Beavers were almost eliminated from three continents before people realized the true value of nature's engineers. Because beavers build their stick-and-mud dams in streams flowing through shallow valleys, the flooded area becomes freshwater wetlands. Such wetlands are rated by ecologists and economists as the landâ€™s most beneficial ecosystem.* Because beaver dams create mini-reservoirs that keep water on the land longer, they can alleviate both droughts and regional floods.
Beavers build leaky dams that slow the flow of streams, creating quiet water nurseries for fish and many other organisms. About half of the rare species require wetlands during their life cycles, according to US EPA. Slowing the flow also allows time for wetland microorganisms to detoxify pollutants, such as pesticides. Beaver dams accentuate the normal filtering function of wetlands by collecting silt, and there can be 90%Â lessÂ sediment in the water downstream. Such water cleansing results in healthier downstream habitats, and less costly treatment is needed at plantsÂ to produce drinking water for people.
But most benefits of beaver wetlands are hidden, and European settlement of North America was driven by the search for â€śbrown goldâ€ť, beaver pelts.Â Few people realized how much had been lost when the fur trade extirpated beavers from most of the United States and southern Canada by 1900. Beaver populations had been wiped out in the majority of Asian and European countries much earlier. During the twentieth-century, American and European wildlife advocates began to protect remnant populations and restore beavers.
Of the estimated two hundred to sixty million beavers (Castor canadensis) that lived in North America prior to the arrival of European settlers, only about ten per cent of that number survives today. When beavers were wiped out, most of the landâ€™s wetlands were lost too. At least sixty million beavers (Castor fiber) once lived throughout Europe and Asia, but by 1900, only about 1,200 Eurasian beavers survived. Thanks to restoration efforts, there are now over 600,000 beavers in Europe - one percent at best of the original number, but a great comeback from the remnant populations of 1900. Asian populations of Castor fiber still urgently need protection.
Hydrologists blame the uncontrolled trapping of beavers during the 1700s and 1800s, followed by intensive drainage for agriculture, for most of North Americaâ€™s major environmental problems today. These include water pollution, massive erosion, and rising species extinction along with escalating damage from major floods and droughts. Similar problems occured in Europe and Asia when beaversÂ were wiped out. Learning to coexist with beavers, and the wetlands they restore is a relatively simple way to improve our environment.
Having many beaver dams in the headwaters of rivers moderates the flow and keeps water on the land longer, which alleviates both droughts and major floods. Such extreme weather events are becoming more frequent due to climate change. It appears a paradox that dams, which may cause local flooding upstream, decrease major floods downstream, yet there's no doubt that this occurs. One hydrologist compared beaver dams to a series of speed bumps.
Plus, marshy beaver wetlands already are, or will become, peatlands, as dead vegetation accumulates underwater. Peatlands are the best ecosystem for carbon sequestration, but draining them allows the peat to oxidize and release carbon dioxide, the major greenhouse gas.
Beaver damming is the natural way to restore freshwater wetlands, the land's most valuable ecosystem. It costs about $10,000 to $100,000 per acre to build manmade wetlands, yet beavers make and maintain them for free. Natureâ€™s engineers are our allies in combating climate change and other major environmental problems.
*Costanza, R., dâ€™Arge, R., de Groot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K., Naeem, S., Oâ€™Neill, R., Paruelo, J., Raskin, R., Sutton, P., & van den Belt, M. (1997) The value of the worldâ€™s ecosystem services and natural capital., Nature (5/15/97), 387: 253-260.