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Sagebrush (99%) <br />As can be seen, comparability was demonstrable at levels of confidence from 95 to 99 percent. Slight <br />differences that exist in total cover between the Expansion and existing Permit Areas are probably at <br />least partly related to recent differences in grazing history. While the ExpansionArea has experienced <br />continuous annual grazing up to the present, significant portions of the Permit Area have been protected <br />from grazing for three to five years. This would appear to be responsible for much of the cover <br />difference in the Western Wheatgrass /Alkali Sagebrush vegetation type, where grazing by sheep and <br />cattle had substantially impacted sorb cover in the Western Wheatgrass /Alkali Sagebrush stands of the <br />Expansion Area prior to quantitative sampling in July 1990. Whereas the forb cover in the Permit Area <br />was 26.4 percent, forb cover in the Expansion Area was only 12.9 percent. <br />In the Mixed Brush and Sagebrush types, the difference in cover seems most strongly driven by the <br />relative lack of shrub cover in the Expansion Area. This, it is believed, reflects the extensive past <br />efforts to remove or reduce woody cover to enhance livestock forage production. Throughout much of <br />the Mixed Brush type, there are charred snags of previously existing tall oaks presumably burned to <br />• reduce shrub cover. It is probable that both the Mixed Brush and the closely intermixed Sagebrush <br />communities were burned at the same time. Aerial photos from 1981 show evidence of the burn having <br />taken place prior to that time. Although there is abundant shrub cover present on these sites again, the <br />9.8 percent and 7.7 percent difference in shrub cover in the Mixed Brush and Sagebrush types, <br />respectively, may reflect the success of the previous brush reduction management. In addition, the <br />differences in relative composition of shrubs in the Sagebrush type (ie., the dominance of sagebrush in <br />unburned areas and the dominance of snowberry in burned areas) also illustrates the effects of Tire. <br />As another view of the comparability of Expansion and Permit area vegetation types, the difference in <br />total vegetation cover was compared to a confidence interval based on the standard error of the mean, <br />s / Jn, at the 95 % confidence level (t = 1.96). Thus the confidence interval is expressed as 1.96 <br />s/Jn. These confidence intervals are plotted in Figure 13, where it can be seen that, at the 95 percent <br />confidence level, there is not proof that the mean total vegetation cover figures observed in the <br />Expansion and Permit areas come from different populations. <br />• <br />28 <br />