2009-04-01_REPORT - C1980005 (3)

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U Biotic Factors Affecting Vegetation Grasshoppers plagued the reclaimed areas of several of the Seneca mines in 2008 and may have negatively affected overall cover and production values. The predominant plant species that appears to have been targeted and denuded by grasshoppers was alfalfa. These effects were most notable at the Seneca IIW mine. Cover Calculation of 90 percent of the cover performance standard appropriate for 2008 sampling is demonstrated below. Mountain Brush Reference Area Allowable first-hit herbaceous cover* = 13.9 x 2 = 27.8 Sagebrush Reference Area Allowable first hit herbaceous cover* = 40.6 x 2 = 81.2 90 percent of the Cover Standard = 0.90 [0.83(27.8) + 0.17(81.2)] = 33.2% * Herbaceous cover adjusted by subtracting noxious weeds if any and annual/biennial plant cover in excess of 10% of the remainder. • As can be seen in Figure 1, allowable cover in the areas of two-year old (2006) and seven-year old (2001) reclamation sampled in 2008 demonstrate that the vegetation is still developing. The 2001 reclamation did manage to reach 90% of the standard at the upper end of its confidence limit. The youngest (two-year old 2006) area did not manage that. This is a pattern that has often been observed during the 20 years of interim monitoring at this mine. Young revegetation that does not meet allowable cover standards in year two or four has been observed to eventually do so as it passes into the upper end of the ten-year liability period. Herbaceous Production Calculation of 90 percent of the production performance standard appropriate for 2008 sampling is as follows: 90 percent of the Herbaceous Production Standard set by the weighted average of the measured Allowable Herbaceous production of the Mountain Brush Reference Area and the Sagebrush Reference Area = • 0.90[0.83(754.8) + 0.17(961.8)] = 711.0 oven-dry lb/ac 13