As we were reminded this past month, management of rivers and streams is an essential aspect of flood prevention. And yet, many modifications made to the riparian environment in previous decades, such as encasing riverways in concrete channels, have contributed to the risk of flooding rather than mitigating it. But experts are now realizing that restoring rivers and streams to their original forms is an effective way to manage flood risk.

Housing and commercial development make creek restoration quite difficult in urban and suburban communities. But what about areas where there is still enough open space to find more radical solutions to restore watersheds? Scientists, advocates, and government officials are beginning to realize that there is a very inexpensive and highly effective solution not only to flooding but also to the effects of drought and wildfires…bring in a couple of beavers!

Source: kingcounty.gov/beavers

Why Are Beavers a Keystone Species?

What is the one thing we all know about beavers? They like to build dams. They do this for their own survival. Their main predators — bears, wolves, coyotes and the like — are land animals, so beavers are safer in the water.

But their dams have beneficial effects that extend far beyond ensuring beavers’ safety. The dams slow down the rivers, forcing the water to spread across a wider expanse in a network of smaller waterways and shallow ponds. These ecologies support a wide variety of plant and animal life. The marshy wet meadows absorb ground water, raising the water table, and protect vegetation from dying during periods of drought. The waterways also act as fire breaks. And by slowing down the water and siphoning it into tributaries, beaver dams greatly reduce the effects of flooding.

As beavers bring up mud, they diversify the habitat for invertebrates on the pond floor.

An explosion of research in the past 20 years or so shows the positive effects of beaver dams. In a 2020 study, researchers showed that beaver-dammed corridors were relatively unharmed by wildfires compared with adjacent areas without beaver damming. Author Dr. Emily Fairfax noted that “The differences in burn severity, air temperature, humidity, and soil moisture between the beaver complex and the adjacent landscape were huge.”  

For all these reasons, the modest, unassuming beaver is considered a keystone species due to their stabilizing and broad impact on local ecosystems. In contrast to keystone species like wolves that stabilize ecosystems through predation, beavers are engineers whose constructions become rich ecosystems that support and protect many other species.

How Do Beavers Get the Job Done?

Beavers are not conventionally attractive crowd-pleasers like monarch butterflies or pandas. But if you can get beyond surface appearances, you will see that beavers are very awesome creatures. Their chunky bodies are perfectly constructed for swimming and cutting down trees, activities crucial to their survival.

Beavers’ teeth aren’t gorgeous, but they get the job done.

Take their teeth, for instance. It’s hard to find a weirder smile than one dominated by extraordinary long teeth the color of a Cheeto. But their teeth are orange because they contain so much iron, which makes them super strong. Their teeth also grow continuously and are self-sharpening, ensuring that beavers will always be able to cut down trees to make dams and lodges, as well as to procure the leaves, twigs, and bark they rely on for food.

Other aspects of their facial features are also perfectly adapted to their lifestyle. Their eyes are small and have a transparent cover, called a nictitating membrane, that can be drawn across their eyeballs like goggles, so they can see while under water. Structures at the back of their mouth prevent water getting into the lungs so they can gnaw on or carry branches while submerged. And their lips can close behind their teeth, also handy when you are swimming with a mouthful of branches.

Source: pbs.org

No one would mistake a beaver’s physique for that of a competitive swimmer. Averaging around 50 pounds, these large rodents look ungainly on land, but their bodies are custom built for survival in ice cold water.

For one thing their body mass is big relative to their body’s surface area, and thus helpful in maintaining their body heat. Plus, they are covered with a coarse outer layer of fur to keep out the rain and a soft under layer to provide warmth.

	A nice wide tail helps stabilize the beaver on land.

Their flexible and muscular tails have many important functions. First, the tail is a storehouse of fat for the winter and acts as a rudder when they are swimming. On land, where beavers are a bit klutzy, their tail helps prop up them up. And, of course, they smack the water with their tails to warn each other of danger and warn off predators.

Just one more enchanting thing about beavers…their social life. Beavers mate for life and raise a “kit” of little beavers every one or two years. The offspring spend about two years at home, taking care of any younger siblings and learning the craft of lodge and dam building. Then they take off in search of a river to call their own.

Beavers don’t hibernate, but they spend most of the cold months inside their cozy dams, venturing out occasionally to bring back vegetation to nibble on. Cameras placed inside beaver dams show that beavers sometimes host “lodgers,” animals like marmots who stay in a dam for the winter and enjoy the beavers’ food and hospitality.

Home sweet home (source: pbs.org)

Wait, Are There Beavers in Coastal California?

If you asked me two months ago whether beavers were native to coastal California, I would probably have hesitated and said, “Maybe not?” I would have been wrong, but most scientists thought similarly until recently, and beavers have been treated in California as nonnative pests. 

The men in this 1886 photo had apparently not yet heard that beaver hats were no longer in fashion.

