DUNE COMMUNITY CREATION ALONG THE ATLANTIC COAST 



Ernest D. Seneca 



Departments of Botany and Soil Science 

 North Carolina State University 

 Raleigh, North Carolina 27650 



The information that I report is 

 the result of research conducted along 

 the Atlantic Coast by Dr. W. W. 

 Woodhouse, Jr., Dr. S. W. Broome, and 

 me. Suggested references include 

 Woodhouse (1978) and Woodhouse et al. 

 (1968, 1976). We have received support 

 from the Coastal Engineering Research 

 Center, U.S. Army Corps of Engineers; 

 the University of North Carolina Sea 

 Grant Program; and the North Carolina 

 Coastal Research Program. 



I am going to describe the function 

 of sand dunes along the Atlantic Coast; 

 how to build and stabilize them, what is 

 good and bad about them, some applica- 

 tions, and some of the knowledge that we 

 have accumulated during the past 15 yr 

 of research. 



Coastal dunes are natural features 

 of most sandy shorelines, especially in 

 temperate regions. They result largely 

 from sand being trapped by vegetation. 

 Onshore winds move sand onto the beach. 

 Along the North Carolina coast, north- 

 east winds are primarily responsible for 

 moving this sand from deposits above the 

 high tide line, on a berm, onto the 

 dunes. Almost any obstruction in the 

 path of blowing sand will cause it to 

 settle out, accumulate, and build a 

 dune. Perennial grasses are especially 

 efficient at facilitating this task. 



The native dune community along the 

 Atlantic Coast is dominated by perennial 

 grasses. Northward of Virginia, American 

 beachgrass ( Ammophila brevil igulata ) is 

 dominant; from North Carolina southward 

 to Florida and along the Gulf coast to 

 Texas, sea oats ( Uniola pa niculata ) dom- 

 inates. Because of their dominance and 

 their superior sand-trapping capacity, 

 perennial grasses are used to initiate 

 dune development. 



Although these perennial grasses 

 reproduce both sexually and asexually 

 (vegetatively) , vegetative reproduction 

 by extensive rhizome systems is most 



important in stabilizing the sand and 

 building a dune. The principal grasses 

 used in dune creation along the Atlantic 

 Coast are American beachgrass, sea oats, 

 and bitter panicum ( Panicum amarum ). New 

 shoots and roots arise intermittently 

 along the rhizomes of these grasses. In 

 the case of American beachgrass, rhizome 

 growth can enable a dune to migrate to- 

 ward the sand supply at a rate of about 

 1.4 m (4.4 ft)/yr. 



Coastal dunes are flexible bar- 

 riers. They are part of the nearshore 

 dynamic zone that changes with the wave 

 climate both seasonally and in response 

 to sporadic storm activity. Dunes serve 

 as sand reservoirs to nourish the beach 

 during storm attack. A portion of the 

 dunes may be eroded, the material car- 

 ried out in the surf zone and deposited 

 on offshore bars, and then returned at 

 some later time. As much as 3 m (10 ft) 

 of sand at the base of the dune may be 

 taken out during a severe storm. A sig- 

 nificant portion (over half) of this 

 sand may return within the next two or 

 three tidal cycles; in time most of it 

 may return. Unfortunately, man does not 

 often appreciate the fact that foredunes 

 are a part of this dynamic zone, which 

 is continually undergoing change. 



Further, sea level is rising; it 

 may be only 2 to 3 mm (0.08 to 0.12 

 inch) a year, but coastal lands are 

 being claimed by the sea and the forces 

 of erosion. Coastal dunes are not 

 effective barriers against this type of 

 situation. Nature is taking what it 

 needs to establish new beach and shore- 

 line profiles. There is little that man 

 can do without tremendous expenditures 

 to change this trend. 



Coastal dunes can be built in many 

 ways and the method used may influence 

 the vegetation that exists on them. 

 Substrate moisture conditions in dunes 

 are related to the texture of the sand 

 which in turn may be a result of the 



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