When it comes to the rivers of the Southwest, tamarisk, or salt cedar, has long been public enemy number one.

Introduced for erosion control, the non-native tree came to dominate riverside habitats where cottonwoods and willows once flourished. It's been blamed for declining water quality and quantity on the Rio Grande and the Pecos River in West Texas.

Tamarisk was attacked with herbicides and bulldozers. More recently, scientists have imported one of the plant's natural enemies – the tamarisk leaf beetle. Beetle larvae feed on tamarisk leaves.

A leaf beetle project launched in the Big Bend in 2006. And the results here have been promising.

An Old World native, tamarisk was in...