The data show a clear and remarkable linkage between the presence of wolves and the health of an entire streamside ecosystem, including two species of cottonwoods and the myriad of roles they play in erosion control, stream health, and nurturing diverse plant and animal life.
The findings of these studies were recently published in Ecological Applications, a journal of the Ecological Society of America, and the journal Forest Ecology and Management.
"In one portion of the elk's winter range along the Lamar River of Yellowstone National Park, we found that there were thousands of small cottonwood seedlings," said Robert Beschta, professor emeritus in the College of Forestry at OSU and an expert on streams and riparian systems. "There should also have been hundreds of young trees, but there were none. Long-term elk browsing had been preventing any seedlings from getting taller."
That pattern was common throughout the study area - lots of seedlings in combination with large cottonwood trees generally more than 70 years old, but little or nothing in between.
Young cottonwoods, willows, and other streamside woody species are a preferred food for browsing elk during the harsh winters in northern Yellowstone, when much of the other forage is buried under snow. But when packs of wolves historically roamed the area, food was not the only consideration for elk, which had to be very careful and apparently avoided browsing in high-risk areas with low visibility or escape barriers.
Wolves were systematically killed in the Yellowstone region and many other areas of the West beginning in the late 1800s. A
Contact: Robert Beschta
Oregon State University