Reader Submitted

Bedford Land Trust column: Beavers are Ecosystem Engineers

Friday, May 23, 2014


Special to the Journal

Have you ever spotted a dome-shaped lodge in the middle of a flat pond or along the edge of a flooded river or stream and wondered what type of animal might be living there? Have you ever seen a stump sharpened to a point with wood chips around the base and wondered what happened to the rest of the tree?

There is a good chance you may have been observing evidence of beaver activity.

Beaver are the largest rodents that live in North America, and adults can weigh from 30 to 100 pounds. They have large webbed hind feet for swimming, and broad, flat, tails to steer and propel them through the water.

The teeth of beaver grow continuously throughout their life, and they wear them down chewing on wood. Beavers eat leaves, bark, twigs, sprouts and aquatic plants. They prefer to eat small diameter stems, and their favorite woody plants include alder, aspen, birch, maple and willow. Beaver store tree and shrub branches next to their lodge underwater for winter food.

Beavers live in colonies. These colonies are families that typically include a monogamous adult pair, their young from the current year, called kits, and their young from the previous year, called yearlings.

When beaver are 2 years old, they leave the colony and travel to a new territory to create a new colony. The territory of a beaver colony typically is around one-half a mile along a waterway, and scent mounds are used to mark the boundary of their territory.

Beavers are a keystone species. Keystone species are essential to sculpt a habitat that is needed for other species’ survival.

A special type of keystone species, an ecosystem engineer, physically modifies its habitats. Examples of ecosystem engineers include gophers, ants, woodpeckers, corals and beavers.

Beavers modify rivers and streams by building dams, which cause more wetland habitat to be formed. The flooding from the beavers’ dams kills woody vegetation growing around the stream.

Beavers also influence the succession of the forest habitat around their habitat due to food preferences. The wetlands created or expanded by the activities of the beavers provide a home for a wide variety of plants and animals, and there is evidence that beavers’ modifications of their habitat leads to a richer habitat with increased biodiversity.

Species of amphibian, fish and birds can benefit from beavers’ ecosystem engineering. Also, the dams built by the beavers trap sediments behind the dam. These sediments are full of nutrients, and these areas often form meadows when they are abandoned by the beavers.

Beavers have an immense influence on the places where they live, even long after they are gone.

Did you know there are colonies of beavers on both the Van Loan Preserve and Pulpit Rock Conservation Area properties? Visit the Bedford Land Trust website at for maps of these two properties, and during your visit, look to see if you can spot any evidence of beaver activity and habitat modifications.

The photos in this article give you an idea of signs indicating that you might have discovered the territory of a beaver.

Rebecca Martin is a Bedford Land Trust trustee.

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