A few days before a volunteer project with students from Mt. Hood Community College, I walked down to a riparian area along Beaver Creek in Gresham. Trees planted five years earlier stood taller than me and began to shade out invasive grasses along the stream bank.
I returned three days later with the student volunteers. Instead of trees, we found tree stumps and the conspicuous beaver-chew stems: pointy and scribed with teeth marks. An equally conspicuous drag trail led to a newly constructed dam.
Perhaps I should have paid more attention to the name of the stream, but evidence of beavers was not common along this reach of Beaver Creek. Our work to restore the riparian area probably attracted beavers to our new forest stand. We planted food and building material favored by beavers, and they came. Time to start thinking more deeply about how to work with beavers to create healthy streams and wetlands, I thought to myself.
The masterful manipulations of the landscape by beavers result in well-documented benefits to watershed function and wildlife habitat. Beaver dams and habitat complexes increase water storage and base flows, create wetlands, increase habitat complexity, trap sediments and contaminants, capture woody material and foster nutrient recycling.
Beaver habitat is the original one-stop shopping center for hundreds of species. One of the most noteworthy is juvenile salmon, which use the slow water behind beaver dams for rearing periods and overwintering. Chinook and steelhead also use beaver habitat, as do amphibians like red-legged frogs and chorus frogs. Waterfowl and migratory birds find shelter and nesting sites in the shrub thickets along beaver complexes and protein-rich food for rearing young and refueling for long-distance travel.
Historically, beavers were widespread and common in Oregon watersheds. Their numbers declined significantly due to trapping from 1600 through the 1800s to supply pelts for hats and clothing. Today, habitat loss and conflict with human infrastructure limit beavers.
Fortunately, beavers are adaptive generalists that seem to need little encouragement to move back into suitable habitats. In areas without beavers, establishing their preferred food and building materials are often enough to lure them. Although beavers will use just about any suitable material for dams, including plastic bags, trash and invasive plants like reed canarygrass, I plant their preferred species, including hardwoods such as willows, red alder and cottonwood.
We know that beavers may consume the desirable food and building materials and temporarily migrate elsewhere. To make sure the abandoned beaver habitat does not revert to weeds, which are present in most of our region’s riparian and wetland habitats, I also plant species unpalatable to beavers, such as cascara, red elderberry and Pacific ninebark. Beavers tend to avoid those plants, so they persist after the beavers move out. Finally, I plan for the strategic planting of willows mixed with other preferred species to provide a continuous source of plants preferred by beavers.
If beavers are successful, they build dams, create flooding and cut down trees – while paying no attention to property lines. At Metro, we know beavers might impact our neighbors, and we strive to work with neighbors to reduce conflicts. The challenge of keeping beavers in our developing landscape means working collaboratively with partners to address conflicts between property protection and beaver behavior. Our ecosystems and wildlife evolved with beavers as significant sculptors of the land. Working with them to create healthy watersheds is the natural thing to do.