Table 9. Species diversity in each of four 

 plant communities, August 1973. 



Number of species sampled per 100 plots. 



Backshore 10 



Foreslope 20 



Mid-dune 36 



Mid-island 58 



Total species sampled (400 plots) 74 



morning-glory, railroad vine, gulf croton, sea oats, saltmeadow cordgrass, and seashore 

 dropseed are early colonizers. Establishment of seed-dispersed species may be aided by the 

 temporarily stable sea purslane dunes. Bitter panicum, an important early colonizer and 

 apparently dispersed only vegetatively, failed to appear on the transects. 



Rhizomatic growth and tillering of these grasses, especially sea oats and bitter panicum, 

 is stimulated by the accumulation of fresh sand continually blown inland from the shore. 

 Windblown sand is trapped by exposed grass blades and eventually stabilized by the root 

 and rhizome system. The morning-glories generally do not function in dune building, but 

 rapidly grow over barren sand and partially stabilize the dunes. Single plants of sea oats 

 and bitter panicum, and to a lesser degree saltmeadow cordgrass and gulf croton, continue 

 trapping and growing through accumulating sand, forming isolated hummock dunes that 

 grow vertically and horizontally in aU directions (Fig. 8). Few other species can survive on 

 rapidly growing dunes, but the protection afforded the backshore leeward of the hummock 

 dunes from wind, salt spray, sand accumulation, and minor surges, allows several species of 

 forbs to exist. 



Fed by fresh beach sand blowing inland, the unconnected hummock dunes of sea oats, 

 bitter panicum, and saltmeadow cordgrass continue growing and eventually interconnect, 

 forming a dune ridge. New hummock dunes begin forming shoreward, and in tins manner, 

 the foredune grows toward the gulf. This shoreward growth eventually eliminates fresh sand 

 accumulation on the rear of the dune ridge, and affords additional protection from wind 

 and salt spray. Less salt-tolerant species and species not adapted for growing in accumulating 

 sand then become established, e.g., seacoast bluestem, thin paspalum, gulf dune paspalum, 

 broom groundsel, and beach groundcherry. 



At this stage, the foredune system is relatively stable, but is vulnerable to storm surges 

 and wind-activated blowouts. Minor hurricane surges, e.g., Hurricane Celia. periodically 

 destroy the young, early successional backshore dunes, but the foredunes remain 

 undamaged. The backshore vegetation remains at a lower successional level due to its 

 vulnerability. During infrequent severe storms, front parts of the foredunes may be 

 destroyed, but eventually reform shoreward by the processes previously described. 



