Wednesday, September 10, 2008
A beaver pond that has evolved into an alder swamp on its way to becoming part of the neighboring forest.
This photo was taken merely by turning around in the spot where the third one up from this was taken showing the the current, 2008, beaver dam and water course. This photo shows a bog, or swamp, that is gradually becoming a field where there had been a beaver pond and open water 25 years ago. It's now home to a rich and diverse plant community that includes alder, which is nitrogen fixing and improves soils where it grows, spirea (meadow sweet), sedge, viburnum, several species of grass, and some small red (or swamp) maple seedlings. It's a good bet that it is gradually becoming part of the existing forest that surrounds it. So this is the natural climax of beaver dams and ponds. Once the beaver impound water and form a pond it begins the long process of becoming a swamp, or field, or forest. A few conclusions that could be drawn from this brief (and incomplete) exploration are: 1.) beaver dams and ponds, though they may exist for several decades are at best ephmeral phenomenon. They're transitory in nature and mark a transition in the evolution or development of the landscape. They help heal scars left by perturbations like forest fires, poor logging practices, and hurricanes. 2.) Looking a bit below the surface of beaver activity we might conclude that the real benefit to the local ecology is a marked improvement in the nutrient content of the local soils. We'll look at that feature a little later. This is kind of the end of the beaver dam story for now. I'd like to return to this theme next spring, though, and include an article in the blog that goes into more depth about the plants that grow around the beaver ponds including some that are rare.