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Shrub and tree data for affected areas were analyzed statistically <br /> using the same OSM formula as for cover and production, with density used <br /> for the x value. <br /> 2.2.5 Calculation of Plant Diversity <br /> Species diversity indices for each affected and reference community <br /> were determined with the formula: <br /> species diversity = S/ log N, <br /> where S equals the number of species in a sample and N equals the total <br /> number of individuals ( transects) in a sample (Whittaker 1975) . cquitability <br /> indices were determined for each community using the formula: <br /> ni ni <br /> _L N log , <br /> where ni equals the cover value for each species encountered in a community <br /> and N equals the total vegetation cover in a community. <br /> 2.3 Reference Areas <br /> During initial field trips, all major disturbances (roads, portals, <br /> storage piles, office buildings, coal washing plant , repair shops, etc. ) <br /> were visited to determine which vegetation types had already been disturbed. <br /> Mine plans were reviewed to determine if additional vegetation types would be <br /> disturbed by planned future activities. <br /> A representative reference area was then located for the dominant <br /> successional sere of each affected area vegetation type. Criteria used <br /> in selecting representative reference areas included species composition, <br /> cover, production, slope, aspect , elevation, and long—term management <br /> practices. <br /> Comparability of reference areas and analogous affected areas was <br /> evaluated statistically for cover and production with the formula <br /> Cn <br /> 2 <br /> x` _ x21 + n2 <br /> where x, = mean cover or production for the affected area <br /> x'� = mean cover or production for the reference area <br /> t = a t—statistic value, which varies depending on desired <br /> level of confidence and sampling size <br />