Sea Island Maritime Forest

This system encompasses a range of woody vegetation present on stabilized upland dunes of barrier islands and near-coastal strands, from central South Carolina (from approximately the Cooper River) southward to Volusia County, Florida. It includes vegetation whose structure and composition are influenced by salt spray, extreme disturbance events, and the distinctive climate of the immediate coast. Examples are known from the barrier islands of Georgia and Florida, such as Big Talbot Island, Florida, and probably Sapelo Island, Georgia. Most typical stands are dominated by oaks, primarily Quercus virginiana and/or Quercus geminata. Vegetation may also include different woodland communities often dominated by southern pine species. Pinus palustris, Pinus serotina, and Pinus elliottii var. elliottii are all important in documented examples. These examples tend to have densely shrubby subcanopies and understories with species such as Quercus virginiana, Quercus geminata, Quercus hemisphaerica, Quercus chapmanii, Quercus myrtifolia, and Magnolia grandiflora. Unlike maritime vegetation to the north, this system may be more heavily influenced by natural fire regimes that may help to explain the predominance of the fire-tolerant pine species. It has been postulated that the natural fire-return interval is from 20 to 30 years.

Most typical stands are dominated by oaks, primarily Quercus virginiana and/or Quercus geminata. Vegetation may also include different woodland communities often dominated by southern pine species. Pinus palustris, Pinus serotina, and Pinus elliottii var. elliottii are all important in documented examples. These examples tend to have densely shrubby subcanopies and understories with species such as Quercus virginiana, Quercus geminata, Quercus hemisphaerica, Quercus chapmanii, Quercus myrtifolia, and Magnolia grandiflora.

The primary range of this system coincides with the Sea Islands, a chain of more than 100 low islands off the Atlantic coast of South Carolina, Georgia, and northern Florida, extending from the Cooper River to the St. Johns River. Many of these islands have a long history of human use and occupation, including Spanish missions and garrisons in the 16th century. In addition, the Sea Islands were the first important cotton-growing area in North America. The degree to which this system has been altered by these events is unknown.

This system is found on these islands and associated near-coastal strands, on stable dune and swale topography in somewhat more protected environments. These areas are generally landward of the foredune and transitional backdune zones. Examples typically include forests and/or shrublands that are found in somewhat more protected environments than adjacent dune and coastal grassland vegetation. The system typically includes a series of stabilized dunes and interdune swales oriented parallel to the coastline. Soils are primarily wind- and wave-deposited, well-drained quartz sands of Appalachian origin (Drehle 1973, Johnson and Barbour 1990), sometimes with a substantial shell component, that have been stabilized long enough to support trees and shrubs. As the forest establishes, soil temperature fluctuations moderate and humus begins to build up over the well-drained sands, contributing to moisture retention and leading to more mesic conditions, especially in swales where soil moisture is typically higher (FNAI 1990).

Maritime forests occur in the most stable portions of barrier islands, but the maritime environment is still extremely dynamic. Wind events and hurricanes will have significant impacts on this system. The environment for these forests may be severely altered or destroyed by geologic processes, such as the slow movement of dunes or their catastrophic destruction by storms. Sand movement may also create new sites for this system to occupy. Extreme salt spray or saltwater flooding in storms can severely disturb vegetation, though it recovers if the landforms have not been altered. Mature Quercus virginiana trees are fire-resistant when mature, and their litter also does not easily burn (Stalter and Odum 1993). Fire may have occurred naturally yet infrequently in this system, but probably was not an important factor.

The vegetation of this system has a structure and composition that is influenced by salt spray (sea salt aerosol), extreme disturbance events, and the distinctive climate of the immediate coast. Extreme salt spray or saltwater flooding in storms can severely disturb vegetation, although the vegetation recovers if the landforms have not been altered. Unlike maritime vegetation to the north, this system may be more heavily influenced by natural fire regimes that may help to explain the predominance of the fire-tolerant pine species. It has been postulated that the natural fire frequency is from 20 to 30 years.

Conversion of this type has primarily resulted from clearing and development. Maritime forests occur on the most stable portions of barrier islands and are very attractive building sites. Clearing lots for houses involves disturbing or destroying most, if not all, the natural vegetative cover to make space for homes, parking areas, drainage fields, and septic systems. Following construction, native vegetation is often replaced by lawns and ornamental shrubs, many of which are exotic (Bellis 1995).

Remnants of maritime forest systems are also threated by edge effects and fragmentation. Breaks in the canopy create eddies in the wind and increase deposition of salt spray. Removal of vegetation on the seaward side increases salt spray deposition on interior portions and can lead to their death. Adjacent clearing, small openings for houses, and roads all contribute to these problems. In addition, several studies have confirmed that road building on barrier islands affects salt transport patterns into the interior of maritime forests (Eaton 1979, Seneca and Broome 1981).

Common threats and stressors include road construction, which is a direct cause of habitat fragmentation. Roads threaten the growth patterns and species composition because opening the forest canopy allows increased salt penetration to the forest interior. Generally, at least one main road is constructed along the entire length of a barrier island, above the dune ridge at the perimeter of maritime forests, to permit easy access to beaches. Other roads are built laterally to the trunk road for access to developments and private residences. Roads threaten the growth patterns and species composition because opening the forest canopy allows increased salt penetration to the forest interior. Several studies have confirmed that road building on barrier islands affects salt transport patterns into the interior of maritime forests (Eaton 1979, Seneca and Broome 1981).

An additional stressor to wetland communities in this system is the removal of groundwater from barrier island aquifers. Rainfall is generally the only source of freshwater on barrier islands, and the maritime forest community acts as the primary watershed. Precipitation entering the watershed is rapidly drawn deep into a freshwater lens, which floats above the denser saltwater in the permeable sediments beneath barrier islands. Pumping of groundwater can dry out wetlands in dune swales. Excessive pumping of freshwater from the lens for residential and commercial purposes can lead to loss of the hydrostatic head in the freshwater lens, which could, in turn, increase the rate of saltwater intrusion into surface waters on the island (Ward 1975, Winner 1975, 1979, Bellis 1995).

The most significant potential climate change effects over the next 50 years include rising sea level and an increase in storms. The climate is expected to be warmer, and estimates of changes in rainfall amounts vary widely. Most maritime upland forest sites are more than 1 m above sea level, and are unlikely to be directly inundated. Even if the Outer Banks of North Carolina collapses and most of it is lost, the wide areas that support most of the maritime forests will remain as islands. However, erosion of foredunes and the resulting increased salt spray may be a significant impact. Coastal erosion will likely reduce their extent. Increased hurricane activity, with associated storm surge into the lower portions, heavy salt spray and windthrow will increase mortality of trees and other vegetation (NCDENR 2010). Under possible conditions of climate change, increased natural disturbance by wind, salt spray, and storm surge intrusion will be significant, but the magnitude is quite uncertain. Examples of this system contain species that can recover from these disturbances, but increased frequency will result in younger canopies, more time spent in recovery stages, and shifts toward the most tolerant species. Some maritime forests will likely become maritime shrub and some maritime shrub will become grassland (NCDENR 2010).

This system occurs from central South Carolina (Cooper River) southward to approximately Volusia County, Florida (ca. 28°30'N latitude).