Despite their relatively small size, beaver have a tremendous impact on their environment. Ecologists refer to them as a keynote species for this reason. In their article, Browse selection by beaver: effects on riparian forest composition, Carol A. Johnston and Robert J. Naiman write that beaver affect the structure and the dynamics of an ecosystem beyond their immediate needs for survival. While animals like moose and snowshoe hares can influence forest succession and the nutrient cycle, only the beaver has the ability to cut down mature trees and cause dramatic changes in the overstory.
Johnston and Naiman report that a single beaver may cut down about 2,866 pounds of woody material per 2.5 acres of territory in a year. By way of comparison, a moose browses only about 200 pounds per 2.5 acres. A second comparison is even more revealing: a colony of six beavers harvests twice as much biomass per area as a herd of ungulates on the Serengeti plain; over 4.8 tons. A beaver doesn’t need all that it harvests for food. In captivity beaver eat only about 660 pounds of food per year.
Over the short term, beaver can cause a shift in the composition of the forest around their pond. Through their influence, beaver activity can change an aspen-dominated forest area to show an increase in balsam poplars and birches, which beaver prefer less. In the long run, beaver harvesting can change a stand of deciduous trees into a tangle of shrubs, alder, and beaked hazel giving slower growing conifers, which beaver find unappetizing, an advantage. Thus, beaver have a diversifying effect on the forest. When you hike by a beaver pond, notice the types of trees beaver have gnawed on, and the ones they have left alone.
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