Saltcedar Biological Control:
Methodology, Exploration, Laboratory Trials,
Proposals for Field Releases, and Expected Environmental Effects

Thomas B. Egan

USDI Bureau of Land Management
150 Coolwater Lane
Barstow, California 92311
Phone: 619-255-8723
FAX: 619-255-8799
E-mail: tegan@ca2234.bara.ca.blm.gov

An Approach to Site Restoration andMaintenance
for Saltcedar Control

"If a tree dies, plant another in its place."
Linnaeus (1707-1778)
Swedish Botanist

There is more relevance in the above statement with regard to the control of saltcedar (Tamarix ramosissima, T. parviflora, T. chinensis) and other exotic plant species than one might recognize initially. However, the successful realization of this simple concept in many of today's natural areas can be quite complicated. Vegetative site restoration and long-term maintenance of such efforts in any natural area are difficult tasks in and of themselves. When combined with having to do battle with 1) a plant species such as saltcedar that has an incredible capacity to invade, i.e., ability to allocate a large proportion of available resources to seed production and vegetative growth as well as adaptations for both wind and water dispersal of these elements; and 2) native streamside and wetland plant communities that have characteristics of easy invasibility, i.e., areas with a large perimeter to volume ratio, altered natural disturbance regimes, mesic habitat conditions and contact with human activities (Bossard 1992); site restoration and maintenance can prove to be a daunting task.

Major obstacles to site restoration and maintenance when one is involved with saltcedar and other exotic plant control efforts often include:

1) a lack of adequate funding for the detection and effective control of exotic plants, as well as site restoration/maintenance, in non-agricultural systems;

2) inadequate site restoration planning and techniques;

3) a lack of strong public agency policy toward resolving conflicts that influence the effectiveness of control efforts, such as allowing continued livestock grazing, use of travelways, water diversion, flood control, etc. in restoration areas;

4) continued, as well as new, ground surface or water flow disturbances;

5) reintroductions of exotic or invasive plant species;

6) lack of regular, sustained maintenance; and

7) an underfunding of biological and ecological studies of invasive species and the communities they invade (Schierenbeck 1995).

Many of these obstacles pose distinct challenges for project managers, but with a little creativity, these challenges can be overcome, or at least the influence of these obstacles minimized. Above all, natural area site restoration and maintenance is an evolving management field that should be viewed as a combination of art and applied science. Techniques, strategies and planning frequently have to be revised or modified to fit the needs or realities at a particular site.

Even though it has become increasingly obvious that intensive management is required for the maintenance of natural ecosystems (Brussard 1991), the amount of on-the-ground site restoration and maintenance work necessary to achieve effective saltcedar control can range from little effort over an extended time (Neill 1985) to intensive effort on an annual basis (Taylor 1994), depending on whether the particular system is open to water flow or closed, the degree of saltcedar infestation, control techniques used and the amount of labor/supply resources dedicated to control efforts.

Due to the inherent resilience of streamside and wetland plant communities, site restoration goals can often be achieved with minimal effort as long as control effort planning encompasses a large enough area, control efforts are sustained and land management practices are altered to promote conditions conducive to native plants rather than saltcedar (Lovich et al. 1994, Dudley and Collins 1995). Long-term maintenance of such restoration work in relation to saltcedar in the American Southwest is more problematic, depending foremost upon how open the system is to waterborne saltcedar sources; the proximity of potential windborne saltcedar seed sources; and the degree to which site restoration was effective in establishing both ground and canopy vegetative cover.

Site restoration is a relatively young field of research in terms of available empirical information. Each site, each system, is different and we still have a lot to learn. The following seven point approach to site restoration and maintenance is recommended as general guidance for individuals and organizations currently involved in, or contemplating, saltcedar control in natural areas.

Seven Point Approach to Site Restoration and Maintenance

1. Look at the entire watershed or system and try to understand the factors which allow the invader and desired plant species to proliferate as well as the influence of human perturbations to the particular system, using as historic a background as feasible. Plan with a long-term vision. Control, restore and maintain strategically.

2. Plan for a sufficiently large enough restoration site size in order to maintain the small scale natural disturbances necessary to promote plant and animal community diversity but try to focus on a goal of plant community transition zone or "edge" habitat reduction. Focus restoration maintenance efforts in such "edge" areas.

3. Make use of natural system processes as well as control efforts to assist in site restoration and maintenance.

4. Eliminate livestock grazing, minimize road influences and modify fire suppression efforts in affected natural areas. Minimize soil disturbance, protect native vegetation, utilize fire to assist in non-indigenous plant species control and follow suppression efforts with whatever additional control efforts are needed to effectively kill burned non-indigenous plant species.

5. Minimize the conflicts between conservation and recreation within or near the subject natural area. Be cognizant of the full array of recreational uses that may occur and their associated influences upon non-indigenous plant species control, site restoration and maintenance goals.

6. Monitor and maintain project efforts on a regular basis. Revise control, restoration and maintenance strategies accordingly. Even a minimal monitoring effort can help ward off stumbling blocks to achieving your restoration goals and is likely to be cost-effective in the long run.

7. Lastly, keep informed. Maintain close liaison with others involved with habitat restoration work, particularly those involved with non-indigenous plant species control.

The principles outlined in the above approach rely heavily upon information summarized in Schierenbeck's 1995 documentary, "The Threat To The California Flora From Invasive Species: Problems And Possible Solutions" as well as a review of saltcedar control efforts to date. This approach is offered specifically for saltcedar control, but may also have applicability in the control of other non-indigenous plant species that threaten southwestern streams, wetlands and other sensitive natural areas.

Literature Cited

Bossard, C.C. 1992. Factors leading to invasiveness and invasibility. Proceedings of the Second California Exotic Pest Plant Symposium. Morro Bay, Calif.

Brussard, P.F. 1991. The role of ecology in biological conservation. Ecological Applications 1:6-12.

Dudley, T. and B. Collins. 1995. Biological invasions in California wetlands, the impacts and control of non-indigenous species in natural areas. Pacific Institute for Studies in Development, Environment and Security. Oakland, Calif.

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. Proceedings of the 46th Annual California Weed Conference, California Weed Science Society. San Jose, Calif.

Neill, W.M. 1985. Tamarisk. Fremontia 12:22-23.

Schierenbeck, K.A. 1995. The threat to the California flora from invasive species: problems and possible solutions. Madrono 42:164-174.

Taylor, J.P. 1994. A comparison of mechanical and herbicide/burn saltcedar control techniques. U.S. Fish and Wildlife Service Agency Environmental Assessment, Bosque del Apache National Wildlife Refuge, Socorro County, New Mexico.


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