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23 <br />CONCLUSIONS <br />• Soil depth was the most important factor influencing <br />aboveground production and structural dynamics of the seeded <br />communities. Aboveground production was as great on 15 cm of <br />topsoil as on 60 cm of topsoil ten years after seeding. The <br />addition of P to the underlying spoil nor the use of disking or <br />deep ripping to reduce spoil compaction had any affect on species <br />composition or aboveground production. <br />Different species displayed different production patterns in <br />response to soil depth. The most productive species on the site, <br />smooth brome, was favored by increasing soil depth. The most <br />productive forb, cicer milkvetch, was favored by shallow soils as <br />was Kentucky bluegrass. Species composition formed a gradient on <br />• the four topsoil depths, with the deep and shallow sites as <br />extremes. This gradient response pattern provides evidence that <br />soil depth was at least an indirect factor causing a structural <br />mosaic on the site. The direct factor causing composition <br />differences was probably competition for soil moisture and <br />nutrients. Perennial grasses, and smooth brome in particular, had <br />greater (>50$) production on the deeper topsoil depths and almost <br />totally dominated the site under these favorable growing <br />conditions. The shallow topsoil sites were somewhat less favorable <br />to growth of most perennial grasses and resulted in less dominance <br />of site resources and more opportunity for other lifeforms to <br />become established. As a result of these interactions, species <br />• richness (i.e. number of species present) was lower on deeper <br />