Exotic species often compete for resources utilized by native species and in many cases disrupt ecological cycles. Modern ecologists are now well aware of the problems caused by the invasion of exotic species into natural areas and some consider this to be the greatest single threat to biodiversity globally. Tamarisks, or saltcedars (Tamarix spp.), are a genus of plants native to the Old World. Introduced into the United States in the early 1800's, they now occupy over 607,050 hectares (1,500,020.5 acres) of riparian habitat in the western United States. Some, such as T. ramosissima, T. chinensis, and T. parviflora, are considered to be undesirable because of their rapid spread and potential dominance in native plant communities.
Tamarisk has several real and potential impacts on biodiversity at all levels of organization. At the broad level, ecosystems exhibit heterogeneity that contributes to biodiversity at lower levels of organization. Spatially extensive assemblages of any species have the potential to alter geomorphology and geomorphic processes through bioturbation, alteration of nutrient or fire cycles, and patterns of succession. Previous studies suggest that tamarisk spread has significant effects on river channel morphology including the ability to decrease channel width, increase overbank flooding, stabilize sand bars at river bends, and enlarge and stabilize islands. Others have challenged the ability of tamarisk to modify channel morphology proposing that natural erosion, dam building, precipitation patterns, flood frequency, and watershed management are responsible for observed changes in southwestern river channels.
At the level of communities, tamarisk has been implicated in the decline of riparian cottonwood forests along the Rio Grande in New Mexico by limiting the amount of germination sites available to cottonwood. The higher soil salinity tolerance of tamarisk gives it a competitive advantage over native riparian plant species in some areas. Similarly, in Australia, where tamarisk is not native, it is capable of replacing native plant communities with an assemblage comprised of only a few species of introduced and salt tolerant plants. Tamarisk also promotes increased fire frequencies in plant communities that are generally fire-intolerant. The suitability of tamarisk as wildlife habitat has been a subject of considerable debate. Most studies show that tamarisk-dominated riparian areas have depauperate faunas, even in the native range of tamarisk. In contrast, other species assemblages, most notably birds, will utilize, and sometimes appear to prefer, tamarisk woodlands in the southwestern United States, although preferences may vary geographically.
At the level of individual species, responses of various animals to tamarisk domination of their habitats also varies. Although no species are known to have become extinct as a result of tamarisk spread, local declines of some are attributed to the invasion including desert pupfish and Southwestern willow flycatchers. In contrast, some birds are known to nest in tamarisk-dominated plant communities including doves, Mississippi kites and Black-chinned Hummingbirds in the Grand Canyon. Ironically, some populations of Southwestern willow flycatchers also nest in tamarisk. Tamarisk may have the potential to cause the extinction of narrowly distributed, endemic and endangered species such as the desert slender salamander if it invades their habitat.
Andersen, D. C. 1994. Demographics of small mammals using anthropogenic desert riparian habitat in Arizona. Journal of Wildlife Management 58:445-454.
Anderson, B. W. 1996. Salt cedar, revegetation and riparian ecosystems in the southwest. In: J. Lovich, J. Randall, and M. Kelly (eds.), Proceedings of the California Exotic Pest Plant Council. In press.
Anderson, B. W., and E. R. Miller. 1990. Revegetation and the need to control exotic plant species. In: Yosemite Centennial Symposium Proceedings. Natural Areas and Yosemite: Prospects for the future. pp. 350-358.
Angermeier, P. 1994. Does biodiversity include artificial diversity? Conservation Biology 8: 600-602.
Ball, J. T., J. B. Picone, and P. D. Ross. 1994. Evapotranspiration by riparian vegetation along the Colorado River. Report to the U.S. Bureau of Reclamation under contract No. 1-CP-30-08910. Submitted by the Biological Sciences Center of the Desert Research Institute. 188 pp.
Barrows, C. W. 1993. Tamarisk control II: a success story. Restoration and Management Notes 11:35-38.
Baum, B. 1967. Introduced and naturalized tamarisks in the United States and Canada (Tamaricaceae). Baileya 15:19-25.
Brooke, R. K. 1982. The bird community of Tamarix-clad drainages, northwestern karoo, Cape Province. Ostrich 63:42-43.
Brotherson, J. D., and D. Field, 1987. Tamarix: impacts of a successful weed. Rangelands 9:110-112.
Brotherson, J. D., and Von Winkel. 1986. Habitat relationships of saltcedar (Tamarix ramosissima) in central Utah. Great Basin Naturalist 46:535-541.
Brotherson, J. D., J. G. Garman, L. A. Szyska. 1984. Stem-diameter age relationships of Tamarix ramosissima in central Utah. Journal of Range Management 37:362-364.
