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• Aspen <br />Trees thoroughly dominate the cover in the Aspen vegetation type -- this dominance of a <br />vegetation type by a single lifeform was exceeded only by shrubs in the Mountain Brush <br />vegetation type. Based on 1990 and 1992 sampling the understory was dominated by <br />shrubs with 12/12 species, and native perennial forts with 44/45 species; both of these <br />lifeforms were highly diverse when compared to 'stress-site' types such as Western <br />Wheatgrass/Alkali Sagebrush or Steep Mountain Brush, but very similar to the more mesic <br />types of Mountain Brush and Sagebrush. Within the Aspen vegetation type, the abundance of <br />annual and biennial forts was the lowest of any type, probably due to the very high <br />abundance of perennial competition. The introduced growth forms had both low cover and <br />species density. In terms of species density, native perennial forts are more abundant <br />(20.1/15.7 species per 100 sq.m.) in the Aspen vegetation type than any other, and shrub <br />species density is only slightly less than in the shrub-dominated Mountain Brush and <br />Sagebrush vegetation types. <br />Mountain Brush <br />• Based on 1990/1992 sampling the Mountain Brush community was dominated by shrubs <br />with 10/14 species. With 4.4/4.8 shrub species per 100 sq. m., this type had the highest <br />shrub species density of all community types. The native perennial fort growth form had a <br />total occurrence 48 to 57 species, the greatest of any community. The other native growth <br />forms were well represented with moderate numbers of species. The introduced growth <br />forms were dominated by annual/biennial (orbs, and were slightly more prevalent than in <br />the Aspen type, but did not contribute greatly to cover. The fact tfiat this community was <br />similar to the Aspen vegetation type in terms of species density and cover for the different <br />growth forms, attests to the similarity of their environments. The absence of quaking aspen <br />appeared to be compensated by the increased diversity in all growth forms (compared to <br />aspen) and the cover dominance by shrubs. <br />Sagebrush <br />Within the Sagebrush vegetation type, species densities for native perennial grasses, native <br />perennial forts, and native annual biennial (orbs, were 5.60/6.73, 11.33/10.93, and <br />1.47/2.00 species per 100 sq. m., respectively. This community demonstrated a <br />descending dominance progression from shrubs to grasses to forts. Reduced dominance by <br />• the shrubs, compared to the Mountain Brush type, was accompanied by increased diversity <br />and/or cover in the native perennial grasses and forts. Introduced species were <br />27 <br />