A Word from the Watershed: Happy Beaver, Happy Watershed

By Corrie Aiuto

The beaver is a biodiversity engineer. Hoping to harness the power of this rodent to restore stream complexity and bolster habitat for Coho salmon, we at the Upper Nehalem Watershed Council (UNWC) are busy building and observing beaver playgrounds, otherwise known as Beaver Dam Analogues (BDAs), and a new report released in April shows promising results.

American Beaver, Wikimedia Commons

Beaver Basics

The North American beaver, Castor canadensis, is a nocturnal, semiaquatic rodent with a dense fur coat, webbed hind feet, enormous orange incisors and a flat paddle of a tail. They are the second largest rodent in the world, growing continually throughout their life, averaging 50 to 60 pounds and three to four feet in length. They are graceful swimmers, sporting goggle eyelids and a fur lining behind their teeth to seal out water. They can stay submerged for up to 15 minutes by slowing their heart rate, thereby avoiding predators and navigating to submerged dens and lodges. When they are not cutting down trees for construction they are chopping vegetation for food; despite stories of beaver eating fish, they are entirely herbivores.

Males and females typically inhabit a space as a mated pair, often for life, and colonies include newest kits, which average four to a litter, and the one year old kits. Two year olds often leave the colony to build their own den. Together a colony will gather food, raise young, and studiously repair dams. So vigilant are they that removing a beaver dam is considered pointless, often being rebuilt overnight.

Many of us are familiar with the image of the beaver: a pump body resting on a river bank, front paws clutching a leafy twig, a large, flat tail propped behind, and out of a small round head, beady eyes scrutinizing you through the thick, luscious brown fur that thousands of trappers so desired. Their fur is incredibly dense; a postage stamp size beaver fur has as many individual hairs as an entire human head. And surprisingly soft to the touch; underneath a layer of long, coarse guard hairs you feel a downy under coat, simultaneously silky and fluffy. European hat makers felted the pelts, formed them into fashion and made beaver fur a coveted and valuable commodity.

The first fur trading in North America happened almost as soon as white people arrived, trading for furs with Native Americans in the 1500s, but major trapping and trade began in the 1600s. Throughout that century and the next, hundreds of millions of beaver were trapped and relieved of their coats. By the 1840s the species was nearly extinct.

Thankfully, beaver have recovered. Populations are estimated around 15 million, and although that’s nowhere near the estimated 400 million pre-colonization, it’s enough for the species to be considered stable.        


Drain The Swamp? Maybe Not

Here in the 21st century, we are beginning to understand the significant impact beaver had on the North American landscape 300 years ago. Streams and rivers were backed up and impounded all over the place. Water filled the valleys and the beaver reigned supreme from atop lofty lodges. Rather than rushing, babbling streams neatly confined to a trench-like bed, one would have seen dam after dam holding and pooling water, giving way to wetlands, marshes, and bogs and connecting floodplains to waterways.

If I’m honest, from my human perspective, it sounds awful. It sounds like mosquitoes and snakes and nowhere dry for days. But that perspective is a naïve one. The reality is that the slog and swamp-like muck is actually a cradle of life, a refuge for biodiversity.

In the United States, only 2% of land is wetland, and yet wetlands account for 80% of our biodiversity. Thousands of species depend on wetland habitat: fish, birds, mammals, reptiles, amphibians, insects and plants. Beaver are a keystone species because they create habitat used by so many others and without them, some species collapse entirely. Encouraging beaver to colonize our waterways can increase the riparian footprint and vegetation, cause a seasonal stream to become perennial, capture pollution, sediment, carbon and nitrogen, lessen flood devastation, and retain cool water during summer.

“Let The Rodent Do The Work”

Here in our corner of Oregon, the UNWC wants to encourage beaver to resume their dam building and habitat creating as a way to bolster Coho salmon rearing, spawning, and juvenile survival and there is hope that beaver activity could increase the Upper Nehalem’s resiliency to climate change. To this end the UNWC and Steve Trask of Trask Consulting, Inc. began the Beaver Dam Analogue Pilot Project in 2018. Last month Trask released the Upper Nehalem BDA Pilot Project Year 2 Post Implementation Monitoring report with promising results.

Beaver Dam Analogue, Trask Consulting, Inc.

A BDA is essentially a fake beaver dam, intended to lure beaver into a constructive attitude. Formed by of a line of posts driven into the stream bed with branches woven between them, these playgrounds often come complete with food caches and newly planted willow stakes for grazing.

In August 2018, 27 BDAs were installed in four of the Nehalem’s tributaries: Buster Creek, Bear Creek, Rock Creek and Lousignont Creek. Then, one year later in August 2019, an additional 30 BDAs were installed along Deer Creek, Walker Creek, and upper Fishhawk Creek above the Lake. The chosen BDA sites are legacy beaver sites, but showed no signs of beaver activity at the time of installation.

In the new 2020 report, 15 out of 57 BDA sites were colonized by beaver with an additional 30 natural beaver dams constructed between the BDAs. This has added over 30,000 square feet of pool surface area and greatly increased the Coho salmon rearing potential. Some BDAs not colonized by beaver held back water and increased pool surface area well for the first winter, but are no substitute for active rodent maintenance and by year two they are beginning to fail. Overall the project appears to be successful and monitoring will continue into 2021 to assess longer term impacts.

Because of this success, the UNWC has definite plans to strategically encourage the expansion of beaver colonies throughout the watershed along designated anchor habitat reaches in cooperation with interested landowners and engaged managers.

If you want to learn more about beaver, the UNWC, or to view the 2020 BDA Pilot Project report, visit our website at unwc.nehalem.org.

Originally published on 5.7.2020 in Vernonia’s Voice.