Gulf Coast Maritime Forest

This system encompasses a mosaic of woody vegetation present on barrier islands and near-coastal strands along the northern Gulf of Mexico, from the Florida panhandle to southern Mississippi. Examples may include forests and/or shrublands that are found in somewhat more protected environments than East Gulf Coastal Plain Dune and Coastal Grassland (CES203.500). Such areas include relatively stabilized coastal dunes, sometimes with a substantial shell component. Vegetation structure and composition are influenced by salt spray, extreme disturbance events, and the distinctive climate of the immediate coast. Stands may be dominated by a variety of needle-leaved and broad-leaved evergreen trees, including Pinus clausa, Pinus elliottii var. elliottii, Pinus palustris, Quercus virginiana, Sabal palmetto, Carya glabra, and Carya pallida. Wetland inclusions may be dominated by Taxodium ascendens and Magnolia virginiana. The most heavily salt-influenced examples may appear pruned or sculpted.

Stands may be dominated by a variety of needle-leaved and broad-leaved evergreen trees, including Pinus clausa, Pinus elliottii var. elliottii, Pinus palustris, Quercus virginiana, Sabal palmetto, Carya glabra, and Carya pallida. Wetland inclusions may be dominated by Taxodium ascendens and Magnolia virginiana. Understory trees and shrubs may include Quercus geminata, Quercus myrtifolia, Ilex vomitoria, Serenoa repens, Morella cerifera, Ilex glabra, Vaccinium arboreum, Juniperus virginiana, Zanthoxylum clava-herculis, Sideroxylon lanuginosum, Persea borbonia, Conradina canescens, and Callicarpa americana. Herbs may include Spartina patens, Juncus roemerianus, and Panicum virgatum. Wetland inclusions may contain Cladium mariscus ssp. jamaicense.

This system is found on barrier islands and near-coastal strands, on stable dune-and-swale topography in somewhat more protected environments along the northern Gulf of Mexico. More specifically, these areas are generally landward of the foredune and transitional backdune zones. Examples may 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).

The maritime environment for these forests is extremely dynamic, even though they occur on the most stable portions of barrier islands. Maritime forest systems remain subject to periodic severe physical stresses. The environment for these forests may be severely altered or destroyed by geologic processes such as the slow movement of dunes or their destruction by storms and hurricanes. Sand movement may also create new sites for this system to occupy or degrade them through erosion or sand burial. Chronic salt spray (sea salt aerosol), as well as intense salt spray during storms are important influences on vegetation structure and composition; however, the extent to which plant communities found in this system are shaped by salt spray varies. The most heavily salt-influenced examples of these systems may appear pruned or sculpted. Extreme salt spray or saltwater flooding in storms can severely disturb vegetation, though it recovers if the landforms have not been altered. Fire may have naturally occurred infrequently in this system, but probably was not an important factor. Mature Quercus virginiana trees are fire-resistant when mature, and their litter also does not easily burn (Stalter and Odum 1993).

Hurricanes frequently make landfall in the northern Gulf of Mexico and have a significant impact on coastal systems. Even when they do not make landfall in the region, the storm surge and wave action generated by an off-shore storm can have a significant impact. For example, a total of 112 hurricanes made landfall from Wakulla County, Florida, to Hancock County, Mississippi, during the period 1926 to 2005 (Jarrell et al. 1992 with updates); 36 major hurricanes (Category 3 or higher) made landfall along the Gulf Coast from Louisiana to the Florida Panhandle between 1851 and 2004 (Blake et al. 2005). Hurricane-associated storm surges can overwash the dune system and cause significant erosion and/or sand burial of maritime forests (Landfire 2007a).

The role of fire in this system is poorly documented. The majority of this system occurs on narrow barrier islands along the northern Gulf of Mexico. FNAI (1990) indicates that the mesic conditions and insular locations of well-developed maritime hammock communities inhibit natural fires, which occur no more frequently than once every 26 to 100 years. Mature Quercus virginiana trees are fire-resistant when mature, and their litter also does not easily burn (Stalter and Odum 1993). Liu et al. (2003), in their study of sediment cores from Little Lake, Alabama, suggested that wildfires have been common in the coastal ecosystems in Alabama; however, they offered no frequency estimates. They did suggest a correlation between hurricanes and fire. This correlation was also supported by Meyers and van Lear (1998) who suggest that interactions between hurricanes and fires once played a major role in the development of ecosystems in the southern U.S., influencing their composition, structure, and pattern on the landscape (Landfire 2007a).

The following fire-return interval estimates were based on Huffman and Platt (2004) and the return interval in similar ecological systems on the mainland. Fire interval and intensity depend on the patch vegetation type. In Quercus/Ceratiola ericoides-dominated ridges, there is little fuel to sustain surface fires; in this vegetation type, fires are typically replacement fires that burn through the shrub crowns. This return interval was estimated to be 25 to 100 years. These fires were more likely to have occurred following a hurricane or other intense storm-related event when more fuel became available and fire intensity presumably would have been higher. Pine-dominated swales and flats most likely burned more frequently than the Quercus/Ceratiola ericoides-dominated ridges. Fires in these swales were primarily light surface fires occurring every four years during the growing season. More intense replacement fires may have occurred following hurricanes, when more fuel was available as a result of storm damage (Landfire 2007a).

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, of 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).

Roads threaten the growth patterns and species composition because opening the forest canopy allows increased salt penetration to the forest interior. Areas without extensive fragmentation into small lots will still suffer degradation from construction of roads, even those that parallel the axis of the barrier island (Bellis 1995). Any kind of canopy opening exposes the uncleared areas of forest vegetation to increases in salt aerosol impact, wind shear, and altered drainage (Gaddy and Kohlsaat 1987). 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. These feeder roads, such as those constructed to provide beach access, are typically parallel to the direction of onshore winds, and serve to intensify the effects of salt spray and wind shear, further degrading the canopy. These would be regarded as having moderately severe degradation. The presence of only roads parallel to the axis of the barrier island represent low severity of degradation, although these are cumulative processes and the degradation will continue to increase with time.

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. Erosion of foredunes and the resulting increased salt spray may be significant impacts. 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 is found along the northern Gulf of Mexico, from the Florida panhandle to southern Mississippi, restricted to the most coastward part of the "Gulf Coast Flatwoods" (Ecoregion 75a of EPA (2004)).