Geological study cuts tamarisk a break

This photo of Chinle Wash in Canyon de Chelly National Monument shows the extent to which tamarisk dark green foliage) and Russian olive trees (gray-green foliage) dominate the floodplain. Bands of native Fremont cottonwood (bright green trees) grow on the outer margins.

Tamarisk, a Eurasian transplant that’s taken over riparian areas throughout the West and long been disparaged as a water waster and unfriendly to native wildlife, may be getting a small reprieve.

A recent study by the U.S. Geological Service says tamarisk, commonly known as saltcedar, consumes no more water than native plants such as cottonwoods and willows.

Also, the report says tamarisk-dominated landscapes aren’t totally inhospitable to wildlife. Reptiles, amphibians and birds, including the endangered southwestern willow flycatcher, use and breed in tamarisk stands.

The report was requested by Congress asking for a review of the scientific literature about tamarisk and Russian olive to assess the impacts, distribution, water consumption and control methods for the two invasive species.

Researchers also assessed the impacts to wildlife use and the challenges associated with revegetation and restoration following control efforts.

When it comes to water consumption, the report noted the removal of tamarisk from floodplain areas along rivers generally leads to replacement by other vegetation that consumes roughly equal amounts of water.

Removing tamarisk might not produce measurable water savings once the replacement vegetation is established.

“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.

However, tamarisk and Russian olive also grow on river terraces that are too high and dry for cottonwoods and willows, the report says. According to the reports, some scientists have suggested that revegetation with native dry-site species could save some water for human use. But the effectiveness of such an approach has not been demonstrated, the report says.

Studies looking at wildlife use of tamarisk-dominated landscapes indicate that while tamarisk does support some wildlife, it isn’t hospitable to certain specialized species, such as cavity dwelling birds.
“Dense tracts of pure saltcedar are typically unfavorable for most wildlife,” the report says, and goes on to note that many birds still prefer native cottonwood or willow habitat.

Other negative impacts of dense stands of tamarisk and Russian olive can include impeded access to riverside recreational areas, increased wildfire hazard and clogging of irrigation ditches, the report says.

According to the Geological Service, tamarisk and Russian olive are now the third and fourth most common streamside plants in 17 western states.

The plant arrived in North America in the 1800s when immigrants from southern Europe or the eastern Mediterranean brought tamarisk to the United States as an ornamental plant. It later was used as windbreaks and to stabilize river banks.

Removing tamarisk includes everything from herbicides and bulldozers to biological controls such as insects. The tamarisk or saltcedar leaf beetle has been used successfully in western Colorado and five other states.

However, scientists emphasize that once the tamarisk is eliminated, the replacement vegetation must be carefully selected.

“Research and monitoring could be particularly important in the context of biological control of saltcedar,” Shafroth said. “The beetle that has been released for biological control has been defoliating saltcedar and spreading rapidly in some watersheds. We really need to understand the effects of biocontrol on these ecosystems, to better inform river and riparian restoration.”


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