35 



of waterlogged soils. All species except Betula nigra that have an FTI 

 number of 4 to 6 are facultative wet (FACW) or FAC and are rated as 

 moderately or weakly tolerant. B. nigra, an obligate species, occurs on 

 well-drained soils, often on natural berms . FTI numbers were computed 

 only for bottomland forests and do not reflect occurrence in other wet- 

 land types (e.g., pocosins and Carolina bays); thus, slight deviations 

 from the above pattern should be expected for some species. Also some 

 species may have genetic variants that possess varying degrees of flood 

 tolerance. Hook et al. (1988) reported that interspecific variation in 

 tolerant to waterlogging exists in loblolly pine (Pinus taeda) . This 

 may also be true of other species. 



Although the system using the National Wetlands Inventory (NWI) 

 indicator status (Reed 1988) does not allow comparison of hydrologic 

 definitions, the actual average duration of flooding in this study com- 

 pared with Hook's (1984) waterlogging tolerance rating definitions 

 yields strong agreement. For example, assuming an average 225 -day grow- 

 ing season, the most tolerant rating can be defined as approximately 

 200 days (Appendix E) . The boundary between Zones 2 and 3 (which theo- 

 retically would be slightly drier because the designation most tolerant 

 is best compared to Zone 2, not the boundary between Zones 2 and 3) has 

 a duration of inundation/soil saturation that ranges from 92 to 

 198 days. Highly tolerant ranges from 30 to 90 days versus 20 to 

 66 days for the Zone 3-4 boundary. Weakly tolerant ranges from 1 to 

 4 weeks, while the Zone 4-5 boundary ranges from 8 to 31 days. "Least 

 tolerant" is defined as waterlogging for a few days, but usually less 

 than 2 percent of the growing season. Using the 225-day growing season, 



