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FRO Resources <br />r 1 <br />U <br />• <br />Sagebrush-i~eatarn Wheatgrasa (C) <br />Western Wheatgrass tI) <br />Western Wheatgrass-Gordon Saltbush tI) <br />Annual Forb (I) <br />Sagebrush tC) <br />Sagebrush-Cheatgrass tIl <br />Moderately-Deep, Loamy <br />Shallow, Loamy to Clayey <br />Shallow, Clayey, Feeding <br />Area <br />• <br />Shallow, Clayey, Past and <br />Present Erosion <br />Deep, Loamy, Overgrazing <br />and Erosion <br />Moderately Deep, loamy, <br />Past Surface Disturbance <br />The foregoing illustration demor~stratea two of the essential features that <br />interact in the formation and maintenance of the patchiness within the big <br />sagebrush-wheatgraes vegetation types. The third factor is somewhat <br />implicit: the ecological amplitudes of the species that occupy the permit <br />area. An appropriate exaxple of how the factors disoussed have produced <br />the patchiness is the Hig 5agebrush-Colorado Wildrye category and its <br />inclusions. Big sagebrush is favored on sites where soils are of moderate <br />textures and moderately deep. Prior to the grazing pressures initiated in <br />the 18G0's, these sites were relatively open and a wall-developed <br />understory composed of perennial grasses and fortis was present, although <br />cyclic with the ocourrence of wildfire tYoung et al. 1979). Patches of <br />Colorado wildrye were also present occupying places where soils were more <br />shallow and of coarser textures. Little rabbitbrush pockets on sandy <br />soils or eolian drift areas were also present. Following grazing and the <br />decrease in natural wildfire the sagebrush densities were increased on <br />sites where soils were somewhat deeper and finer in texture. This <br />increase in shrub density was accompanied by a correspondent decline in <br />the herb layer. On sites where soils were moderate in depth and texture <br />the herb layer declined with the exception of increasing conditions <br />favorable to Colorado wildrye. This species is tolerant of trampling and <br />is drought resistant. As a result, while other grasses decreased in the <br />interspace between shrubs, Colorado wildrye increased and has been able to <br />maintain its distribution due to the bunching habit it exhibits. Lose of <br />surface soil materials resulting from accelerated erosion produced by <br />II.F-37 <br />