Dr. Jeff Lovich
United States Geological Survey
Department of Biology
University of California
Riverside, CA 92521-0427
Saltcedar, or tamarisk, is an invasive exotic plant species that is well established in the southwestern United States, particularly in riparian areas. There is widespread, but not unanimous, recognition that saltcedar is undesirable from the standpoint of maintaining vigorous native ecosystems, and the species has the dubious distinction of being included on the California Exotic Pest Plant Council's list of exotic pest plants of greatest ecological concern.
The rapid spread of saltcedar throughout the southwestern United States has been partly facilitated by large-scale modifications of environmental conditions associated with human activity. One such major disturbance was the damming of rivers in the Southwest for flood control, energy generation, and irrigation projects. Natural flooding regimes were changed and floodplain ecosystem characteristics were altered to the degree that an exotic species like saltcedar, better adapted to these new abiotic characteristics than were the native species, proliferated. Saltcedar is now found in a wide variety of climates and soils where human disturbances have created favorable conditions for its establishment.
However, saltcedar is not restricted to areas disturbed by past human activities. In the Colorado Desert of southern California, it has become established in remote mountain springs, streams and washes, such as Buzzard Spring in the Eagle Mountains of Riverside County, where no signs of human disturbance are apparent, many miles away from the Colorado River, and sometimes thousands of feet above grazed or cultivated areas. In parts of Buzzard Spring for instance, saltcedar did not merely become an integrated component of the original plant community of arrowweed and cattail; it became overwhelmingly dominant, altering completely the species composition and yielding nearly monotypic stands of saltcedar. The debate on whether saltcedar is an aggressive invader or simply an opportunistic species is largely academic: the presence of saltcedar in riparian habitats of the southwestern United States is a warning sign that something is very wrong with the ecosystem.
The recent listing of the Southwestern Willow Flycatcher (a native species that nests in saltcedar) under the Endangered Species Act of the United States has challenged efforts to move forward with release of insects for biocontrol of saltcedar. Concern for the Southwestern Willow Flycatcher, a species that evolved in native riparian plant communities, should not ignore the plight of numerous other legally protected, sensitive, and even common species that are negatively affected by saltcedar. I believe that the key to conservation of biodiversity rests with the preservation of natural habitat. To that end, in a recent issue of Conservation Biology, Murphy et al. (1994) noted that "Conservation strategies that try to restore and maintain natural habitats offer greater promise than strategies that attempt to conserve species apart from their habitats. Habitat-based strategies also increase the chances that other species occupying the same areas will not become endangered."
Past efforts to characterize saltcedar as good wildlife habitat ignore or dismiss the importance of native co-evolved plant communities in contributing to overall biodiversity of native species. In addition, purported benefits of saltcedar to selected bird species do not necessarily extend to other animals. Making the best of a bad lot is still a bad lot. From an evolutionary and ecological perspective we should move decisively to restore ecosystem function and health by controlling saltcedar and eliminating conditions that foster its success.