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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology 9 REVEGETATION Issue 7 Potential Interference with Revegetation and Reestablishment of the Native Plant Community THE WILSHIRE GROUP POSITION The Wilshire group (Wilshire et al., 1993) raised the concern that long-term integrity of vegetation established on the covers of the waste repository trenches will be compromised because of ''misconceptions about revegetation enhancements of the cover design.'' They emphasized that the raised aspect of the cover and its isolation from surface-water flow runon from the desert in the surrounding area would result in the lack of sufficient moisture to maintain vegetation on the cap. In support of their position, they cited publications that demonstrate the "dependency" of desert plants on soil recharge from surface flows (e.g., Schlesinger and Jones, 1984). Water erosion and infiltration through the cap was considered a consequence of the resulting absence of vegetation. THE DHS/U.S. ECOLOGY POSITION The DHS and U.S. Ecology point to their Revegetation Plan for the Ward Valley site in response to the Wilshire group's assessment. In the view of the site developers, this plan includes the potential for successful revegetation, not only through active revegetation but through natural revegetation from plant disseminules from the local area. THE COMMITTEE'S APPROACH Revegetation Plan The committee reviewed the site revegetation plan, and other pertinent literature, and invited independent revegetation experts and experimenters to participate in the open meeting to share their knowledge and experience. At the time of the review of the Ward Valley documents, US Ecology had not developed a comprehensive revegetation program. Their plans called for establishing a revegetation program with three phases: (1) procedures for transplanting cacti and yuccas during construction, (2) procedures for revegetation of caps of completed trenches during
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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology operations, and (3) procedures for restoration of the entire site after closure. Qualified biologists will be invited to participate on an ad hoc committee to help develop revegetation procedures and criteria for evaluating success of revegetation efforts. Selection of these biologists should be based on (1) fundamental knowledge of Mojave Desert ecosystems, for example, individuals who were involved with the International Biological Program (IBP) Mojave Desert validation site near Mercury, Nevada (see Wallace et al., 1980), (2) experience in restoring disturbed Mojave desert sites, and (3) familiarity with different biotic and abiotic components of desert ecosystems, for example, vegetation, vertebrates, invertebrates, and microorganisms. The revegetation program, which is planned to follow a set of guidelines established by US Ecology for their revegetation activities, such as use of native species and restoration of soil mycorrhizae, will be greatly strengthened if the committee of experts represents not only a broad spectrum of biological expertise, but also expertise in soil hydrology and ecology, and micrometeorology. Although the revegetation program has yet to be developed, there are many individuals who have had extensive experience in revegetation of disturbed Mojave Desert locations. Vasek (1975 a,b) has used his knowledge of Mojave Desert ecosystems to restore disturbed pipeline corridors. Wallace (Wallace et al., 1980) was one of the leaders at the Mercury, Nevada IBP study site. Based on this multi-year effort, his group established guidelines and described problems that should be considered in desert restoration. Others have participated in these and similar efforts and could contribute considerable knowledge and real-word experience to any revegetation program at Ward Valley. The use of individuals with this level of desert restoration experience, and the development of a detailed revegetation program, is essential for this location. Although natural revegetation occurs on disturbed sites within the Mojave Desert, it may initially create a sparse vegetation cover that will be insufficient for its role as a soil stabilizer and transpiration agent (Vasek, 1979/80). Consequences of Elevated Trench Cover Elevation of the trench cover above the surrounding terrain will prevent runon and thus the upper end of the cover (caps) will receive only incident precipitation while the lower end will receive some runon from the upper end (limited because of the 518 m catchment length). A consequence of this moisture gradient will be a vegetation cover gradient, the upper end of the trench caps having sparser plant cover and possibly plants less robust than at the lower end. The vegetation cover gradient should not cause a problem relative to soil erosion. The upper end of the trench cap will receive only rainfall and thus will not be impacted by surface flow erosion. On lower portions of the cover, and in the troughs between the trench caps, the increased runoff will be compensated by an increased vegetation cover. It is quite possible that soil erosion and water percolation may be no different between the upper and lower areas of the trench (Schlesinger et al., 1989). Planning and development of the revegetation program must take into account the potential occurrence of a natural moisture gradient and concomitant vegetation gradient, on the trench cap. Plantings of native plants should be
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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology designed to produce densities and cover equivalent to that expected in the high density areas on the lower end of the trench cap. This density, equivalent to the natural desert plant distribution, is expected to be maintained on the lower cap, while thinning will occur on the upper cap. However, climatic variables following active revegetation of the caps will control future densities, plant vigor and invasion by native species. CONCLUSIONS AND RECOMMENDATIONS1 In the opinion of the committee, the guidelines presented as part of the revegetation plan have been put together with an understanding of desert plant ecology, and do not reveal any "misconceptions about revegetation enhancements", as charged by the Wilshire group (Wilshire et al., 1993). The emphasis on use of native species, establishment of appropriate desert soil conditions and mycorrhizae that will enhance moisture and nutrient uptake by transplanted and invasive plants, and protection of seedlings from insects and other animals is extremely important to the success of a revegetation program that will depend on both active transplanting and reinvasion by native plant propagules. Care should also be taken to reduce the number of non-native plants which potentially could occupy much of the newly prepared trench cap. The committee recommends that U.S. Ecology and its ad hoc committee of biological experts adhere closely to these guidelines in the design of the revegetation program. It was not within this committee's charge to develop a revegetation program for this site. However, it is the committee's opinion that the revegetation program to be designed by US Ecology and the ad hoc committee of expert biologists, soil scientists, and micrometeorologists is likely to succeed if it takes into account (1) the guidelines for revegetation presented by US Ecology, (2) anticipated gradients in vegetation density and cover resulting from the moisture gradients on the trench caps, planning for higher density and letting natural conditions "thin" the community, and (3) the need for continual monitoring of the revegetation areas as part of the long-term monitoring program. REFERENCES Schlesinger, W. H., P. J. Fonteyn, and W.A. Reiners. 1989. Effects of overland flow on plant water relations, erosion and soil water percolation on a Mojave Desert landscape. Soil Science Society of America Journal 53:1567-1572. Schlesinger, W. H., and C. S. Jones. 1984. The comparative importance of overland runoff and mean annual rainfall to shrub communities of the Mojave Desert. Botanical Gazette 145:116-124. 1 M. Mifflin dissented from this conclusion. See Appendix F for his views on this issue.
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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology Vasek, F. C. 1979/80. Early successional stages in Mojave Desert scrub vegetation. Israel Journal of Botany 28:133-148. Vasek, F. C., H. B. Johnson, and G. B. Brum. 1975a. Effects of power transmission lines on vegetation of the Mojave Desert. Madrono 23:114-130. Vasek, F. C., H. B. Johnson, and D. H. Eslinger. 1975b. Effects of pipeline construction on creosote bush scrub vegetation of the Mojave Desert. Madrono 23:1-64. Wallace, A., E. M. Romney, and R. B. Hunter. 1980. The challenge of a desert: Revegetation of disturbed desert lands. Great Basin Naturalist Memoirs 4:214-218. Wilshire, H., K. Howard, and D. Miller. 1993. Memorandum to Secretary Bruce Babbitt, dated June 2.
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