Why You Should Give a Dam About Beavers
Everybody knows about beaver dams, but I don't think everybody realizes how valuable they are from ecological and hydrological perspectives. This post will briefly highlight three big reasons why beaver dams are an integral component of a healthy North American ecosystem.
Downstream Flow Moderation
When you look at a beaver dam, you might not realize that its effects go well beyond the dam itself. Any river or stream is likely to experience periods of flooding and drought. A beaver dam has the beneficial effect of moderating those extremes for the downstream area. An interesting exercise to try during a drought period is to try to find both the inlet and outlet of the dam. You will likely see very visible differences in ecology. The effect wears off as distance from the dam increases, but even a small area offers refuge for wildlife to occupy until rain brings back normal flow. The dammed water itself can also offer refuge for low flow tolerant species.
Cities and towns often try to emulate this process using artificial dams. Unfortunately natural dams aren't quite reliable enough when a failure could have lethal consequences for downstream communities.
Longer Residence Time on Land
It's almost always preferable for water to make a gradual descent from its origins on land to the ocean. This is because rivers and streams are like water treatment plants. Dirt and debris settles in the riverbed along with any associated pollutants, while plants and algae soak up excess nutrients. A gradual descent means cleaner surface water is available in greater quantities for residents of the watershed, and in some cases there is also improved groundwater recharge.
Slower flow is good for landlubbers and sea life alike, since once that water enters the ocean it will be much cleaner. An example of what happens when water flows too quickly into the ocean is the eutrophic Gulf of Mexico. Polluted water from many agriculturally rich states plunges through the channelized rivers and streams, carrying with it nutrient rich runoff which fuels suffocating algae blooms. The end result is the complete collapse of vibrant marine ecosystems into 'dead zones'.
Since beaver dams dramatically increase the residence time of water in rivers and streams, they could be a valuable tool for restoring the health of our freshwater and saltwater environments.
The last, and most obvious benefit, is that beaver dams create high diversity and high value ecosystems. It's often erroneously believed that dams are harmful for fisheries. While the shallow, stagnant pools in front of the dam may not be ideal fish habitat, the downstream effects mentioned earlier more than make up for that. In addition, beaver wetlands are breeding havens for many insect populations, and a boost in regional insect populations means more food for fish!
The wetland also attracts all sorts of birds, mammals, and amphibians. This is partly due to the unique variety of terrestrial, emergent, and aquatic plants that thrive along the water's edge and in the calm, shallow pools.
Wetland ecosystems are among the most threatened environments, mainly thanks to agricultural expansion. Land has been drained, watercourses have been channelized, and beavers dams continue to be destroyed throughout North America. These actions have a negative environmental impact and real social costs, such as reduced stormwater storage. Thankfully the North American Beaver is not threatened, but its current abundance is still very low historically speaking. By some estimates, only around 15% of the historic population remains. Hopefully with our improved understanding of and appreciation for environmental science, we will see beaver populations recover further still.