Unwelcome Immigrant
Salt cedar has become a menace on the Rio Grande.
By D.J. Carwile
Texans are fighting a scourge of western rivers.
In the 1820s the tamarisk, a shrubby tree native to Asia and the Middle East, arrived at East Coast nurseries, destined to make a name for itself. Short, with a stumpy trunk and peeling bark that resembled that of the cedar, the hardy tamarisk made a fine ornamental for the garden, especially when it exploded into bloom with thousands of tiny purple flowers. Because of its dense root structure, California landowners planted tamarisk along rivers, hoping to control erosion. That’s when the trouble began.
The dense roots held the soil, all right, but many little tamarisks sprouted from those roots and turned into dense thickets. The tamarisk had another less-than-charming quality. Through its long taproot, it guzzled water voraciously, as much as 200 gallons a day, and deposited salt into the ground, making it uninhabitable for other plants. By the 1920s, the tamarisk had become unpleasantly familiar and better known by its common American name, the salt cedar.
Salt cedar has become an invasive scourge, and has replaced more than 1 million acres of native vegetation. It kept moving east, sprouting thickets along the banks of endangered West Texas rivers, including the Rio Grande and the Pecos. Ten years ago salt cedar invaded a short stretch of the Colorado River near San Angelo and quickly claimed 5,000 acres. In West Texas, where plants typically store water rather than squander it, salt cedar is a menace.
“The humidity outside may be 15 percent, but in a salt cedar thicket it could be 100 percent,” says Danny Allen, a Texas Parks and Wildlife Department wildlife habitat biologist. “On a dry summer day, you can walk through a stand of salt cedar and walk out the other side wet.”
To make matters worse, salt cedars seem to have little value for native wildlife. The scaly leaves are not suitable for browsers, and the seeds, produced prolifically, contain little protein. Biologists studying a stretch of Nevada’s Colorado River found that 100 acres of native plants can support more than 150 bird species, while 100 acres of salt cedar support only four.
Biologists and landowners have tried bulldozing, root cutting and simple hand-pulling to eliminate salt cedar, but such methods are expensive, time-consuming and not very practical. The best results have come by using herbicide.
For the last three years, biologists from Texas A&M University have suppressed salt cedar along a 118-mile stretch of the Pecos River by spraying it from a helicopter with a chemical whose trade name is Arsenal. By using a helicopter instead of an airplane, the biologists have made precise applications of the herbicide, which inhibits photosynthesis in trees but is deemed harmless to animals. They estimate they have killed enough salt cedar to save 6,380 acre-feet of water per year, enough to meet the needs of roughly 10,000 households.
Jack DeLoach, Ph.D., from the USDA Agricultural Research Station in Temple, may have found biological solutions in the leaf beetle, Diorhabda elongata, found in China, and the mealybug, Trabutina mannipara, found in Israel. These bugs feed solely on salt cedar. After extensive testing in the laboratory, DeLoach recently released a few hundred beetles into an isolated thicket in Baylor County.
Eliminating salt cedars solves only part of the problem they create. The salty soil they leave behind can retard native plants such as willow and cottonwood for years. One observer says that salt cedar is only part of the problem in riparian corridors. If we had not dammed our rivers, naturally occurring floods might flush out salts and drown many of the salt cedars.
Destroying the salt cedar population has met with some opposition, though. Some biologists are concerned about the impact on the southwestern willow flycatcher. This federally endangered bird uses native willows for nesting, but has been forced to use salt cedars in infested areas.
Although the Texas Department of Agriculture has urged the legislature to ban the sale of salt cedar, this invasive plant is still for sale in some Texas nurseries. When a bill is proposed this legislative session to ban the sale of harmful species, the salt cedar is certain to be on the list.
