- November 12, 2015
Last summer in rural, agrarian, upstate, New York, I was at a picnic with neighbors and I mentioned how beavers (Castor canadensis) were busy at work on my property. As an ecologist I was elated. They were creating a diverse riparian ecosystem in my backyard that provides habitat for kingfishers, herons, migrating ducks, fishers, and various other wildlife I frequently witnessed visiting the landscape. I even benefited from a winter of ice skating on the large ponds. One neighbor chimed in, “Beavers! I hate those things. I’d hunt and kill them all if I could.” And he is not alone.
Prior to European settlement of the Americas it is estimated 60 to 400 millionopen_in_new individual beavers inhabited North America. As Europeans settled, hunting of beavers intensified, and by the beginning of the 20th century most of the largest rodents of North America were extirpatedopen_in_new.
Known for altering the landscape with powerful flat tails and enormous incisors, their near elimination was due more to the value of their pelts, limited regulation on hunting, and sentiments similar to my neighbor’s. People’s preference for trees along narrow, confined creeks and sprawling riparian habitat also fuels the dislike of beaversopen_in_new.
Beavers quickly change landscapes. An individual beaver can cut down 300 trees a year. Over the course of that same year their teeth will grow about 48 inches–continually worn down by their logging endeavors. In the mid-1900s, as populations began to rebound, an important question was asked: What ecological role do beavers play in land management? The answer; beavers are keystone speciesopen_in_new.
Keystone species are plants or animals that play a critical ecological role. Without them, ecosystems change rapidly or cease to exist. Keystone species carry the weight of the world in their ecological adaptations. Many other species rely on the presence and activity of keystone species to create the conditions they, themselves, need to survive. Beavers are keystone species in healthy, freshwater streams that, when damned, create wetland habitat, and support a vast array of unique plants and animals.
Most urban and suburban landowners live in areas without habitat suitable for beavers. For rural landowners or those that live near natural wetland areas, however, understanding the important role that beavers play in their landscape–how they benefit other plants and animals, especially those found in ecologically sensitive wetlands–is an important consideration when encouraging or discouraging their presence.
Researchers studying beaver wetlands in Canadaopen_in_new and Arizonaopen_in_new found that invertebrates, amphibians, migratory waterfowl, moose (Alces alces), muskrat (Ondatra zibethicus), passerine birds, wolves, and coyote populations all benefited from the establishment or expansion of riparian beaver habitat. If you like wildlife diversity on your property encouraging beaver activity could be one option to consider.
Are there any negative consequences of beaver activity on landscapes? The simple answer is, yes. Below is a bulleted list of the positive and negative impacts of beaver activity.
In healthy riparian woodlands, beaver cutting is tolerated and even provides a form of rejuvenation since there is often vigorous coppice resprouting and clonal suckering of cottonwoods and willows. Conversely, excessive beaver cutting can thin riparian woodlands and provide another stress on declining populations [of riparian trees].
Wetland habitat to support species diversity
Removal of nitrogen from water (important in agricultural areas)open_in_new
Food resource for larger predators
Increase water retention in dry landscapes
Elevation of water table in dry landscapes
Negative Impacts of Beaver Activityopen_in_new:
Blocked irrigation ditches and culverts
Girdled or fallen timber
Flooded pastures, roads, and crops
Expansion of wetland shoreline
Decrease in or elimination of Populus tree species–cottonwood and aspen– their prefered food
One recently discovered beaver benefitopen_in_new was found while studying nitrogen concentrations in Northeast streams, rivers, and creeks in agricultural landscapes. Nitrogen run-off can be abundant in agricultural regions where farms have increased fertilizer use in monoculture farming practices to resupply their nitrogen-depleted soils. The problem, called eutrophication, arises when excess nitrogen in water bodies cause algal blooms and low oxygen levels that choke-out fish and other aquatic life.
Researchers found that a beaver dam can slow water flow enough to allow bacteria to capture the excess nitrogen and transform it into nitrogen gas, thereby removing it from the water. This process is referred to as denitrification. The conditions created by beavers could minimize the amount of nitrogen in water by 5-45%open_in_new, providing an excellent ecological service to wetland habitats.
Beavers may also play a role in carbon sequestration, a potentially valuable activity in the era of climate change. Similar to nitrogen, carbon, which is also abundant in agricultural run-off, was found trapped in the sediment in beaver ponds built in South West England.open_in_new Approximately 16 tons of carbon were stored in the pond sediment of one family of beavers, which is equivalent to the average yearly emissions of six British citizens–not a bad ratio for one family of industrious rodents..open_in_new
Here at the Cornell Lab of Ornithology, we have a healthy population of beavers that have created flooding issues in the surrounding Sapsucker Woods. To continue to benefit from the services that these rodents provide, but also protect the trails, fields, and property, the Cornell Lab hired Beaver Solutions LLC. They installed a Flexible Pond Leveler system to keep the beavers from plugging key drainage areas important for minimizing flood risks. This management practice is a win-win because it allows us to maintain our beaver population, but minimize their damage to our property. To learn more about this project, watch this short video on the work that was completed in the summer of 2015.
Beavers can be considered a nuisance. My neighbor is not alone in preferring to keep his timber standing rather than allowing beavers to build elaborate dams with his hardwoods. However, it is important to understand and respect the ecological role these animals play in our landscapes, and recognize that, when managing our property, we have choices and must weigh our priorities.
To let the beavers build or not to let the beavers build? That is a question only you can answer. If you decide to encourage or tolerate the construction of a dam on your property, the Habitat Network salutes you. Make sure to document on your map where your wetland habitat is and comment that it is maintained by the important Castor canadensis, a North American keystone species.