Low and high pocosins are discussed together because they grade into one another in the landscape, and small depression pocosins have similar physical and floristic characteristics. Low pocosins occur in areas of deeper peat (usually 1 to 5 m deep) than high pocosins (peat depth of 1.5 m or less), otherwise both communities occur on oligotrophic wet sands (Schafale and Weakley 1990).
Pocosin communities differ in species composition and name throughout their range. These pocosins are included in the pine-ericalean pocosin type (Kologski 1977). They are also referred to as a type of evergreen shrub bog (Wharton 1978). Low and high pocosins are referred to under the same names in North Carolina's classification (Schafale and Weakley 1990) and as short and tall shrub bogs in Georgia's classification (Wharton 1978). Nelson (1986) combines these types as pocosin in South Carolina. Similarly, Ambrose (1990) calls these communities Coastal Plain shrub bog/seeps in Georgia. Penfound (1952) calls them evergreen shrub swamp or Ilex-Cyrilla-Zenobia community in Louisiana. In Virginia, low pocosins are called palustrine dwarf scrubs (Rawinski 1990), while high pocosins are called oligotrophic scrub (Rawinski 1990). Florida calls high pocosin a bog (FNAI and FDNR 1990). Small depression pocosins are called so in North Carolina (Schafale and Weakley 1990), while they are called swale pocosin in South Carolina (Nelson 1986), and correspond to Grady pond forest in Mississippi (Wieland 1994).
Range/Distribution
These pocosins occur primarily in the outer Coastal Plain and less commonly in the inner Coastal Plain. Low pocosins are mostly restricted to North Carolina (Schafale and Weakley 1990). The range of these communities extends from Virginia to Florida (Doyle 1990c). Small Depression Pocosins occur in isolated areas throughout the Coastal Plain and sandhills in North Carolina and South Carolina (Doyle 1990a, Schafale and Weakley 1990). Similar vegetation thought to represent this community type also occurs in Mississippi, Georgia, Florida, and Virginia (Doyle 1990a).
Environmental Factors
Topographic Position
Low pocosin occurs in the centers of extensive outer Coastal Plain interstream peatlands ("peat domes"), and grades into high pocosin, which occurs on the margins of these domes. Additionally, high pocosin occurs in the middle Coastal Plain in peat-filled Carolina bays and swales; low pocosin occasionally occurs in this situation (Doyle 1990b, c; Schafale and Weakley 1990). In Georgia, pocosins are described as occurring on downslopes protected from fire, usually at the base of clay ridges or sandhills (Wharton 1978). Small depression pocosins occupy isolated depressions in upland community types and may be surrounded by sand ridges (Doyle 1990a). They are commonly seasonally flooded or saturated (Schafale and Weakley 1990).
Hydrology
The hydrology is palustrine, seasonally flooded, or saturated (Schafale and Weakley 1990). The water table stays close to the soil surface throughout winter and early spring due to low rates of evaporation and transpiration (Campbell and Hughes 1991). Flooding usually occurs in the early spring (Penfound 1952). Later in the spring, high temperatures, wind, evaporation, transpiration, and low rainfall produce a rapid drop of the water table. Although late summer thunderstorms or hurricanes may maintain high water table levels, the lowest water table levels usually occur in early fall (Campbell and Hughes 1991). No water drains into low pocosins as they occupy the centers of domed peatlands and are higher than surrounding land; little water may drain into high pocosins from low pocosin areas. Thus, these communities are completely or largely ombitrophic (receive all nutrient inputs from rain and dryfall).
Disturbance Regime
These communities are fire-dependent. Severe fires associated with droughts occur periodically under natural conditions; from 3 to 8 years in "high diversity" pocosins and less frequently in those dominated by titi (Cyrilla racemiflora; Wharton 1978). Ground fires, or those burning the peat itself, can kill much or all of the above-ground vegetation (Doyle 1990b, c; Schafale and Weakley 1990). A single fire set or lightning strike fire may alter vast areas of low and high pocosins (Cruise 1996). Fires in low pocosins of Dare Bombing Range, NC, have usually occurred in April and May. They typically kill all above-ground vegetation structure while most underground parts survive. Plants resprout and the recovery of vegetationstructure and biomass is rapid after fire. Severe fires during droughts may burn into the peat, killing roots and creating small patches where hydrology has been altered. Species diversity and productivity are highest after fire, and they gradually decline thereafter (NCNHP and TNC 1995). Since small depression pocosins are nested within other communities, their fire regime varies with that of the surrounding habitat (Doyle 1990a).
