There are several different names for this plant community. Atlantic white cedar (AWC) swamp is the name used in classifications for Alabama and South Carolina (Nelson 1986). In the classification for Mississippi, this community is synonymous with white cedar forest or cedar bog (Penfound 1952). In North Carolina, this community type is further divided into two types: peatland AWC forest and streamhead AWC forest (Schafale and Weakley 1990). In Florida's classification system, AWC forests are types of bottomland forests (FNAI and FDNR 1990). In Virginia's classification, they are a type of mesotrophic saturated forest (Rawinski 1990).
Range/Distribution
AWC forests occur throughout the Coastal Plain, primarily in the peatlands of the outer Coastal Plain, but also on the middle Atlantic Coastal Plain (Landaal 1991b, Schafale and Weakley 1990). According to Landaal (1991b), the range of this type is the same for that of AWC, occurring in a narrow coastal range 50 to 130 miles wide from southern Maine to northern Florida and west to southern Mississippi. However, this species only forms extensive stands in a few areas, including the New Jersey pine barrens, the lower terraces of North Carolina and Virginia Coastal Plains, and northern Florida (Christensen 1988).
Environmental Factors
Topographic Position
AWC swamp forests are usually associated with deep peats; often peats occurring over sandy substrates (Christensen 1988). They are found on shores of lakes, rivers, streams, or estuaries in isolated basins, or on seepage slopes or streamheads (Schafale and Weakley 1990, Moore and Carter 1987). They may also occur onislands in lakes and rivers (Landaal 1991b). In North Carolina, AWC swamp forests occur on the outer parts of domed peatlands on poorly drained interstream flats. They also occur on shallow peat-filled Carolina bays and swales (Schafale and Weakley 1990). They are typically in drier locations than other pocosin types (Schafale and Weakley 1990). In Florida, they occupy valleys of small streams through deep sandhills where soils are perennially moist or wet from constant seepage of groundwater, but are only briefly, if at all, flooded. They have also occupied boggy pine flatwoods near the coast in panhandle Florida (Clewell and Ward 1987).
Hydrology
AWC seedlings are intolerant of flooding, and adults cannot tolerate much flooding. Authors have described these forests as occurring in nontidal, seasonally flooded, saturated, semipermanently flooded, or permanently flooded areas (Landaal 1991b) and areas with or without flowing or seepage water (Schafale and Weakley 1990). The water table in AWC forests characteristically fluctuates between highs of 20 to 30 cm above the surface of the bottoms of the deepest hollows in the micro topography to 20 cm below the surface (Golet and Lowry 1987, Ehrenfeld and Schneider 1991). Because of the hummocky microtopography of this habitat, different surfaces experience different degrees of inundation and moisture. In one study of a natural AWC forest, 25 percent of the area was likely to be regularly flooded every year, 25 percent was within the likely range of variation in high water levels, and 50 percent was unlikely to experience flooding except during unusually wet years, when it would experience, at most, soil saturation during periods of high water (Ehrenfeld 1995). Under undisturbed conditions, AWC forests may be flooded and have shallow standing water in depressions from mid-winter to mid-summer with seasonal high water occurring in early spring (Moore and Carter 1987, Ehrenfeld and Schneider 1991). The duration and depth of the hydrologic regime varies with precipitation, however, and there is considerable variability among sites (Ehrenfeld and Schneider 1991, Golet and Lowry 1987).
Disturbance Regime
AWC does not establish under the shady conditions of mature stands. Thus, this community is dependent on the open conditions created by intense crown-killing fire (Christensen 1988, Landaal 1991b, Schafale and Weakley 1991), clearcutting, extensive windthrow (Little 1950, Moore and Carter 1987) or flooding (Moore and Carter 1987). Although hurricane or tornado blowdowns may fell substantial tracts, only fire could be expected to kill standing timber and remove debris, exposing the open seedbed for regeneration (Frost 1987). The community regenerates best aftera light fire on bare mineral soil, as this removes competing vegetation and allows the viable seeds in the seed bank to survive; a fire that burns deep into the peat may destroy the seeds (Landaal 1991b, Schafale and Weakley 1991). Fire return intervals ranging from 25 to 250 years may be necessary for regeneration (Frost 1987).
