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The Shannon-Weiner index is used to communicate and cong~are species <br />diw.xsity for the mixed brush type/aspen subtype and upland sagebrush <br />oa~m~nities on affected and control areas. This index is based on t'~e <br />Shannon-Weiner function from the field of information theory (Margalef, <br />1957; MacArthur and MacArthur, 1961; Lloyd and Chelardi, 1964; Pielou, <br />1966). As a diversity index for camwzity analysis, the function <br />describes the average degree of uncertainty of predicting the species of <br />a given individual picked at random from the commnity. This uncertainty <br />and the index increase both as the number of species increases and as <br />the individuals are distributed more and irore equitably arrong species <br />already present. The general formula for this index is as follaas: <br />H = - E pi loge pi <br />where pi = decimal fraction of total individuals belonging to the i~ <br />species (in this case, percent basal Dover is used to express pi). <br />This index may vary from a value of 0 for habitats containing a single <br />species (e.g., an alfalfa field) to values of 4 or 5 for communities <br />containing many species, each with a small number of individuals. The <br />application of this formula to basal cover data to provide estimat=s of <br />species diversity is illustrated by the following example: <br />~ Basal _ p,loa p. <br />Life Form Species Cover i 'e i <br />Gass ~robolus cryptandrus 3.9 0.36 <br />Forb Lappula texana 1.5 0.31 <br />Salsola kali 0.6 0.19 <br />Sisymbrium altissimimi 0.6 0.19 <br />Sphaeralcea coccinea 1.1 0.26 <br />Sub-shrub GUtierrezia sarothrae 0.8 0.22 <br /> 8.5 1.52 <br />Shannon-[Feiner Index = 1.52 <br />~- <br />-17- <br />