Dealing with ecosystem engineers
The largest rodent in North America is the beaver. It lives in nearly all 50 states, and it’s the official mammal of New York State. Their strong jaws allow them to decimate trees quickly, and just one animal can chew down several hundred trees every year. Beaver dams flood farmland, timber and roads, and can ruin fruit and shade tree plantings.
Falyn Owens, wildlife Extension biologist, North Carolina Wildlife Resources Commission, noted during the Colonial Era, North Americans benefitted from a thriving economy based on beaver products.
“There were no caps on how many beavers could be removed,” said Owens. “Vast numbers of beavers were harvested across the U.S. as trappers pushed farther west. Many people made livelihoods and fortunes exporting beavers to Europe.”
Beavers intentionally fell trees to access living branches, then drag those branches into the water and shove them into the muck at the bottom of a pond, which serves as a refrigerator to store fresh branches through winter.
“They have the name ‘ecosystem engineers’ because they’re geniuses in modifying the environment for their benefit,” said Owens. “These animals are beneficial to humans and the environment in many ways. They’re neither pests nor saints – it’s somewhere in between.”
Owens explained the benefits of beaver ponds and the dams that create them: “It’s nature’s version of something we humans create all the time – retention ponds. Slow-moving water is filtered as it moves through soil and plants in the area. It creates cleaner, healthier waterways, and slower water helps prevent erosion.”
In arid areas, beaver ponds help hold water so it’s available during drought conditions. Still water drains slowly into the ground and replenishes groundwater aquifers. Beaver ponds provide valuable resources for game species, waterfowl game, game fish and other wildlife.
Beaver activity is important for water and waterway health, which Owens admitted seems counterintuitive. However, beaver ponds help reduce flooding.
“If an area wasn’t a pond, then suddenly becomes a pond, beavers slow the water and prevent it from rushing down the water systems,” she said. “This helps to slow water and prevent large-scale flooding.”
Along major rivers where downstream issues may create a flood risk, any opportunity along the water course to slow water flow reduces flooding – beaver ponds accomplish that.
Despite the benefits, there are costs associated with beavers’ presence. “When beavers build ponds where humans have built infrastructure, it can cause serious issues, mainly flooding of roads and property,” said Owens. “We can’t just let beavers do what they do. They cause costly damage and we need options.”
Relocation isn’t a good option because beavers are territorial and have good homing instincts. Most relocated beavers don’t stay where they’ve been placed and will try to return to their original area. Beavers also carry and spread some diseases, including tularemia and giardia, into waterways.
Owens reviewed three options for beaver management: flow devices that trick beavers into not continuing to build dams while allowing water levels to flow normally; exclusion by physical means; and responsible, regulated trapping.
In managing beaver habitat, it’s important to understand why beavers build dams. They need aquatic habitat. The presence of water doesn’t initiate the instinct to build dams – it’s the sound of running water.
Owens referenced research from the 1960s in which a speaker played the sound of running water in an area where there was no water. Despite the absence of water, beavers piled twigs close to the speaker to stop the sound of running water. When the sound stopped, beavers no longer built dams.
“Understanding that drive is why we can use flow devices that help trick beavers into not building dams where we don’t want them,” said Owens. “A ‘beaver deceiver’ device shunts water and allows it to flow underwater so the sound of running water isn’t created.”
Water moves through the beaver dam, and because water flowing underground doesn’t make a sound, beavers are no longer driven to block water flow.
Flow devices also use a form of exclusion, or fencing, to act as a physical barrier to keep beavers away from the pipe outlet so they don’t block the outlet when they hear running water. Such devices can be highly effective in some situations, but not all.
“Regular maintenance is an important factor,” said Owens. “Devices can get stopped up with leaves and mud even if beavers are gone. They can freeze in cold water, which causes pipes to burst. If you use a flow device, understand that it will require maintenance.”
Exclusion is an option for certain areas. Ponds with trees along the water almost guarantee that any beavers in the area will cut down trees.
“If you’re producing timber and worried about an area of trees, you aren’t worried about individual trees,” said Owens. “But if you have specimen trees, protect individual trees from beaver access. Individual fences around the trunks are effective in keeping beavers from chewing on trunks.”
Beavers’ large teeth are constantly growing, and they require constant chewing to keep them worn down. An effective beaver fence must be made of good, stiff wire. Heavy wire fences also prevent damage by deer, squirrels or rabbits.
If beavers are flooding a portion of property that isn’t as important as other areas, consider allowing that area to flood. In some cases, the area may be usable for waterfowl hunting, fishing or kayaking.
Laws for lethal options such as trapping vary, so be sure to check state and local regulations and use traps legally and within humane standards. Licensed trappers can provide this service.
“Beavers are very beneficial,” said Owens. “We reintroduced them intentionally, and a lot of states are still trying to do that because they are crucially important for healthy waterways and aquatic wildlife, and they help reduce large-scale flooding.
by Sally Colby
