Beaver ecology -- what we know and don't know
As beavers make their presence known more and more, the public and the private sectors will both have to make difficult decisions. It would be nice if we knew the best way to handle these various issues, but there is much we don't know. As scientists, there is very little research we can look to for answers about how to balance the needs of various wildlife species with the needs of landowners.
Beavers and salmon
Salmon are a big deal in the Northwest. Several West Coast salmon and steelhead populations have been listed under the Endangered Species Act. Lots of agencies and private groups work hard towards the goal of salmon recovery. So when a person sees a beaver dam on a salmon stream, often the first response is: "This dam cannot be good for salmon," and the inclination is to remove the dam or the beaver. But salmon and beavers evolved together and both lived and did a fine and successful job at reproduction long before humans came along. It is true that we have altered natural conditions substantially over the past 150 years and this new landscape that salmon and beavers find themselves in present new challenges. But when it comes to salmon swimming upstream past a beaver dam, our first assumption is the salmon will find a way around one way or another. Only if this assumption is proven wrong do we consider possible intervention.
Beavers historically occupied much more area than they do currently. Their ponds create habitat for a wide array of wildlife and plant species. For this reason, some people call beavers a "keystone" species because of how they affect so many other populations. Without beavers to create ponds and wetlands, a great deal of aquatic habitat is lost for many other species as well. Prior to European settlement, beavers could choose any area they wished to live in, but the amount of lands available for beaver occupation is much reduced now compared to pre-European settlement. Our landscape is quite different than it was historically...there is a lot less beaver habitat. There is also a lot less good spawning habitat for fish, and there are a lot more people with varied economic and other interests in the lands around them.
The following article gives a broad overview of the impacts of humans on beavers, beavers on the land, and the loss of beavers in natural systems. The Benefits of Beavers by the National Parks Conservation Association is a great article for information about historical beaver populations and their ecology. But there is so much we do not know. Here are just a few of the questions we do not know the answers to:
- Do beavers now use lands that they might not have prior to European settlement? Do beavers now eat vegetation they might not have previously? Are they constructing dams from materials they did not use historically? And if so, what might the implications be?
- Assuming the presence of beaver ponds benefit many species, and assuming that eventually a beaver pond is exhausted of its usefulness by the beaver and abandoned (maybe after decades), what species might benefit from the release of all those nutrients when the dam eventually breaks? What species might decline as a result? How temporary or long-lasting might the effects of such a dramatic change be?