A tamer view of tamarisk
Study lightens up on the West’s most notorious weed

SideStory: Beetlemania – Tamarisk beetle continues to spread

Levi Jamison of the Tamarisk Coalition, sweeps for beetles feeding on Tamarisk Trees on the Dolores River below Gateway last May./Photo by Stephen Eginoire

by Will Sands

The “vampire of Western watersheds” may be more bark than bite. New findings indicate tamarisk – the poster child for weeds in the West – is not as harmful to water supplies and wildlife as once believed.

Tamarisk, or saltcedar, is a native of Eurasia introduced to North America by nurseries and originally sold as an attractive, hardy ornamental. Lacking natural predators, the trees spread rampantly from front yards to river corridors and beyond. Since its first introduction, the tenacious plant has seeded itself all over the West, displacing more than 1.6 million acres of willows, cottonwoods and other native vegetation. It is also estimated that each year the thirsty trees consume 2 to 4.5 million acre-feet of water from Western rivers, water that could meet the needs of 20 million people or 1 million acres of irrigated farmland a year.

However, this level of water consumption may not be out of the ordinary, according to a U.S. Geological Survey report released last week. The study indicated that tamarisk, along with Russian olive – a weedy tree plaguing the Animas River watershed – do not consume any more water than the natives they have displaced. The report went on to note that removing tamarisk along rivers can open the door to other vegetation that consumes roughly equal amounts of water. It then went on to draw the conclusion that tamarisk control is unlikely to produce measurable water savings. The findings come as bad news for thirsty downstream states like California and Arizona, who had pinned some hopes on tamarisk removal.

“None of the published studies to date, which include projects removing very large areas of saltcedar, have demonstrated production of significant additional water for human use,” said Curt Brown, Director of Research for the Bureau of Reclamation, a partner in the study.

In addition, research found that stands of tamarisk do not always harm streamside habitat and wildlife productivity, as was widely believed. The USGS found that many reptiles, amphibians, and birds use tamarisk and Russian olive as habitat. In addition, the endangered southwestern willow flycatcher frequently breeds in tamarisk stands.

The news comes as no big surprise to Stacy Kolegas, executive director of the Grand Junction-based Tamarisk Coalition. The coalition reached similar conclusions in 2008, but counters that tamarisk impacts much more than water supplies.

“It is true that when you replace tamarisk with trees like cottonwoods or willows, you’re not going to see a huge water savings,” she said. “But there’s also a bigger picture here.”

“Monotypic stands of tamarisk make for very poor habitat,” he said. “Tamarisk is so invasive and grows so densely that nothing else can take root. Monocultures of any kind threaten biological diversity.”

In addition, the USGS did find that tamarisk and Russian olive can grow on river terraces that are too high and dry for cottonwoods and willows. Also, there is a possibility that revegetation with native dry-site species could save some water for human use. Pat Shafroth, a USGS scientist and lead editor of the report, noted that specific rehabilitation – while costly – could lead to more downstream flows.

“The vegetation that replaces saltcedar, with or without restoration actions, will influence the quality of wildlife habitat, amount of water use and other ecological conditions,” he said.

The Tamarisk Coalition shares the USGS’ optimism for a wetter Western future.

“Just making a blanket statement like tamarisk doesn’t use more water than native trees doesn’t get us anywhere,” Kolegas said. “The stands can be replaced by natives like sumac, rabbit brush and grasses. With very careful decision making and rehabilitation, we can get to those original management goals.” •