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-~ ~ . . TheAlien SaItcedar ~ Inger ecological shili js underw>y. Patten believes native cottonwoods and willows can outCOIll- pete saltcedar under. 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 floodplain, the ..l<<eda" are leli to seed ~he lowest, wettest, lea.S[ suble areas. The cessation of grazing in the woodland has had an effect also, because catde prefer the laste of cortonwoods and willows. William Neill disputes Patten's belief th.t returning rivers to . n.tural flooding regime .nd reducing or eliminating ripari.n graz- ing will be enough. "Wh.t'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 imerested in saltced;u in the late 1970s during. visit to Death Valley N.tional Monument. Eagle Borax Spring had been a verdant, marshy oasis-criticJI wildlife h.bitat in the dry heart of the Moj.ve Desert. But by the 1960s, dense saltcedar growth had caused surface water to disap- pear, native grasses and reeds to dry up. and nearby mes~uitC' trees to suffer &om groundwater depletion. The NatIOnal Park Service suffbegan burning sahcedar as part of a control program in 1972. For the next 10 years, rangm and volunteers cut bad the resprouting saltcedar and dosed the stumps with a systemic herbicide that kills the root system. [he only effec- tive way to kill sahcedar. By 1982 the saltcedars were gOlle. water IN:lS pooling on the surface, grasses and reeds were coming bJck, and the mesquites were healthy again. What was good for E.g1e Borax Spring was good for other areas [00. '" sr.arted seeing tam.arisk aU around," S3ys NeiU, who hJS become sahcedar'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 M,anagement [0 let rum institute control programs on its land. He also org:mized vol- unteer work parries at various preserves. Neill's 7amarisk Nrwslf'ltfT publishes tlie latest findings on cutting saltcedar groves and 'pplying herbicides, and periodically announces the temporary repuhion of the invader from selected. springs and rip.arian .areas in southern California. These I.abor-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, saltceclar monocultures cover an estimated 50,000 to 60,000 acres-far too It has been estimated that aU the saltcedal'in the' Southwest annu~ uses twice as much water as aU the cities of southern California. it comes b.ck stronger than before:' says William Neill, a saltcedar- control advocate in southern California. "It is not balanced by narural predation or diseJses, 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. million winged seeds in a ye.,.......,eeds so tiny it takes 100,000 to make up a gram. When they sprout, the seedlings can grow up to 10 feet in . year. Given such proAigacy, it's no surprise that saltcedar escaped the homesteads and pasmres 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, sal(cedar was unknown before 1912. By 1915 it had spread to 600 .cres of delta land. By 1925 it covered 12,300 acres. In 1960 the most comprehensive survey to date estimated that sahcedar covered 900,000 acres from Oklahoma to southern California, Colorado to Sonora. Today experts place that figure at abom a million acres. Though it thrives best in hot areas below 4,000 feet in elevation, it has been seen JS far north and east as Idaho. Oregon. and Nebraska. otanists have typically ascribed the plant's phenome- nal spread [Q 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 Parten, a plant ecologis.t ar Arizona St;J,te Universlt)'. He believes saltcedar exploited changing environmental conditions that put native speci~ at a disadv.mtage. "If you want to ge~ rid of lama risk," he says, "you have to SlOp grazing and building dams." As evidence Pauen 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 lree of cattle grazing since the preserve was established in 1987. And because the Hassayampa is an undammed river, f100dpbin vegeration 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 sahcedar-eradic.ation program organized by the Nature Conservancy, but Parten think5 a 46... AMERICAN FOP-ESTSjANU.....llv/FEIJRU.....RY 199:' j 1 '~ i --+.;.. ';Ie ~