The relationship between poplars and beavers in the Kootenay ecosystem – Castlegar News


Beavers are not only our national animal, North America’s largest rodent and skilled builders, they are a key species. A key species is a living being that fulfills an essential role in its ecosystem that no other species can.

Our friendly beavers are ecosystem engineers and one of the only mammals capable of changing a habitat. The trees that beavers fall to build their dams and lodges are also a source of food for them. Unfortunately, this practice has had a negative impact on the populations of young poplars in our river systems (riparian).

The question is: are beavers harming the diversity of our region by selectively cutting down the trees they prefer?

The importance of poplars

Beavers aren’t the only animals that depend on poplars for their homes, local bird species such as owls and woodpeckers use tree hollows as nesting sites. Poplar trees in riparian areas create shade that keeps the water cool and provides healthy habitat for fish. Riparian vegetation keeps the banks stable, thus keeping the water clean.

As deciduous poplars shed their leaves, organic matter becomes a vital part of the food chain supporting small invertebrates and microorganisms which in turn are consumed by larger creatures. Poplar ecosystems are also valuable to humans, as many like to use these areas for recreational activities. Since beavers and poplars each play an essential role in our environment, it is important to find a balance between the management of the two species.

Cotton poplars are the largest species of poplars in North America. They grow quickly and can reach heights of 30 to 50 meters when mature. The average lifespan of a poplar is 80 to 120 years, although some have even exceeded 400 years.

We often see poplars growing by riversides as they favor floodplains and moist soils, requiring moisture and many nutrients to grow successfully. Mature poplars are scarce in the region due to dam regulation systems, streams are redirected, and streams have been channeled and dammed. Without these changes, much of our shoreline would be thriving poplar ecosystems. The remaining trees are valuable and therefore need to be protected.

Handle the problem

Prior to 2021, Selkirk College staff used to have a beaver lodge on the backwater near the Castlegar campus. Noticeable changes were discovered in the spring when it was observed that the majority of the young poplar population was depleted.

Students in the Recreation, Fish and Wildlife program at Selkirk College responded to this problem by wrapping selected trees with wire cages near the confluence of the Columbia and Kootenay rivers. This protects some young trees while leaving others untouched for the beavers. Wrapping trees is a popular way to deter beavers from overharvesting. As this issue evolves, local staff, students and professionals will continue to monitor the results to ensure that poplars and beavers thrive to promote a diverse and healthy ecosystem.

Lillie Strong and Celeste McEwan are second year recreation, fishing and wildlife students at Selkirk College.

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