A 500-700 year old rock painting by the Chumash tribe that appears to depict a beaver…but wait, is it playing pickleball? (source: baynature.org)

Prior to 1900, beavers were commonly found throughout most of California (Source: baynature.org)

In fact, beavers were abundant throughout coastal California until the 1800s, when they were hunted to near extinction by Spanish, English, and Russian maritime traders whose ships sailed up and down the coast procuring seal, otter, and beaver pelts. Overland fur trappers like Kit Carson and Jedediah Smith also reduced the beaver population in California, moving inland and searching as far south as the Sacramento and San Joaquin valleys.

By the mid 1800s the beaver trade began to drop off but by that time beaver populations across the country were declining rapidly, eventually dropping from hundreds of millions to just 10-15 million today.

Amazingly, it was not until 2013 that a multidisciplinary group of researchers made creative use of archival data to show how prevalent beavers had once been in coastal California and the Sierra Nevada mountains. They catalogued archeological findings of beaver teeth and bones discovered in shell mounds and learned of rock formations in the Sierras with paintings of beavers by Native artists. Linguistic research revealed that indigenous languages had a word for “beaver.” And historical research turned up writing by early explorers noting that Native people used beaver pelts for clothing.

No one source can be called definitive, perhaps, but the various kinds of data add up to a convincing argument. It is now well accepted that the beavers were critical to the creation and maintenance of an extensive network of wetlands throughout California.

	“Hairdresser Sherri Tippie, the top live trapper of the species in North America, rescues unwanted beavers in the Denver suburbs and then places them with farmers and beaver enthusiasts who eagerly provide new homes for them” (Click to see source)

Emerging Role of Beavers in Habitat Restoration

It is hard to believe that only ten years ago beavers were considered a non-native pest in California. As such, they were subject to state-permitted removal from areas where their dams resulted in flooded roads or backyards. In 2013, for instance, the California Department of Fish and Wildlife issued 172 depredation permits, each one allowing the removal of multiple beavers on an individual site.

These days, beavers are finally getting their due, recently being described as “untapped, creative climate solving heroes” by the California Department of Fish and Wildlife (CDFW). In the past year, CDFW has allocated $3 million dollars to hiring staff for the purpose of beaver restoration in the state.

Meanwhile, there is some evidence that beavers are making a comeback in the Bay Area, with recent sightings along various rivers in the South Bay. Not everyone is ecstatic about welcoming the chubby critters to their neighborhood. Beavers are not always a good fit for a particular ecology, and sometimes need to be removed. There are a number of remedies other than the formerly common one of extermination.

Beaver dam analogue on Miners Creek in Scott River watershed

One experiment with introducing beavers for the purpose of wetlands restoration took place on the Scott River in Northern California, an area where beavers used to be plentiful but whose numbers are greatly diminished. Beaver dam analogues were constructed on several creeks running through agricultural land to attract beavers to areas that needed restoration. The restoration team worked closely with the landowners to ensure that the project satisfied their goals as well as those of environmentalists. In all cases, real beavers arrived, took over the dams, and began the ordinary work of maintaining and extending them. The dams improved habitat for the coho salmon, and increased water availability for the landowners.

So now we know…One of the world’s least flashy animals is perfectly suited to restore and maintain resilient, productive, and beautiful riparian environments…all at a very low price.

Want to Learn More?

Watch a wonderful episode of the PBS show Nature called Leave it to Beavers about how beavers can revive a landscape that has undergone a drought period.

If you don’t have time to watch all of Leave it to Beavers, here are a few clips:

www.pbs.org/wnet/nature/busy-beavers-backyard-nature/28116/ and

www.pbs.org/wnet/nature/leave-it-to-beavers-video-how-beavers-build-dams/8847/

Watch this charming Youtube video by Dr. Emily Fairfax depicting the process by which beaver dams can protect land against drought and wildfires and restore biodiversity.

Ready for a deep dive into the history of beavers in the US? Check out Leila Philip’s new book called “Beaverland: How One Weird Rodent Made America” and/or read the New York Times review by Jennifer Szalai.

Another informative and highly readable book is “Eager: The Surprising, Secret Life of Beavers and Why They Matter” by Ben Goldfarb. A New York Times reviewer couldn’t help quipping that “Goldfarb’s wonderful book might just tail-slap a politician or two into realizing how much we need them to restore our critical wetlands.”

For a historical perspective, here’s a great article in Bay Nature about the evidence in support of beavers’ widespread existence in California prior to the 1800s.

Read more about benefits of restoring beavers to watershed areas in this interesting article by the Public Policy Institute of California.

Learn more about the Occidental Arts and Ecology Center, a research, demonstration, advocacy and organizing center in Sonoma County whose purpose is to design and cultivate resilience to ecological, social and economic challenges.

That’s it for this installment of the Environmental Forum of Marin Notebook!
Learn more about EFM and the Notebook at marinefm.org.