on the denuded backshore, is vegetatlvely dispersed by wave and wind action. 

 Clumps of sea purslane trap sand, forming small dunes that rise only slightly 

 above the beach surface. Beach morning glory (Ipomoea stolonifera) , railroad 

 vine, gulf croton, sea oats, saltmeadow cordgrass, bitter panicum, and 

 seashore dropseed are early colonizers (Dahl, et al, , 1975). 



Rhizomatic growth and tillering of these plants, especially sea oats and 

 bitter panicum, are stimulated by the accumulation of fresh sand continually 

 blown onshore. Eolian sand is trapped by exposed grass blades and it 

 eventually becomes stabilized by the grass roots and rhizomes. Nourished by 

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

 bitter panicum, saltmeadow cordgrass, and seashore dropseed continue growing 

 and eventually interconnect, forming a dune ridge (Fig. 3). New hummock dunes 

 begin forming shoreward, and in this manner, the foredune grows toward the 

 gulf. This shoreward growth eventually eliminates fresh sand accumulation on 

 the rear of the dune ridge, and gives additional protection from wind and salt 

 spray. The less salt-tolerant species and those not adapted to growing in 

 accumulating sand then become established, e.g., seacoast bluestem, gulfdune 

 paspalum, broom groundsel (Senecio riddeZlii) , and beach groundcherry (Dahl, 

 et al., 1975). 



The time scale for these sequences depends on the intervals between 

 storms, the severity of previous storm damage, the proximity of undamaged 

 colonizing species, and the precipitation cycle. The area containing the 

 present study plots was barren in 1937, but a vegetated foredune ridge had 

 appeared with a vegetated plain to the west by 1948. After Hurricanes Carla 

 and Beulah in 1967, the dune ridge was absent, and the area was again barren 

 with a field of active sand dunes migrating west. 



III. METHODS AND PROCEDURES 



1. Elevation Surveys of Experimental Dunes . 



A summary of the five experimental dune areas evaluated in this report 

 is in Table 1, which corresponds with the study-site map in Figure 4. The 

 exact location of these areas referenced to two surveyed base lines (east and 

 west) is in Appendix A. Elevational profile surveys for the five areas (one 

 unplanted control and four planted) were conducted in March 1975, August 1975, 

 March 1976, August 1976, September 1977, and March 1981. 



a. Foredune Profiles. Cross-sectional profiles were made in each of the 

 five experimental dunes. Elevations were taken at 3-meter intervals (rod 

 readings to the nearest 0.003 meter). Profiles were made in the following 

 locations: 



(1) Unplanted control dune - eight profiles, 30 meters 

 apart, from 30 meters seaward of the natural dune area 

 to 61 meters across the foredune. 



(2) Planted dunes - 30 meters seaward of the grass extension 

 of the dune to 58 meters across the dune. 



(a) 366-meter sea oats dune - 12 profiles, 30 meters 

 apart. 



13 



