Atlantic Coastal Plain Pocosin and Canebrake

This system includes wetlands of organic soils, occurring on broad flats or gentle basins, primarily on the outer terraces of the Atlantic Coastal Plain of the Carolinas and southeastern Virginia. Under current conditions, the vegetation is predominantly dense shrubland and very shrubby open woodlands. A characteristic suite of primarily evergreen shrubs, Smilax species, and Pinus serotina dominates. These shrubs include Cyrilla racemiflora, Ilex coriacea, Ilex glabra, Lyonia lucida, and Zenobia pulverulenta, along with Smilax laurifolia. Pinus serotina is the characteristic tree, along with Gordonia lasianthus, Magnolia virginiana, and Persea palustris. Herbs are scarce and largely limited to small open patches. Under pre-European settlement fire regimes, stands of Arundinaria tecta (canebrakes) would have been more common and extensive. Soil saturation, sheet flow, and peat depth create a distinct zonation, with the highest stature woody vegetation on the edges and lowest in the center. Catastrophic fires are important in this system, naturally occurring at moderate frequency. Fires generally kill all above-ground shrubs in large patches. Mortality of Pinus serotina varies, creating a shifting mosaic. Vegetation structure and biomass recover rapidly in most of the burned areas, primarily by sprouting. Pinus serotina can regenerate from serotinous cones if killed.

Vegetation is a series of distinctive associations known as pocosins. Under current conditions, the vegetation is predominantly dense shrubland and very shrubby open woodlands, ranging to nearly closed forests. Herbaceous associations are present only as small patches. Vegetation is typically zoned. The lowest stature vegetation occurs in the center of the system, with woodlands on the edges and in the smaller occurrences. The communities have in common a dense shrub layer of wetland shrubs tolerant of the organic soils, low nutrient conditions, and fire. Ilex glabra, Lyonia lucida, Lyonia mariana, Cyrilla racemiflora, Ilex coriacea, and Zenobia pulverulenta are characteristic and usually dominant in some combination, along with Smilax laurifolia. Pinus serotina is the characteristic tree, and it along with a set of evergreen hardwoods, including Gordonia lasianthus, Magnolia virginiana, and Persea palustris, are generally the only trees present. Under pre-European settlement fire regimes, stands of Arundinaria tecta (= Arundinaria gigantea ssp. tecta) (canebrakes) would have been more common and extensive. Component communities tend to be low in plant species richness, and woody species richness exceeds herbaceous in most associations, with herbs being limited to small open patches. These areas would have formerly been more extensive under pre-European settlement fire regimes. The dominance of pond pine and evergreen shrubs as opposed to a canopy of deciduous hardwoods distinguishes this system from nonriverine swamp forests (CES203.304).

This system occurs on broad interfluvial flats and in small to large, very gentle basins and swales, largely on the outermost terraces of the Outer Coastal Plain. Some occurrences are in large to small peat-filled Carolina bays (Bennett and Nelson 1991, Nifong 1998). Smaller patches occur in shallow swales associated with relict coastal dune system or other irregular sandy surfaces. Soils range from wet mineral soils with mucky surface layers to peats several meters deep. Most of the largest occurrences are domed peatlands with the deepest peat associated with topographic highs in the center, but deep peats are also associated with buried drainage channels. Hydrology is driven by rainfall and sheet flow. The low hydraulic conductivity of the organic material limits interaction with the groundwater. The raised center of domed peatlands is fed only by rainwater and is therefore a true ombrotrophic bog. More peripheral portions are fed by sheet flow from the center, and so receive only acidic water low in nutrients. Occurrences in Carolina bays and other basins appear to be similarly isolated from surface or groundwater inflow from adjacent areas. Soils are normally saturated throughout the winter and well into the growing season, though the organic material may dry enough to burn during droughts. Standing water is limited to local depressions and disturbed areas. Soil saturation and peat depth, with its corresponding nutrient limitation, are the primary drivers of vegetational zonation as well as the distinction between this system and adjacent ones, but their effect may be modified by drainage patterns.

Fire is an important factor in these systems, with the pre-settlement fire regime probably being very different from that observed under current conditions. Natural fire-return intervals are not well known, but are probably on the order of a decade or two in the wettest areas. Peripheral areas may be subject to fire as often as the surrounding vegetation burns, which may naturally have been an average of 3 years. Fires are typically intense due to density and flammability of the vegetation; all above-ground vegetation is often killed, though Pinus serotina are resilient to fire and may survive. Fires are followed by vigorous root sprouting by shrubs and hardwoods, leading to recovery of standing biomass within a few years. Pinus serotina recovers by epicormic sprouting or by regeneration from seeds released from serotinous cones. Fires during droughts may ignite peat, forming holes that take longer to recover. Herb-dominated openings in pocosins may depend on peat fires for their creation, though this is not well documented. Natural fires occur in large patches, creating a shifting patch structure in the system that interacts with the vegetational zonation created by peat depth. The intensity of fire in these systems makes fire control difficult; prescribed burning is seldom done, and wildfires during drought continue to be a significant influence. The larger peatlands are believed to have been created by paludification following natural blocking of drainage (Otte 1981). Peat buildup raises the water table in the center, creating the domed structure of the largest peatlands and allowing the wetland to spread out as wetness is increased at the edges. Many of the deeper pocosin peats contain fossil logs that indicate dominance by a swamp forest in past millennia. Otte (1981) noted that peat fires likely limit the height to which the peat can accumulate, in proportion to how high it can raise the local water table.

Alterations to the natural hydrology threaten this habitat, especially drainage. Some extensive peatland pocosin areas have been converted to intensively managed pine plantations, or cleared for agriculture. Drainage is used for both plantation forestry and agriculture. Peat can decompose more rapidly when it is drained and exposed to aerobic conditions.

Altered fire regimes are a threat to most remaining areas. These habitats are naturally prone to fire spreading from the adjacent pinelands, and from lightning strike fires which start within the pocosins. The occasional burning of patches provides for habitat diversity. Prescribed burning is difficult to conduct in pocosins. Due to land development and the associated fragmentation of natural lands in the vicinity of pocosins, the risks, complexity, and costs of prescribed fire are increased. Uncontrollable wildfires occur mainly during droughts, and if the peat is ignited, it can burn for months. Certain firefighting practices sometimes can be very destructive, resulting in extensive soil disturbance and sometimes in pumping of salt-containing water. Altered hydrology interacts with wildfires. Artificially drained peats are more subject to deep and prolonged burning. Deep peat fires can lower the land surface and kill roots so that pocosin vegetation does not sprout.

This system is found primarily in North Carolina, extending into Georgia and southeastern Virginia.