It is strange but true that as species disappear, the empty spaces they leave behind come to be accepted as ‘natural’. How many times during wildlife reintroductions has the objection been raised that deer, pronghorn, elk, sheep, bison, horses, bear, wolves, – and now beaver – no longer ‘belong’ in our wild places; or that across the Southwest our empty deserts are endangered by a restoration of biodiversity?
NOTE: this article below was featured in the June 2018 edition of ScienceMag.org It was written by Ben Goldfarb
Artificial beaver dams are a hot restoration strategy, but the projects aren’t always welcome.
In 1836, an explorer named Stephen Meek wandered down the piney slopes of Northern California’s Klamath Mountains and ended up here, in the finest fur trapping ground he’d ever encountered. This swampy basin would ultimately become known as the Scott Valley, but Meek’s men named it Beaver Valley after its most salient resource: the rodents whose dams shaped its ponds, marshes, and meadows. Meek’s crew caught 1800 beavers here in 1850 alone, shipping their pelts to Europe to be felted into waterproof hats. More trappers followed, and in 1929 one killed and skinned the valley’s last known beaver.
The massacre spelled disaster not only for the beavers, but also for the Scott River’s salmon, which once sheltered in beaver-built ponds and channels. As old beaver dams collapsed and washed away, wetlands dried up and streams carved into their beds. Gold mining destroyed more habitat. Today, the Scott resembles a postindustrial sacrifice zone, its once lush floodplain buried under heaps of mine tailings. “This is what we call ‘completely hosed,’” sighed Charnna Gilmore, executive director of the Scott River Watershed Council in Etna, California, as she crunched over the rubble on a sweltering June morning last year.
All is not lost, however. Beyond one slag heap, a tributary called Sugar Creek has been transformed into a shimmering pond, broad as several tennis courts and fringed with willow and alder. Gilmore tugged up her shorts and waded into the basin, sandals sinking deep into chocolatey mud. Schools of salmon fry flowed like mercury around her ankles. It was as if she had stepped into a time machine and been transported back to the Scott’s fecund past.
This oasis, Gilmore explained, is the fruit of a seemingly quixotic effort to rebeaver Beaver Valley. At the downstream end of the pond stood the structure that made the resurrection possible: a rodent-human collaboration known as a beaver dam analog (BDA). Human hands felled and peeled Douglas fir logs, pounded them upright into the stream bed, and wove a lattice of willow sticks through the posts. A few beavers that had recently returned to the valley promptly took over, gnawing down nearby trees and reinforcing the dam with branches and mud.
“It’s fantastic to see beavers working on this,” Gilmore said as she bent to examine a chewed stick. “They do a much better job than we do.” The result is a bit too orderly to be a beaver dam, a touch too messy to have been created solely by humans.
Gilmore’s group is just one of many now deploying BDAs, perhaps the fastest-growing stream restoration technique in the U.S. West. Federal agencies such as the U.S. Forest Service, nonprofits such as The Nature Conservancy, and even private ranchers have installed the structures to return life to deeply eroded streams and, in some cases, to help re-establish beavers in long-abandoned territories. In Wyoming, BDAs are creating wet meadows for a vulnerable bird. In Oregon, they’re rebuilding salmon streams. In Utah, they’re helping irrigate pastures for cattle.
Part of the allure is that BDAs are cheap compared with other restoration techniques. “Instead of spending $1 million per stream mile, maybe you spend $10,000,” says Joe Wheaton, a geomorphologist at Utah State University (USU) in Logan who’s among the leading proponents of beaver-based restoration. “Relying on the labor of a rodent helps a ton.”
The BDA craze is experiencing growing pains, however. Regulators unfamiliar with the approach are sometimes skeptical, and some landowners and government agencies are loath to aid a rodent infamous for felling valuable trees, flooding property, and clogging road culverts. Last year alone, the U.S. Department of Agriculture (USDA) killed more than 23,000 beavers deemed to be nuisances.
Beavers might be vaunted ecosystem architects, says Joe Cannon, an ecologist at The Lands Council in Spokane, Washington, a group that has installed BDAs and relocated beavers in the eastern part of that state. “But we’ve got greater protection on tree squirrels.”
FROM OUR 21ST CENTURY vantage, it’s hard to conceive how profoundly beavers shaped the landscape. Indeed, North America might better be termed Beaverland. Surveying the Missouri River Basin in 1805, the explorers Meriwether Lewis and William Clark encountered beaver dams “extending as far up those streams as [we] could discover them.” Scientists calculate that up to 250 million beaver ponds once puddled the continent—impounding enough water to submerge Washington, Oregon, and California. Castor canadensis even paved the way for agriculture: By trapping sediment in their ponds, beavers “produced the rich farm land … of the northern half of North America,” paleontologist Rudolf Ruedemann wrote in Science in 1938.
But Beaverland could not withstand the fur trappers who arrived in New England in the 17th century and quickly spread west. By 1843, naturalist John James Audubon found the Missouri Basin “quite destitute.” At the outset of the 20th century, researchers estimate, just 100,000 beavers survived—less than 1% of historic numbers.
The slaughter transfigured North America’s waterways. In a healthy, beaver-rich creek, dams slow water flows, capture sediment, and counteract erosion. But after beavers and their speed bumps disappeared, streams eroded into their beds, cutting deep gullies in a process called incision. These steep-sided, straitjacketed streams lost the ability to spill onto their floodplains and recharge aquifers. Some groundwater-fed streams dried up altogether.