The Benefits of Beavers

This is an article from a recent newsletter from the Anoka Conservation District (ACD), in the Twin Cities area in Minnesota.  Thanks to the ACD for their permission to share this article.

Beavers Connecting Rivers to Floodplain Wetlands

 By Breanna Keith, Water Resources Technician, Anoka Conservation District
During a recent site visit to explore wetland restoration opportunities, ACD staff came across a fantastic example of beaver's “engineering” skills in action! A series of three beaver dams, located near the outfall of a Rum River tributary, were effectively slowing and spreading the stream’s flow into the surrounding floodplain wetlands. Healthy connections between streams and their floodplains provide numerous water quality and habitat benefits, and in this case those benefits also extend to the Rum River immediately downstream.

Many streams, in modified landscapes, take on excess water from artificial drainage features like ditches and storm pipes. Over time and especially during extreme precipitation events, these higher volumes of water often increase erosion within the stream, which can lead to the straightening and downward-cutting (“downcutting”) of the stream channel and, as a result, the disconnection of the stream from its floodplain (see the figures below, produced by American Rivers).

Floodplain reconnection efforts are an increasing priority amongst many conservation organizations, but they can be costly and complicated – particularly if development has occurred within the floodplain. However, in areas where streams have room to spill into their floodplains, allowing and even promoting beaver activity can be a very cost effective way to help restore riparian corridor.  

Parks Canada's website has a wonderful piece about the benefits of beavers HERE.  They list five big benefits that beavers impart with their engineering and hydrologic modification.  

1. They create wetland habitat for other species
   Beavers create wetlands by constructing dams and creating ponds. This in turn creates habitat for other species including fish, mammals, waterfowl, songbirds, amphibians, and insects. In 2010, wetlands made up approximately 24% (720 square kilometres) of the park area. Research in RMNP detected as many as 28 dams/km along one watercourse, and by some estimates, beaver are responsible for the existence of 50% of the wetlands in the park. Our 2016 aerial beaver survey estimated beaver cache abundance in RMNP at 2649 total caches in 2016 (an increase from 1684 in 2013). The experts suggest that there are usually on average 5-6 beavers per food cache.
2. They increase biodiversity
   The influence of beavers and their activity is far reaching. In some areas of RMNP, as much as 50% of the area is either wetland, flooded, or subject to beaver foraging. Beaver activity can increase plant diversity by as much as 33%. As trees are removed and land is flooded, other plant species emerge in its place. These plants provide food and cover for new species. Riparian habitats (wetland areas near water) expand as wetlands are formed, and plants spread into the newly available habitat. This effect does not stop at plants, there is an increase in the diversity of all species including fish, invertebrates, and wildlife.
3. They improve water quality
   Beaver dams and pools reduce soil erosion and retain sediment, which absorb and filter pollutants such as heavy metals, pesticides, and fertilizers. This improves the quality of water downstream used by humans and other species.
4. They store water during droughts
   Riding Mountain National Park is on the high ground at the headwaters of 15 watersheds and has often been described as a large sponge, holding a significant amount of water and slowly releasing it downstream. The often maligned beaver is major contributor to keeping the sponge wet. Beaver can help lessen the effects of drought because they cause water to be stored on the surface and absorbed into the sub-surface of the land due to the impoundment of water by their dams. This can increase stream flow during drought periods and make ecosystems less vulnerable during dry periods.
5. They minimize flood risk and mitigate flooding peaks
   Ironically, beavers help minimize flood risk the same way they minimize the effects of drought. As we mentioned, RMNP is like a large sponge, holding a lot of water and slowly releasing it. Beaver dams help minimize flood risk by slowing the flow of water, which can delay and reduce flood peaks further downstream. We are also working with local landowners and neighbouring Conservation Districts to determine through research,  if there are risks with beaver dams breaking and causing flooding and what might be done to identify and mitigate these risks for our neighbours.