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FRO Resources <br />noteworthy that although cheatgrass occurs in the western wheatgrass type, <br />• its importance is low. The major factor attributed to this relationship <br />is the loss of competitive advantage to the cheatgrass in heavy clay soils <br />on which the western wheatgrass refugia stands occur. <br />Scattered shrubs occur in the cheatgrass-annual forb type, but no true <br />shrub layer exists. Large numbers of certain shrub species do occur, <br />however. Total mean shrub cover in this type is 21.8%. Of this value big <br />sagebrush accounts for 93% of the total or a mean cover value of 20.2%. <br />Other shrubs'that occur but are of less importance are little rabbitbrush <br />- 0.6%, spiny hopsage - 0.4%, greasewood 0.3%, fourwing saltbush - 0.1% <br />and Gordon saltbush - 0.1% (Figure 4, Table 6). Shrub densities are big <br />sagebrush - 14,137/Ha, little rabbitbrush - 875/Ha, fourwing saltbush - <br />512/Ha, greasewood - 362/Ha, spiny hopsage - 325/Ha and Gordon saltbush - <br />175/Ha (Table 7). <br />Primary productivity for the cheatgrass-annual forb type is highly <br />variable. Biomass production apparently is reliant upon the amount of <br />• cheatgrass and western wheatgrass versus the importance of annual forbs. <br />Annual forbs do not produce a significant amount of biomass, so that a <br />large amount of these species in a site reflect low primary productivity. <br />Productivity in the sites sampled averaged 3.9 9/m2. The former value <br />is the lowest obtained for the permit area (Figure 5, Table 9). Important <br />grass producers in this type with mean production values are western <br />wheatgrass - 2.3 g/m2 and cheatgrass - 0.6 g/m2. The above grasses <br />produce 74% of the total biomass. Forbs that contribute to production are <br />baby blue eyes - 0.2 g/m2, aster - 0.1 g/m2, peppergrass - 0.1 g/m2, <br />stickseed - 0.1 g/m2 and fleabane daisy - <0.1 g/m2 (Table 9). <br />U <br />The cheatgrass-annual forb vegetation type is a highly successional <br />vegetation type. This type has replaced mixed grasslands dominated by <br />western wheatgrass and other perennial grasses. It is apparent that <br />overgrazing in the presence of annual invaders was the principal factor <br />II.F-47 <br />