Montana Public Radio

How Human-Made Beaver Dams Could Help With Habitat Restoration

Nov 25, 2019

University of Montana ecologists are researching human-made beaver dams as a potential habitat restoration tool. Early case studies show the dams could dull the impacts of climate change seen in rivers and streams. The U.S. Forest Service is looking to use the simple structures on new sites in the state, but first, officials want to better understand the science behind simulated rodent engineering.

Beavers aren’t called ecosystem engineers for nothing. Their dams can rebuild eroded streams and create lush wetland habitat suitable to elk and insect alike. Meanwhile, the dams create ponds that can store water longer in the face of drought.

The benefits of beaver labor are so compelling that western land managers have started copying their work, building what are known as beaver dam analogs, or BDAs. Basically, wooden posts pounded into a stream, then woven through with tree branches.

Early work on the concept suggests these look-alike dams are a cheap and effective tool to replicate how beavers alter landscapes.

Resource conservation student Jared Smith stacks brush between wooden posts pounded into Fish Creek for a beaver dam analog, Oct. 19, 2019.
Credit Kevin Trevellyan / Montana Public Radio

But University of Montana aquatic ecologist Lisa Eby says many western ecosystems no longer look like those occupied by beavers before settlers trapped them to near extinction. Eby thinks researchers need to learn more about how human-made beaver dams impact modern rivers and streams.

“We're having to make these management decisions and we're having to say, where should we put these BDAs? Where will they be become problems? Where will they be successes? But we don't have the science behind it to really make the best informed decisions we can,” she says.

That’s why officials from the Lolo National Forest and Missoula-based conservation group Clark Fork Coalition approached Eby last year to install and monitor multiple BDAs at three test sites. The Forest Service is largely funding the multiyear project.

A beaver in a pond on Gold Creek near Missoula.
Credit Courtesy Josh Burnham

Researchers have several big questions. One: how much water do these human-made dams actually store?

“Especially during drought times this should increase base flows that are good for not only fish and wildlife, but irrigation," Eby says. "But we don't know, is this just a drop in the bucket or is this really building ecological resilience?”

Managers also want to know how fish are affected before peppering their streams with BDAs.

Researchers say beaver complexes can provide first-rate trout habitat. But it’s unclear how well Montana’s native westslope cutthroat would navigate today’s low river flows with human-made mimics.

As for beaver ponds, their sun-drenched surfaces are warmer than rushing streams. Andrew Lahr, a Ph.D student in Eby’s lab, says that could create better habitat for invasive fish already displacing native trout.

“Here in Montana and across the western United States, we introduced eastern brook trout that have been really good invaders. They're able to inhabit places that have become warmer — too warm for cutthroat to be.”

Lahr will track brook trout to see how analog dams affect their populations at the research areas.

One of them is Teepee Creek on the Lolo National Forest, which received 13 BDAs for this project. Beavers once inhabited Teepee Creek’s watershed; Forest Services officials recently found a natural dam built there some time during the previous century. But the furry rodents are now less common in the forest. The streams look different. Some were straightened to build roads and mines, and it’s difficult for beavers to raise dams in quick flowing water.

Traci Sylte with the Forest Service says human activity in the early 1900s probably eroded Teepee Creek too. Surrounding land doesn’t store enough water to support rich streamside habitat. Sylte says that kind of degradation is common around western Montana.

"Historically our small streams have had a lot of impacts, whether that be by historic grazing, homesteading, to roads, culverts and other means,” she says.

Another BDA research area, Fish Creek, is among those impacted waterways. Ph.D. student Andrew Lahr says previous owners likely overgrazed the site. It's now managed by a national conservation nonprofit.

Katie Racette, stewardship coordinator with the Clark Fork Coalition, reaches for a pair of shears before trimming tree branches for a beaver dam analog on Fish Creek in western Montana, Oct. 19, 2019.
Credit Kevin Trevellyan / Montana Public Radio

Undergraduate volunteers were there on a recent fall Saturday to help researchers install eight analog dams. On the floodplain, students with shears pruned tree branches for others to stack across the muddy streambed. Hand tools, piles of slash — it wasn’t a sophisticated operation. Sylte says that’s central to the appeal of beaver dams.

“Beavers work very simply. You know, you bring in an excavator for some of this work, you're working at $1,000 a day, and often disturbing the land a lot more than what's necessary to provide these resource benefits,” she says. 

Sylte says she has wanted to use BDAs in the Lolo National Forest for 15 years. She’ll have to wait a little longer while scientists track changes at the test sites, seeing how well humans can replicate beaver dams and studying the potential consequences. Depending on the results, Katie Racette with the Clark Fork Coalition says the analog dam could have a place in the toolbox of agencies and nonprofits when repairing small streams in Montana.

That’s significant, because most of the country’s water comes from small creeks. But restoring them?

“I think that that is something that is going to be like a never-ending, a never-ending chore,” Racette says.

Which is why many are embracing the beaver as a self-sustaining land manager of sorts. BDAs are often placed near established beaver colonies so the buck-toothed squatters can move in to build and maintain their own dams.

Two of eight beaver dam analogs built on Fish Creek in western Montana, Oct. 19, 2019. The stream is eroded several feet below its floodplain. This section runs through land owned by the Nature Conservancy, an environmental advocacy nonprofit.
Credit Kevin Trevellyan / Montana Public Radio

UM ecologist Lisa Eby prefers teaching to pounding sticks into the mud.

“We don't want to be beavers for the next 50 years. Beavers are industrious, hard-working creatures,” she says.

It remains to be seen whether researchers can establish a beaver colony at the Fish Creek site, but it didn’t take long to notice a slight change in the environment after the BDAs were installed. Water had already risen several inches around the new dams before the research crew left to peel away damp waders and hop in their trucks.