In the Gulf Coast populations of AWC, gap regeneration may be more important than regeneration after fire (Clewell and Ward 1987). Fire is seldom observed in this area because seepage saturated soils and broad-leaved understory vegetation suppress fire initiated by lightning strikes and other sources (Ward and Clewell 1989). As a result, other disturbances that create open conditions, such as flooding, windthrow, and logging, are necessary for regeneration on the Gulf Coast (Landaal 1991b). Most white cedar seedlings in a gap die following closure of the canopy. Infrequently, a second gap in the canopy develops before all of the seedlings of a cohort have died; this allows the survivors to grow as long as suitably spaced breaks in the canopy continue to exist. As they grow, they are better able to survive periods of reduced light and become permanently established upon reaching the canopy. Once becoming emergent in the canopy, however, the trees become susceptible to lightening, which is their most common cause of death (Clewell and Ward 1987).
Soil
The community usually occurs on peat soils underlain by sand (Buell and Cain 1943). It has been observed that the proportion of swamp hardwoods in cedar stands increases with the amount of silt and clay in the subsoil (Korstain 1924), although Laney and Noffsinger (1987) did not find such a correlation in Dare County, NC. Soils are more sandy in AWC swamp communities along the Gulf Coast than the Atlantic Coast (Landaal 1991b).
Physiognomy/Structure
In the Carolinas and Virginia, this community typically exhibits a dense, even-aged canopy dominated by AWC. In these areas, shrub and herb layers are relatively open (Landaal 1991b). The even-aged type probably reflects regeneration after large-scale disturbance such as fire, more common in the northern part of the range (Landaal 1991b). In the Gulf states, AWC shares dominance with a variety of species (Christensen 1988), and stands are not even-aged (Landaal 1991b). Shrub cover may exceed 80 percent in the understory (Christensen 1988). The herbaceous layer is composed of sphagnum moss and ferns (Christensen 1988). The uneven-aged mixed-species stands typical of the southern AWC forests are a consequence of gap succession in the absence of fire (Clewell and Ward 1987).
Commonly Associated Plant Communities
This community may occur in a mosaic with pond pine woodland, bay forest, other pocosin types (Landaal 1991b), and non-riverine swamp forests (Schafale and Weakley 1990). Near shorelines it may grade into estuary-fringe, loblolly pine forest, tidal cypress-gum swamp, or marsh communities. Streamhead types grade abruptly into sandhill or wet pine flatwoods, or small stream swamps along stream courses (Schafale and Weakley 1990).
Successional Relationships
This community is early successional but consists of long-lived trees. AWC lives to be more than 250 years old (Frost 1987). The community usually succeeds itself following fire, as long as the fire is not so hot that it kills the seed bank. In dry periods when fire causes the upper peat layer to burn, the community may be replaced by other pocosin types, gum-cypress swamp (Ash et al. 1983), or a pure stand of slash pine (Garren 1943). In the absence of fire this community may succeed into bay forest or a more species-rich swamp community (Landaal 1991b), although this is not well documented and the time for this to occur in the absence of logging is not well known (Fussel et al. 1995). Weakley and Schafale (1991) also suggest that AWC swamp forest can succeed into pond pine woodland in North Carolina.
Biological Composition
This community is dominated by AWC (Chamaecyparis thyoides) occurring in pine or mixed stands. In mixed stands, characteristic subdominants include red maple (Acer rubrum), sweet bay (Magnolia virginiana), and swamp tupelo (Nyssa biflora) (Landaal 1991b). The shrub layer is often dominated by sweet pepperbush(Clethra alnifolia) and highbush blueberry (Vaccinium corymbosum) (Landaal 1991b), but can also include fetter-bush (Lyonia lucida ), sweet gallberry (Ilex coriacea), bitter gallberry (Ilex glabra), and red bay (Persea borbonia) (Christensen 1988). Peat moss (Sphagnum sp.) and Virginia chainfern (Woodwardia virginica) are important species in the herb layer (Christensen 1988), as are partridge berry (Mitchella repens) and poison ivy (Rhus toxicodendron) (Landaal 1991b).