Beaver dam
Beaver dams create ponds that protect beavers and reshape ecosystems.
A beaver dam, also known as a beaver impoundment, is a structure built by beavers to create a pond that protects against predators and holds food during winter. These dams modify the natural environment in ways that cause the overall ecosystem to build upon the change, making beavers a keystone species and ecosystem engineers. Beavers build prolifically at night, carrying mud with their forepaws and timber between their teeth.
- minimum_water_depth
- 0.6 to 0.9 metres (2 ft 0 in to 2 ft 11 in)
- largest_known_dam_location
- Wood Buffalo National Park, Alberta, Canada
- second_largest_dam_location
- Three Forks, Montana
- time_to_rebuild_destroyed_dam
- approximately 8 hours
Lore & Background
Beavers start construction by diverting the stream to lessen water flow pressure. Branches and logs are driven into the mud of the stream bed to form a base, then sticks, bark, rocks, mud, grass, leaves, and other materials are used to build the superstructure. Beavers can transport their own weight in material, dragging logs along mudslides and floating them through canals. Once the dam has flooded enough area to form a protective moat for the lodge, beavers begin construction of the lodge. Trees approaching a diameter of 90 centimetres (2 ft 11 in) may be used, though the average is 10 to 30 centimetres (3.9 in to 11.8 in). Log length depends on tree diameter and beaver size. A beaver takes about 20 minutes to cut down a 15-centimetre (5.9 in) wide aspen by gnawing a groove around the trunk in an hourglass shape. Beavers are most active in maintaining dams in fall and spring in colder climates, while in ice-free climates they may maintain dams year-round with reduced activity in summer. A study in Poland found beavers could rebuild a destroyed dam and restore water levels in approximately 8 hours. Some people consider dam building to be tool use behavior.
Reader's Guide
Beaver dams have significant ecological effects, helping to restore damaged wetlands. Benefits include flood control downstream, biodiversity by providing habitat for different species, and water cleansing through breakdown of toxins and retention of silt. Beaver dams reduce erosion and decrease turbidity that can limit aquatic life. Almost half of endangered and threatened species in North America rely upon wetlands. A 2012 systematic review on impacts of beaver dams on fishes and fish habitat found benefits cited more frequently than costs. Benefits included increased habitat heterogeneity, rearing and overwintering habitat, flow refuge, and invertebrate production. Negative impacts included impeded fish movement, siltation of spawning habitat, and low oxygen levels in ponds. Beaver dams smooth out water flow by increasing the area wetted by the stream, allowing more water to seep into the ground. Rivers with beaver dams in their headwaters have lower high water and higher low water levels. Beaver ponds can remove nutrients like phosphates and nitrates from stream flow, and bacterial populations in the cellulose-rich bottom can metabolize herbicides and pesticides. Studies have shown beaver dams contribute to denitrification, converting nitrogen compounds back into nitrogen gas. Beaver dams and ponds can provide nurseries for salmon and trout.
Did You Know?
- A beaver can cut down a 15-centimetre (5.9 in) wide aspen in about 20 minutes by gnawing a groove around the trunk in an hourglass shape.
- Beaver dams can help remove nutrients and pesticides from streams through bacterial activity in the cellulose-rich bottom.
- A study in Poland found that beavers could rebuild a destroyed dam and restore water levels in approximately 8 hours.
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