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It has been esthnated that all the saltcedar in the Southwest annuallyy uses twice as much water as all the cities of southern California, f it comes back stronger than before," says William Neill, a saltcedar- .control advocate-in southern California. "It is nor balanced by rAttiral predation or diseases, so it displaces the native species. It sur vives extreme environmental conditions very well —fire, salinity, immersion, drought, dense shade." And its reproduction is copious: A single saltcedar can produce up to half a million winged seeds in a year —seeds so tiny it takes 100,000 to make up a gram. When they sprout, the seedlings can grow up to 10 feet in a year. Given such profligacy, it's no surprise that saltcedar escaped the homesteads and pastures where it had been introduced, by the early 20th century it was spreading quickly. On Lake McMillan, a reser- voir on New Mexico's Pecos River, saltbedar was unknown before 1912. By 1915 it had spread to 600 acres of delta land. By 1925 it covered 12,300 acres. In 1960 the most comprehensive survey to date estimated that saltcedar covered 900,000 acres from Oklahoma to southern California, Colorado to Sonora. Today experts place that figure at about a million acres. Though it thrives best in hot areas below 4,000 feet in elevation, it has been seen as far north and east as Idaho, Oregon, and Nebraska. otanists have typically ascribed the plant's phenome- nal spread to its aggressive growth and prolific repro- duction. But recently some ecologists have asked why it did not spread explosively until the turn of the century. One of those scientists is Duncan Patten, a plant ecologist at Arizona State University. He believes saltcedar exploited changing environmental conditions that put native species at a disadvantage. "Ifyou want to get rid of tamarisk;' he says, "you have to stop grazing and building dams." As evidence Patten points to the Nature Conservancy's Hassayampa River Preserve, a five -mile stretch of well - preserved riparian forest in the Sonoran Desert of central Arizona. The woodland has been free of cattle grazing since the preserve was established in 1987. And because the Hassayampa is an undammed river, floodplain vegetation is wiped out periodically by high water. Patten has monitored vegetation changes on the preserve since 1988 and has seen seedling cottonwoods and willows thrive and saltcedars decline. Some of that is due to a saltcedar- eradication program organized by the Nature Conservancy, but Patten thinks a 46 ... AMERICAN FQRFsTsJAN-u RYLFFuk_uARY_l9JS- larger ecological shift is underway. Patten-believes native cottonwoods and willows can outcom- pete saltcedar under .a natural flooding regimen, in part because the natives release their seeds earlier in the year than the invaders do. Shaded out of higher parts of the floodpWn, the saltcedars are left to seed the lowest, wettest, least stable areas. The cessation of grazing in the woodland has had an tffect also, because cattle prefer the taste of cottonwoods and willows. William Neill disputes Patten's belief that returning rivers.to a natural flooding regime and reducing or eliminating riparian graz- ing will be enough. "What's going to make the difference is remov- ing the big seed trees;' he says. "The natural trend is for more tamarisk and fewer native species, unless there's proactive human involvement:' Neill, a petroleum engineer, became interested in saltcedar in the late 1970s during a visit to Death Valley National Monument. Eagle Borax Spring had been a verdant, marshy oasis — critical wildlife habitat in the dry heart of the Mojave Desert. But by the 1960s, dense saltcedar growth had caused surface water to disap- pear, native grasses and reeds to dry up, and nearby mesquite trees to suffer from groundwater depletion. The National Park Service staff began burning saltcedar as part of a control program in 1972. For the next 10 years, rangers and volunteers cut back the resprouting saltcedar and dosed the stumps with a systemic herbicide that kills the root system, the only effec- tive way to kill saltcedar. By 1982 the saltcedars were gone, water was pooling on the surface, grasses and reeds were coming back, and the mesquites were healthy again. What was good- for Eagle Borax Spring was good for other areas too. "I started seeing tamarisk.all around;'says Neill, who has become saltcedar's most energetic enemy. "It gradually got to be a bigger and bigger part of my life." He received a herbicide applica- tion license and convinced the Bureau of Land Management to let him institute control programs on its land. He also organized vol- unteer work parties at various preserves. Neill's Tainarisk NVru6letrrr publishes the latest findings on cutting saltcedar groves and applying herbicides, and periodically announces the temporary repulsion of the invader from selected springs and riparian areas in southern California. These labor- intensive techniques work well at isolated desert springs and preserves, where saltcedar may cover only a few acres. But in areas such as the lower Colorado River corridor, saltcedar monocultures cover an estimated 50,000 to 60,000 acres —far too