bance-adapted successional species. Fire 

 is the most common precursor to white 

 cedar development, though flooding, wind- 

 throws, or logging yield the same effects. 

 Atlantic white cedar is usually found in 

 bog stream swamps on peat overlying sandy 

 soils that are characteristically poor in 

 nutrients, in a unique tidal forest type, 

 or in acid backswamps of certain Florida 

 rivers. 



Dominance Types of Zone III 



Zone III includes the wet flats, 

 bank-edge strips, low levees, and depres- 

 sions in Zones IV and V. Dominance types 

 (Table 12) in this zone are semi-perma- 

 nently inundated for a major part of the 

 growing season, as well as in winter and 

 spring. Although the hydroperiod is long 

 (about 6 months). Zone III areas are sub- 

 ject to annual drydown. Soils are satu- 

 rated 40% of the year (Leitman et al. 

 1981). 



Pioneer dominance type (1) . The banks 

 and point bars of the southeastern rivers 

 often are occupied by the black willow 

 ( Sal ix nigra ) and other species such as 

 silver maple ( Acer saccharinum ), and some- 

 times Cottonwood ( Populus ~ deltoides ). 

 These early serai stages are succeeded by 

 Zone IV types as elevation increases from 

 soil accumulation. The successional se- 

 quence is a function of meander movement 

 rates and point bar formation. Rivers 

 with intact forests on fine cohesive sedi- 

 ments migrate so slowly that mature forest 

 establishment keeps pace with the river 

 channel, and pioneer stages never develop. 

 Swift meander movements over unconsolida- 

 ted sands produce tapered slopes on point 

 bars, and several serai stages may be 

 found. 



Shrub, small tree, and herb dominance 

 ty pes (2-4) . Semi -permanent pools occur 

 in depressions, old oxbows, and scour 

 channels. They are dominated by several 

 species of willows, shrubs (e.g., may haw 

 ( Crataegus aestivalis )), and small trees 

 (e.g., water eTrii [Planera aquaticum )). 



O vercup oak-water hickory dominance 



WW . 



types (5-10) . The most poorly drained 

 flats of the floodplain, in which water 

 stands well into the growing season, are 

 characteristically dominated by the over- 

 cup oak-water hickory ( Quercus lyrata - 



Cary a aquatica ) type (Figure 32) and its 

 variants. These flats are relatively small 

 (about 2 ha or 5 acres) in the Southeast, 

 and seldom are dominated exclusively by 

 these two species. The wet flats of the 

 Congaree River (SC) are dotted with numer- 

 ous depressions, so small as to be occup- 

 ied by a single overcup oak. Overcup oak, 

 undesirable for lumber, often is left by 

 loggers. A near-virgin stand of overcup 

 oak on the Santee River floodplain (SC) 

 contains trees approaching 1.2 m (4 ft) in 

 diameter. Additional sites occupied by 

 this type include small shallow depres- 

 sions in Zones IV and V, and narrow bands 

 bordering deeper depressions that contain 

 cypress-tupelo or water elm. Both overcup 

 oak and water hickory avoid seedling and 

 sprout mortality from inundation by leaf- 

 ing out late in the spring. Both species 

 reproduce well; overcup oak through con- 

 sistently good acorn crops, and water 

 hickory through good mast and prolific 

 sprouting (Eyre 1980). Water locust 

 ( Gleditsia agjjatica) -water hickory stands 

 are rare variants of this type. The ex- 

 tended hydroperiod in the sites occupied 

 by overcup oak-water hickory and water 

 locust-water hickory forests inhibits herb 

 growth, and thus the understory is re- 

 stricted to small trees and shrubs (Eyre 

 1980). 



Dominance Types of Zone IV 



Zone IV (Table 13) forms the bulk of 

 the floodplain on Coastal Plain alluvial 

 rivers above tidal influence, chiefly on 

 flats or terraces of low relief. Two 

 irregularities are common: "washboard" 

 terrain caused by parallel scour channels 

 (often sandfloored) and "hummocky" terrain 

 where trees either stand above the general 

 floodplain level on hummocks or have tor- 

 tuous scour channels around and through 

 them. Zone IV is seasonally inundated or 

 saturated for 1 to 2 months of the growing 

 season, and more or less continuously 

 inundated during winter and early spring. 

 Soils are saturated about 22% of the year 

 (Leitman et al. 1981). Shrub and herb 

 layers are scanty. Stiff clay soils or 

 subsoils act as aquicludes which pond 

 rainwater on alluvial floodplains, while 

 the more porous sands dominating black- 

 water floodplains preclude this ponding. 

 The diamondleaf oak (Quercus lauri folia ) 

 appears to dominate both the alluvial and 

 blackwater floodplains. It is remarkably 



55 



