2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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great for germination. Therefore, it seems logical that multiple -lift topsoiling may increase establishment of volunteer plant species from stored propagules in the topsoil; if such species are desirable from a synecological standpoint, ultimate plant community diversity may conse- quently also be increased. It should be recognized that the above relationship of multiple - lift topsoiling to vegetation diversity is presently at best only a logical hypothesis unsubstantiated by data. However, if the hypothesis is ultimately proved by future research, multiple -lift topsoiling may become a valuable strategy to increase vegetation diversity on mined lands. Topsoil Depth As noted previously, considerable research has been conducted in the Northern Great Plains Region on effects of topsoil replacement depth on total vegetation productivity and /or cover. However, published infor- mation on the influence of topsoil depth on plant community composition and diversity is surprisingly limited and often somewhat contradictory. Pinchak (31) noted no significant differential effects of topsoil depths from 20 to 60 cm on vegetation diversity on uranium mined lands in Wyoming revegetated primarily to perennial grasses. However, a number of other researchers have demonstrated definite differences in establishment /growth among different plant species or growth forms in response to topsoil depth variation. Redente et al. (35, 36), for example, noted shrub productivity to generally and consistently increase with increasing topsoil depth while perennial grass productivity in- creased only to a certain point; forb productivity was actually highest under the shallowest topsoil depth evaluated. Biondini and Redente (4) further noted differences in performance among types of perennial grass species, with bunchgrasses more responsive to increased topsoil depth than rhizomatous grasses. The above authors and Allerdings and Redente (1) actually found highest vegetation diversity under shallowest topsoil depths evaluated, although total productivity was reduced. The above results indicate that topsoil depth can indeed influence plant community composition and diversity, and that diversity and productivity may not always be similarly affected by increasing topsoil depth. They suggest that if adequate diversity within plant communities is an important reclamation goal, topsoil should sometimes be reapplied at depths shallower than those necessary to maximize total productivity. In short, "intermediate" topsoil depths may provide, in many cases, an optimum compromise between diversity and productivity. Topsoil Treatment /Management Although topsoiling may usually be expected to improve initial and /or potential minesoil fertility, numerous studies in the Northern Great Plains have indicated generally positive effects of N and P ferti- lization on vegetation productivity. Consequently, fertilization has become a common reclamation practice in the region. However, while 263