Beavers–Important Ecological Actors

The Healthy Planet — Aspen Edition

By Wendy Keefover-Ring
Director, Carnivore Protection Program

Because wetlands can forestall oceanic events, Hurricane Katrina brought the issue of wetlands protection squarely back into the news. Wetlands perform important life-preserving functions—both for wildlife and humans.

In the West, one species is the keystone to wetlands’ function.

Small, only weighing between 35 and 50 pounds, beavers’ ecological effects prove profound. They transform the world—one dam at a time. Beaver build lodges from primal materials: logs, sticks, and mud. Beaver dams alter mountain streams, creating ponds, which enriches the landscape and increases species diversity. Beavers’ ponds and their tree-felling habits can benefit willow and aspen communities. Ponds provide homes for a variety of species, including water-loving moose to water-wading or arboreal birds. While beavers increase species’ richness and these saw-toothed rodents also enhance ecological function.

Beaver lodges hold back silt, which spreads out behind their earthen dams. The silt acts not only as a fertilizing agent, but as an enormous sponge that retains water, even during dry spells. Dams slow the flow of water, maintain lush wetlands, keep water tables high, and literally keep streams flowing above ground. Because of beaver dams, cleaner water percolates downstream for extended periods—sometimes staving off drought.

Ironically, an indirect benefactor of beavers, wolves, sometimes use North America’s largest rodent as food. Without wolves, beavers face fierce competition from a seemingly benign creature—elk. But the two share common food preferences. If elk over-proliferate, as is the case with Rocky Mountain National Park (which has no wolves), elk can lay waste to willow and aspen communities, leaving little sustenance and building materials for their aquatic counterparts.

The results are devastating. Without beavers, water tables sink, wetlands and life-bearing streams transform into parched parks. Fishes, otters, muskrats, moose, and variety of birds lose precious real estate.

In a study conducted by Bruce Baker of the U.S. Geological Survey, in Rocky Mountain National Park, where elk have been excluded by fences, beavers thrive.

In Yellowstone National Park, on the other hand, the U.S. Fish and Wildlife Service restored wolves in 1995. As a result, beavers have thrived because wolves moved once-sedentary willow-chomping elk out of riparian corridors and into forested hills and reduced their numbers. Willow and aspen stands have returned and are teeming with beavers and other wildlife.

But despite their ecological import, beavers have been hard hit by humans since Europeans landed in the New World.

Today, beavers only occupy about half of the streams in Wyoming and surrounding states, according to Mark McKinstry of the Bureau of Reclamation, and their ecological processes occur in only about 30 percent of the streams he surveyed in Wyoming.

Profoundly important ecological actors, beavers are still trapped in some places and considered a nuisance. In Colorado, despite a trapping ban on public lands, a federal agency trapped and killed 223 Colorado beavers in 2004. Nationwide the U.S.D.A.’s Wildlife Services killed 31,286 beavers because their dams caused flooding where people did not want it, or brought down trees that people wanted.

Beavers provide the ecosystem services that we humans need to survive. Beavers and their wetlands defend against drought conditions and they contribute to both water quantity and quality. Thus, we need to rethink their embattled status.


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