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18 <br />competitive species can express their growth potential would be <br />• reduced. It appears that our results provide additional support <br />for Auston's hypothesis. <br />This relationship between topsoil depth and species diversity <br />has obvious implications for the reclamation of drastically <br />disturbed lands. If species diversity is a reclamation objective, <br />then attention needs to be given to the creation of heterogeneity <br />within a site to increase species numbers (DePuit and Redente <br />1988). This can be done by varying such factors as topsoil depth <br />and topsoil quality across the landscape to obtain desired levels <br />of production and diversity without sacrificing either attibute. <br />Plant Community Dynamics Over Time <br />During the first growing season of this study all treatments <br />• were dominated by annuals and there were no lifeform differences <br />among the four topsoil depths (Figure 6). These annual species <br />quickly declined over time and were all but absent by the fifth <br />growing season (1985). Between 1981 and 1985 there was a <br />substantial increase in aboveground production with perennial <br />grasses becoming the dominant component with perennial fortis a <br />subdominant. In 1985 there was significantly more grass production <br />on 60 cm of topsoil compared to 15 cm of topsoil and the response <br />in forb production was directly opposite. Five years later (1990) <br />there was little change in lifeform composition but an apparent <br />decline in production had occurred on all topsail depths except 15 <br />cm. This decline in production may be attributed to an <br />accumulation of litter over time. Grasses were still the dominant <br />r~ <br />U <br />