Distribution and Composition of Pocosins and Large Shrub Bogs

Pocosins in the strictest sense are shrub bogs that occur on domed peatlands that have developed on clay soils in shallow basins and divides between ancient rivers and sounds in the Atlantic Coastal Plain (Richardson 1991). Pocosin-like vegetation also occurs in large Carolina bays with deep peat. The largest domed peatlands occur primarily in North Carolina, but pocosins and pocosin-like vegetation extend into South Carolina and Georgia. Many pocosins are large in extent covering thousands of acres.

Nutrient inputs and hydrology are dominated by rainfall, and soil formation processes are influenced by hydroperiod. Precipitation is the only form in which water and nutrients enter the system. Hardpans of clay or other substances underlie peat deposits and pond water; thus, pocosins have long hydroperiods, typically 6-9 months per year (Sutter and Kral 1994). The water table is highest in winter when evapotranspiration is low and lowest in summer, even though the rainfall is most abundant July through September (Richardson and Gibbons 1993, Sharitz and Gresham 1998). Soils are deep peats and organic mucks that have formed because of the long hydroperiod. These soils are extremely low in nutrients, particularly phosphorus. Domed peatlands are topographically elevated above the surrounding communities and water exits these systems through streams and rivers that form on peatland margins (Richardson and Gibbons 1993, Sharitz and Gresham 1998).

Vegetation of domed peatlands is often somewhat concentrically arranged, but also can have a mosaic pattern produced by fire. Low pocosin typically occupies central portions of peat domes and grades into high pocosin in intermediate portions of peat domes. (Weakley and Schafale 1991). Pond pine woodland, bay forests or Atlantic white cedar swamp are found on outer portions of peat domes and depending on moisture regime those communities grade into either savannas and flatwoods on drier sites or swamp forest where communities grade into lakes or other water bodies. The zonation of vegetation is less clear in large Carolinabays where both high and low pocosin can occur than in large domed peatlands (Weakley and Schafale 1991). High and low pocosins in Carolinabays are often surrounded by frequent fire communities such as pine flatwoods, or pine savannahs (Weakley and Schafale 1991).

The large domed peatlands occurrence of high pocosin, and low pocosin, are associated with gradients of soil depth and nutrient availability, though fire frequency may also play a role (see successional relationships). Low pocosins have deep peats 1 – 5 m (3-16 ft) and extremely low available nutrients. High pocosins have peat deposits that are shallower, typically up to 1.5 m (5 ft). Nutrients tend to be less limited where peat is shallow because vegetation can root in mineral soils where nutrients are more available than in peat (Sharitz and Gresham 1998, Weakley and Schafale 1991).

Vegetation

The vegetation of high pocosin and low pocosin share some dominant species but differ in vegetation structure (except soon after fires). Low pocosins are characterized by low shrub stature, less than 1.5m (5 ft) and a sparse tree canopy. Dominant low pocosin vegetation includes titi (Cyrilla racimiflora), fetterbush (Lyonia lucida), and (Zenobia pulverulenta). Greenbrier (Smilax laurifolia) is a common vine, and trees include pond pine (Pinus serotina), red maple (Acer rubrum), sweetbay magnolia (Magnolia virginiana), red bay (Persea borbonia), and loblolly bay (Gordonia lasianthus) (Richardson 1991, Weakley and Schafale 1991). Openings in low pocosin (occasionally in high pocosin) often have standing water and can include herbaceous species such as Virginia chain fern (Woodwardia virginica), grasses (Andropogon glomeratus), sedges (Carex striata), non-vascular plants (Sphagnum spp.) and carnivorous plants such as (Sarracenia flava), (Sarracenia purpurea), and sundews (Drosera spp.) (Weakley and Schafale 1991, Christensen 1981).

High pocosin is characterized by taller shrubs than those of low pocosin, 1.5 to 3 m tall, with an overstory that is more dense than that of low pocosin, but still scattered (Weakley and Schafale 1991, Sharitz and Gresham 1998). Titi, fetterbush, and gallberry (Ilex glabra) dominate high pocosin vegetation. Switch cane (Arundinaria gigantea) may also occur in high pocosin. Herbs in high pocosin are uncommon to absent, except immediately following fire.

Pond pine and Zenobia are considered indicators of pocosin vegetation and the latter is essentially an endemic of pocosin vegetation (Weakly and Schafale 1991, Sharitz and Gresham 1998).

Rare plants in high and low pocosin are generally associated with herbaceous openings (Robertson et al 1998), which fires are important in creating, and the pond pine woodland ecotone, which is fire maintained. Various pitcher plants and other carnivorous plants are found in these openings. The federally endangered rough leaved loosestrife (Lysimachia asperulifolia) can be found in low pocosin within Carolina bays and other habitats (USFWS 1987). The once federally listed white wicky (Kalmia cuneata) can also be found in Carolina bay pocosins (USFWS 2000). Several other rare species tracked by state heritage programs are also associated with herbaceous openings in pocosins (Robertson et al. 1998).

Animals

There has been very little research on pocosin fauna. There are no known animals that are endemic to pocosins. Generally, the animals that are characteristic of the region are found in pocosins. Pocosins likely serve an important function as regional refugia for many species of wildlife, in large part because they are the only natural areas that remain (Richardson and Gibbons 1993).

The invertebrate fauna of pocosins is not well studied. Two species that are commonly cited as being associated with pocosins include the swamp specializing palamedes swallowtail butterfly (Papilio palamedes) and the Hessel’s hairstreak (Mitoura hesseli), whose larval food plant is Atlantic white cedar (Chamaecyparis thyoides) (Richardson and Gibbons 1993, Sharitz and Gresham 1998). Atlantic white cedar is an occasional inhabitant of high pocosin. Presumably, the suite of species associated with insectivorous plants such as pitcher plants (Sarracenia spp.) and sundews (Drosera spp.) are present.

Fish that inhabit larger water bodies situated within pocosins include typical game fish of the region. Likewise amphibian and reptile species characteristic of the region are presumed inhabitants of pocosins. Rare species include the eastern diamondback rattlesnake (Crotalus adamanteus), and the American alligator (Alligator mississippiensis) (Sharitz and Gresham 1998).

Avian fauna are somewhat better studied, but like other groups, the inhabitants are characteristic of the region. High pocosin and pond pine woodland tend to support suites of bird species that are similar to regional suites of species. Low pocosin is relatively low in bird diversity and abundance probably due to low levels of structural diversity. Eighty-three species of wintering birds have been documented from high pocosin. Three abundant species of low pocosin include common yellow throat warblers (Geothlypis trichas), eastern wood peewees (Contopus virens) and rufous-sided towhees (Pipilo erythrophthalmus) (references in Sharitz and Gresham 1998).

Typical mammals of pocosins include common species such as white tailed deer, raccoon and possums as well as animals specializing in wetland habitats such as northern river otters, mink, and marsh rabbits. Small mammals include common shrews, and mice. The southernmost occurrence of bog lemmings is in unmodified pocosins in central North Carolina (Mitchell et al. 1995). The black bear will use large tracts of pocosin and is now dependent on large tracts of pocosin vegetation for cover (Sharitz and Gresham 1998, Robertson et al 1998).