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Digging up saltcedar won't boost water supplies

April 28, 2010 |  8:24 pm

Westerners who'd like to wring more water out of their rivers and streams aren't going to do it by getting rid of saltcedar, a new federal report suggests. The report, released Wednesday, undercuts the long-held perception that the non-native shrub is the vampire of Western watersheds. For decades saltcedar, also called tamarisk, has been known as an invader with a big thirst that sucked water out of rivers and depleted aquifers, leaving less for people and livestock.

But an extensive review of scientific studies found that the plant uses about the same amount of water as native trees, such as willows and cottonwoods, and isn't nearly as thirsty as it is has been portrayed in popular accounts. “The conclusion, looking across all of the published literature, is that we haven’t seen clear evidence of a significant increase in water supply for consumptive human use through the removal of saltcedar,” said Curt Brown, one of the report's editors and research director of the U.S. Bureau of Reclamation.

Federal, state and county agencies across the West have uprooted saltcedar in the belief that erasing it from riverbanks would save water. “In the West we're always looking for ways to stretch our water supply," Brown said. "And sometimes it takes a while for the science to catch up with the common belief.”

“If the primary interest was in stretching water supply," he added, "there are a number of other ways to conserve and augment water supply ... that are much more reliable and predictable." 

Saltcedar has also been considered a threat to wildlife, since it pushes out native vegetation. Though studies have found that some kinds of wildlife don't do well in saltcedar, other species fare just fine.

More than half the known breeding sites for the endangered Southwestern willow flycatcher occur in riparian stands that include the invader. "Studies found no evidence of reduced survivorship or productivity," compared with those nesting in native vegetation, the report says.

Saltcedar was introduced to the U.S. in the late 1800s as an ornamental plant used for erosion control. Dam construction helped the shrub spread across the arid West by changing riverbank conditions. By the 1960s, tamarisk was common along the lower reaches of the Colorado, Rio Grande, Gila and Pecos rivers.

The report, compiled by the U.S. Geological Survey in conjunction with the reclamation bureau and the U.S. Forest Service at the request of Congress, reached a similar conclusion about another common non-native, the Russian olive.

-- Bettina Boxall

Illustration credit: Los Angeles Times