Thinking like a beaver: A BDA primer

In the first snow of October 2018, along Basin Creek outside of Butte, Montana, I volunteered to be a beaver. Or, lacking all the right anatomy, I at least tried to think and act how nature's best woodworkers might.

In this restoration project – using simple cutting and digging tools, plus a dose of aquatic ingenuity  – I worked with colleagues to mimic the masters and build a series of beaver dam analogues (BDAs). Such low-tech earth-shaping seemed shallow next to the chasm at the nearby Berkeley Pit, but I knew these BDAs promised deep impacts, enhancing stable flows for Basin Creek's westslope cutthroat trout, and for the people of Butte, who draw on these waters to drink, wash and flush every day. 

I was particularly eager to learn with Amy Chadwick, a senior ecologist at Great West Engineering and one of Montana's leading BDA pioneers. With partners ranging from the Blackfoot Challenge to the Blackfeet Nation, Amy has installed hundreds of BDAs around the state. Her expertise in beaver mimicry has changed a once-obscure restoration practice into a common-sense tool deployed by diverse allies in the conservation community. 

At particular sites and wider ecosystems, connectivity drives the need for BDAs in conservation today. The single-thread, steep-banked channel of Basin Creek had cut at least four feet into the earth, a vertical depth which denied the creek's lateral access to a dynamic, fertile floodplain. Waters could once lasso about in spring runoff, but in becoming a knife instead of a braided rope, the creek prevented the floodplain from its nominal function. And, without seasonal inundations to recharge, the riparian zone had hardened and dried. 

Not far off, amidst the conifers encroaching where willows once grew, a peculiar earthen berm revealed the disconnection impacting a far wider scale: a defunct beaver dam, partly subsumed and entirely overgrown after decades of neglect. Beavers once stored water behind the dam to enhance their own safety and access to food, and in doing so, they supported countless other species, recharged groundwater reserves and stabilized surface flows through the year. But without this keystone species, their beneficiaries and ecosystem services collapse too.

Unfortunately, that dilemma of disconnection at Basin Creek is too common across the Intermountain West, where 80 percent of biodiversity exists on the two percent of the region in wetland and riparian habitat. The Swan Valley has been able to boast that 16% of its surface area is covered in water, but in a rapidly changing climate, such a statistic cannot be taken for granted. While beavers narrowly escaped extinction in the Fur Trade Era, the legacy of their decline continues. The quandary posed at Basin Creek – and at many sites throughout the Swan Valley – remains: How can recovering beavers overcome the obstacles that developed in the decades of their absence? Where roads hem in rivers, where ponds become pastures and where creeks constrict into irrigation networks – how can beavers adapt?  

While relocating beavers often seems the quick response, this tactic alone can't address the habitat concerns that might estrange transplants from the old haunts of their kin. Montana Fish, Wildlife & Parks rarely authorizes beaver relocation, which can perpetuate a "nuisance" mentality and considerable risk to the family-oriented rodents themselves. This is where BDAs come in – not as a replacement for beavers, but as a tool for improving conditions so that beavers have incentive to return.

A BDA is not a once-and-done, forever-fixed product, after all. It is a bridging step in the restoration process, and one that can shape our thoughts towards working with beavers for the wetter landscape that we – and so many other species – will need. The promise of BDAs is not impermeability but the low-tech potential to link healthy streams, human stewards and recovering beaver populations.

The Flathead National Forest's Mid-Swan Project (currently under review) contains a significant BDA component on our public lands. SVC is encouraging good site selection and community engagement.

We're also eager to partner with landowners to advance the potential of BDAs and beaver restoration on private land, so please be in touch to explore the opportunities for related work where you live (406-754-3137; rob@svconnections.org). BDAs do require permitting and planning and I'll be keen to share a conversation, resources and/or a free site visit. No single person has all the answers to the past losses and future threats in our watersheds, and Homo sapiens can't think their way through these issues alone. But together, with beavers, we can.