Scientists are investigating the population of tamarisk trees in the Southwest because they have been spreading rapidly, and there is worry about their impact on the environment.

The species of tasmarisk, or salt cedar, in Arizona are known for being drought, heat and salt-tolerant, and some are taking over areas where native trees once flourished.

Susanna Pearlstein, a doctoral student in the University of Arizona's Department of Soil, Water and Environmental Science, is studying tamarisk-rich ecosystems in the Colorado Plateau and Great Basin.

She says the plants were brought to the United States from Eurasia in the 1800s and have spread to almost every state.

"It was a valuable import," Pearlstein says. "They were these beautiful plants, and they have a very beautiful flower and yet, and they were also brought over for soil erosion."

Scientists and others who are concerned about its proliferation have introduced a beetle, also from Eurasia, that evolved with the tamarisk and helps to reduce its population in its native habitat.

"It was released in 2001 and since then it has spread," she says.

Pearlstein is studying the relationship between the insects and the tamarisks, and the impact on areas such as Arizona's riparian habitats.

"They are certainly reducing tamarisks' water use," she explains. "In one study that I'm on we've seen a 50 percent reduction in water use in just one year of beetle arrival."