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significantly more abundant/diverse here than either the Aspen or Mountain Brush types, <br />possibly because this type attracts more grazing use. • <br />Western Wheatgrass /Alkali Sagebrush <br />The Western Wheatgrass /Alkali Sagebrush vegetation type exhibited codominance by <br />shrubs, native perennial forbs, and native perennial grasses. The total species occurrence <br />for introduced annual grasses (2 species), and the cover for native perennial forbs (19.3 <br />percent), were higher here than in the other vegetation types. The species occurrence of <br />native perennial forbs (23 species) was, however, the lowest of all sampled vegetation - <br />rypes. High cover by native perennial forbs in this type is largely attributable to the local .. <br />abundance of patches of Wvethia amolexicaulis, Balsamorhiza sagitta, or Helianthella <br />uniflora. The species occurrence for shrubs was also low with only 6 species. Overall <br />species density of 14.6 species per 100 sq. m. in 1992 was approximately one-half that of <br />Aspen, Mountain Brush, and Sagebrush. These relatively low values reflect the fact that the <br />environmental conditions in this type were the least favorable of all the types due to <br />shallow, very heavy soils. (Note that the somewhat earlier sampling of this type in 1990 <br />encountered more of the spring ephemeral species characteristic of these heavy-soil sites, <br />and overall species density then was actually higher (31.5 species per 100 sq. m.) than • <br />any other type except Aspen). Although bare soil and litter cover were at a maximum in <br />this type, the normally aggressive introduced species had not utilized these available <br />microsites to any great extent. <br />Mesic Drainage <br />The Mesic Drainage vegetation type was dominated by native perennial grasses (16/19 <br />species total occurrence, and 24/28 species per 100 sq. m.), but was also greatly <br />influenced by introduced species. This type had the highest species occurrence (7 species) <br />and second highest cover (12.9 percent) for introduced perennial grasses; the second <br />highest cover (4.1 percent) for introduced perennial forbs; and the highest cover (4.8 <br />percent) and the second highest species occurrence (9 species) for introduced <br />annual biennial forbs, reflecting historical agricultural activities in the type. This <br />vegetation type exhibited the greatest signs of disturbance (with the exception of Improved <br />Pasture) based on growth form composition. Grazing and browsing pressures by cattle and <br />wildlife have been continuing sources site disturbance and have extended the presence of <br />introduced and weedy species. This community would probably change significantly, with <br />respect to the species densities of The different growth forms, if the disturbances were to be • <br />removed or at least moderated for an extended period. <br />28 <br />