Southern Atlantic Coastal Dune Grassland

This ecological system consists primarily of grasslands and related shrublands of Atlantic Coastal Plain barrier islands and related coastal areas from North Carolina south to northern and central Florida. On the Florida coast from south of Cape Canaveral to the sandy portions of the Florida Keys, this system occurs in a more attenuated fashion. This ecological system includes upland dune grasslands and maritime wet grasslands and shrublands, which are not tidal, but may be flooded for short periods of time from storm surge or heavy rain. The environment of this system is highly dynamic. Reworking of sand by storms or by slower eolian processes may completely change the local environment. Vegetation responds to these natural coastal processes through primary succession. The combined effects of chronic and extreme salt spray and periodic ocean overwash by seawater prevent or dramatically inhibit woody plant growth.

Vegetation consists of a set of grassland and other herbaceous associations. Uniola paniculata is the characteristic dominant on the youngest dunes and those most exposed to salt spray and less commonly Panicum amarum (Pinson 1973). Spartina patens or Schizachyrium littorale tend to dominate older dunes and sand flats. Component communities tend to be low in plant species richness, but have a characteristic set of forbs and occasional low shrubs associated with them. Wetter sand flats and dune swales may be dominated by a variety of herbs and sometimes have fairly high species richness. Also included in this system are patches of transition shrub communities or shrub thickets.

Occurs on barrier islands and similar coastal strands, on sand dunes and sand flats. Strong salt spray is an important influence on vegetation in many parts. Overwash by sea water during storms is important on sand flats not protected by continuous dunes. On dunes, present or recent sand movement is an important factor. The combination of these factors prevents the dominance of woody vegetation. Sites may be either dry or saturated by freshwater from rainfall and local water table. Areas connected to tidal influence and areas with ponded freshwater are placed in other ecological systems. Soils are sandy, with little organic matter and little or no horizon development. Soils may be excessively drained on the higher dunes. Soils are low in nutrient-holding capacity, but aerosol input of sea salt provides a continuous source of nutrients. North of the Sea Islands region of coastal Georgia and South Carolina, barrier islands that face south tend to have better developed dune fields, and often have extensive maritime forest systems, and east-facing barrier islands naturally have less continuous dunes and more overwash flats. On islands that face east, the northern portion tends to experience shoreline and dune erosion and the south end may experience accretion. Many of Georgia's barrier islands (known as Sea Islands) show this pattern.

The environment of this system is one of the most dynamic in existence for terrestrial vegetation. Reworking of sand by storms or by slower eolian processes may completely change the local environment in a short time, changing one association to another or changing this system into a different system. Many of these sites are fairly early in the process of primary succession on recent surfaces. Chronic salt spray is an ongoing stress. Overwash and extreme salt spray in storms is a frequent disturbance. Vegetation interacts strongly with geologic processes; the presence of dune grass is an important factor in the development of new dunes. Artificial enhancement of dunes by sand fencing or planting off-site species, including Ammophila breviligulata, can alter the dynamic processes of the dunes. Fire is probably not a major natural factor in this system, but may have been important locally. Most vegetation is too sparse to carry fire well.

Threats include recreation (vehicle traffic and excessive foot traffic), beach cleaning (removal of wrack), beach renourishment (if not planned and carried out in a way compatible with the beach ecosystem), sea-level rise, coastal residential and commercial development, and coastal engineering such as beach armoring, seawalls, jetties and other structures which interfere with sand movement and shoreline migration (Defeo et al. 2009). Coastal engineering hard structures reflect wave energy, constrain coastal sand migration and often lead to greater loss of beach and dune sand (Defeo et al. 2009). Structures such as jetties around inlets restrict the natural movement of sand, starving coastal ecosystems of sand. The developed residential and tourism infrastructure of coastal areas has restricted natural dune and beach migration. Increasing sea-level rise associated with global climate change will lead to more loss of beach, especially in developed areas where infrastructure such as seawalls, buildings and coastal roads restrict the potential for inland migration of the beach and dunes. Beach renourishment has been carried out on many beaches along the Florida coast. The use of sand for renourishment which does not match the grain size and composition of the beach to be restored can be a threat, especially where sand is applied deeply. This can be disruptive to the beach and dune ecosystem. Invasive exotic plants which are threats include (along the Florida coast) Casuarina equisetifolia and further north Carex kobomugi and Vitex rotundifolia which can alter beach and dune sand vegetation dynamics (FNAI 2010a). Invasive animals include imported red fire ants (Solenopsis invicta) and feral hogs (Sus scrofa) which prey on the eggs of various animals (Defeo et al. 2009). Feral house cats, dogs, and coyotes are a threat to nesting birds and other small animals which occur in coastal habitats. Horses and other livestock can destabilize dunes by overgrazing the vegetation and tramping the dunes.

This system ranges on the Atlantic Coast from northern North Carolina (Omernik ecoregion 63g, Carolinian Barrier Islands and Coastal Marshes) to central Florida. The northern limit is a transition zone from around Kitty Hawk, North Carolina, to the Virginia-North Carolina border.