Earth’s most prestigious engineer, the beaver (Castor canadensis), as no other mammal alters the shape of the landscape and is as opportunistic, excluding humans. Beavers truly define the term “keystone species,” having once covered a tenth of the continental United States with beaver-built wetlands. Beaver ponds provide homes for hundreds of thousands of species.
Beaver legends have been a part of human culture from the time of pictographs. Flathead Indians believed that beavers were disgraced Indians, changed from their human form by the Great Spirit. Beavers worked laboriously cutting trees and building dams and lodges as atonement for their misdeeds.
Castor demonstrated the effectiveness of its life history strategy by sheer numbers. It has been estimated that 200 million beavers once inhabited the continental United States alone. Beavers cloaked the landscape from the Arctic Circle to the Gulf of Mexico, and from the southwest desert to the north woods of Maine, with water and trees the only constants.
A beaver that hears the sound of running water will immediately try to locate the source and to dam it. Beavers make dams to raise the water level of a stream and to maintain this level during dry periods. Beavers will dig canals, plunge holes, underwater aqueducts, and channels throughout their pond and wetland, creating a safe passage from their home to their food.
Beavers are natural farmers, using nature’s system of replenishment to prosper. Their fall and winter food is tree branches (cambium) that is self-stored in the muddy bottom of their ponds for easy access when the ponds ices over in the winter. Their favorite trees include aspens, cottonwoods, and willows that are pioneer species that colonize flooded, burned, and riparian areas where sunlight is plentiful. As beaver dams slow the water, soil and nutrients from upstream drop out of the water column. Soon natural herbs, such as cattails, arrowhead, pondweed, smartweed, milfoil, pond lily, and a variety of sedges and grasses begin to flourish. Beavers feed on this higher energy food source in spring and summer.
Beaver wetlands act as enormous biological filters. When storm runoff from streams and rivers rush into the stillness of the wetland stream velocity diminishes, silt in the water adheres to aquatic vegetation, and larger particles settle to the bottom. Species in the wetland’s underwater world, including bacteria, freshwater fungus, and phytoplankton, use organic and inorganic molecules, including human-developed pollutants, to survive, creating the base of a complex food web. Zooplankton, such as protozoans, rotifers, and tiny crustaceans (Daphnia), graze on the phytoplankton. Backswimmers, striders, water boatmen, diving beetles, water scorpions, coiled mosquito larva, mayfly larva, dragonfly larva, and many other insects eat the grazers and together act as the food source for amphibians, fish, and birds.
On a grander scale, water detained is more likely to percolate down to the groundwater, raising the water table and creating springs and freshets throughout the watershed. With recurring droughts in many areas of the country, beavers could be an easy, cost-free fix to recharging ground water and keeping water on the land and out of the oceans. When trapping eliminated almost all the beaver in North America, we in effect lost 300,000 square miles of wetland and groundwater recharge.
Clean water is a leading concern for all life. In order to promote healthy waterways, it is important to have a general understanding of what once made North America’s water so pristine, beavers. Knowledge of beavers and the wetlands they create can only aid us in our quest to develop in a more ecologically sound manner. Imagine if we worked with a “natural common sense” how much richer all of our lives would be.