A Brief Review of the Impacts of Tamarisk, or
Saltcedar on Biodiversity in the New World

Jeffrey E. Lovich, Ph.D.

National Biological Service
Palm Springs Field Station
63500 Garnet Avenue
North Palm Springs, CA 92258-2000
Phone: 619-251-4823
FAX: 619-251-4099
E-mail: jeffrey_lovich@nbs.gov

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.

Selected References

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