River, SC floodplain, for instance, 25 

 were canopy trees, while 28 species were 

 shrubs or subcanopy trees, 15 woody vines, 

 2 woody grasses, and 40 herbaceous species 

 (Dennis 1973). The importance of the 

 herbaceous ground cover on a floodplain is 

 a function of light and area! extent of 

 zones of higher elevation (Zones IV and V) 

 where these species are most often found 

 (Knight 1973). In Zone IV floodplains, 

 "sedge glades" are sometin-'es found. In 

 the Congaree Swamp (SC), dominant sedges 

 are Carex lurida and C^. grayi , while C. 

 intumescens . C. atlantica , and Leers i a 

 virginica are commorT] Other common ground 

 cover plants are crossvine (Aniso stichus 

 capreolata ), southern vein orchid ( Haban- 

 eria flava ), violet (Viola affinis )r 

 poison oak ( Rhus toxicodendro n) and swamp 

 milkweed ( Asdepias incarnata ). The major 

 composite is the butterwort ( Senecio 

 glabellus ). Common shrubs and vines on 

 North Carolina floodplains are spicebush 

 ( Lindera benzoin ), buckeye ( Aesculus 

 sylvatica ). Viburnum spp. , Japanese honey- 

 suckle ( Lonicera japonica ), greenbrier 

 ( Smilax rotundi folia ), poison ivy (Rhus 

 radicans ), grapes ( Vitis spp.), and black- 

 berry ( Rubus spp.) (Knight 1973). Herba- 

 ceous ground cover is less extensive in 

 more frequently inundated parts of the 

 floodplain. A characteristic and wide- 

 spread herb in Zone II of many floodplains 

 (in the Coastal Plains) is goldenclub 

 ( Orontium aquaticum ). Useful species 

 lists for floodplain understory and ground 

 cover plants are found in Oosting (1942), 

 Houck (1956), Beard (1958), and Wells 

 (1970). 



Floodplain Transects of Selected South- 

 eastern Rivers 



To provide a sharper focus on the 

 complexity of floodplain ecosystems. 

 Figure 40 portrays nine southeastern allu- 

 vial, blackwater, spring-fed, and tidally 

 influenced floodplains via horizontal 

 transects. The spatial relationships 

 between ecological zones and forest domi- 

 nance types are diagrammed and accompanied 

 by Table 15, which depicts these relation- 

 ships. The rivers profiled here are the 

 same referenced in Tables 11 through 14, 

 where specific site locations were given 

 for dominance types and variants observed 

 in the field. 



The diversity of the bottomland hard- 

 wood canopy increases with the complexity 

 of floodplain topography. Figure 40 and 

 Table 15 describe examples of the varia- 

 tions encountered on floodplain transects. 

 Alluvial rivers, such as the Congaree, 

 Ochlockonee, and Alcovy (Figure 40) often 

 exhibit the greatest topographic and plant 

 community diversity. In contrast, the 

 floodplains of many Coastal Plain black- 

 water and spring-fed rivers (Figure 40) 

 generally are more uniform topographi- 

 cally, and the plant community diversity 

 is lower. 



Regular tidal flooding caused by 

 lunar or wind energy imparts a distinct 

 character to plant communities under its 

 influence. These forests are the least 

 studied of all river swamps (Beaven and 

 Oosting 1939). They occupy the lower 16 

 to 32 km (10 to 20 mi) of many unaltered 

 floodplains, primarily in Florida and 

 Georgia (Figure 40). High tides raise the 

 water levels in the floodplain (or "tide- 

 plain") to the most elevated portions of 

 the relief with fair regularity. Tidal 

 swamp forests usually extend upstream 

 until levees appear. The floodplains of 

 these forests are dominated by Zone II 

 species, except for higher islands con- 

 taining Zone IV species such as diamond- 

 leaf oak, swamp palm, southern red cedar, 

 and cabbage palm. These floodplains are 

 distinctive in harboring animal species 

 characteristic of more brackish downstream 

 waters, such as fiddler crabs (Oca) and 

 square-backed crabs (Sesarma). Another 

 interesting aspect of the tidal forest is 

 the presence of an intertidal zone, either 

 mud or sand, which is often 

 extensive mats or beds of 

 aquatic vegetation (such 

 Ludwigia r epens , Cabomba 

 El odea spp. , or Nuphar lu teum ] 



vegetated by 



submerged or 



as Isoetes , 



cardiniana. 



DISTURBANCE AND SUCCESSION IN BOTTOMLAND 

 HARDWOOD PLANT COMMUNITIES 



Several examples of distrubance and 

 successional trends have been referenced 

 in the preceding sections of this chapter. 

 They will be summarized here along with 

 others that have not yet been mentioned. 



76 



