Last week I wrote about a river restoration project, which included the reintroduction of beavers to the headwaters of Utah’s Escalante River. A reader commented on the blog, elaborating on the role beavers serve in stabilizing rivers.
Along that same line, our publisher drew my attention to a short film that explains how wolves can also help stabilize rivers. There are a few more steps in the logic chain here, involving what the film refers to as a trophic cascade. The film documents what happened after wolves were reintroduced to Yellowstone National Park in 1995 after an absence of about 70 years.
Deer and elk populations had grown tremendously in the wolves’ absence. When the wolves returned—even though there were relatively few of them and they didn’t kill all that many herbivores outright—the behavior of the deer changed; they began avoiding areas like valleys and gorges where they could be easily hunted, and as a result the vegetation in those areas was ungrazed and came back rapidly, including the growth of tall trees. Birds moved into the trees, and beavers also moved into the area and began building dams, which in turn created habitat for fish, amphibians, muskrats, otters, and the like.
The wolves also killed coyotes in the park, which led to an increased rodent population—and with it, more bald eagles, hawks, and other birds of prey, as well as foxes, badgers, and other animals that hunt rodents. The bear population also increased—often feeding on the carrion left behind by the wolves—and the bears also killed a few young deer, reinforcing the effect of the wolves.
Finally, with less grazing and more robust vegetation in the river valleys, the river banks stabilized: less erosion, less meandering, more pools and riffles. The film is about four minutes long and well worth watching, not least for the gorgeous footage.