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-13- <br />Revised O C T 3 0 19 81 <br />• 1961; Lloyd and Ghelardi, 1964 and Pielou, 1966). As a diversity index <br />for commiuiity analysis, the function describes the average degree of <br />uncertainty of predicting the species of a given individual picker at <br />randcan from the community. This uncertainty and the index increase both <br />as the number of species increases and as the individuals are distributed <br />more and mire equitably among species already present. The general formula <br />for this index is as follaas: <br />A = - E Pi loge pi <br />where pi = decimal fraction of total individuals belonging to the ith <br />species (in this case, percent basal cover 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 estimates of <br />• species diversity is illustrated by the following example: <br />$ Basal <br />Life Form Species Covet - pilo`3epi <br />Grass Sporobolus cryptandrus 3.9 0.36 <br />Forb Lappula tPYa„a 1.5 0.31 <br />Salsola kali 0.6 0.19 <br />Sisymbriinn altissimmm~ 0.6 0.19 <br />Sphaeralcea coccinea 1.1 0.26 <br />Sub-shrub Guttierrezia sarothrae 0.8 0.22 <br />'it7PAL 8.5 1.52 <br />Shannon-~4einer Index = 1.52 <br /> <br />