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Geo-Joint: Beaver Back on the Job

Posted on November 18 2015


Birds build nests. So do rats. Termite mounds are pretty impressive. But what other animal (nevermind us) builds anything so impressive as does the beaver? Using nothing but their gnawing front teeth, their legs, and a big paddle of a tail, they construct dams and lodges that are complex and highly effective. Beaver once populated all of North America except the arctic, peninsular Florida, and the desert southwest. As the human population spread and grew across the continent, however, hunting for their rich pelts, and habitat loss cut their numbers back drastically. Estimates of their former numbers range up to 400 million, whereas the current population is somewhere between 6 and 12 million. Often considered a nuisance, some ecologists now say it’s time to re-establish them in parts of their former stomping grounds…or swimming holes. In Scotland, the government has embarked on the “Scottish Beaver Trial,” which in 2008 established four pairs of beaver in a suitable habitat. Scotland had not seen a beaver in over 400 years thanks to rampant hunting. The beaver in the trial are reproducing and having positive effects on the land they knew before. They have even increased tourism, as people are eager to see the beavers.


Beaver build their dams by gnawing down small trees and blocking up creeks and streams. Rocks and mud seal the gaps. The water that backs up behind the dam creates a pond in which they also build a lodge. The whole point of the dam is to create enough water depth to ensure predators won’t be able to get into the lodge, whose entryway is under the water. Where slow moving water is deep enough, beaver will simply dig a den in the stream bank. The dam and lodge plan works very well for the beaver, but unbeknownst to him, his housing arrangement has a beneficial effect on the local environment. Slowing water down (the dams are not impermeable) helps soil deposit on the pond floor, which clarifies the water and creates habitat for other species. The depth of cool ponds provides a haven for fish in hot summer weather. Water caught behind a dam has more time to percolate down into the water table, be naturally filtered, and emerge again farther downstream later in the season. This helps keep raging rainstorm torrents from racing downstream to the sea, and provides a continuous water flow during the drier parts of the year. Landscape near a beaver pond benefits from the general dampness that seeps out into surrounding meadows, storing water, greening the area for foragers such as deer, and increasing insect populations that feed birds and fish. For their outsized influence on environmental dynamics, they are called a keystone species.


By the lack of all these beaver services, the drought in California is probably made worse than it might have been. Scientists studying the beaver’s talents think the reintroduction of beaver to Sierran environments could help conserve the limited water that still flows down mountain and valley streams. Of course, this is disputed by others who think imported beaver will only cause problems, especially in populated areas. Trees felled onto roads, water backed up onto homes, or property intended for other uses, and more chance of Giardia transmission are concerns. Questions remain as to the extent of the historical beaver population range, so some areas may not be appropriate for their introduction. While beaver can keep a functioning water system in good balance, they can’t manufacture any water when the rain doesn’t fall. If there is insufficient water to provide for a beaver’s needs, he’ll pack up and move elsewhere, or simply perish if conditions are beyond his ability to survive.


So the idea of bringing back the beaver is not a panacea and could create some problems, but ecosystems perform best when all their original members are contributing their functions to the program, be it hunting, foraging, pooping, leaving a carcass….or dam building. Having the beaver back in the mix is good for the land.

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