Soil
These pocosins occur on soils ranging from wet, peaty sands to peat that is 5 meters deep, with low pocosins occurring on the deepest peat. Low pocosins are the most nutrient poor because of their ombitrophic position. Small depression pocosins are likely to be more fertile than other pocosin types because they can receive nutrients released by fires in surrounding communities (Schafale and Weakley 1990).
Physiognomy/Structure
Low pocosins are dominated by shrubs less than 1.5 meters in height, but may contain distantly spaced, stunted, and gnarled pond pine. High pocosins have a shrub layer that ranges from 1.5 to 3 m tall. High pocosins have scattered bay shrubs and hardwood species that form a subcanopy, and they may exhibit an open canopy of pond pine. Small depression pocosins may resemble either low or high pocosins in their physiognomy (Doyle 1990a).
Commonly Associated Plant Communities
Low pocosins grade into high pocosins, which grade into pond pine woodlands. At the edges of depressions, high pocosin may grade into a drier, non-pocosin community (Schafale and Weakley 1990). Pocosins may occur along the drier edge of bay swamps, or they may form a ring around cypress ponds (Wharton 1978). They may also grade into sandhill terrain, increasing in species diversity with higher fire frequency. In North Carolina, they may grade into gum-cypress swamps, as well as long leaf pine savanna and its associated herb bog community (Ash et al. 1983). Small depression pocosins are isolated inclusions within pine flatwoods or longleaf/turkey oak sandhills (Schafale and Weakley 1990).
Successional Relationship
High pocosin may succeed into bay forest in the absence of fire. Low pocosins do not appear to succeed to other communities in the absence of fire (Christensen 1988). Some high pocosins may once have been dominated by cane (Arundinaria sp.) brakes in times of more frequent fire, as they still have these as inclusions (T. Cruise, 18 April 1996). In Georgia, pocosins have been observed to succeed to grass-sedge savanna following severe fire (Wharton 1978).
Biological Composition
Low Pocosins
A canopy of widely scattered and stunted pond pine (Pinus serotina), swamp red bay (Persea palustris), loblolly bay (Gordonia lasianthus), and sweet bay (Magnolia virginiana) often occurs. The dense shrub layer is usually dominated by fetter-bush (Lyonia lucida), titi, zenobia (Zenobia pulverulenta), or gallberry (Ilex sp.). Blaspheme vine (Smilax laurifolia) is common. Pools or openings dominated by leatherleaf (Cassandra calyculata), Walter's sedge (Carex walteriana), Virginia chainfern (Woodwardia virginica), yellow pitcherplant (Sarracenia flava), bushy beardgrass (Andropogon glomeratus), peat (Sphagnum sp.), and, rarely, cranberry (Vaccinium macrocarpon) may occur within the low pocosin (Schafale and Weakley 1990).
High Pocosins
In North Carolina, the canopy/subcanopy usually consists of pond pine (<25% cover), swamp red bay, loblolly bay, and sweet bay (Schafale and Weakley 1990). Red maple (Acer rubrum), swamp tupelo (Nyssa biflora), and sweet gum (Liquidambar styraciflua) may also occur across the range of this community (Doyle 1991b). In North Carolina, the shrub layer is dominated by fetter-bush, titi, and zenobia. Regional shrub dominants may also include red bay (Persea borbonia). Greenbriar (Smilax sp.), especially blaspheme vine, are also common in high pocosins. Switch cane (Arundinaria tecta) may occur. Herbs are generally absent, but in recently burned sites, Virginia chainfern and bushy beardgrass may occur (Schafale and Weakley 1990).
Small Depression Pocosins
These communities have a sparse to dense canopy that may include pond pine, red maple, swamp red bay, sweet bay, pond cypress (Taxodium ascendens), loblolly pine (Pinus taeda), and loblolly bay. The dense shrub layer consists of fetter-bush, titi, bitter gallberry (Ilex glabra), sweet gallberry (I. coriacea), sweet pepperbush (Clethra alnifolia), dangleberry (Gaylussacia frondosa), myrtle-leaved holly (Ilex myrtifolia), highbush blueberry (Vaccinium corymbosum) and Carolina sheepkill (Kalmia carolina); wetter areas may support zenobia and leatherleaf. Blaspheme vine and wild sarsaparilla (Smilax glauca) may be common. The sparse herbaceous layer may include cinnamon fern (Osmunda cinnamomea), Virginia chainfern, netted chainfern (Woodwardia areolata), and sedge (Carex spp.) (Doyle 1990a, Schafale and Weakley 1990).