31 



occasionally occur in lower zones (Table D-3, Zone 3), but the 

 individuals do not survive to maturity unless the hydrologic regime is 

 drastically altered. 



The average importance value was plotted for each species in every 

 zone where it occurred in the study. Although a species can be expected 

 to occur in a number of zones, many had a peak occurrence in a particu- 

 lar zone (Figure 4). However, because this study did not analyze a 

 continuous gradient, FTI numbers were calculated from mean importance 

 values across the entire study and do not necessarily represent the 

 maximum in ecological amplitude for a species. 



Three general species distribution patterns are shown in Figure 4. 

 The first pattern includes species such as water tupelo (NYAQ) and bald 

 cypress (TADI) , in which mean importance value is greatest in Zone 2 and 

 the species no longer occurs after either Zone 3 or 4. This pattern is 

 indicative of species having the strongest competitive advantage in 

 areas of greatest duration of inundation/soil saturation. The second 

 pattern is typified by species such as water oak (QUNI) , loblolly pine 

 (PITA) , sassafras (SAAL) , and white oak (QUAL) , in which the greatest 

 mean importance value occurs in Zone 6 (uplands) and decreases from Zone 

 5 to 2 . Hence they have a stronger competitive advantage in areas where 

 inundation/soil saturation is less than 5 percent of the growing season. 

 However, some of these species (e.g., water oak and loblolly pine) may 

 occasionally occur as dominants in wetlands. The third pattern is typi- 

 fied by species having the greatest mean importance values in Zones 3, 

 4, and 5. Species in this group sometimes occur as dominant species in 

 either Zone 2 or 6 , but are best adapted for occurrence at some point in 

 Zones 3, 4, and 5. Species having the greatest mean importance values 



