IMPACT, BIOLOGY, AND ECOLOGY OF SALTCEDAR (TAMARIX SPP.) IN THE SOUTHWESTERN UNITED-STATES

Eight species of Tamarix were first brought to North America in the 18 00s from southern Europe or the eastern Mediterranean region. Many of the species escaped cultivation and by the 1920s invaded about 4,000 h a of riparian habitat in the southwestern United States. By 1987, it. was estimated to have increased to at least 600,000 ha. The success of saltcedar in the southwest can be attributed to sever.al factors rela ted to its growth habit, reproduction, water usage, ability to tolerat e highly saline conditions, and redistribution of salt from deep in th e soil profile to the soil surface. The flowers produce small, numerou s, and tufted seeds that can be carried long distances by wind or wate r. The seeds, however, have a short period of viability, and must come in contact with suitable moisture within a few weeks of dispersal. Un like obligate phreatophytes, such as willows and cottonwoods, saltceda r is a facultative phreatophyte and is often able to survive under con ditions where groundwater is inaccessible. The high evapotranspiration rates of saltcedar can lower the water table and alter the Aoristic c omposition in heavily infested areas. Mature plants are tolerant to a variety of stress conditions, including heat, cold, drought, flooding, and high salinity. Saltcedar is not an obligate halophyte but survive s in areas where groundwater concentrations of dissolved solids can av erage 8,000 ppm or higher. In addition, the leaves of saltcedar excret e salts that are deposited on the soil surface under the plant, inhibi ting germination and growth of competing species.