Of wolves and water.

The gray wolf's near demise in the western half of the U.S. has affected more than just prey populations. That's according to an Oregon State University study conducted in Gallatin National Forest and replicating an earlier one in Yosemite National Park. The findings were reported in Environment magazine.

According to the report, when elk and other grazing animals became less fearful of attacks by wolves, they spent more time at previously dangerous sites--places like streams, where terrain changes. The result: Elks browsed unimpeded on streamside vegetation including cottonwoods and aspens, eating young trees before they could become established, and setting the whole ecosystem in decline.

Two OSU researchers, Robert Beschta and William Ripple, measured willow growth along a stretch of the Gallatin River and Tepee Creek, including an area designated high-risk for prey and one designated low-risk. They found not much had changed in the low-risk area but there were big changes in the one designated high-risk--the percentage of willows dropped from 92 percent in 1998 to 0 in 2002. The researchers pointed to other benefits of the wolf reintroduction, including more stable stream-banks (thanks to more riparian trees) and less erosion, Environment said. Better biodiversity and a larger beaver population were expected benefits.

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