Vegetation has been used to stabilize dunes to varying degrees along the Northeast, 

 Middle and Southeastern Atlantic shorelines, Florida, the northern coast of the Gulf of 

 Mexico, and Texas. Although the New Orleans District of the U. S. Army Corps of 

 Engineers and the Soil Conservation Service initiated some dune plantings on Grand Isle 

 in the past, the use of vegetation to build and stabilize dunes along the Louisiana coast 

 has been generally overlooked. 



SAND DUNE COMMUNITY 



Sand dunes are windblown accumulations which form in the shape of mounds, 

 ridges, and/or bands when a supply of sand is available. Although dunes may be 

 completely unvegetated, such as large mobile dunes which continually move as dictated 

 by eolian forces, the majority of dunes on barrier islands have some degree of plant cover 

 which may vary from exceedingly sparse to highly dense. 



Vegetation aids in building dunes by first reducing wind velocity in its lee and this 

 causes the deposition of sand grains. As more and more sand is deposited, these sand 

 grains accumulate into small mounds. Secondly, the roots of dune plants bind the sand 

 which results in varying degrees of substrate stability, depending on root density. In 

 response to newly accreted sands, which provide a fertilizing effect, vegetational growth 

 is stimulated. In many grasses, horizontal rhizomes give rise to tillers which greatly 

 increase the vegetative spread of the plant. As more tillers are produced, more sand is 

 accumulated until the vegetation may be nearly buried. When burial is even more rapid, 

 shoots are killed and rhizomes stop extending laterally, but continue growing vertically 

 until the new surface is reached, when again tillering takes place. This process allows 

 the vegetational growth to keep pace with sand accumulation and create partially 

 stabilized embryo or hummock dunes. As these dunes increase in number, they begin to 

 coalesce to form a dune line. Hence, a foredune is created. The configuration and 

 height of a dune line is a function of the sand supply and intensity and direction of 

 prevailing winds relative to the orientation of the barrier beach. Onshore winds normally 

 form large dunes while alongshore or offshore winds form dune lines which are more open 

 and lower in physiognomy. 



The above dune-building processes primarily occur on the backshore (i.e., the 

 horizontal or gently sloping part of the beach that is inundated only by storm waves and 

 extremely high tides) of Louisiana's barrier islands. This zone of the beach often 

 contains small hummock dunes and sparse vegetation. Densely vegetated dunes have 

 been estimated to occupy less than 3% of the total Louisiana barrier island area 

 (Mendelssohn et al. 1982), although the sandy backshore-dune-swale zones account for 

 approximately 18% of the islands' area. Since vegetated sand dunes are important 

 sources of sediments to these islands after storm events, it is clear that in their present 

 state, the barrier islands and beaches of Louisiana only have a limited source of 

 sediments in the form of back beach and dune deposits. 



The dunes of Louisiana's barrier islands are poorly developed as a result of a limited 

 amount of eolian transported sand and the high frequency of overwash resulting from 

 hurricanes and storms. Most of Louisiana's barrier islands and beaches have only one 

 primary dune line which is relatively low in profile and only moderately vegetated. 

 Barrier islands without well-developed dunes, such as in Louisiana, have limited sand 

 reserves and, thus, a limited mechanism of reducing net beach erosion. Since vegetation 

 aids in building of dunes and is essential for sand stabilization, dune vegetation plays a 

 key role in maintaining this important source of sediments on the barrier islands. 



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