Brown, B. T. 1992. Nesting chronology, density and habitat use of black-chinned hummingbirds along the Colorado River, Arizona. Journal of Field Ornithology. 63:393-400.
Brown, B. T., and M. W. Trosset. 1989. Nesting-habitat relationships of riparian birds along the Colorado River in Grand Canyon, Arizona. Southwestern Naturalist 34:260-270.
Busch, D. E., and S. D. Smith. 1993. Effects of fire on water and salinity relations of riparian woody taxa. Oecologia 94:186-194.
Busch, D. E., and S. D. Smith. 1995. Mechanisms associated with decline of woody species in riparian ecosystems of the southwestern U.S. Ecological Monographs. 65:347-370.
Busch, D. E., N. L. Ingraham, S. D. Smith. 1992. Water uptake in woody riparian phreatophytes of the southwestern United States: a stable isotope study. Ecological Applications 2:450-459.
Clout, M. 1995. Introduced species: the greatest threat to global biodiversity. Species (Newsletter of the Species Survival Commission-The World Conservation Union) No. 24:34-36
Crins, W. J. 1989. The Tamaricaceae in the southeastern United States. Journal of the Arnold Arboretum 70:403-425
Davenport, D. C., P. E. Martin, and R. M. Hagan. 1982. Evapotranspiration from riparian vegetation: water relations and irrecoverable losses from saltcedar. Journal of Soil and Water Conservation 37:233-236.
DeLoach, C. J. 1989. Prospects for biological control of saltcedar (Tamarix spp.) In riparian habitats of the southwestern United States. In: pp. 307-314, E.S. Delfosse (ed.). Proceedings VII International Symposium on the Biological Control of Weeds. Ist. Sper. Patol. Veg. (MAF). 6-11 March, 1988, Rome, Italy.
DeLoach, C. J., M. J. Pitcairn, and D. Woods. 1996. Biological control of salt cedar in California. In: pp. 30-31. DiTomaso, J., and C. E. Bell (eds.). Proceedings of the Saltcedar Management Workshop. Sponsored by the University of California Cooperative Extension, Imperial County and U.C. Davis, and the California Exotic Pest Plant Council.
DiTomaso, J., and C. E. Bell (eds.). 1996. Proceedings of the Saltcedar Management Workshop. Sponsored by the University of California Cooperative Extension, Imperial County and U.C. Davis, and the California Exotic Pest Plant Council. 61 pp.
Everitt, B. L. 1979. Fluvial adjustments to the spread of tamarisk in the Colorado Plateau region: discussion. Geological Society of America Bulletin, Part I 90:1183.
Everitt, B. L. 1980. Ecology of saltcedar - A plea for research. Environmental Geology 3:77-84
Garman, J. G., and J. D. Brotherson.. 1982. Comparisons of sites infested and not infested with saltcedar (Tamarix pentandra) and Russian olive (Elaeagnus angustifolia). Weed Science 30:360-364.
Gay, L. W., and L. J. Fritschen. 1979. An energy budget analysis of water use by saltcedar. Water Resources Research 15:1589-1592.
Glinski, R. L., and R. D. Ohmart. 1983. Breeding ecology of the Mississippi Kite in Arizona. The Condor 85:200-207.
Graf, W. L. 1978. Fluvial adjustments to the spread of tamarisk in the Colorado Plateau region. Geological Society of America Bulletin 89:1491-1501.
Graf, W. L. 1979. Fluvial adjustments to the spread of tamarisk in the Colorado Plateau region: reply. Geological Society of America Bulletin, Part I 90:1183-1184.
Griffin, G. F., D. M. Stafford Smith, S. R. Morton, G. E. Allan, and K. A. Masters. 1989. Status and implications of the invasion of tamarisk (Tamarix aphylla) on the Finke River, Northern Territory, Australia. J. Environmental Management 29:297-315.
Hagenmeyer, J., and Y. Waisel. 1988. Excretion of ions (Cd2, Li+, Na+, and Cl-) by Tamarix aphylla. Physiologia Plantarum 73:541-546.
Hereford, R. 1984. Climate and ephemeral-stream processes: twentieth-century geomorphology and alluvial stratigraphy of the Little Colorado River. Geological Society of America Bulletin 95:654-668.
Horton, J. S., 1977. The development and perpetuation of the permanent tamarisk type in the phreatophyte zone of the southwest. USDA Forest Service General Technical Report, U.S. Rocky Mountain Forest Range Experiment Station 43:124-127.
