Save a wolf, save a tree

Natural History, Feb, 2004 by Stephan Reebs

Something is amiss in the cottonwood groves of Yellowstone National Park. Seedlings grow in abundance on the riverbanks, along with a fair number of old trees. But young trees are nowhere in sight. Robert L. Beschta, a forester at Oregon State University in Corvallis, decided to investigate what's been killing off the seedlings.

By comparing the trunk diameters of the park's old cottonwoods with the diameters and visible growth rings of cores extracted a decade ago from other cottonwoods in the area, Beschta found that none of the large cottonwoods in Yellowstone's Lamar Valley were younger than age sixty. But what could have happened back then that could explain why young cottonwoods stopped maturing? Well, in the mid-1920s wolves were eliminated from Yellowstone, as they were across much of the West.

In the following years, Beschta points out, elk started venturing into the once-dangerous habitats where cottonwood seedlings grew, and the animals began to devour the seedlings--that is, until wolves were reintroduced in the park in 1995. Now that the balance among carnivores, herbivores, and plants has been restored, aging cottonwood communities should finally be getting some young recruits. ("Cottonwoods, elk, and wolves in the Lamar Valley of Yellowstone National Park," Ecological Applications 13:1295-1309, October 2003)