fresh to mildly brackish water on top of the saltwater under even the 

 smallest dunes (Berenyi, 1966) and may create substantial reserves of 

 freshwater under larger dune systems. This resistance to mixing may also 

 allow plants an escape from salt damage following flooding. If the sand 

 is moist, the seawater will drain off with little infiltration into the 

 freshwater and little or no effect on the plants, except in low spots 

 where it becomes trapped and evaporates, leaving a high concentration of 

 salt. 



Another possible mechanism in reducing the salt effect of inundation 

 is the rise of the water table in the beach and dune area that accompanies 

 a general rise in the tide level. The freshwater lense tends to rise with 

 the water table leaching salt from the root zone. 



Salinity is not usually a major barrier to the establishment of 

 adapted foredune species on most U.S. coasts, but it can become a serious 

 problem in the gulf coast where low sites have to be planted under condi- 

 tions of warm to hot temperatures, low and erratic rainfall, and high 

 evaporation rates. Dahl, et al. (19 75) observed this in planting hurri- 

 cane surge washovers on South Padre Island. They constructed a broad 

 flat dune across a washover pass by trapping sand with 60- centimeter sand 

 fences to leach out salt so bitter panicum and sea oats could survive. 

 This lowered the subsurface salinity from 15 parts per thousand to near 

 zero in 1 year. 



Dahl, et al. (1975) also planted exposed back beaches and protected 

 areas on North and South Padre Islands to study the effect of inundation 

 on survival of transplants. Results were erratic — some plantings were 

 essentially eliminated by storm surges and some were little affected. 

 In general, established plantings were more tolerant to exposure but the 

 increased survival on protected sites could not be attributed to only 

 salinity differences. Drifting sand appeared to be equally important 

 in several instances. 



(3) Fertilization . Dune and beach sands undergo extensive leach- 

 ing during formation, transport, and deposition. Consequently, they are 

 inherently low in most nutrients essential to the growth of higher plants. 

 In nature, most dune plants persist under a chronic deficiency of these 

 nutrients. While typical dune species are well adapted to a low nutrient 

 regime, most respond noticeably to fertilizers. This does not mean that 

 the general use of fertilizers in the dune and beach system is desirable, 

 but that fertilization can be a useful management tool. 



Fertilization is useful for rather definite and restricted purposes: 

 to speed up the establishment of new plantings, increase growth, and in- 

 crease sand-trapping capacity, and thus improve their chance of survival; 

 and to revive declining stands to maintain protective cover in areas 

 receiving a reduced or intermittent sand supply. 



Response to fertilizers is usually most pronounced on old, leached 

 sands in back-dune and deflation plain areas that are cut off from fresh 



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