University, Corvallis, supports the theory that ecosystems are damaged by the loss of key predators.