(HOST) As wetlands all around us begin to thaw, and life returns to the marsh, commentator Ted Levin observes that the beaver is to northeastern woodlands what the bison once was to the Great Plains – a KEYSTONE species whose presence supports a truly impressive range of biodiversity.
(LEVIN) The activities of a few very species of animals significantly alter landscapes, thus modifying biodiversity of surrounding regions – like reef-building coral. The term ECOLOGICAL ENGINEERS now expresses the effects of those rather unique species.
As you might imagine, beaver are elite ecological engineers.
When beaver reconfigure a stream they create broad pools stitched together by short series of braided channels – channels everywhere flanked by shallow banks that grade into lush, fertile meadows of sedge and rush. Biomass surges. In fact, a beaver pond and its surrounding marshland may be five times more productive than the riffling stream below the dam.
A beaver engineered-wetland is a series of both pools and swifter flowing water, which collectively support both still and rushing-water species. One suite of invertebrates prefers soft mud – another, the riffles. Still another prefers the rotting sticks of the dam and lodge. Decaying trees have their beetles – marshes have their bees and wasps, butterflies and moths. Even the mud is a mosaic of anaerobic and aerobic microorganisms that aid in the decomposition of organic matter and the release of oxygen for plant roots. Dragonfly nymphs prefer pools. Stonefly nymphs prefer riffles. Everything has a place. Everything has a purpose.
My home overlooks a seventy-acre wetland. In the spring of 1998, my first as the steward of Coyote Hollow, beaver actively maintained a series of dams and channels across the valley. The dead trees attracted beetles, which in turn attracted five species of woodpeckers, all of which used the dead trees. Their abandoned cavities were claimed by swallows, chickadees, and nuthatches. Kingbirds and redwings sang from the snags. Hawks hunted the expanded wetland by day; owls by night. A wayfaring bald eagle spent a summer afternoon drifting from one dead tree to another.
American bitterns, marsh wrens, and swamp sparrows nested among the reeds; yellow warblers, common yellow throats, and redwings in the peripheral shrubs.
When the beaver abandoned the wetland seven years ago the water table receded. The biodiversity and abundance of animals and plants drastically decreased.
Last spring, beaver returned, creating a wider, deeper wetland. Within weeks of their return a pair of hooded mergansers nested in a wood duck box. (They eventually hatched five young.) Bitterns returned, and a family of mink moved into the marsh.
One warm late afternoon thousands of dragonflies filled the airspace above the marshland dining on a hatch of midge. Lured by the dragonflies, a migrating kestrel fed on the wing, cutting pirouettes above the marshland.
Vermont’s ecological potential is predicated on rodent engineering. Biologically speaking, without beaver we’d be poverty-stricken — like Africa without elephants — or the Everglades without alligators.
Ted Levin is a writer and photographer and winner of the 2004 Burroughs Medal for Nature Writing.