Of note, they say, is that elk populations now are actually higher than they were in the mid-1960s, when aspen trees were still in significant decline. The major change from that period of time is the presence of wolves. The effect of behavioral changes may be equal to or even greater than lower elk population levels in allowing tree survival, the researchers said in their report.

In riparian zones, where wolves can most easily sneak up on elk, and gullies or other features make it more difficult for elk to escape, weve seen the most aspen recovery, Ripple said. We did not document nearly as much recovery in upland areas, at least so far, where elk apparently feel safer. But even there, aspen are growing better in areas with logs or debris that would make it more difficult for elk to move quickly.

This element of fear, the OSU scientists said, is a concept that is now getting more attention in ecology it factors in not just the numbers or species of animals, but also their behavior and the reasons for that behavior. Predators such as wolves or cougars, OSU researchers have shown, have the ability to strike fear into their prey and significantly change their behavior as a result.

The recovery of aspen, the researchers said, appears to have no link to climate or local terrain, since unbrowsed aspen in upland sites are growing just about as much as those in riparian zones. More details on this research and the findings can be found on the web at www.cof.orst.edu/cascades

The issue of aspen decline in the American West is huge, and their recovery will depend on local conditions and issues in many areas, Ripple said. In northern Yellowstone, we finally have some good news to report. Its just a start, but its a pretty good start.