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that Rubber Rabbitbrush cover has not increased in plant cover between 2006 and 2010. <br />Another means of evaluating the similarity of shrub density as detailed in the DRMS regulations, <br />Vegetation Guideline and Bond Release Guideline, is to use the "t- test" statistical comparison <br />to compare the mean density of this plant using the 2006 data as compared to the 2010 data. A <br />"t -test" comparison of these data resulted in a t value of 0.0165. The corresponding t or tabular <br />t value is 1.697. Since the t, or tabular t value is greater than the corresponding t value it can be <br />concluded that there is no statistical difference in the density of Rubber Rabbitbrush between the <br />2006 and 2010 sample periods. Therefore, it can be concluded that Rubber Rabbitbrush density <br />has not increased between 2006 and 2010. <br />Extensive revegetation studies performed by Colorado State University in the oil shale region in <br />Garfield County of western Colorado confirms these results. In these studies it is reported that <br />Rubber Rabbitbrush acts as an early successional species, readily becoming established on <br />disturbed and revegetated sites but after approximately 18 years there is a rapid decrease in this <br />plant as other later successional species become established. Given the larger number of Rubber <br />Rabbitbrush plants that have very poor vigor, or which have died on this site, it is obvious that <br />this species is disappearing from the revegetated stands at the Southfield Mine as well. It is our <br />professional opinion, and we could find no published evidence suggesting that this plant will <br />take over these sites and these site specific data as well as the published literature relative to the <br />ecological role this plant plays in the revegetation process, suggest that these concerns are <br />unfounded. These data confirm that the presence of this plant on these reclaimed sites is <br />indicative of a natural ecological process and there is insufficient evidence to conclude there is <br />any reason for concern. <br />16 <br />