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woodland: Winter 2013

Leave it to Beavers

By Madeline Bodin

Skip Lisle has been living with beavers all his life. The relationship hasn’t always been a peaceful one. As a child, his family moved to a forested valley in southern Vermont. Lisle grew up hunting and fishing, so when beavers dammed the road culvert next to the house, threatening to flood the road, his parents assigned him the chore of shooting the beavers to eliminate the problem. But soon, new beavers came and dammed the same culvert.

Lisle, young as he was, knew there had to be a better way to deal with the beavers. He began developing a solution as a teenager. After years of working in construction and earning a master’s degree in wildlife management, he perfected it.

Today Lisle lives with his family in the house where he grew up. The house is surrounded by a horseshoe-shaped beaver pond and expansive wetlands. The dirt road next to the house remains dry. Wood ducks and mergansers nest on the pond. Frogs trill and red-winged blackbirds sing there each spring. Moose wade, looking for lunch. On summer evenings Lisle and his wife relax on a deck at the water’s edge, keeping an eye out for the v-shaped wakes on the pond that show that their busy neighbors are at work.

Beavers Play a Role 

“Beaver flowages are incredibly valuable ecologically,” says Lisle. In Vermont, as in most of the United States, beavers create wetlands where they otherwise wouldn’t exist. These wetlands are rich in wildlife. Frogs, salamanders, songbirds, water birds and bats benefit from the wetlands that beavers create.

These rare habitats take up just 1 percent of the eastern landscape, says Lisle, the owner of Beaver Deceivers International, a beaver consulting and mitigation firm.

In the West, beavers provide an additional benefit. “In the arid regions, water is life,” says Jeremy Christensen, a wildlife associate with the Grand Canyon Trust, a group that works to conserve the Colorado Plateau. “When beavers build dams, they create a capture-and-storage system for rainfall and snow.”

Water in the West comes primarily from each year’s melting snow— too much water in early spring is a liability, while any water available in late summer and early fall has great value, says Trey Schillie, an ecosystem services analyst for the U.S. Forest Service. Beaver dams hold back the snow melt and release water slowly through the year.

Beaver wetlands also help with water filtration and erosion prevention. When the devastating Hayman Fire burned above Denver 10 years ago, Schillie says, it scorched away vegetation on the hills above two of the city’s reservoirs, leaving nothing to catch the dirt and ash. Sediment clogged the reservoirs and they had to be dredged. The city paid $10 a cubic yard for the dredging. If beaver dams had been upstream of the reservoirs, he says, the sediment would have settled there instead. Schillie calculates that each beaver dam in such a situation would be worth $1,000 to $15,000. “The value starts to add up,” he says.

The Pacific Northwest has plenty of rain, but research suggests that beaver ponds provide an important service there, too—helping protect water sources for Coho salmon and cutthroat trout.

The Problem

“Since humans want to harvest trees and beavers want to harvest trees, it can be hard for them to coexist,” says Michael Callahan, owner of Beaver Solutions, a Massachusetts based beaver consultant and mitigation expert.

When they have a choice, beavers eat willow and aspen, trees with low value. But tree chewing is usually a minor issue, the experts say. It is the beavers’ dam building that typically causes the most costly damage, plugging culverts and flooding roads. Sometimes beavers will create a pond over a well or other drinking water supply, which is a health hazard.

To reap the benefits that beavers provide, says Callahan, “the key is to keep them welcome, and that means intervening when they cause problems for people.”

Assess First

Be wary of anyone who claims to have a solution to a beaver problem before assessing it, the experts say. There is no single technique that works in every situation.

“Commercial trappers don’t want to educate you, because they will get to come back the next year and trap again,” says Sherri Tippie, owner of the beaver consulting and relocation firm Wildlife 2000, based in Colorado. “When you call me, I don’t pop up and take the beavers away. I educate you.”

For help with this assessment, there are several places where woodland owners can find professional advice. There are mitigation consultants like Lisle, Callahan and Tippie who can both assess the problem and implement the solution. There are university extension services, like the one at South Carolina’s Clemson University, which can offer expertise and advice. A regional biologist from a state wildlife department may be able to offer some hands-on help, and the U.S. Department of Agriculture’s Wildlife Services program is yet another option.

The experts say that when beavers are trapped and either killed or removed from the area, other beavers will soon move in if the appealing habitat remains. Trapping and other lethal methods—as Lisle learned as a child—are temporary when used alone.

“There are only so many ways that beavers are going to need to be dealt with,” says Christensen. “We have a variety of options to try to do that. If you have a problem with beavers taking down trees, you can use fencing. If flooding is a problem, we have flow-control devices.”

Flow-control Devices

Flow-control devices usually turn out to be the least expensive way to solve the flooding problems in the long run, and are better for the environment.

It was a flow-control device that allowed Lisle to have all the benefits of beavers while protecting his road and his home. He started working on his device nearly 40 years ago and keeps it around partially for sentimental reasons and partially because it still works.

