Zion's Cottonwoods Could Soon Vanish
|
Park Service examines how to restore canyon's ecosystem
ZION N.P., UTAH—Lingering effects from decades of human manipulation of the Virgin River have placed the spectacular cottonwood trees at Zion National Park in danger.
"We have an aging forest that is gradually going to die," said Jeff Bradybaugh, chief resource manager at Zion. "In 30 to 60 years, there will be very few if any cottonwood trees in the canyon." |
Reflection of cottonwoods in Zion National Park. Part of the historic landscape that may soon vanish. | |
That prediction echoes the findings of a recent study conducted by the park and the Grand Canyon Trust. "Without active intervention," the report states, "the magnificent canopy of cottonwood trees, part of the historic landscape within Zion Canyon, will vanish."
The trees are simply not regenerating, the study revealed. The main culprit is a series of revetments, stone levees that are reinforced with wire mesh, built in the 1930s to protect the road and facilities from the flood-prone river. Although successful in protecting infrastructure, they have also altered the canyon's ecosystem.
The river no longer reaches its floodplain, where it once left sediments and nutrients crucial to cottonwood seed germination. Its flow is now faster during snowmelt and significant precipitation, scouring away young cottonwoods. And, the water table has lowered, making it tougher for established cottonwoods to get moisture.
As a result, there has been almost no reproduction or replacement of the cottonwoods. The revetments have also affected the river's riparian and aquatic systems, jeopardizing the indigenous fish species.
The report recommends a restoration program that entails removing the revetments along a two-mile stretch of the river, as well as a reconstruction of the river's natural bed, which would spur growth of new cottonwoods to replace the old ones.
The park's final decision won't be easy, though. Aside from the cost, preliminarily pegged at $5 million, concerns abound on protecting the park's infrastructure from the river and preserving water quality for downstream users.
"We're taking the slow approach on this," Bradybaugh said, "evaluating all effects, both short-term and long-term."
The park is gathering information on various actions, from complete removal of revetments in the canyon and reconstruction of the river channel to simpler alternatives such as removing the revetments and letting the river establish a channel within the available floodplain.
The ultimate goal is to restore the floodplain and riverine environment in Zion Canyon, Bradybaugh said, thereby restoring the processes that affect the biological communities in the river.
Park Superintendent Martin C. Ott has said a formal proposal is at least a year away, after extensive study and input from the public.
