driven over. Sand fencing, used to protect irrigation pits, has been shredded. Survey marker 

 posts, although painted and numbered, commonly are used for firewood. Concern for 

 protection of natural and artificial foredunes has resulted in strict enforcement of protective 

 measures on the national seashore. Camping and driving on vegetation is prohibited, and 

 excessive foot traffic in critical areas is discouraged by information signs. Examples of the 

 effects of human damage are shown in Figure 43. 

 6. Long-Term Considerations. 



a. Dune Growth. After the initial 50-foot-wide planting, followed several months later 

 by fertilization, the transplants begin active growth by sending out new tillers and an 

 abundance of stiff leaves. The sand transported by prevailing onshore winds moves through 

 the planting, either as individual grains, or as small, low dunes. When plant cover has 

 attained a certain density (usually the first summer), the sand is moved into the planting and 

 the leaves and stems disrupt wind movement, preventing the sand from moving out again. 

 The plants exploit this fresli sand with more shoots, roots and tillers, and the process 

 continues. When large amounts of sand are transported into the planting in a short period, 

 e.g., during strong onshore winds in dry weather, the front of the planting traps the sand 

 first until capacity is reached (near the tips of the leaves). More sand is swept across the 

 slope and deposited immediately behind it, often forming a slip face 1 to 2 feet steep. The 

 dune continues growing in this manner; sand reaches the back part of the dune only when 

 the plants on the front part are covered nearly to the top. 



b. Dune Growth: Sand Accumulation. After the first year following planting, the 

 growing dune has the capacity to trap nearly all sand transported inland from the beach 

 (Figs. 37 and 38). All major north Padre experimental plots were surveyed periodically. The 

 growth at these sites is shown by mean cross-sectional profiles at approximately yearly 

 intervals in Figures 37, 38, 44, and 45. Volumes of sand accumulated by the various 

 plantings as of March 1974, (January 1974, for the south 400-foot sea oats) are given in 

 Table 53, along with average yearly accumulation. Complete cross-sectional profile volumes 

 from selected stations and means for all surveys, are given in Tables 54 and 55. The amount 

 of sand available for dune building at the experimental plot sites has ranged from 3.3 to 5.2 

 cubic yards per linear foot of beach per year, with an average of 4.3 cubic yards per linear 

 foot of beach per year. In comparison, a 50-foot-wide planting of American beachgrass in 

 North Carolina trapped between 10 to 11 cubic yards per linear foot of beach in 3 years, or 

 about 3.5 cubic yards per linear foot of beach per year (Savage and Woodhouse, 1968). 



It is believed that a 50-foot-wide sea oats or bitter panicum planting has the capacity to 

 trap considerably more than this amount, if enough sand becomes available. Similarly. 

 Savage and Woodhouse (1968) reported that a 100-foot-square plot of sea oats in North 

 Carolina accumulated as much as 16 cubic yards per linear foot of beach in 15 months. This 

 was an abnormal situation, as sand was avaUable from all directions, but it illustrates the 



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