If one lives in the north woods, beavers are a fact of life – always interesting, but sometimes maddening. What is interesting is the products of their industry, e.g., dams and houses (lodges); what can be maddening is cut-down trees, sometimes prized trees in one’s yard. Regardless of what one may think of them, nobody can deny that beavers are hard workers.
A recent walk in the forest near our cabin reminded me how busy a beaver can be. When I got to the edge of a large wetland near a small stream, I found an area about 200 feet long where most of the trees had recently been cut down (Fig. 1). Beavers love trees with soft wood, such as poplars, alders or willows, but they are perfectly content to gnaw on ash trees or some other hardwoods, as well. With their massive incisor teeth, they begin about a foot to 18 inches above the ground and then work their way around the entire trunk until at first all of the bark is removed. Then they keep chipping away at the wood in a perfectly symmetrical manner until the remaining heartwood in the trunk is too thin to support the weight of the tree, which then collapses – sometimes still connected to the stump (Fig. 1), but at other times separated (Fig. 2).
Once a tree is down, what does a beaver do with it? Lots of things. It may continue eating some of the bark of the trunk (Fig. 3), but more likely it will turn its attention to the branches, which are easier to handle and are more tasty (Fig. 4). What is impressive is how systematically beavers go about eating their woody meal. Very early one summer morning, I was on our dock when a young beaver swam directly beneath me with a 2-3-foot alder branch in its mouth. It then sat in the shallow water and picked up the stick with its hands, much like we would hold a cob of corn. Starting at one end, it quickly gnawed off all the bark from one end to the other. When it got to the end of the stick, it then slightly rotated the stick and proceeded to gnaw its way back to the first end. The beaver continued to gnaw and rotate until no bark remained and all that was left was a classic denuded beaver stick at the edge of the lake. This entire process took no longer than 2-3 minutes.
Beavers usually take smaller branches (up to 3″ in diameter) into the water, where they are used for building their lodges or dams. In order to get the branches to their destinations, the industrious beavers often construct channels through the intervening wetlands (Fig. 5). In the fall, beavers stockpile branches in deeper water off the entrances to their lodges. Then during the winter, they grab individual sticks and eat the bark for their winter snacks.
One of the ecological consequences of major beaver activity is opening small areas of former dense forest land to sunlight. In any dense woods, small plants and trees are spread out over the ground. Many of these will be eaten by deer or rabbits. Others remain stunted because they don’t get enough sunlight to thrive. When a larger tree is downed, either by beavers or a storm, the plants beneath the former canopy of that tree are now exposed to greater amounts of sunlight, leading to a competition among the plants to see which will grow the fastest so that the winners will shoot up and themselves become parts of the new canopy.
Click on image to enlarge
