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ERO Resources <br />• <br />f . yE$T RN AT A.RR TVP <br />(1) Location and Distr ibutien: <br />The western wheatgrass vegetation type occurs on upland knolls and ridges <br />as an inclusion in the big sagebrush-wheatgrass type and on upland valleys <br />and side slopes as a major type. The distribution of these grasslands is <br />controlled by soil type and differentially, by surface disturbance <br />including grazing and wildfire. Total affected acreage for this type is <br />10.3 acres (Table 5). The wheatgrass type occurs on shallow, clayey soils <br />and on moderately deep, loamy soils (Table 4). Nhere these sites have <br />been disturbed the wheatgrass has either declined or disappeared. <br />Depending on the nature and extent of disturbance the species that <br />typically invade or replace western wheatgrass sites correspond to a <br />complex comprised of soil type and disturbance. Gordon saltbush invades <br />sites that are high in clay. In the majority of these sites the A horizon <br />has been truncated leaving the clayey 8 layer or decomposed shale parent <br />materials exposed. Annual fortis, principally African mustard and <br />• peppergrass, invade disturbed sites overlying clay soil, but not subject <br />to extreme erosion. Cheatgrass irnades western wheatgrass areas overlying <br />deeper and more coarse-textured soils. Cheatgrass indicates an original <br />disturbance that does not persist to any high degree in a perennial manner <br />(Daubenmire 1942). Instead, the cheatgrass remains as an obvious marker <br />of the past disturbance. <br />(2) Structure and CQ~position: <br />• <br />Ground cover values for the western wheatgrase stands sampled are <br />summarized in Figure 4 and Table 6. The mean values for affected stands <br />sampled are litter - 31.2X, rock - 0.2X, soil - 57.2X and woody species - <br />1.3X. <br />The herb layer is well developed, within degrees of disturbance with a <br />mean cover value of 13.1X. The two most important grasses in this type <br />are western wheatgrass and cheatgrass with mean values of 4.1X and 7.9X, <br />II.F-40 <br />