by Paul Ferrell | March 1, 2014 4:56 pm
When it comes to the ability to manipulate their environment on a large scale, beavers are second only to humans. Some people love beavers; some hate them. Either way, no one disputes that they have a big impact on their territory.
Beavers are busy; they build dams, construct their homes, dig canals and tunnels and cut down trees. All these construction activities create surroundings the aquatic rodents can live in, and they create an environment many other animals, and humans, appreciate as well.
However, occasionally beavers and humans come into conflict. Sometimes beavers will cut down a favorite tree or block a culvert, clog an irrigation ditch, or flood a pasture.
Jeremy Christensen is a beaver consultant. For ten years he worked in the field of natural resources, mostly with beavers. His small business in Mancos, Colo., Flow Control Consulting, finds ways to deal with problem beavers.
Christensen said most people assume trapping is the only way to stop a beaver from behaving badly. “That’s generally people’s first thought, but trapping is the last resort,” said Christensen. Trapping or shooting beavers, along with dynamiting their dams, often turns out to be an exercise in futility and those who are successful in removing beavers from their land sometimes end up regretting their success.
Marilyn Colyer is a rancher and biologist who spent 40 years with the National Park Service. Colyer’s land is on what Christensen calls the “interface” between wilderness and civilization. Over the years Colyer has seen large numbers of people move into the interface.
“People more and more are getting on pieces of land so small that people are living right close to a creek, where they wouldn’t use to live that close,” she said. When beavers and humans live in close proximity problems sometimes develop.
Once trees begin to fall, property owners sometimes try to evict the large rodents. As a biologist, Colyer knows beavers don’t engage in clear-cutting. “Once they get their dams made they basically quit cutting. They don’t cut that many trees down again, they’ll eat willows and grass.”
Colyer said she had a neighbor who removed his beavers and their dams, then came to regret it.
“He blew out all the beaver dams on his land, and then he wished he hadn’t. He wished he hadn’t because the water table went way down – he dried up his land. Sub-irrigation is extremely important around here. Then he built some fake dams, which aren’t very good, they’re just rock and some logs and they won’t be functioning dams for very long.”
Beavers maintain their dams and they function for generations. The still waters in ponds behind the dams gradually soak into earth and raise the water table. After many generations the ponds fill in with silt, creating a grassy meadow growing on rich soil. “You go up on the national forests and you see these big lush meadows that are grass and wildflowers and native plants,” said Christensen. “Very likely that used to be a big beaver pond that was filled in with sediment and was colonized by the vegetation.”
Beaver dams create an environment that supports a wide range of species and are helpful to humans too. In addition to raising the water table, they help prevent flooding and erosion.
Colyer has witnessed the effects of beaver evictions near her ranch, “If you go down Cherry Creek, the banks are like 10 to15 feet high of raw dirt because the people have taken out the beaver dams,” she said.
Christensen said beaver dams hold water that slowly percolates into the soil, helping the forest endure droughts.
“Mountains act like a sponge with beaver dams,” he said. The beavers’ ponds improve water quality by removing sediment, and during forest fires beaver ponds serve as a natural fire break.
At three feet in length and weighing up to 55 pounds, beavers are the largest rodent in North America. They have a wide, flat tail, webbed feet, thick fur and long, hard teeth that enable them to gnaw through a fiveinch- diameter tree in 30 minutes. In most cases, signs of beaver are obvious: gnawed tree stumps, dams, canals, lodges, bank dens and slides.
Christensen can even spot signs of beaver that are decades old. “The beavers forage and harvest the willow,” he explained, “and they use it to build dams. Those old dams become new stands of willow. So when we’re investigating old beaver habitat and we see these long stands of willow that are running perpendicular to the stream flow, that’s where we know there was an old beaver dam.”
Beaver ponds in the Rockies freeze during the winter, but beavers do not hibernate. They swim under the ice and emerge through their lodges to eat bark. They do not eat the inner wood of trees, only the bark, leaves and soft, tender branches. In the summer their main food supply is forbs and grasses.
They have few predators; occasionally a coyote will prey on a beaver found on dry land, and mink sometimes eat the kits. In the spring a litter of four of five kits is born inside the lodges. A major cause of death in the wild is drowning during floods.
Beavers nearly became extinct in the 19th century. They were extensively trapped for their fur; the dense under-fur was used to make felt for hats.
But by the middle of the 19th century, felt hats were replaced by silk hats and the beavers made a comeback.
The beavers are back, but they’re not back in all the places they used to be. “They’re not endangered or threatened,” Christensen said, “but they’re not occupying the vast majority of their historic habitat.”
Although many mountain landscapes appear to be the home of a healthy natural habitat, it is unnatural and incomplete without them, he said.
“Beavers on the national forest take care of, and anchor, and build, and engineer, and maintain that whole riparian system,” explained Christensen. “Everything relies on the riparian area, and the riparian area relies on the beaver. So if you take the beaver out of the system, it all unravels.”
