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• area total were mule's ear (Wvethia amolexicaulis) and one-flower woodsunflower. 1992 <br />supplemental sampling showed that native annual and biennial forb cover totaled 3.2 percent cover, <br />compared to 0.3 percent cover in the 1990 baseline area sampling; the difference was due mainly <br />to the abundance of Douglas knotweed (Polygonum douglasii) in the 1992 samples of the Sagebrush <br />vegetation type (Table 83). <br />Western Wheatgrass / Alkali Sagebrush (Figures 4,13) <br />Total top layer vegetation cover in the Baseline Area of the Western Wheatgrass /Alkali Sagebrush <br />vegetation type was 57.5 percent (Table A4), bare soil was 12.7 percent, litter cover was 29.6 <br />percent, and rock was 0.3 percent. The average species density was 31.5 species per 100 sq.m. <br />The average production estimated for 1990 was 1067.1 Ibs/acre (Table A10). Shrub density <br />averaged 4,330 stems per acre (Table A17). <br />In the Supplemental Area sampling of the Western Wheatgrass /Alkali Sagebrush vegetation type <br />(Table 84), total top layer vegetation cover amounted to 45.1 percent. Bare soil and litter in the <br />Supplemental Area came to 20.7 and 33.4 percent, respectively. Species density in the <br />Supplemental Area was 14.6 species per 100 sq. m. The large difference in species density (and <br />• part of the difference in bare soil) between the two areas may have been due to the slightly later <br />sampling date in 1992, by which time the rather numerous spring ephemeral species, especially <br />those of the family gpjaceae had dried, broken off at ground level, and disappeared. Production was <br />not assessed in the Western Wheatgrass /Alkali Sagebrush vegetation type in 1992. Shrub density <br />averaged 9,689 stems per acre (Table 621), over twice as high as the Baseline Area due primarily <br />to the far greater (and more exclusive) abundance of alkali sagebrush. <br />The following discussion describes species dominance in the Western Wheatgrass /Alkali Sagebrush <br />vegetation type based on the all-laver relative cover values. All percentages given in the following <br /> <br />three paragraphs refer to this cover statistic. <br />In the Baseline Area, this vegetation type was an approximately even mix of grasses, shrubs and <br />forbs. The native perennial forbs contributed 34.7 percent cover. The native perennial grasses <br />contributed 32.7 percent cover, and the shrubs contributed 28.1 percent cover. Introduced annual <br />forbs and grasses have a combined cover of 4.0 percent and 100 percent frequency which was <br />greater than the previously discussed vegetation types and may be indicative of a greater level of <br />• disturbance and exposure to introduced species. <br />11 <br />