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Beavers as Ecosystem Engineers

Beaver dam at Plum Brook Pond

Along with humans, beavers are one of the few species that can alter their environment on a large scale. In recent years, we’ve finally begun appreciating the benefits that these “ecosystem engineers” provide—but we all know that sometimes beavers’ plans for the landscape conflict with our own.

Case in point, the Pond Loop Trail at Kestrel’s headquarters on the Sweet Alice Conservation Area. In March 2023, a small culvert crossing the trail at the mouth of the pond was replaced, allowing more water to flow through a narrow channel to the pond.

Ever sensitive to changes in the water around them, the resident beavers soon got to work constructing a dam that eventually spanned 20 feet through the existing marshy woods on the pond’s shore. (See the header photo at the top of this post.) Their solid construction quickly flooded a significant portion of the trail and created a new mini-pond in the woods. The beavers removed a number of mid-size and small trees as well, leaving behind the tell-tale “pencil points” of gnawed tree trunks.

Left, the flooded Pond Loop Trail at the mouth of Plum Brook Pond as a result of a large beaver dam built in the spring 2023. In the fall, our team built a new accessible boardwalk, right, to reopen the trail. Come check it out and see the impressive beaver architecture!

The largest member of the rodent family (averaging 50 pounds), beavers are adapted to an aquatic environment with broad tails, webbed hind feet, and un-webbed front feet that allow them to dig and carry materials like mud and grass.

Beavers thrived in New England before colonization by European settlers, but by 1800 trapping decimated their populations. Beavers were reintroduced to Massachusetts in 1932 and are now found in most of the Commonwealth.

Beavers build dams to create deeper ponds that won’t freeze at the bottom so that they can access the underwater entrance to their lodges. They feed on the twigs, leaves, and bark of woody plants and aquatic plants. In the fall, they collect branches from their preferred food trees (aspen, willow, birch, alder) anchoring them at the bottom of the pond near the entrance to their lodge for winter feeding.

The Benefits Are Significant
Beaver activity has a surprising range of benefits for many species, including humans. The ponds they create provide new habitat for amphibians, turtles, fish, muskrats, herons, wood ducks, and otters—all of which have been spotted at Plum Brook Pond. Their engineering also supports wetland and aquatic plant species, with one study finding 33% more variety of plants in wetlands created by beavers. Because beavers remove some trees, they also help create new early-successional forest habitat—patches of young trees and shrubs—that are increasingly rare and critical for many bird species.

Beaver with twig in water
Beavers are important contributors to wetland habitat for other species, and their work can also benefit human infrastructure.

Humans benefit from beaver wetlands because they improve water quality by filtering and trapping sediment, chemicals, and excess nutrients. During periods of heavy rains, beaver infrastructure helps to store and slowly release flood waters, reducing downstream flooding. These wetlands can also recharge and maintain groundwater and support streamflow even during droughts. And, in an era of climate crisis, beaver dams and the wetlands they create are an important storage area for climate-warming carbon emissions.

For all of these reasons, we value our beaver neighbors at Plum Brook Pond. This fall our stewardship staff and volunteers constructed a new 165-foot boardwalk above the new extended pond so that human visitors can once again enjoy the full loop trail—and the beavers can continue their work as ecosystem engineers.

 

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