The fate of the Mancos River ecosystem in Mesa Verde National Park could lie in the hands of an unlikely source: beavers.
A National Park Service project aims to restore a 5-mile stretch of the Mancos River that runs along the eastern boundary of the park by encouraging beavers to inhabit and reshape the area.
“Some people call them ecological engineers,” said Andrew Spear, a biological science technician with Mesa Verde and the leader of the project.
“Beavers can support fish. They can support riparian trees and vegetation. ... Beaver can even support amphibians,” he said.
A grant from the Desert Fish Habitat Partnership, which aims to protect desert fish across the Southwest, allowed scientists with Mesa Verde to begin addressing the diminished and threatened water resources of the park.
Historic grazing, drought and upstream diversions have all altered Mesa Verde’s stretch of the Mancos River, Spear said.
Roundtail chub and flannelmouth and bluehead suckers should be swimming in the river, which runs through the Upper Mancos River Canyon, but the effects of the roughly 20,000-acre Bircher Fire in 2000 and poor habitat have left them largely absent.
“One of the main things (the project is) designed to do is really create more habitat for fish in the river,” said Nathan Brown, a wildlife biologist and the leader of the park’s wildlife program.
“We’re really just trying to build a functioning riparian corridor again,” he said.
Beavers are key to park’s restoration efforts, which are also meant to combat the increasingly visible effects of climate change and drought.
“They help build more structure and function for the riparian system which benefits fish,” Brown said.
In summer 2022, Spear and the park plan to place about 25 to 30 simulated beaver structures along a portion of the Mancos River following the practices of low-tech processed-based restoration, which was developed by researchers at Utah State University.
They will build beaver dam analogs and imitate the natural buildup of wood in river systems with wooden posts and create strategic blockages. The technique is less invasive than other river restoration efforts and low-cost – all the material will come from trees removed during Mesa Verde’s construction of a new bike path.
“One strategy is called post-assisted log structure. It’s literally just pounding in (wooden) posts and you’re creating a log jam,” Spear said. “It’s that simple, but the impacts can be huge.”
Though the Mancos River is perennial, meaning it runs year-round, drought, poor runoff and diversion can all deplete the river and leave flows dangerously low.
“We’ve seen more years in the last decade or two and there’s more anecdotal reports of our reach of the river losing flow entirely,” Spear said.
“When we lose flow in our (stretch of the river), the fish population is really relying on pools that naturally exist and there’s a limited amount of those,” he said.
By recreating beaver structures, scientists slow, but don’t stop, the river, which allows water to back up and create more habitat for fish, beavers and other animals.
“When you’re moving water laterally against the banks, there’s erosional processes that are happening that are helping to carve out pool habitat,” Spear said.
Slowing the flow of the river and creating more and deeper pools also sustains the river over the summer months when water resources often dwindle.
“It’s really helping hold that water so that when flows start to drop, groundwater is supporting base flows (of the river),” Spear said.
Restoring groundwater not only helps the river maintain its flow, but it also allows riparian vegetation such as cottonwoods to thrive, which creates more habitat for animals like elk, mule deer and bears.
Spear and his team hope that establishing the analogs and jump-starting the restoration process will attract beavers from the Ute Mountain Ute Reservation to recolonize the park’s stretch of river.
“We really feel like it could be key for fish habitat, but then also support our beaver population,” he said.
“Once you start building dams and staggering them, they’re all kind of supporting one another so that (beaver) can have higher success,” he said.
Though the project is not slated until next summer, park staff members have already seen signs of beaver, Brown said.
On Spear’s second visit to the project’s Mancos River site, his team found a beaver dam that was beginning to form. Spear has also captured at least two beavers on a trail camera monitoring the area.
If beavers can re-establish themselves, building their own structures and expanding the ones that scientists have built, they could completely reshape Mesa Verde’s riparian ecosystem and do much of the restoration work that Spear and Brown say is necessary.
“We don’t expect these (analogs) to be anything permanent,” Spear said. “... We put wood in the system so hopefully the beavers can sustain and improve it and build them back.”
“The project goes well beyond fish. It’s supporting overall riparian health and beavers who are such an important part of (river) ecological processes,” Spear said.
Visitors to the park won’t likely see beavers anytime soon. Mesa Verde’s stretch of the Mancos River is still inaccessible even for park staff members, who must rely on surrounding landowners to grant NPS access, Brown said.
While the project will remain invisible to the tens of thousands of visitors who flock to Mesa Verde, these restoration efforts are no less important.
“We’re trying to maximize the ability of the (riparian) system to support native wildlife and native ecosystem structure and function, which benefits everyone,” Brown said.
ahannon@durangoherald.com
