October 2, 2009
What to Do About Beavers
For those who say beaver flooding and tree damage can only be fixed by trapping, we say it's not so
The beaver is making a come-back. Nearly driven to extinction by the fur trade, nature’s engineers are now 6-12 million strong in the United States.
We’re slowly realizing that this return can provide significant benefits to a continent that has lost much of its wetlands to development or agriculture.
But we’re also finding ourselves in conflict with beavers, usually over who gets to occupy floodplains. While it’s environmentally appropriate for beavers to build and live in these areas, it is far less so for humans.
Because of this, we should recognize the environmental benefits we can derive from working with, rather than against, the beaver.
The two most common problems associated with beavers are the flooding that results from blocked structures, such as culverts, and the damage to trees.
Flooding can become a crisis after unusually heavy rain or snow brings on water that has nowhere to go.
On the other hand, dams can store water during periods of drought and slow down the movement of water from land to river systems that is often responsible for serious floods and significant financial damage downstream.
Damage to trees in urban and suburban areas is likely to be noticed before it becomes critical but perhaps not before a valuable tree or two have been lost.
Operators of commercial forests, especially in the southeast, attribute millions of dollars of timber loss annually to beaver.
Beavers can play an important role in establishing and maintaining wetlands—a key reason to try to live peacefully with these animals. Beaver dams enhance their environment by
- Providing habitat for many sensitive plant and animal species.
- Improving water quality.
- Controlling floods by slowing water movement.
People enjoy watching and photographing beavers and the habitat they create. Public education can thus be key to a growing recognition of the benefits beavers can bring.
Place homemade tree guards around the trunk. The guards should be about three feet high and made of galvanized welded wire (2 x 2 or 2 x 3 inch is recommended). This material can be found in any large hardware or home improvement store, usually sold as fencing. Try not to use the lighter chicken wire, as it is generally too flimsy to provide good protection.
Finer-mesh screening—such as that used for windows as bug screen—is more expensive, and you don’t need to resort to it unless welded wire is unavailable. These can be especially effective in protecting small (two- to six-inch-in-diameter) ornamental or specimen trees.
You may need to pin guards to the ground around larger trees, and it’s a good idea to mulch within the guard to keep weeds from becoming a problem.
Paint and sand
The USDA has shown some success in protecting trees by painting their base with a mixture of coarse mason’s sand (30–70 mil) and exterior latex paint. (The ratio is twenty ounces of sand to one gallon of paint.)
The abrasive quality of the mixture may deter beaver. You can match the paint color to the tree, so it will blend in.
Because beavers are not good climbers, three to four-foot-high fencing can also be a highly effective way to block their access to larger groves.
Check the fences frequently to make sure they are intact and that beaver haven’t pushed under them, especially where the fences cross established haul-outs, where beaver like to come from water to land.
An electrified wire strung approximately four inches off the ground can also prevent beaver from entering an area. This type of fence can be especially effective in a small garden or crop plot when set up to protect plants for a few weeks and taken down afterward.
In the past, “solutions” to the presence of beaver dams have often involved the use of heavy machinery to tear the dams apart or explosives to blow them up.
Neither approach is particularly useful: Beavers will quickly attempt to rebuild their structures using new material. This only exacerbates any perceived or real damage they may have done in the first place.
Likewise, trapping or shooting resident beavers is ineffective, because it only creates a vacuum into which new beavers will move, often sooner rather than later.
And all of the strategies aimed at removal or destruction deny the presence of beaver wetlands—landscapes that are both appropriate and needed.
As with any good nonlethal approach, the various devices experts use to discourage beaver dams take advantage of the behavior of the beavers themselves.
Scientists believe that beavers are motivated to build and repair dams using cues from the sound and perhaps feel of flowing water. One possible reason is that a draining pond could quickly expose the beaver colony to predators.
The design and installation of beaver devices is complex, and technical assistance from experienced professionals is recommended when using them. Experience in reading sites and predicting how beaver will respond to attempts to defeat their dam behavior can be invaluable. It is also necessary to be aware of local, state, and federal regulations when planning to install these devices.
Here are some the devices (both venerable and new) that can help prevent or control flooding caused by beaver dams:
- The “Clemson Leveler” (used for more than thirty years).
- The Beaver Deceivers™, Round Fence™, and Castor Master™ (all developed by Skip Lisle—simple but rugged enough to withstand the force of ice).
- CulverClear™ technologies (developed by Mike Callahan).
Whether constructed of wood or steel frames, the overall savings these devices represent compared to the cost of repeated beaver removal or dam destruction, make them highly cost effective as well as humane.
Notching an existing dam and running a pipe through the gap will stimulate the beaver to repair the dam at the site of the notch but not at the pipe ends, which will allow the water to be set at a level that meets human needs.
To ensure the upstream end of the system isn’t blocked by beavers or debris, a filtering device, often called a Round Fence™, can be installed. These devices consist of a flexible corrugated plastic pipe, sized to the particular job but usually somewhere between eight and fifteen inches in diameter.
In the past, the culvert pipes installed under roads were often undersized and hence easily plugged by beaver. Newer installations generally take beaver activity into account and are designed correctly from the start to prevent plugging, but there are still a lot of smaller ones out there
For these, you can use the Beaver Deceiver™, sometimes in conjunction with Round Fence™ and a pipe system at its front, or as a stand-alone device.
This strategy involves creating a fence barrier in front of the culvert (usually shaped like a trapezoid but adaptable to different configurations as well) that takes the beavers so far away from running water at the culvert head that their instinctive motivation to dam seems to be defeated.
It has long been suggested that beaver may be responsible for outbreaks of the parasitic disease giardiasis in humans.
However, recent studies and examination of past outbreaks suggest that other factors, such as contamination of drinking sources with human waste, may play a larger role in the spread of the disease than beaver do.
» Living with Wild Neighbors in Urban and Suburban Communities: A Guide for Local Leaders gives elected officials and other decision-makers the tools to implement long-lasting, nonlethal solutions to community wildlife conflicts.
» Organizations and individuals to contact for information about beaver and assistance with beaver conflicts include:
Beaver Deceivers International
1187 Cabbel Road
Grafton, VT 05146
Beaver, Wetlands and Wildlife
146 Van Dyke Road
Dolgeville, NY 13329
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