Dominance Types of Zone II 



The dominance types of Zone II (Table 

 11) occur in the wettest parts of the 

 floodplain: very wet flats, swales, 

 sloughs, and backswamps. Soils are satu- 

 rated throughout the growing season (100% 

 of the tine; Leitman et al. 1981) although 

 fall drydown of water occurs in a number 

 of types. Saturation in some types is 

 maintained by seepage or by tidal fluctua- 

 tion. The liverwort (Po rella pinnata ) 

 growing on trunks of trees in this and 

 other zones in an indicator of flooding 

 depths and duration (Figure 23). 



Gum-cypress dominance types (1-10) 

 (Figures 24-27) . Subtle factors determine 

 the relative dominance of baldcypress 

 (Taxodium distichum ), water tupelo ( Nyssa 

 aquatica ), swamp tupelo (N^. biflora ), and 

 Ogeechee tupelo {H. ogeche ) in the tupelo 

 gum-cypress types. Although water tupelo 

 occurs on disjunct Piedmont sites, it is 

 restricted primarily to alluvial flood- 

 plains of the Coastal Plains. Swamp 

 tupelo is prominent in floodplains of the 

 Coastal Plain, but it is also common in 

 upland swamps and ponds and in the brack- 

 ish waters fringing estuaries (Penfound 

 1952). Water tupelo tolerates deeper and 

 longer flooding than does swamp tupelo and 

 dominates on sites characterized by this 

 hydroperiod. Ogeechee tupelo is limited 

 to the Coastal Plain and occurs in two 

 distinct growth formations (see types 4, 

 7, 8, 9) on both alluvial and blackwater 

 floodplains. Baldcypress is replaced by 

 the tupelos on many sites because of its 

 erratic reproduction, slower growth rates, 

 and insignificant stump and root sprout- 

 ing. These factors are intensified by 

 frequent disturbance, such as periodic 

 logging, further favoring tupelo dominance 

 (Putnam et al. 1960; Eyre 1980). Pond 

 cypress (Ta xodium a scendens ) is the co- 

 dominant with tupelo gums on some black- 

 water floodplains. 



Tree and shrub subcanopies occur in 

 many gum-cypress types (2, 3, 4, 9, 10, 

 15, 17-21) and may be extremely dense in 

 some (types 15, 17, 20, 21). Subcanopy 

 vegetation in other types may be limited 

 (type 1) because of low light intensities 

 and extended flooding. The herbaceous 

 layer is insignificant in most types but 

 is surprisingly dense in others (types 4, 

 12, 16). 



Swamp tupelo dominance types (11-16, 

 18, 19) (Figure 28) . These types occur on 

 organic black mucks or peats (the latter 

 if bays are present). The deeper the 

 peat, the denser the shrub understory (see 

 type 15, which may be characteristic of 

 blackwater river floodplains at elevations 

 approaching sea level). These types on 

 alluvial floodplains often occupy the 

 swales and filled-in oxbows that flank the 

 upland. Swamp tupelo types dominate stag- 

 nant, non-flowing, oxygen-poor sites and 

 can tolerate saturated soils for long 

 periods. 



Bay swamps and shrub bogs dominance 

 types (20, 21) . These conparatively rare 

 floodplain environments strongly resemble 

 their upland wetland counterparts. Field 

 observations were made at two sites (Table 

 11). The shrub bog on deep peat (type 20) 

 had an unclosed pond pine canopy and 

 appeared somewhat raised above the flood- 

 plain surface. The bay swamp (type 21) 

 was moist from constant seepage. 



Tidal forest dominance types (22-27) 

 (Figures 29-31) . Tidal forest types occupy 

 the floodplains of all rivers within the 

 zone of tidal influence, as far as 32 km 

 (20 mi) inland along larger rivers. Soils 

 are peats, tightly bound by interwoven 

 root mats (Figure 29). The water table is 

 continually high because of lunar or 

 "wind" tides. Herbaceous layers are 

 remarkably diverse and little studied. 

 These flat floodplains include higher 

 "islands" or hummocks whose tops are all 

 at the same level (about that of storm 

 tides) and supporting species that occur 

 on alkaline floodplains (type 26). South- 

 ern red cedar ( Juniperus s i licicola ) 

 occupies the banks and higher elevations 

 of the tidal forest floodplains along 

 spring-fed (alkaline) rivers (Figure 30). 

 It prefers a basic or high-calcium sub- 

 strate. Stands of southern red cedar have 

 been severely reduced in Florida by exten- 

 sive logging by pencil companies (Wharton 

 et al. 1977). The southern red cedar is 

 an important component of the "hydric ham- 

 mock," a seepage wetland vegetated by live 

 oak ( Quercus virginiana ) and cabbage palm 

 ( Sabal pa lmetto ), along Florida's gulf 

 coast (Wharton et al. 1977). 



Atlantic white cedar dominance types 

 (28-30) . Atlantic white cedar ( Chamaecypa- 

 ris thyoides ) is believed to be a distur- 



44 



