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• 4.4 Effects of Stand Age <br />The 2002 investigation found differing responses (as identified by best-fit curves and <br />equations) in reclamation aeeas with differing stand ages. In the 2002 investigation the <br />older reclamation areas were ultimately concluded to best represent responses to <br />precipitation due to their more developed vegetative condition. The stand age of the <br />reclamation areas used in the predictive equations ranged from seven to thirteen years in <br />the 2002 investigation. In this addendum, the stand ages employed ranged from three to <br />nine yeazs. Employing the 2002-2004 data in this investigation, it was further observed <br />that the drought conditions affected the long established vegetation of the Osgood Sand <br />Reference Area less than the reclamation areas. <br />It was concluded that the relatively young stand age of the reclamation areas in this <br />investigation may have been more adversely affected by environmental changes (i.e., <br />drought and varied precipitation regime) than either the Osgood Sand Reference Area or <br />the older reclamation aeeas employed in the 2002 investigation. <br />4.5 Comparison of 2002 and 2002-2004 Results <br />Table A4 provides a tabular representation of the best-fit equations and correlation <br />coefficients for total vegetation cover and total herbaceous production for the Osgood <br />Sand Reference Area, the 1985, 1986, and 1987 Reclamation Areas (from the 2002 <br />. investigation), and the 1995, 1997, and 1998 Reclamation Areas (from this investigation). <br />The table also presents predicted values of total vegetation cover and total herbaceous <br />production for the various predictive equations over the range of precipitation values <br />sampled over the years. <br />4.5.1 Total Vegetation Cover <br />Best-fit curves and equations for the Osgood Sand Reference Area from both the 2002 <br />investigation and the current investigation reflect convex polynomial curves with high <br />levels of correlation. Calculated cover values for the 2002-2004 data (Table A4) for a <br />range of precipitation values (within the range sampled) reflect a broader curve with <br />overall elevated total vegetation cover values in the mid precipitation range with a <br />negative inflection at the highest precipitation levels. For these reasons, the best-fit curves <br />from the 2002-2004 data do not improve on the predictive ability of the equations <br />developed in the 2002 investigation. <br />In the case of best-fit curves and equations for total vegetation cover from reclamation <br />aeeas, the shape and correlation of curves derived from the 2002-2004 data changed <br />significantly from that in the 2002 investigation. Best-fit curves in the form of a broad <br />concave polynomial or logarithmic exponential differ in both shape and overall level of <br />correlation from the Osgood Sand Reference Area and reclamation areas in the 2002 <br />investigation. The best-fit curve shape from the 2002-2004 data in the reclamation areas <br />• generated higher overall cover values at low and mid range precipitation values that <br />Coors Energy Compary Keenesburg Mine Page 10 <br />2005 Addendum to Revisbn of Revegetation Success Crfterfa <br />