Whether you live here or just vacation in the Greater Topsail Island area, you encounter our coastal treasures. Treasure Realty is the trusted local expert for real estate and vacation rentals. We also enjoy sharing our coastal treasures.
This week’s blog is dedicated to the treasured dunes that protect Topsail Island, and the vegetation that is vital to that protection. This week’s guest blogger comes from Sea Grant North Carolina Coastwatch and NC State University.
By Spencer Rogers and David Nash with illustrations by David Williams.
Only a few species of plants can adapt to the dunes closest to the ocean and beach, where high levels of salt spray, continuous winds, large amounts of wind- blown sand, and other environmental factors continuously impact these “pioneer zone” species.
Coastal dune plants must be able to survive in soils that are low in nutrients and moisture and have extreme fluctuations in temperature and ocean overwash. Dune species thrive in this harsh environment because they are highly adapted to tolerate the extreme conditions.
Vegetation aids in forming the dune and plays an important role in the coastal dune ecosystem. Plants trap blowing sand, causing the formation of sand dunes and the stabilization of barrier island soils. As the dune field grows, multiple dunes line the beach, providing habitat for animals, birds, amphibians and reptiles.
Salt spray and blowing sand are the two main factors contributing to the zonation of plant species across the barrier island. The highest salt concentrations occur on the beach, gradually decreasing with distance. Dune plants tolerate the highest levels of salt spray and even an occasional overwash by sea water.
Most plants have a low tolerance for burial over their stems and roots. In contrast, dune plants thrive on wind- blown sand deposits, and collect sparse nutrients from the incoming sand, stimulating growth and reproduction. The harsh conditions in the pioneer zone allow the dune vegetation to grow without competition from less tolerant plants.
Inland from the shoreline and behind the shelter of the dunes, the conditions moderate to allow a wider variety of moderately tolerant grasses, shrubs and trees, resulting in distinctive plant zones forming across barrier islands — from the ocean to the estuary. The older dune ridges are farthest from wind-blown sand and salt spray. Plant species with less tolerance for salt spray and other adverse conditions may thrive in the back dune zone, where other plants and dune ridges block the sand and salt spray carried by the wind.
Climate and Native Species
Climate is the primary factor limiting the geographic range of pioneer zone coastal plant species. Along the mid-Atlantic coast, the dunes between the Chesapeake Bay and Cape Lookout are the approximate transition zone for several species.
For example, sea oats prefer the warmer climate found south of this area and appear to be limited in their northern range by cold temperatures. American beachgrass is the dominant pioneer zone species north of the transition zone, tending to die back when stressed by the hot, dry conditions found farther south. Both species are excellent sand trappers and dune stabilizers.
Since local plants take years to evolve, they are usually best adapted to the climate where they were first grown. For example, South Florida sea oats do not adapt as well in the cooler climate of North Carolina as they do in Florida, and American beachgrass from New Jersey is not well suited to North Carolina’s warmer climate.
Therefore, whenever possible, it is always best to obtain dune plants grown from seeds or parent material originating within a 100-mile radius of the beach where they will be planted. Often, however, the need for plants after the worst storms overwhelms local supply capacity, making it necessary to buy stock from farther away.
Whether patching the frontal dune adjacent to a beach cottage or planting several miles of a beach nourishment project, the primary goal is likely to be the same: to trap and stabilize the blowing sand so that it will repair or enhance the storm protection that dunes provide.
The Role of Vegetation in Natural Dune Recovery
Surviving plants slide off the face of the eroded dune as the scarp dries and collapses, where plants take root. Dune recovery following a storm usually evolves in several ways, depending on the remaining topography and severity of the storm.
During typical seasonal fluctuations in the berm width, the seaward edge of the vegetation sends rhizomes a few feet into the back edge of the berm during the growing season, only to get pruned during the season’s worst erosion.
In severe storms — where the dune is not overtopped but a significant volume of sand is removed from the dune — vegetation recovery is usually initiated at one of the three points where remaining vegetation may survive (Figure I and Figure J).
The most severe storms may leave remnants of surviving vegetation near the old vegetation line, initiating the most seaward pioneer plants in the next growing season. The near vertical erosion scarp is highly unstable. In the days to weeks following the storm, the moist sand in the scarp dries, and the scarp gradually collapses, becoming a flatter, more stable slope.
As the scarp collapses, vegetation from the top of the dune is carried with it. Some of the vegetation survives the slide to the toe of the dune, initiating the recovery over the new slope. Remaining vegetation at the top starts the recovery from above.
Therefore, on high dunes, vegetation recovery following storms can begin at three locations: surviving plants on the dune top; plants sliding seaward with the collapsing scarp colonizing the toe of the dune; and sometimes, the old vegetation line, if the erosion isn’t too deep.
After a storm flattens the dune and overwash deposits bury the vegetation, some plants grow through the deposits and initiate dune recovery.
Dune vegetation has the ability to survive varying depths of burial by overwash. Although the plants seem to disappear following a storm, they can pop up out of nowhere at the beginning of the next growing season and initiate the dune recovery. Buried too deep, the vegetation will not survive, and recovery must start farther landward.
Dune plants colonize bare sand primarily by spreading rhizomes or runners from a parent plant. Storms can leave debris deposits or wrack lines that contain a few viable seeds or plant remnants and help jumpstart the dune recovery.
The densest clumps of vegetation trap the most sand and are stimulated to grow denser and spread even faster. As the dune grows in height and vegetation density, the area farther landward begins to be affected. By trapping most of the sand in the first dense vegetation, the sand supply to more inland areas is reduced. As the seaward dune height increases, dunes farther landward lose their sand supply and become more sheltered from the wind speeds necessary to deliver the sand.
Over time, most dune growth — in both width and height — occurs in the seaward direction. During each season, the seaward edge of the dune grows farther seaward, followed by the rising dune crest. In contrast, the landward side of the dune captures very little sand.
In this way, dunes grow from landward to seaward. However, at some point the seaward growth is halted when the vegetation line reaches the landward limit of seasonal berm fluctuations. As the slope of the dune face steepens, future increases in dune height slow considerably. Understanding the way that dunes grow in width and height — and their effect on the growth of more landward dunes — is critical in applying the dune and vegetation management strategies.
Thank you Sea Grant North Carolina Coastwatch and NC State University. We appreciate the dedication and work you continue to do on behalf of the all the treasure coasts of our great state! To read the entire article online you may visit by clicking on this provided link;
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