Beavers create wetlands that greatly increase biodiversity. Native trout and other native fish species easily cross beaver dams, and fish populations as well as fish size increase with beavers on the streams. Beavers construct habitat for numerous species of birds, fish, amphibians, insects and mammals.
“It’s pretty staggering, the trickle-down effects,” Christensen said. “They really are a keystone species. They’re really at the apex of the whole forest system.”
“When they’re in the creeks and the ponds they’re providing beneficial services,” he said.
“They’re providing sub-irrigation, they’re providing water storage, they’re providing water filtration and purification, they are recharging aquifers and they’re supporting riparian vegetation. They’re providing habitat for pretty much every other species on the mountain. So they’re incredibly important when they’re in their natural settings, but then they occasionally get into irrigation ditches, they get into the water-delivery systems where that’s not a natural setting. That’s where they become a nuisance.”
When beavers become a nuisance, Flow Control Consulting goes into action. “When we get a call it’s either because they are chewing and cutting down trees or they’re blocking a culvert or interfering in some way with the water-delivery system,” he said.
“So they’re either clogging an irrigation ditch or building a dam in a inconvenient place or their pond is becoming too big and flooding either pasture land, private property, or flooding somebody’s basement.”
When beavers begin to cut down aspens along a streambed, Christensen tells people not to be too concerned.
“Aspen are really fast-growing,” he said, “the pruning action from beavers is actually beneficial because aspen and beaver co-evolved together. The pruning action of the beaver is good for the root mass — the clone system — which supports the aspen trees. So I tell them to fence the remaining mature trees to protect the esthetics of the property.”
Trees must be fenced with heavy welded wire fencing — chicken wire will not work.
Beaver have been eating aspen for millennia, Christensen said. “That pruning action of beaver is actually beneficial to the stand of aspen. It thins out older mature trees, allowing younger trees to come up. That pruning action sends a chemical signal to the root to send up new shoots.
“Every time a beaver takes down an aspen tree the root mass sends up 30 more shoots based on that chemical signal that’s sent from the pruning action.”
When a beaver pond becomes too large, Christensen can bring it down to size. “There’s a really easy engineering solution,” he said. “You could install a drain in the pond and you could control the pond at any size you want it. A lot of people want to have that water storage but they want to control it at a certain size so that it doesn’t flood a whole bunch of acres or it doesn’t flood their basement. You can engineer a really simple drain; we call it a pond leveler. It’s kind of a generic term.”
Such flow-control devices have been developed by many different people and are now being used by the Forest Service, the BLM, many road departments, and other people, he said.
Beavers blocking culverts are a common problem, but it can be dealt with.
“We build protective culvert fences, trapezoidal- shaped fences on the upstream side of a culvert that may be being blocked by beaver. The sound of the water moving through makes for a natural target for them to dam. So we build these as big as the site will allow us.
“That forces the beaver out and away from the sound of the running water. They either lose interest or are unable to dam around the perimeter of the [structure] so it stays free and clear.
“In certain situations we’ll have to combine that with a pond leveler so instead of allowing them to dam across the culvert we’ll build this fence, allow them to dam around the fence, and then we’ll put a pond leveler through that. We call that a fence and pipe system.” Christensen has seen beavers threaten the integrity of man-made dams. Beavers will sometimes build their lodges by digging into earthen dams, levees and dikes.
“The Division of Wildlife excavated a dike and it was like Swiss cheese from the beaver having gotten in there,” he said.
For burrowing beavers, Christensen uses chain-link fencing – horizontally. “We lay chain link along a bank where they’ve been digging excavation bank lodges; it deters them from that area.”
Occasionally Christensen will live-trap and relocate a beaver. “If the beaver is there we can usually catch them with a live trap,” he said. “We use a scent lure that brings them in and it’s pretty reliable. So we had good success in doing the live trapping and being able to trans-locate them.”
Colyer had beavers relocated onto her ranch.
“I’ll take all the beavers anybody wants to bring on my land up here on the West Mancos,” she said. “I had three brought in. I had to do paperwork and get both neighbors to agree, and the Division of Wildlife looked the habitat over. My neighbors weren’t sure if they wanted to agree, but they did. It had to be in writing that they agreed. One neighbor was the one that had wished he hadn’t blown his dams out before. I had three brought in – and they went on up to the neighbor above me.”
Colyer has no interest in selling her land, but she wonders what the impact of having beavers on a particular property would be. “There could be half of the potential buyers would frown on beavers,” she said, “the other half would love to have a pond there.” Colyer sides with the latter. “I guess everything has a love-hate relationship when you get right down to it. People conflict with people, and people conflict with wildlife, right? But if you have to make a choice, I would take the beaver.”
Jeremy Christensen, owner of Flow Control Consulting, can be reached at flowcontrolconsulting@ gmail.com, 801-403-8560.
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