How beavers are helping and harming salmon restoration in WA (2024)

CHINOOK BEND NATURAL AREA, Carnation — Chocolaty brown and marvelously fat, this was one very well-fed beaver, chomping away on the restoration site’s new plantings.

The hungry behavior is adding wrinkles to King County’s plans to restore salmon habitat. The beavers, which ultimately help salmon in a balanced ecosystem, are eating so much that they are undoing some of the costly work it takes to bring salmon back to these wetlands in greater numbers.

Beavers bring many benefits when they build dams and slow river flows, creating more habitat through how they live on the landscape. But the shade from plants is key to healthy salmon habitat. So the county is working to find a way to keep beavers around while growing the streamside plants, trees and shrubs needed for fish, especially salmon that need cool, clean water to prosper.

The trifecta of success for the county is beavers, fish and vegetation, all thriving together.

Experiments in the Skykomish River found that beaver dams could lower summer water temperatures. And historical analysis in the Stillaguamish River basin found that the loss of beavers had greatly decreased the productive capacity of streams, especially for coho. So figuring out how to grow shade, beavers and salmon together could be a big win.

Jennifer Vanderhoof, a King County senior ecologist and beaver expert, is ready with a plan for these rodents that can eat a restoration site bare. This winter, she with other partners launched an experiment at a pond to try to both welcome and work with hungry accomplices in the county’s salmon restoration work.

An invasive weed, reed canary grass, is thriving in the sun at the site, and there isn’t enough shade to cool the water. So managers are trying to get shrubs and trees growing. They were glad when the beavers came back here all on their own — but that has also meant the restoration site where they are trying to grow shade has become an all-they-can-eat beaver cafe. This experiment marks Round 1 in scientists versus beaver appetites.

The goal is to grow more vegetation than the beavers can eat. Without some extra effort, instead, they will just grow fatter beavers.

Why bother?

Beavers are ecosystem engineers that can make salmon habitat better and faster than people can, crucially in the era of climate change. Coho salmon thrive in stream systems where beaver dams have helped slow, clean and cool the water. And salmon benefit more than 123 species of wildlife, from tiny bugs to bears, and, of course, people like to eat them, too.

On a recent spring evening, Vanderhoof was touring the planting sites to see how the different approaches were working, and she showed off four different planting styles started this winter.

She pointed at tall sticks. Short sticks. Bundled sticks. Fenced sticks — in an effort to keep the residents out. So far, everything but the sticks behind the fences were being eaten to one degree or another.

But she was hopeful to see so many leaves still growing on the sticks recently put in the mud to sprout.

Here, all the benefits of beaver presence were reflected in the biodiversity of the pond created by their dams.

There were far more than beavers there. There were ducks and ducklings. Muskrat and otter. Kingfishers clattered and swallows dipped and swooped. A great blue heron fished. Swainson’s thrush sang their evening song, and the water was dimpled with insects.

Signs of beavers were everywhere — even the walking stick that Vanderhoof carried was beaver-chewed. She walked past holes in the ground where the beavers were denning in the bank. “They are a winner species,” she said of beavers, which are highly adaptable to people.

Once nearly trapped to extinction, beavers today are back on the landscape and have proved able to live in culverts, drainage ditches, just about anywhere they can find water to work with and enough to eat.

“We were not actively trying to restore beavers,” Vanderhoof said. “We are trying to restore salmon.” That’s where the new experiment and a manual on planning restoration sites with beavers in mind, recently published by the county, comes in.

“You need to feed the engine,” she said of the beavers. “But you also need to protect the plants or they will never grow.” It is an abundance strategy: Plant so much material that the beavers can’t eat it all — but also stay on the land and balance an ecosystem, Vanderhoof said.

“That’s my dream.”