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and B30 are summaries of the species present in each of the vegetation types present in the two <br />study areas. <br />In the vegetation type descriptions below, for types that occur in both the Yoast Baseline and Yoast <br />Supplemental areas, the initial description is based on the 1990 data, followed by comments on the <br />comparative composition of the types observed in 1992 in the Supplemental Study area. Top layer <br />cover refers to the 'first hit' cover; all layer covet reflects the extent of cover by all plants <br />whether overlapped by taller plants or not and as such is taken to be a statistic more revealing of <br />overall abundance in the plant community. <br />Aspen (Figures 1,10) <br />Total top layer vegetation cover in the Baseline Area Aspen vegetation type was 89.9 percent (Table <br />A1), bare soil was only 0.3 percent, and litter cover was 9.9 percent. The average species density <br />was 33.4 species per 100 square meters (sq.m), making this the most diverse of the Yoast <br />vegetation types. The average herbaceous production estimated for 1990 was found to be 856.5 <br />Ib/acre (Table A7). <br />In the Supplemental Study Area, the total top layer vegetation cover in the Aspen vegetation type • <br />was observed to be 86.8 percent in 1992 (Table B1). Species density averaged 28.4 species per <br />100 sq. m., which although less than the Baseline Area Aspen in 1990, still represented the most <br />diverse of the Supplemental Area vegetation types. Average herbaceous production totaled 1270.5 <br />Ib/acre in 1992 (Table 812). Top layer cover by quaking aspen (popylus tremuloidesl trees in <br />the Supplemental Study Area was 38.9 percent, nearly 20 percent less than the Aspen type of the <br />Baseline Area. Tree density in the Aspen type of the Baseline Area averaged 515 live stems per acre <br />(73 dead stems per acre, Table A14); while in the Supplemental Area the figure was 356 live <br />stems per acre (165 dead stems per acre, Table 818). Shrub density in the Aspen type of the <br />Baseline Area averaged 6,524 live stems per acre (Table A13), while in the Supplemental Area, <br />shrub density averaged 5,691 live stems per acre (Table B17). <br />The following three paragraphs describe species dominance in the Aspen vegetation type based on the <br />all-laver relative cover values. All percentages given in the following paragraph refer to this <br />cover statistic. <br />species Gomoosition -Baseline Area <br />The tree canopy of the Baseline Area Aspen type dominated with relative all--I r cover of 35.8 • <br />percent. Quaking aspen was the only tree canopy component sampled in this type, although <br />6 <br />