Southern Atlantic Coastal Plain Nonriverine Swamp Forest

This system consists of poorly drained, organic or mineral soil flats of the Atlantic Outer Coastal Plain. These areas are saturated by rainfall and seasonal high water tables without influence of river or tidal flooding. Fire is generally infrequent but may be important for some associations. Vegetation consists of hardwood or mixed forests of Taxodium distichum, Nyssa spp., bottomland oaks, Acer rubrum, or other wetland trees of similar tolerance. The lower strata have affinities with pocosin or baygall systems rather than the river floodplain systems that have affinities with the canopy. The combination of hardwood/deciduous canopy dominants and nonriverine, non-seepage hydrology distinguishes this system from other Coastal Plain systems. Stands with a high cover of Chamaecyparis thyoides formerly occupied much of the acreage of this system. This phase is presently only present in high-quality examples, and it helps distinguish this system from other Coastal Plain systems. Disturbed and fire-disrupted examples (those dominated by Nyssa spp., bottomland oaks, Acer rubrum) may be hard to distinguish from other wetland forests based purely on canopy composition.

Vegetation is a closed-canopy forest of wetland trees. The wetter sites are dominated by combinations of Taxodium distichum, Nyssa biflora, and occasionally Nyssa aquatica, Pinus taeda, Chamaecyparis thyoides, Liquidambar styraciflua, and Liriodendron tulipifera. Less wet sites have canopies of wetland oaks such as Quercus laurifolia, Quercus michauxii, and Quercus pagoda. Most communities have a well-developed shrub layer that has more floristic affinities with pocosins or baygalls than with river floodplain communities that have similar canopies. The shrub layer is usually dominated by Clethra alnifolia, Leucothoe axillaris, or species shared with pocosins. The herb layer is not usually well-developed but may be dense where shrubs are atypically sparse. Wetland ferns, such as Osmunda regalis and Woodwardia areolata, and Carex spp. usually dominate. In the Atlantic white-cedar-related phase of this system, stands that regenerated from crown fire often have nearly pure cover of Chamaecyparis thyoides. The most common subcanopy species are Acer rubrum, Persea palustris, and Magnolia virginiana. Typical shrubs include Ilex glabra, Ilex coriacea, Eubotrys racemosa (= Leucothoe racemosa), Itea virginica, and Lyonia lucida. Herbs, chiefly ferns and sedges, are typically sparse, but mosses may be common (C. Frost pers. comm.).

This system occurs on flat areas of the Atlantic Outer Coastal Plain from Maryland to Georgia, where soils are seasonally to nearly semipermanently saturated because of low relief, poor soil drainage, and seasonal high water table. The largest areas are on broad interfluvial flats, but substantial areas occur on organic deposits in drowned river valleys in the Embayed Region of North Carolina and Virginia, beyond the reach of the influence of wind tides. Hydrology is dominated by rainfall and sheetflow, and overbank flooding, tidal flooding, and seepage are a secondary influence, if at all. Soils may be loamy to clayey, or may be shallow to deep organic. A distinctive small subset has soils with limestone near the surface, influencing soil chemistry. Natural fire is infrequent in this system, and varies from a minor to a significant influence on vegetational composition and structure. Infrequency of fire may be an important factor in differentiating this system from Atlantic Coastal Plain Peatland Pocosin and Canebrake (CES203.267) and the various wet longleaf pine forest systems. In a phase or component of this system on mucky peat soils (Terric or Typic Medisaprists) up to 3 m deep and occasionally on mucky sand or wet mineral soils with an organic epipedon, Chamaecyparis thyoides was the most common dominant species; it occurred in a fire-generated patch mosaic in which the various patch dominants are a variable combination of Acer rubrum, Chamaecyparis thyoides, Nyssa biflora, Pinus serotina, and Taxodium, most frequently Taxodium ascendens. While this is fire-dominated, it is only found in substantially fire-sheltered portions of the landscape where scarps or water bodies prevent easy access by fire, resulting in a long fire-return interval. The original vegetation constituted a true shifting mosaic. The original extent was up to 1 million acres of which at least 400,000 acres were Atlantic white-cedar in Mapzones 58 and 60. This is a long-interval, fire-dependent, forested peatland with its greatest extent found on the Pamlico Terrace of Virginia and North Carolina. The largest sites lie at less than 9 m (30 feet) above sea level (C. Frost pers. comm.).

Fire is an important influence in a subset of this system. Communities dominated by Chamaecyparis thyoides depend on fire for regeneration of the canopy trees. The occurrence of fires on the time scale of several decades to a century or more may determine the mosaic of Chamaecyparis thyoides forests and other associations. Some areas may once have been canebrakes, with dominance of Arundinaria determined by more frequent fire. In the oak-dominated communities and in wetter Taxodium and Nyssa communities, fire is probably of little ecological significance because the vegetation is not flammable. Without fire as a major factor, most communities probably occur naturally as old-growth multi-aged forests dominated by gap-phase regeneration. Hurricanes may create larger canopy gaps, and sometimes cause more extensive damage. Examples in drowned river valleys are subject to influence by rising sea level and can be expected to evolve into tidal swamp systems, sometimes fairly quickly.

In specific relation to the Chamaecyparis thyoides-dominated phase of this system, succession pathways depend on water table depth at time of replacement fire. Having the water table at the surface results in regeneration of Chamaecyparis thyoides from the seedbank. If the water table is slightly to moderately below the surface, the seedbank is destroyed and succession is dominated by some combination of Acer rubrum, Nyssa biflora, Pinus taeda, and related taxa. If the water table is well below the surface, the seedbank is destroyed and a deeper hole is created in the peat. In this case, succession is dominated by Taxodium distichum and a deeper water area is created with Chamaecyparis thyoides only on the edge.

Logging, land conversion, and hydrologic alteration have been the main threats to this system. Conversion to pine plantation destroys the natural vegetation, while other logging has often been followed by failure of regeneration of Taxodium, Chamaecyparis thyoides, or Quercus spp., changing the natural vegetation to long-term successional forests. Clearing for agriculture has destroyed much of the area of this system in the past, and continues to be a threat.

Ditching and artificial drainage have contributed to alteration and destruction of these systems, facilitating conversion and logging, and altering the hydrology of other examples. Reduced hydroperiod caused by ditches alters vegetation, and can make organic soils prone to destructive peat fires. In areas near sea level, ditches can also bring brackish or oligohaline tidal water into these nonriverine systems. Penetration of even mildly salty water, associated with storm surges or ongoing sea-level rise, stresses or kills the salt-intolerant vegetation in these communities. Road building also alters hydrology, both by the ditches that accompany them and by the filled road beds blocking natural sheetflow and potentially impounding water. Roads can also contribute to fragmentation and edge effect in examples of this system. Feral hogs (Sus scrofa) are an invasive species which is destructive in wetland forest ecosystems. Lonicera japonica, Microstegium vimineum, Triadica sebifera, and other non-native plants are a threat, especially to drier examples of this system.

This system ranges from Maryland to Georgia. This system is most abundant in the Embayed Region of northeastern North Carolina and southeastern Virginia (south of the James River), where it covers large expanses.