with 135 cubic meters per meter. However, the natural foredune had a volume 

 of 459 cubic meters compared with only 258 cubic meters in the experimental 

 dunes (Table 4) . The annual rate of new sand accumulations to the beach and 

 foredunes was about 9.3 cubic meters per meter of beach since 1974 on the dune 

 near the Ranger Station access road, which is less than the 11.5 cubic meters 

 per year being added to the experimental dune areas since 1975. Dune crests 

 of natural dunes are no higher, about 7.6 to 8.2 meters MSL, than the 

 experimental dunes resulting from grasses planted in 1969 to 1972. However, 

 the natural dunes are much wider at the base. Plants becoming established 

 naturally do not grow in parallel rows nor are they spaced as closely together 

 as when planted by man. Consequently, sand is blown inland from the beach in 

 and around pioneer plants, but much of it passes on through, accumulating over 

 a broad area and extending 244 to 274 meters landward from MSL. The unplanted 

 control area in the experimental dunes now has a sand floor for the newly 

 forming dune 2.6 to 3.0 meters above MSL. The way dunes form naturally can be 

 approximated from the data accumulated on the unplanted control section. 

 Hurricane Allen caused erosion of the sand in front of this section, leaving 

 the pioneer vegetation in line with the other naturally formed dunes. A new 

 dune line is now distinguishable (Fig. 3) and crests are already 4.0 to 4.6 

 meters above MSL. This area is expected to take on a definite dune form 

 within the next 2 to 5 years and it should have a relatively broad base. It 

 appears that about 25 years (from Hurricane Carla in 1961) is required for an 

 effective dune to reform naturally on north Padre Island. This would be true, 

 however, only if no major storm occurred during the interim with sufficient 

 energy to erode the newly forming foredunes. It is desirable to plan for a 

 broad based dune at the outset for any dunes to be constructed from planted 

 vegetation. 



6. Coastal Vegetation . 



a. Vegetation on Experimental Foredunes . In the experimental foredune 

 plantings, Dahl and Goen (1977) reported sea oats and bitter panicum have 

 spread seaward about 1.6 meters per year. Apparently, both species continue 

 to spread at about the same rate. 



Invasion of unplanted species into the experimental foredunes continues 

 to be extremely slow. Gulf croton increased significantly only on the 

 366-meter sea oats dune (Table 8) and, except for occasional plants of beach 

 groundcherry and beach morning glory, no other species have occurred even 

 after 12 years. 



Although many other species can tolerate salt spray, some protection from 

 salt spray allows for better survival. The older planting (landward dune of 

 the dune-width extension dune made in 1969 and 1970, Table 1), has invading 

 plants of several other species (Table 8). The shelter provided by 

 accumulating sand, resulting from the 1973 seaward planting of bitter panicum, 

 has allowed establishment in the landward crest of the dune-width extension 

 dune of prairie senna, beach evening primrose, beach morning glory, beach 

 groundcherry. Corpus Christi fleabane (Erigeron myrionaotis) , and gulf croton. 

 Trace amounts of several other species also occur. 



On the unplanted control area, where a natural dune is reforming, pioneer 

 plants are primarily beach morning glory and sea oats, with Fimbristylis spp., 

 gulf croton, and beach evening primrose being common. An occasional bitter 



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