37 



exhibit bimodal distributions with peaks in Zones 4 and 6. Again, this 

 pattern may have been influenced by fewer samples being taken in Zone 5. 

 The condition of equal tolerances is also violated somewhat. For 

 instance, those species with abundance peaks in Zones 2 and 6 have nar- 

 row tolerances; whereas, those that commonly occur in Zone 4 are also 

 fairly common in other hydrologic zones as well. However, these devia- 

 tions from the conditions for weighted averaging analysis do not neces- 

 sarily render the FTI method invalid. Additional analyses were applied 

 to help determine its validity. 



Statistical Analysis of the Vegetation Data 



To evaluate a method of identifying hydrologic zones based on 

 vegetative associations, the analysis must be based on common species 

 occurring within the region of interest. Species that occur infre- 

 quently may be excellent indicators of hydrologic conditions when pres- 

 ent, but their limited abundance makes evaluating their usefulness in 

 determining a hydrologic zone difficult. For this reason, species 

 occurring relatively infrequently in this study were not used in testing 

 the validity of the weighted averages (FTI numbers) . More than half of 

 the 74 tree species (n = 44) recorded had 20 or fewer individuals 

 throughout the study region and, therefore, were not used in the analy- 

 ses. The remaining 30 tree species accounted for 90.4 percent of the 

 individual trees. One hundred and eighteen species of saplings and 

 shrubs were recorded. Only those 29 species which represented at least 

 one percent or more of the total and together accounted for 78 percent 

 of the total saplings and shrubs data set were used in the statistical 

 analysis. A total of 31 vine species were recorded; the 20 more common 



