BUSY VOLUNTEERS: A volunteer at Friends of Princeton Open Space (FOPOS) paints a latex paint and sand mixture on trees to prevent damage from beavers’ sharp teeth, at Pettoranello Gardens. The municipality of Princeton and FOPOS have worked together to find a solution to challenges presented by the beaver population felling trees.

By Wendy Greenberg

A robust area beaver population provides an ecological benefit, but also presents challenges to open spaces, as the beavers’ sharp teeth can fell a variety of trees, sometimes causing flooding in urbanized areas.

While damming streams to create ponds for building away from human activity can result in more ecological growth by providing a healthier riparian buffer and bird habitat, chewing on softwood and hardwood tree species where human activity and infrastructure are present has been problematic, according to Friends of Princeton Open Space (FOPOS), a longtime nonprofit group that supports space for preservation and protecting natural resources. This activity has occurred in Pettoranello Gardens, and more recently in adjoining Mountain Lakes Preserve.

A solution may have been found, balancing the interests of the beavers, the habitat, and humans. That solution — a pond leveler and tree protection — has seemed to deter the beavers, said Cindy Taylor, open space manager for the municipality.

“We’ve had some success,” Taylor said of a pond leveling project. “It seems to deter them [the beavers], but not 100 percent. We’re still testing and experimenting with the paint/sand ratio (as a tree protector) and we’re observing and learning as we go. We’ll continue to observe and take a population count when possible.”

The tree damage seems to have decreased as well. “We saw a lot less tree damage during fall/winter 2022-2023 as compared to fall/winter 2021-2022,” she said. “I do visit in the late afternoons to look for activity, but haven’t seen active individuals recently to get an idea of a population count.”

While beavers nearly disappeared from New Jersey in the early 1900s, their population has increased due to legislative protections and trapping limitations, according to FOPOS.

The municipality became aware of the problem in November 2021, said  Taylor. “Residents reported tree damage in and along the pond in Community Park North.

“Part of the life cycle of beavers is that they’ll choose an area along a stream bank and dam it up, creating channels to move through it to get more wood. Beavers feel safest when they’re in the water, so that’s what they’ll do; dam it up, flood an area, and build a lodge with an underwater entrance to help protect them from predators. Usually they’ll stay in an area as long as they have enough food to eat, but eventually they move on, the dam breaks, and what you’re left with is a meadow, because all the trees in an area have either been felled or die because of flooding.”

In Pettoranello Gardens, the beaver activity was causing flooding in a fairly urbanized area. “When they were damming on the pond, water continued to flow in, go around the spillway, and cause erosion and other issues,” said Taylor. “If this were happening in an area where humans did not have infrastructure it would have been fine. But we’re trying to balance the ecological benefits of preserving their habitat with the presence of the human infrastructure that needs to be maintained.”

FOPOS became involved when the staffs in the municipal departments of Animal Control, Public Health, Recreation, Public Works, Open Space, and Engineering reviewed possible options for managing the situation. Trapping and humanely killing or trapping and relocating the beaver were rejected, said Taylor. Taylor was familiar with pond levelers — devices designed to prevent pond flooding — and identified companies that provide and install them. “It offered the possibility of allowing the beavers to live their lives without causing further flood damage,” she said.

The pond leveler that was installed is designed to prevent beavers from disrupting the flow of water over the spillway at Pettoranello Pond, and will result in the pond controlled at a safe level.

In addition to the flooding, Taylor noted that the other concern that needed to be addressed was the felling of trees along the edge of the pond that anchor the shoreline and help maintain water quality by serving as a barrier against runoff, a concern which had spread to the lake shore in adjoining Mountain Lakes Preserve as well. Taylor said she was most concerned with maintaining trees around the edge of the pond for shade, with an approach that protects the trees rather than removing the beavers.

Anna Corichi, FOPOS’ director of natural resources and stewardship, said that FOPOS volunteers have painted trees with a mixture of latex paint and sand, a recommended technique. Caging the trees with wire fencing is also an option, but takes away from the aesthetic.

“We did start mitigating the trees that surround Pettoranello Pond and Mountain Lake to discourage the beaver from felling trees,” Corichi said in a press release. “The painting started at Pettoranello last spring, and at Mountain Lake when beaver activity was observed last fall. We’ve also caged some larger trees at Mountain Lake that are too labor-intensive to paint.”

“Whether in the riparian zone or not, our interest is in preserving trees and their ability to store carbon, and as much forested habitat with as much connectivity as possible,” Corichi continued. “We’re a nature preserve and our mission is to support wildlife and preserve their habitat, and if not here, where is there a better place for beaver to make a home?”

Corichi said an additional lesson is that “without the support of volunteers willing to pick up a paint brush or a roll of fencing and pitch in, we can never balance the competing issues of protecting the beaver population, habitat, and water quality.”

Taylor said she has received good feedback. “I’ve chatted with many residents who frequently walk Pettoranello Gardens that expressed the enjoyment they had from watching the beavers,” she said. “Beavers are charismatic fauna, and people seemed really excited that they could quietly enjoy and observe these creatures within walking distance from an urbanized area of Princeton.”