Beavers are builders

American beaver near La Crosse River by Amy Vach, 2023.
Climate Change
Frank Dravis

Our Allies Against Climate Change

No other species in the Driftless region of Wisconsin, perhaps all of the US is such a prolific, industrious, and large-scale builder as the beaver. They are, of course, famous for their dams and lodges. Discussion concerning beavers, especially in northern farming states abundant with flowing rivers and streams, will eventually turn to the question: are beavers beneficial?

The largest rodent in the US, the term rodent applies to beavers because their incisor teeth never stop growing. That means they must chew on things (usually trees) to keep their teeth from growing too large for their mouths. They don’t actually eat the wood but consume the soft inner layers of bark. At forty to fifty pounds on average, a beaver can do a lot of chewing, and it is an example of the majesty of nature that the beaver then uses the felled trees and saplings for both home construction and habitat management. On land the furbearer is ungainly and slow, a target for predators, but in the water it is sleek and fast, propelled by the same large, flipper-like tail that makes it a waddling comedy on land. It builds its lodges in a pond or close to a bank with the entrance, ingeniously, underwater. 

For North America it is estimated there are 10 to 15 million beavers and are listed as “Least Concern” by the International Union for Conservation of Nature (IUCN) meaning very low risk of extinction and at the bottom of the endangered species taxonomy. 

The beaver’s love of building dams is viewed as either a benefit or a detriment depending on, “Where your forty is.” We’ll get to the meaning of that in a second. Climate change, and with it the increasing occurrence of intense and heavy rains is changing the calculus on the benefit/detriment. In the past, the effects of beaver dams were seen as either good or bad, yes/no. depending on what forty acres of land you were standing on. If it was a trail through the La Crosse River marsh near downtown La Crosse, then sighting a beaver lodge and dam added positively to the wildlife experience. If it was a beaver pond in the Kickapoo Valley Reserve where the water temp was near constant and bug hatches plentiful, then you were a happy trout fisherman fishing the forty acres downstream. But if you were the farmer who found his lower forty soggy and flooded, or were the other trout fisherman whose favorite riffle was now a pond, you weren’t so enthusiastic. The homeowner whose driveway culvert became blocked with water flowing everywhere except where they wanted it could be added to the non-enthusiastic list. 

With climate change, however, management policies towards the beaver are changing. In the Western states a critical eye has turned to how the dams can increase water storage, ground water restoration, and ecosystem survival during drought. In Wisconsin, while we can have acute periods of drought, we certainly have flooding, sustained erosion, and sudden washing. Beaver dams act like speed bumps in the streams and help to slow down the water as it moves through the system. “Slower water means less erosion and in some cases less flooding from storms. Ponds also absorb some of the water even if they already appear full, so the volume of water also decreases through a beaver system.”[1] Counter to some popular beliefs, studies have shown that water temps downstream of ponds were almost 5 degrees lower than upstream. The pond recharges groundwater which resurfaces colder downstream. This is important for species survival, such as trout, when a warming climate pushes habitats farther north. 

Another hydrological benefit of a beaver dam, and the resultant pond, is they filter out and store nutrients, sediment, and pollutants (depending on what’s upstream). Water flowing from a beaver dam is therefore cleaner than up stream. If the dam is left in place long enough sediment will gradually fill in behind creating a marshy area which accelerates carbon sequestration. Of course, to sustain an environment where these practices are possible you need land conservation. Filling in wetlands and channeling rivers eliminates the possibility of beaver benefits. 

Given the effects of climate change are increasing, landowners need to consider a wider range of implications the next time they discover a beaver irrigation project near their corn field. Yes, you can call the DNR, remove the dam, and live trap the animal, but stop and think about the last gully-washer that came through, blocked all the culverts, took out the fencing, and stranded the cows. Could it be, with just a little bit of human engineering that you can make peace with your new environmental engineer?

Looking at a beaver damn should no longer be through the binary lens of, “That’s incredible!” or “Look at what those rodents did now!” Instead, consider that small flood control project was built for free, and will be repaired for free. No DNR or Army Corps of Engineers needed.

THANKS TO YOU, Mississippi Valley Conservancy has protected a number of sites where beavers will continue to bring their skills to waterways and wetlands, slowing floodwaters and helping keep water cold and clean.



PHOTO: American beaver near La Crosse River by Amy Vach, 2023