Howe, W. H., and F. L. Knopf. 1991. On the imminent decline of Rio Grande cottonwoods in central New Mexico. Southwestern Naturalist 36:218-224.
Hunter, W. C., B. W. Anderson, and R. D. Ohmart. 1985. Summer avian community composition of Tamarix habitats in three southwestern desert riparian systems. In: pp. 128-134. Riparian Ecosystems and their management: reconciling conflicting uses. U.S. Department of Agriculture, Forest Service, General Technical Report RM-120.
Hunter, W. C., R. D. Ohmart, and B. W. Anderson. 1988. Use of exotic saltcedar (Tamarix chinensis) by birds in arid riparian systems. The Condor 90:113-123.
Johnson, S. 1987. Can tamarisk be controlled? Fremontia 15:19-20.
Kerpez, T. A., and N. S. Smith. 1987. Saltcedar control for wildlife habitat improvement in the southwest United States. U.S. Department of the Interior, Fish and Wildlife Service, Resource Publication 169. 16 pp.
Kunzmann, M. R., R. R. Johnson, and P. S. Bennett (eds.). 1989. Tamarisk control in the southwestern United States. U.S. Department of the Interior, National Park Service, Special Report No. 9 (Revised August, 1990). 144 pp.
Lovich, J. E., T. B. Egan, and R. C. de Gouvenain. 1994. Tamarisk control on public lands in the desert of southern California: two case studies. 46th Annual California Weed Conference, California Weed Science Society. pp. 166-177.
Lovich, J. E. and R. C. de Gouvenain. in press. Saltcedar invasion in desert wetlands of the southwestern United States: ecological and political implications.
Neill, W. M. 1983. The tamarisk invasion of desert riparian areas. Education Foundation of the Desert Protective Council, Inc. Educational Bulletin No. 83-4:1-4.
Neill, W. M. 1985. Tamarisk. Fremontia 12:22-23.
OTA (Office of Technology Assessment), 1993. Harmful Non-Indigenous Species in the United States. OTA-F-565, Washington, D.C.
Rice, J., R. D. Ohmart, and B. W. Anderson. 1983. Habitat selection attributes of an avian community: a discriminant analysis investigation. Ecological Monographs 53:263-290.
Rosenberg, K. V., R. D. Ohmart, W. C. Hunter, and B. W. Anderson. 1991. Birds of the lower Colorado River valley. The University of Arizona Press, Tucson.
Shafroth, P. B., J. M. Friedman, and L. S. Ischinger. 1995. Effects of salinity on establishment of Populus fremontii (cottonwood) and Tamarix ramosissima (saltcedar) in southwestern United States. Great Basin Naturalist 55:58-65.
Soulé, M. E. 1990. The onslaught of alien species, and other challenges in the coming decades. Conservation Biology 4:233-239.
Sudbrock, A. 1993. Tamarisk control I: fighting back. An overview of the invasion, and a low-impact way of fighting it. Restoration and Management Notes 11:31-34.
Thomson, W. W., W. L. Berry, and L. L. Liu. 1969. Localization and secretion of salt by the salt glands of Tamarix aphylla. Proceedings National Academy Science 63:310-317.
USFWS (U.S. Fish and Wildlife Service). 1993. Endangered and threatened wildlife and plant; proposed rule to list the Southwestern Willow Flycatcher as endangered with critical habitat. Federal Register 58:39495-39522.
van Hylckama, T. E. A. 1970. Water use by salt cedar. Water Resources Research 6:728-735.
van Hylckama. T. E. A. 1974. Water use by saltcedar as measured by the water budget method. U.S. Geological Survey Professional Paper 491-E. 30 pp.
Versfeld, D. B., and B. W. van Wilgen, 1986. Impacts of woody aliens on ecosystem properties. In: The Ecology and Management of Biological Invasions in Southern Africa. Macdonald, I.Q.W., Kruger, F.J. and A.A. Ferrar, eds. Oxford University Press, Cape Town.
Viljoen, P. J. 1989. Habitat selection and preferred food plants of a desert-dwelling elephant population in the northern Namib Desert, South West Africa/Namibia. African Journal of Ecology 27:227-240.
Weeks, E. P., H. L. Weaver, G. S. Campbell, and B. D. Tanner. 1987. Water use by saltcedar and replacement vegetation in the Pecos River floodplain between Acme and Artesia, New Mexico. U.S. Geological Survey Professional Paper 491-G. 33 pp.
Weintraub, J. 1993. Effect of tamarisk removal on avian distributions at Camp Cady Wildlife Area in the California Mojave Desert. Ph.D. Dissertation, California State University, Fullerton. 201 pp.
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