There is more relevance in the above statement with regard to the control of native/exotic invasive plants than one might recognize at first glance. This is particularly true in relation to the control of the exotic plant group commonly referred to as saltcedar (Tamarix ramosissima, T. parviflora, T. chinensis ), which has replaced several million acres of native vegetation within southwestern stream and wetland natural areas. Resultant saltcedar-dominated natural areas appear to be affected hydrologically and the saltcedar plant communities subsequently formed have been found to be far less productive, diverse and ecologically functional, than the native plant communities they replace. Several control strategies have been developed to remove saltcedar from natural areas for a variety of management objectives, but vegetative site restoration and maintenance are the only two common elements of those control programs that have been effective over the long term. Vegetative site restoration involves not only restoring the native plant community, terrain and hydrology of a natural area but the ecological processes and disturbance cycles necessary to sustain that native plant community over time. Unfortunately, little has been written as specific guidance for site restoration and maintenance associated with saltcedar control. This document briefly discusses the concept of site restoration and maintenance in relation to saltcedar control and outlines a seven point approach to consider in the implementation of such a control program.
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 challenges to site restoration and maintenance in natural areas affected by saltcedar control programs often include:
These challenges can appear overwhelming for project managers, but a little creativity and networking can go a long way in meeting these challenges, or at least towards minimizing their influence upon project objectives. Above all, natural area site restoration and maintenance is an evolving management field that should be viewed as a combination of art, experimentation and applied science. Selected techniques, strategies and planning have to be frequently designed from scratch, monitored and modified to fit the needs or realities at a particular site.
Although 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/restoration techniques used and the amount of labor/supply resources dedicated to control efforts. Site restoration costs can similarly range from low to high (Egan et al., 1993), with site maintenance costs increasing as site restoration success decreases. Applied restoration techniques have shown both success and failure, but their basis is conceptually sound (Bureau of Reclamation 1990a).
Due to the inherent resilience of streamside and wetland plant communities, site restoration goals can often be achieved with minimal effort if control efforts encompass 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 restored areas in relation to saltcedar in the American Southwest is more problematic, depending foremost upon how open the natural area is to waterborne saltcedar sources; the proximity of windborne saltcedar seed sources; and the degree to which site restoration was effective in establishing both native ground and canopy, vegetative cover.
Site restoration is a relatively young field of natural area management in terms of available empirical information and successfully demonstrated techniques. 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.
1. Look at the entire watershed or system and identify the factors which allow the invader and desired plant species to proliferate, as well as the influence of human activities on the site. Use an historic background if possible. Plan with a long-term vision. Control, restore and maintain strategically.
2. Plan for a sufficiently large restoration site in order to provide for the natural conditions necessary to promote plant and animal community diversity. Focus on a goal of plant community transition zone or "edge" habitat reduction and apply restoration maintenance efforts in such "edge" areas.
3. Make use of natural processes such as flood and fire as well as applied control efforts to assist in site restoration and maintenance when opportunities arise. Two examples include: retention of burnt saltcedar woody material resulting from a controlled fire to create suitable germination sites for seeding; and utilizing floodborne sediment to plant native tree poles.
4. Eliminate livestock grazing, minimize motor vehicle and railroad influences and modify fire suppression efforts in affected natural areas. Minimize soil disturbance, protect native vegetation, utilize fire to assist in saltcedar control and follow suppression efforts with additional control efforts needed to effectively kill burned, invasive plant species capable of resprouting.
5. Minimize recreation conflicts within or near the subject natural area. Be cognizant of the full array of recreational uses that may occur and their associated influences on natural features, upon invasive plant control, site restoration and maintenance goals.
6. Monitor and maintain desired site conditions on a regular basis. Revise control, restoration and maintenance strategies accordingly. Even a minimal monitoring and action effort can 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 are based 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 site restoration for other invasive plant control efforts in our nation's natural areas.
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.
Bureau of Reclamation. 1990a. Vegetation management study-lower Colorado River. Phase 1 Draft. Lower Colorado Region, Boulder City, Nev.
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.
Egan, T.B., R.A. Chavez and B.R. West. 1993. Afton Canyon saltcedar removal first year status report. In, L. Smith and J. Stephenson (tech. coords.), Proceedings of the Symposium on Vegetation Management of Hot Desert Rangeland Ecosystems. Phoenix, Ariz.
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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