This is the first part of a two-part series. Part 1 examines the ecosystem and watershed benefits of beavers. Part 2 will examine the economics of using beavers to both mitigate and adapt to climate change.
Nearly everywhere there was water in what are now the nations of Canada and the United States, there were beavers. Lots of Castor canadensis (Figure 1)—somewhere between 60 and 400 million beavers, scientists estimate. Today there are perhaps 6 to 12 million or maybe 10 to 15 million, but in any case a hell of a lot fewer than before the European invasion that brought with it commercial trapping. Beaver pelts were popular for hats (Figure 2) back in the day. Beavers were also inconvenient to those who wanted to farm, as they backed up water into inconvenient places at inconvenient times. And beaver populations were harmed by massive logging of forests.
Unlike the range of many other species, the original range of North American beavers (Figure 3) hasn’t shrunk in size as much as it has been reduced in density. There are just a lot fewer beaver than there used to be or need to be. Part of the process of recovering the beaver throughout its range is trapping and reintroducing beaver into areas of previous presence. This started being done many decades ago at a small scale (Figure 4).
Figure 3. The range of beaver in North America. Unlike the range of many other species, the range of Castor canadensis has not shrunk, but a lot of areas within the range are currently beaverless. Source: Wikipedia.
Beavers live to impound moving water and don’t care if the water moves through irrigation ditches or highway culverts. Beavers may seem like a nuisance based on human notions about order and territory, but on the whole any annoyance or damage beavers cause to human development is far outweighed by the great ecological, watershed, and climate benefits they provide.
Yes, Oregon’s official state mammal is a rodent (Figure 5). But this largest rodent on the continent, which can weigh 65 pounds, is by no means a mere riparian rat. Beavers, by damming streams and creating wetlands, greatly enrich their ecosystem and watershed far out of proportion to their numbers. Birds, amphibians, fish, and bats all feed on the aquatic insects found in beaver ponds. Native mink, river otter, muskrats, turtles, frogs, and salamanders all use beaver ponds. Because the beaver modifies its environment to make a living and coincidentally creates habitat for numerous other species, it is what biologists call a keystone species.
WildEarth Guardians, Grand Canyon Trust, and The Lands Council have summarized beaver engineering and its benefits thusly:
Beaver dams slow snowmelt runoff, which—
• extends summertime stream flow; and
• restores perennial flow to some streams.
Beaver dams create ponds, which—
• maintain and create wetlands;
• provide nurseries for salmonids and other native fish;
• provide critically needed amphibian habitat;
• increase habitat for small mammals and cavity-nesting birds (using drowned trees);
• contribute to establishment of deep-rooted sedges, rushes, native hydric grasses, and woody riparian vegetation;
• improve downstream water quality by trapping and storing sediment; and
• create mesic meadows in sediment behind abandoned dams.
Water enters groundwater upstream of, beside, and downstream of dams which—
• sub-irrigates the valley;
• allows water to re-enter creeks/streams downstream as cooler seeps, which—
- is critically important to cold-water fish like salmonids; and
- reduces evaporative loss;
• expands and restores riparian vegetation, which—
- shades creeks/streams, which—
-- reduces water temperature; and
-- provides hiding cover for fish;
- buffers banks against erosion during high flows; and
- provides critical fish and wildlife habitat; and
• restores and expands deep-rooted riparian vegetation, which—
- increases bank integrity during high flows; and
- increases critical wildlife habitat.
A series of beaver dams can function as “speed bumps” during high water flows, which—
• spreads water outward on the floodplain;
• recharges ground water near streams;
• locally reduces flood force and gouging;
• increases stream complexity, including creation of backwater and pools;
• expands the presence of water for riparian plant communities; and
• prevents or reduces headcutting.
Beaver dams capture sediment, which—
• raises incised streambeds;
• provides soil for mesic meadows;
• reduces losses of sediment from the forest and into water facilities;
• reduces the conversion of complex stream and riparian habitat to straightened ditches; and
• heals headcuts.
Beaver increase large woody debris in creeks, due to—
• tree cutting;
• dam building;
• existing dams and their remnants which—
- increase complexity of streams;
- increase bank integrity during high flow;
- increase habitat for fish, otter, amphibians, and other aquatic species; and
- reduce expense of human construction/maintenance/repair of instream structures or placement of large woody debris in streams.
One of the species the beaver benefits is the Pacific salmon. “The destruction of salmon habitat in the rivers of the Pacific Northwest started with this near annihilation of beaver in the last half of the nineteenth century,” wrote Jim Lichatowich in his book Salmon Without Rivers (Island Press, 1999). Beaver dams—unlike human dams—do not impede fish passage (Figure 6). A critical component to bring back the Endangered Species Act (ESA) protected coho salmon is to bring back the beaver. Resident fish live in the ponds, and migratory salmon and steelhead can hide from predators and the strong currents.
Beaver Trapping and Slaughter
Alas, according to the market, the highest and best use of beaver is not engineering nature to the benefit of all but for clothing (last May, one Ontario company offered more than 30,000 beaver pelts for sale, averaging $10–11 pelt) or castoreum, a reddish-brown substance secreted by beavers and generally used in perfume ($72/pound for grade #1).
Alas, according to parts of the federal government, beavers are often a nuisance that the Wildlife Services program of the USDA Animal and Plant Health and Inspection Service (APHIS-WS) is happily trapping for anyone who wants them. APHIS-WS reported killing 2.7 million animals in 2016, nearly 1.6 million of which were native species, 21,184 of which were beavers (Figure 7). The real numbers are higher as APHIS-WS underreports its kills (unlike most bureaucracies, which overreport their actions).
A tip of our (nonbeaver) hat to the Center for Biological Diversity, Northwest Environmental Advocates, and the Western Environmental Law Center for making APHIS-WS obey the law. In Oregon, the agency has agreed to stop killing beavers and other aquatically oriented mammals (save for the nonnative nutria) while it consults with the National Marine Fisheries Service to determine the damage the action is doing to ESA-protected species of Pacific salmon.