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• precipitation data (Figure 2), but not as closely tied as that of the September-July <br />precipitation and total vegetation cover of the reference area (Figure 5). The best-fit <br />equation yielded a correlation coefficient (R2) of 0.6790. The form of the best-fit equation <br />differed from that of the January-July precipitation equation as this data yielded a thud <br />order polynomial with a curve position and shape similar to the reference area and more <br />empirically pleasing than the exponential equation from the January-July data. <br />The plots and equations derived for the relationship between September-July precipitation <br />and total herbaceous production at both the Osgood sand reference azea and the <br />reclamation azeas were well correlated. Figures 7 and 8 depict the relationships <br />graphically and reveal the third order polynomials describing the best-fit For the data. <br />Correlation coefficients are nearly equal for both data sets (0.8918 for the reference azea <br />and 0.8552 for all reclamation areas). This represents a significant increase in the <br />explained variation in the relationship on the order of 15 percent. However, the shape of <br />the curves continues to suggest that total herbaceous production decreases with <br />cumulative September-July precipitation in the 13.0-inch range after a general increase <br />from lower cumulative precipitation levels and a steep increase with greater precipitation <br />levels. Again, this relationship appears to contradict that experienced over time in the <br />field. <br />Based on the above comparison of the January-July and September-July precipitation <br />regimes and total vegetation cover and total herbaceous production, the September-July <br />• precipitation regime provided a more definitive relationship with the parameters in the <br />Osgood sand reference area. In terms of total vegetation cover, the September-July <br />precipitation regime did not provide a higher correlation coefficient on the reclamation <br />areas, but it did yield an equation of the same character as that of the reference area and <br />one that fits the generally accepted expectations for such a relationship. The September- <br />July precipitation regime explained more variation within the reclamation areas in terms of <br />total herbaceous production than the January-July precipitation regime. <br />3.2 Comparisons of Stand Ages <br />It has been our contention that native vegetation communities respond differently to <br />environmental conditions than reclaimed and revegetated areas partially based on stand <br />age, reflective of development in the vegetative community. In an effort to explain <br />additional variation within the relationships between the precipitation regime and <br />vegetation parameters, the reclamation areas were sepazated and evaluated by stand age. <br />The 1985, 1986, and 1987 reclamation areas were sampled from 1994 to 1998, and as <br />such represented stand ages ranging between seven and thirteen years. The 1995, 1997, <br />and 1998 reclamation areas were sampled between 1998 and 2001 and represent stands <br />aged between two and six yeazs. It was hypothesized that the older stands respond <br />differently than the younger stands, as would be expected in stands in different seral stages <br />of development. As further comparison, the Osgood sand reference area information was <br />• used as a "control" to assess conditions at a vegetation community that has been <br />established for a long period of time. <br />-7- <br />