Rocky Mountain National Park is suffering from a shortage of dams, a team of scientists says.
The dams built by the once-abundant beaver populations diverted water from mountain streams and spread it across park valleys, helping wetlands inhabited by other animals.
The number of beavers in the park, however, has plummeted to 30 today from nearly 600 in the 1940s.
And in the absence of nature’s corps of engineers, “the valley’s a lot drier,” said Cherie Westbrook, lead author of a beaver study by the team. “You have water tables in the valley that drop 3 or 4 feet in the summer.”
In a national park created to protect its natural treasures, the beaver’s disappearance is creating grasslands where willow-dominated wetlands were once thronged with beaver, waterfowl, other birds and frogs, Westbrook said. “What we think is going on is that there’s this competition among elk, moose and beaver all for the same food source.
“Bringing in more beaver is not the solution,” she said. “We feel that it’s really a willow-availability issue. There’s just too many animals hungry for the same thing.”
The study, conducted with two Colorado scientists, will be published this week in Water Resources Research, a journal of the American Geophysical Union.
The report coincides with a park plan to use rangers or a contractor to reduce the elk herd by shooting the animals at night with silencer-equipped rifles.
The elk plan, which could cost as much as $18 million in the next 20 years, has drawn criticism from environmentalists who want wolves reintroduced as predators, and from hunters who would pay to shoot the elk.
For their food and dam-building supplies, beavers depend on aspen and willow, which have been chewed to the ground in the park by growing numbers of elk that no longer face predators.
Westbrook’s study focused on the Kawuneeche Valley, about 10 miles north of Grand Lake.
The research showed that “beaver not only create upstream ponds, but they flood very large areas downstream of the ponds,” she said. “That’s where the major impact is, actually – downstream.”
In the park, “the valleys are so wide and flat that you can have major flooding beside and below the dams” that can extend thousands of feet downstream.
“The beaver dams cause more water to be stored in the valley over a longer period of time,” she said. Without them, “we’re having a change in the valley from being wet to being dry.”
As a result, “it looks like the willow in Kawuneeche Valley are dying.”
Westbrook, who did her research as a Colorado State University doctoral student, teaches at the University of Saskatchewan.
In the Canadian Rockies, she said, beavers seem to be benefiting from the reappearance of wolves preying on elk herds.
“What they’re actually seeing is a recovery of the beaver population with the wolf.”
Staff writer David Olinger can be reached at 303-820-1498 or dolinger@denverpost.com.
