Nature Conservancy Magazine: Spring 2009

Go Deeper

Tamarisk Removal Helps Restore a Western River
After eight years of tough battle, an ambitious effort led by The Nature Conservancy to remove invasive tamarisk along Colorado’s San Miguel River has reached an important milestone — 120 miles of the river are now tamarisk-free.

Invasive Species and Conservation
The estimated damage from invasive species worldwide is more than $1.4 trillion — find out what the Conservancy is doing to help.

Invasion on the Colorado
Riparian lands in the Western U.S. have been severely impacted by many activities and actions, but none to such a degree as the invasion of tamarisk, a non-native plant. Learn more about Tamarisk.

The din of chainsaws and diesel-powered wood chippers drowns out the serene sounds of the San Miguel River a few dozen miles away from where the river spills from the mountains above the Colorado ski town of Telluride. But the ruckus created by the crew of more than 30 volunteers is welcome on this crisp autumn day, as The Nature Conservancy and its partners complete an eight-year effort to liberate the banks of the San Miguel from one of the West’s most pernicious invasives: the tamarisk tree. This day marks the first time that a river’s banks have been entirely freed from the weed’s chokehold.

Since being introduced as an ornamental plant and windbreak in the mid-1800s, tamarisk has spread to cover 1.6 million acres across the West, mostly along streams. The plant, also known as salt cedar, collects salt in its leaves; when they fall to the ground, they increase the acidity of the soil and water to levels inhospitable to native cottonwood and willow trees. Tamarisk also has the ability to suck water supplies dry: An acre’s worth of tamarisk can reduce river levels or groundwater by 4 feet a year.

Tamarisk “takes away the building block of life on the river itself,” says Peter Mueller, director of the Conservancy’s North San Juan Mountain Project. He is referring to the loss of organic leaf matter from native trees, which then deprives river crustaceans of a food source. That, in turn, affects other wildlife, including trout.

Since launching the eradication effort in 2001, the Conservancy, the Bureau of Land Management, the Colorado Department of Transportation and other partners have scoured 120 miles of the San Miguel and its feeder streams, cutting the bushy trees and applying herbicide to the stumps. The effort cost $1.3 million, drawing on local, state, federal and private funds, including a grant from Marathon Oil.

“I can’t even count the volunteers and different companies that have helped,” says Sheila Grother, the county weed control manager. “But when you look back and see the cottonwoods and willows and native grasses, you can see it’s worth the effort.”

Grother cannot fathom how many trees were cut and treated, but Mueller estimates more than 17,000 hours of labor went into the project.

The effort will receive ongoing help from the tamarisk leaf beetle. After years of research on the potential for igniting a beetle invasion, government scientists have released tens of thousands of the insects, which are native to Asia, along rivers throughout the West. The goal is to beat back the invasive plant, which is often too dense to eradicate by hand. “Over the long term,” Mueller says, “the hope is that as the beetle settles in, it will be a natural check on the plant and prevent further deterioration of the watershed.”

—Joshua Zaffos