San Francisco

THIS month, a group of environmental nonprofits said they would challenge the federal government’s removal of Endangered Species Act protections for wolves in Wyoming. Since there are only about 328 wolves in a state with a historic blood thirst for the hides of these top predators, the nonprofits are probably right that lacking protection, Wyoming wolves are toast.

Many Americans, even as they view the extermination of a species as morally anathema, struggle to grasp the tangible effects of the loss of wolves. It turns out that, far from being freeloaders on the top of the food chain, wolves have a powerful effect on the well-being of the ecosystems around them — from the survival of trees and riverbank vegetation to, perhaps surprisingly, the health of the populations of their prey.

An example of this can be found in Wyoming’s Yellowstone National Park, where wolves were virtually wiped out in the 1920s and reintroduced in the ’90s. Since the wolves have come back, scientists have noted an unexpected improvement in many of the park’s degraded stream areas.

Stands of aspen and other native vegetation, once decimated by overgrazing, are now growing up along the banks. This may have something to do with changing fire patterns, but it is also probably because elk and other browsing animals behave differently when wolves are around. Instead of eating greenery down to the soil, they take a bite or two, look up to check for threats, and keep moving. The greenery can grow tall enough to reproduce.