Beaver dam at Beaver Flat, Alberta, Canada. © J. Ashley Nixon
Castor has been building dams for a long time. No, this is not a story about the work of a construction company! It’s about the beaver, whose scientific name is Castor canadensis for the North American variety and Castor fiber for her European cousin. This semi-aquatic rodent has been engaged in water storage and flood control projects for around ten million years, ever since the species evolved from its ground-burrowing predecessors.
Archaeologists found early evidence of this large mammal’s Navvie work in Nunavut, Canada. Excavations of peat bogs on Ellesmere Island revealed fossilized interwoven matrices of wooden branches. The clearly defined tooth marks on some of the sticks connected the find to an ancient beaver species called Dipoides.
Big dam projects
The largest known example of an active beaver dam is also located in Canada, in Wood Buffalo National Park. Established in 1922, it is the country’s largest national park, one of the largest in the world (over 44km2), and recognized by UNESCO (United Nations Educational, Scientific and Cultural Organization) as a World Heritage site in 1983. Almost 800m long, the horseshoe-shaped construction retains water about one metre deep that drains off the Birch Mountains in the southern-most part of the park in Alberta. Scientists discovered the dam in 2009 after examining satellite imagery for evidence of melting permafrost and landscape changes that result from climate change. How long it has been there hasn’t been established, but map records from elsewhere have revealed that dams can be used and re-used for decades and more across multiple generations of beaver colonies.
Constructed environmental changes
Beaver dams stretch, on average, for about 32m across streams to store and slow down flowing water. Lotic (riverine) ecosystems turn into lentic (lacustrine) ecosystems. This benefits beavers as they can build a more stable lodge with a secure underwater entrance to raise their kits and store food over winter. Unlike otters, beavers do not eat fish. They live off trees (aspen and willow are their favourites in Canada), thanks to their gut microbial flora that help them digest cellulose. This constructed environmental change has other ecological benefits such as increased biodiversity and socio-economic benefits for flood mitigation and climate change adaptation.
Many communities and other places have “beaver” in their name (50 or so in Alberta and over 700 across Canada); strong recognition of this animal’s substantial cultural, economic and environmental values to Canadian society. An excellent location to inspect the masterful building works of these riparian renovators is along the Elbow River, at Beaver Flat (Kananaskis Country), Alberta.
You can view a lodge (probably unused) close to the trail. There is an array of multiple ponds, each with its dam built from matrices of chewed timbers, branches, reeds, rushes, rocks and mud. Look closely, and you will find that these structures are wet dams, leaky enough to let water trickle through and be more resilient to the higher hydraulic pressure.