perpetuating and increasing large cane 

 stands, which are now relict. Though 

 crown fires are rare, ground and surface 

 fires may occur. These fires move rapidly 

 across the floodplain floor, damaging or 

 destroying all trees less than 10 years 

 old, as well as shrubs and herbaceous 

 growth. In addition, ground fires open 

 wounds in larger trees, increasing sus- 

 ceptibility to disease and insect attack. 



Fire is a major determinant of com- 

 munity composition in selected vegetation 

 types. Infrequent but regular fires favor 

 Atlantic white cedar while inhibiting 

 southern red cedar (Eyre 1980). 



H.S. Larsen, writing in Eyre (1980) 

 indicates that fire may sweep into the 

 dense shrub zone of sweet bay-swamp 

 tupelo-red bay sites along the narrow bot- 

 tom of perennial streams during drought 

 years. It is possible that the narrow 

 peaty swamps along small streams with At- 

 lantic white cedar or pond pine canopies 

 (type 29) may burn in drought years. The 

 only recent instance of a widespread fire 

 on a floodplain in the study area occurred 

 prior to 1976 on the Oklawaha River (FL). 



Caddy et al. (1975) described the 

 successional sequence in the Congaree 

 Swamp (SC) that begins with either fire or 

 clearcutting, and proceeds from even-aged 

 sweetgum-intolerant hardwood stands to 

 more mature communities dominated by dia- 

 mondleaf oak and more tolerant hardwoods. 



Windthrow 



Windthrow is the primary disturbance 

 to plant succession on floodplains in the 

 study area. Gaps in the canopy resulting 

 from fallen canopy trees (Figure 41) are 

 common in the floodplain. Topplings due 

 to old age, disease, soft sediments and 

 insecurely anchored root systems, root 

 scour, lightning strike, or fire cause 

 openings in the canopy that temporarily 

 stimulate understory woody and herbaceous 

 growth. The factors that influence suc- 

 cessional response to such gaps include 

 gap size, existing composition of seed- 

 lings and saplings and their relative 

 shade tolerances, possible inhibition due 

 to shading by extensive understory tree 

 (paw paw, holly ( Ilex opaca ), ironwood 

 ( Carpinus caroliniana )) or canebrake 

 development, site characteristics, and 



probability of propagule recruitment. 

 Understory shading may limit the develop- 

 ment of diverse, well -stocked seedling and 

 sapling layers, retarding succession 

 (Gaddy et al. 1975). 



Biotic Disturbances 



At least three categories of biotic 

 disturbances exist in the floodplain: (1) 

 propagule predation and seedling and sap- 

 ling herbivory by browsing animals, (2) 

 disease, and (3) insect outbreaks. The 

 quantitative effects of these variables on 

 plant community structure and composition 

 have received little attention. Cattle 

 and deer browsing can kill seedlings, 

 particularly if floodwaters concentrate 

 browsing on higher ground in the flood- 

 plain. Baldcypress seedlings are even 

 eaten, and water tupelo will survive only 

 one cropping by deer (F. Vande Linde, 

 forester, Brunswick Pulp Land Company, 

 Brunswick, GA; personal communication). 



Conner and Day (1976) discussed the 

 effects of grazing by the forest tent 

 caterpillar on both baldcypress-water 

 tupelo and bottomland hardwood forests in 

 Louisiana. Water tupelo is most severely 

 affected, suffering extensive defoliation. 

 These authors suggested that the increas- 

 ing frequency of outbreaks over wide areas 

 is due to a corresponding increase in the 

 areal extent of tupelo-dominated sites. 

 These sites, in turn, occur as a result of 

 the selective logging of baldcypress (see 

 below). Conner and Day (1976) also specu- 

 late that the susceptibility of water 

 tupelo to defoliation may be one factor 

 that formerly favored the maintenance of 

 nearly pure stands of baldcypress. 



Lumbering 



Selective cutting and clearcutting 

 generate some of the most noticeable 

 changes in floodplain forests. The heavy 

 exploitation of baldcypress is the classic 

 example. Such logging has shifted the 

 forest composition on countless sites. 

 Cypress stumps endure for many years, and 

 their presence may indicate what the orig- 

 inal forest on a given site was like and 

 something of the hydrology. Many areas 

 which now support water tupelo (e.g., the 

 Altamaha River, GA), green ash (e.g., the 

 Great Pee Dee River, SC), or water tupelo- 

 green ash (e.g., the Oklawaha River, FL) 



78 