Culverts are tempting places for beavers to dam, Lisle explains, because in the beavers’ understanding, a culvert is simply a dam with a hole in it, and beavers instinctively fill holes in dams. Like all modern devices that protect culverts from beavers, Lisle’s first flow-control device is essentially a large fence around the culvert underneath his road.

While there are three major styles of flow-control devices, the differences are in the details. Each style excludes beavers from places where they can dam and lets landowners control the water level, usually with a pipe.

“The idea is to fool the beaver as far as where the break is in the dam,” says Greg Yarrow, professor and natural resources department chairman at Clemson University. The Clemson Extension Service publishes a set of plans for its own flow-control device, known as the Clemson beaver pond leveler. “Beavers key in to the sound and movement of running water,” Yarrow says. Flow-control devices work by keeping the beaver away from the sound and feeling of moving water that impels it to build a dam.

Besides protecting culverts, flow-control devices can also prevent a beaver pond from getting too large or from overtopping a nearby road. A pipe is put through the dam at the same level as the maximum desired water level of the beaver pond. The upstream end of the pipe is dozens of feet away from the dam, in the beaver pond, surrounded by a fence.

“These types of devices started in the 1930s with three logs wrapped in flashing and stuck in a dam,” says Yarrow. They continue to evolve. Some consultants prefer polyethylene pipes because they are light and inexpensive, and others prefer PVC pipes because they are stronger and don’t float. The latest innovations in flow-control devices are fish passages, turtle doors and other innovations that let other creatures pass through the device while keeping the beavers out.

Plans for flow-control devices are available online and on DVD from Clemson and Beaver Solutions, so beaver control can be a do-ityourself project. Experts like Lisle, Callahan and Tippie, however, bring years of experience in beaver behavior, stream dynamics and device construction that increase the likelihood of success.

Other Solutions

Studies by the U.S. Forest Service and local public utilities confirm that flow-control devices have a high success rate. But sometimes a landowner can’t use such a device at a beaver problem site, says Jimmy Taylor, the project leader for the U.S. Department of Agriculture’s National Wildlife Research Center.

Property owners in the West, where beavers are still recovering from near-extinction at the beginning of the 20th century, have an option that is not available in the East, where beavers rebounded to fill all the available habitat—and then some. “We have the option of live trapping and relocating the beavers to areas where we would like them,” says Christensen. “It’s an interesting process. Each state is a little different.”

State permits are required for trapping and relocation, and the conditions for those permits vary.

Moving House

Tippie began live-trapping beavers in 1985, when she saw on the news that beavers on a Colorado golf course were going to be killed. A professional dancer and hairdresser at the time, she borrowed traps from the state division of wildlife and found a home in Rocky Mountain National Park for the beavers she caught.

Tippie knows that beavers mate for life and that the kits live with their parents for two years, so she traps at a site until she has the whole family before relocating them. She feels this makes the beavers more likely to stay where she puts them.

For the sake of the young kits, she doesn’t begin trapping until the first week in June and she stops relocating beavers on the first day of September so they have time to build a food cache for the winter at the new site.

“As far as other nonlethal techniques that attempt to scare or repel beaver, in general, they don’t work,” says Taylor. “That doesn’t mean they never work,” he adds. But the National Wildlife Research Center’s testing shows that they aren’t effective.

The technique used to protect individual trees from beaver gnawing is effective, however. Called tree wrapping or fencing, a cylinder of heavy-gauge wire mesh is placed around a tree trunk with at least a two-foot gap between the mesh and the trunk. As the tree grows, the fence must be made wider.

This can be time-consuming work, and the results vary. Lisle says the key factor is what other food is available for the beavers. If there are plenty of favored tree species around, the beavers won’t bother with the protected tree, he says. If a fence is all that stands between a beaver and hunger, however, the fence doesn’t stand a chance.

Because it is temporary, lethal trapping is the method of last resort for beaver problems, but sometimes it is necessary. In some instances, a combination of trapping and flowcontrol devices solves a problem neither method could alone.

Being flexible and focusing on long-term solutions is the key to solving beaver problems, Taylor says. “ Some people say that you have to use lethal trapping, while others say that you only can use nonlethal methods. You don’t want to take either extreme.”

While others may look at beavers and see a nuisance, Lisle, sitting in his living room overlooking the beaver pond, sees redemption. “ When the Earth is losing natural landscapes every day,” he says, “it is incredibly powerful and encouraging that we are gaining these marshes and meadows.”

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  • Heidi Perryman
    It's a very good idea to talk about the benefits of beavers to wildlife and the riparian border, but that's a photo of a nutria - not a beaver. The animals are very different and their impact on the ecosystem couldn't be more disparate.

    Heidi Perryman, Ph.D.
    Worth A Dam
  • Heidi Perryman
    Thanks for swapping the photo! Much better story without the confusion!