Nature’s engineers: How beavers alter ecology

AMENIA — Clear, sunny skies welcomed a group to the paved trails at the Cary Institute Saturday, Oct. 19, for an educational hike and lecture on beaver ecology led by wildlife biologist Mike Fargione.

The hike started at a small parking area on the north edge of the Cary campus, where Fargione presented a collection of beaver pelts to the group. He explained that beavers were almost totally eradicated from New England after fur traders hunted them to near-extinction in the 1600s. Until the 20th century, he said, beavers were absent from the New England landscape, a region that at one point hosted hundreds of millions of the semi-aquatic, dam-building rodents.

Now, as a result of careful mangement and reintroduction, Fargione said the beaver population has grown to about 2 million.
This brings challenges, but it also allows the landscape to return to the transitive nature it had prior to European settlement 400 years ago. Fargione said the modern, agricultural landscape that exists in Dutchess County is the result of human intervention and the removal of beavers. Before beavers were nearly eradicated, the rodents carefully redirected water, manipulating wetlands and low-lying forests and fields to create cyclical habitats. Human farmers responded by channelizing streams, drying swamps and driving out beavers to create more consistently dry farmlands.

Now, as beavers make their return, their incessant need to dam up streams and create beaver ponds is in direct conflict with human infrastructure.

Roads on Cary’s campus have started to show serious signs of damage from the beaver’s hydro-engineering. One path has been completely closed because erosion has created a sinkhole in the middle of the pavement. One group of beavers created a pond that was flooding the nearby New York State Police Troop K headquarters on Route 82. Fargione took the group by a low-lying brush pit to demonstrate the huge changes beavers can cause.

Before the beavers came in, the low-lying area was a dense forest full of alders, red maples and aspen trees, beavers’ preferred foods. Two streams came down the mountains from the south, feeding water into the low-lying area, and heavier-than-usual storms started to flood the patch. Noticing the new flooding and the tasty wood, beavers got to work damming up the edges of the patch, creating a 20 acre area of standing water five feet deep at its deepest point. In a matter of weeks the slightly-wet forest was transformed into a murky swamp, bringing different animals and vegetation. The day of the hike the pond was dry, but Fargione said the water didn’t just evaporate.

“A lot of that water goes back into the water table, recharging our aquifer,” Fargione said.

The habitats created by beavers are essential to local wildlife. “There’s lots of wildlife here just because beavers changed the ecology,” Fargione said.