Factors Effecting Vegetational Zonation on Coastal Dunes

The coast of North Carolina is discontinuously paralleled by a series of narrow, usually elongate islands. These lowlying sandy "banks" may support a sclerophyllous forest in which live oak (Quercus virginiana L.) predominates and which includes numerous characteristic species -of southern affinity. Descriptions of the general nature of the vegtation are available in several papers: Johnson ('00), Kearney ('00), Coker ('05), Lewis ('18), Wells ('39). Because of the full exposure to almost constant wind from the ocean, a slight disturbance of the vegetative cover may result in extensive "blow outs" of the unconsolidated soil. Once initiated, the shifting of the sand may not be checked naturally for years. Man's activities have contributed materially to the destruction of cover. Grazing has been particularly serious, for it has indirectly transformed several of the banks into almost barren seas of shifting sand. Today, grazing has been largely discontinued and, on government controlled areas particularly, much time and effort have been expended in attempts to stabilize the shifting dunes. Miles of brush barriers have been constructed and thousands of acres have been planted with grasses. The success of these attempts cannot yet be evaluated. One of the most effective native sandbinding grasses is sea oats ( Uniola paniculata L.) which is found in abundance on these coastal dune areas. The importance of this species and its associates as natural stabilizers prompted an investigation of the environmental factors governing their distribution. A portion of Bogue Bank near old Fort Macon at the entrance to Beaufort harbor, North Carolina, was chosen for intensive study. The area has been relatively undisturbed in recent years and illustrates all degrees of stability and vegetational development. The exposed position of the bank subjects it to the full sweep of the ocean wind and the pounding surf. The ocean side of the bank is bordered by a sand beach of varying width which terminates at a low (5-15 ft.) foredune. Behind this is an extensive depression sometimes covered with small dunes in all stages of development and stability, sometimes blown out to a depth very near the water table. This area may be only 150 feet wide but is often 600 feet or more in width, and it terminates inland at a relatively high rear dune which may be 40 feet high. The rear dune forms a