Living with Beavers

While they are sometimes thought of as a pest or nuisance, beaver populations have had a major part in shaping and maintaining productive river ecosystems throughout the North American landscape, including our Oldman River Valley.

Beavers are the largest rodent in North America and the second largest rodent in the world next to the capybara of South America. They are a vegetarian species whose entire diet consists of leaves, young plant shoots and the inner bark of deciduous tree and shrub species. Their diet is complex and changes through the seasons. Woody plants make up 32% of a beaver's diet in spring, 16% in summer, 60% in fall and 86% in winter.

Public perception of forest damage reflects this seasonal cycle and is why so many public concerns regarding lost trees are fielded in the fall months, when beaver families are preparing their winter food cache. 

• Beaver at Elizabeth Hall Wetlands Photo credit: Doug Petriw

Ecosystem Engineers

Beaver activity creates habitat for countless other wildlife species to feed, nest or rest, including birds, insects, amphibians, reptiles, fish and other mammals. The presence of their lodges or dams maintain certain species of riparian plants that rely on moist or sodden soil. In other words, beaver don't just inhabit an area, they modify and regulate it for the benefit of many other organisms.

In Lethbridge there are beaver that build bank lodges and those that build dams in the small tributaries and oxbows. Both benefit the health of the river valley in countless ways.

Bank lodges

• The bank lodge creates deeper water and pools around it which cool the water and make excellent fish habitat.
  
• Slow water movement by providing obstacles to absorb the stream or rivers speed, therefore reducing erosion.
  
• Old dens are used by waterfowl, garter snakes, mink and muskrats.
  
• Photo of bank lodge along the Oldman River
  

Oxbow/tributary dam builders

• Dams capture and store water: As a result, they reduce the impacts of both flood and drought in Lethbridge.
  
• Slowing down water: Beaver dams and lodges act as speed bumps to slow running water. This reduced stream power is easier on infrastructure built along the river.
  
• Water filtration: slower moving water means sediments and nutrients have more time to sink out of the water or be absorbed by surrounding plant life.
  

Benefits to the riparian forest

Contrary to how it sometimes looks, beaver activity typically has a positive impact on river valley (riparian) forests. When beavers take down cottonwood trees, the remaining stump and root system regenerates by sending up multiple new shoots to form new trees. In areas where the bigger trees do not all come back, it creates space for understory species to flourish such as sandbar willow, and wild licorice. These native plants have extraordinary root systems which work to reinforce soils and prevent erosion of the stream and river banks. 

Challenges

Felling trees, damming rivers and streams and creating mud lodges on the banks can impact local infrastructure. Living with beavers can be tricky but is worth it for the benefits they provide to local ecosystems. Some methods the City of Lethbridge is developing and utilizing are:

Tree wrapping

Using heavy wire mesh to deter beaver from taking down trees in areas identified as priorities or those with large population of beaver. While other cities may wrap up to 80% of trees in impacted areas, the City of Lethbridge is taking a more situational approach.

Cottonwood trees are being wrapped in areas where a lot of beaver activity has been observed. Trees of differing sizes will be wrapped to ensure succession of the river valley forest.

Monitoring

Information regarding beaver activity, is being tracked by parks operations. This includes areas where trees that have been wrapped and service requests from the public regarding beaver activity. This data will be used to create a monitoring schedule.

Parks Master Planning

Comprehensive information on how to best manage beaver populations within the city will be explored in an upcoming Beaver Management Strategy and included in the update to the Parks Master Plan. More information will be added once these studies are complete.