On Wednesday, Feb. 7, the road to the Delicate Arch viewpoint in Arches National Park was closed due to flooding, even though it didn’t rain that day.
The flooding has become a more frequent problem as tamarisk trees choke the washes that run near the road, said National Park Service Chief of Maintenance John Lewis. To protect access to the popular site, the NPS is taking on an unprecedented 54-acre tamarisk removal project.
The road to Delicate Arch and the Delicate Arch viewpoint was flooded for more than 30 days last year due to an overgrowth of the invasive tamarisk, Lewis said.
“What happens is the water slows down because of the road and then due to the tamarisk, they start coming in so it blocks off the water and then it backs up onto the road. Each year we’ve looked at it, we’ve had increasing amounts of time we have to close the road,” Lewis said.
The Park Service is using excavators to remove entire trees, including their root balls. After tree removal, NPS will dig channels to simulate the drainages that were there before the tamarisk came in.
The invasive species has a long history in the Southwest.
“The tamarisk is from Eurasia and they brought it over to stabilize the banks almost 100 years ago. Then, especially in the Southwest, it really went crazy,” Lewis said. “The only predator for the plant ... was a beetle over in the same locations and they studied it for many years and they finally—I think it was 2002—they released it.”
NPS ecologist Liz Ballenger said that the project would have positive effects beyond reducing flooding.
“This project was driven by a maintenance need,” Ballenger said. “However, removing the tamarisk should have really great beneficial effects in the long term to the vegetation communities out there and wildlife habitat and all of that because we’re expecting native species, especially in the wet riparian areas, to rebound quickly and we’re going to be doing follow-up work to control tamarisk re-sprouting and any other invasive species that might be coming into the area.
“There are a lot of negative effects from exotic species invasion, everything from taking over plant communities, crowding out the natives. Our native species are really important for wildlife, for even aesthetics for park visitors. Having intact native communities is one of the goals that falls under the Park Service mission of preserving and protecting our resources.”
The project will leave vast areas of bare soil, Ballenger said, which could allow other invasive species to come in.
“That’s potentially a problem, so we’re looking at ways to stabilize these large areas of sediment deposit and doing something like [biological soil crust] inoculation could be a huge help. The [U.S. Geological Survey] is helping us figure out how we might do that.”
Adding to the park’s efforts is an unlikely partner: the tamarisk beetle. Grand County Weed Control Supervisor Tim Higgs helped introduce the beetle to the area. He said the beetle currently causes approximately a 50 percent mortality rate to the trees. That number could grow to be as high as 70 percent.
“With tamarisk, it’s just a long-term process because of how many acres there are. It’s not going to be done because it’s going to cost a lot of money,” Higgs said. “It’s not cheap to go in and do it mechanically or any way really. [The beetle] actually has killed some to where we’re seeing things fall over … There’s a lot less tamarisk than what there used to be.”
The excavation of tamarisk in the Delicate Arch area will continue until April 1, at which time the park will stop operations to accommodate migratory birds that will be passing through the area. Lewis said the work is more than a third of the way done. The project will finish next winter.