and thus achieves stability sooner. The most common and widespread colonizers of the 

 backslope were beach evening primrose and railroad vine. The foreslope of all dunes 

 contained only two species: railroad vine and sea purslane, neither of which was very 

 common. 



The slow invasion rate should not be considered undesirable to the long-term stability of 

 the dune. All dunes are still actively growing, and are not near maturity. A more complex 

 plant community should continue to develop, particularly on the lee side as the sand supply 

 is eventually choked off. 



g. Modifications to the Ecosystem. Dolan (1972b) reported that artificial barrier dunes 

 on the Outer Banks of North Carolina increased beach erosion, narrowing the beach width 

 from 660 feet to less than 98 feet since stabilization (about 30 years). This is one reason he 

 concludes that a stabilized barrier dune ridge is detrimental to the long-term equilibrium of 

 the island. As discussed earlier, there is no evidence that a similar process is occurring in 

 areas of long-stabilized foredunes on northern Padre or Mustang Island, or as a result of the 

 artificial dune line. Comparison of an unplanted beach section with a 5-year-old dune 

 (Fig. 53) shows similar beach configurations to 400 feet inland where the artificial dune 

 begins. Comparison of the same beach profile over a 2-year period (Fig. 54) also shows no 

 real difference except for continued dune growth. Since the east coast erosion occurred 

 during winter and tropical storm surges, monitoring Padre Island dunes through a severe 

 storm is necessary to determine if this is also occurring^ Additional beach profiles are 

 presented in Figure 55 for the 2-year-old, 1,200-foot dune-width bitter panicum plot, and 

 the recently planted (winter 1973-74) southernmost plot. 



A profile of a natural foredune and beach is shown in Figure 56; photo of this site 

 appears in Figure 7 (foreground). The extensive vegetation and dune growth shoreward of 

 the foredune has been greatly curtailed in areas of heavy vehicular traffic, such as the beach 

 in front of the experimental plots. The profile is representative of the backshore and 

 foredune foreslope of the pedestrian beach, although in most of that area the natural 

 foredune is higher and extends farther west. 



Growing artificial dunes modify the environment to their leeward side in the following 

 ways: (a) most sand blown inland from the beach is trapped and stabilized; the sand does 

 not migrate farther inland to feed the barren dune fields and therefore, they gradually 

 decrease in size; (b) inundations from storm surges penetrate no farther inland than the 

 dune line, thus leeward areas are no longer subject to saltwater flooding and subsequent liigh 

 soil salinity; and (c) salt spray is decreased in the shadow of the foredunes. The combination 

 of decreased salt spray, and elimination of drifting sand, sand abrasion, and saltwater 

 inundation has resulted in a rapid colonization of the leeward area by native plants 

 (Fig. 57). The relative species composition of tins area in September 1973, is shown in 

 Table 58; a permanent transect established in the same area yielded the information in 

 Table 59. Plant succession on south Padre, behind the North Section Fence dune, is not 

 progressing as rapidly, nor with the same species (Table 60). Here the most important 



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