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).

Several community types occupy large domed peatlands and are often arranged somewhat concentrically. In the interiors of these peatlands, low pocosin occupies the deepest most nutrient poor peats. High pocosin is intermediate in nutrient status and peat depth. On the outer portions of these peat domes, where peat is most shallow, are either bay forests, pond pine woodlands or Atlantic white cedar forests or other swamp forests (Weakley and Schafale 1991). Herbaceous communities can be scattered throughout. Similar community types can be found on smaller peatlands. It is clear that fire, hydrology and nutrient availability play roles in which communities develop where, but their exact roles and interactions are not well studied.

There are two opposing theories of succession in large domed peatland communities. One theory (Wells 1928) proposes that fire is the controlling factor, where frequent fire promotes low pocosin, intermediate frequencies result in high pocosin and very low frequencies result in bay forests. The other theory (Otte 1981 cited in Sharitz and Gresham 1998 and Richardson and Gibbons 1993) suggests that nutrients are the controlling factor. There is a gradient of nutrient availability (phosphorus being most limiting) from very limited nutrient availability in low pocosin to high pocosin to more available nutrients in bay forest (Richardson and Gibbons 1993). In the development of these peat domes, as peat accumulates and becomes deeper, nutrients become more and more limiting as plant roots fail to reach underlying mineral soils. Thus, according to Otte’s theory, the successional trajectory is from marsh to swamp to bay forest to high pocosin to low pocosin, reflecting the build-up of peat and the decreasing availability of nutrients.

Others have recognized that nutrient limitations on domed peatlands may be a special case, and where nutrients are not so limiting, fire frequencies are more critical in determining community type (Christensen 1981, Frost 1995). Frost (1995) described the pre-settlement occurrence of these community types with respect to fire frequencies, soil fertility and organic matter depth.

Despite lack of study and different theories some patterns do seem clear. Atlantic white cedar forests develop under a very specific fire regime, where seed sources are available after infrequent, catastrophic, high intensity surface fires (crown fire), when water tables are high and peat doesn’t ignite or doesn’t burn deeply. Small Atlantic white cedar does not tolerate even low intensity fire, thus for stands to exist fires must not be frequent (Schafale and Weakley 1990). In the absence of fire Atlantic white cedar forests are believed to become bay forest, pond pine woodland or other types of swamp forest.

Relatively more frequent fire favors pond pine woodland rather than Atlantic white cedar forest or bay forest (Schafale and Weakley 1990). On sites where nutrients are not as limiting as in the high and low pocosins of large domed peatlands, the vegetation sequence goes from pond pine woodland to high pocosin to low pocosin with increasing frequency of fires (Frost 1995). High and low pocosins on large domed peatlands tend to maintain vegetation structure and composition even in the absence of fires thus lending credence to the nutrient limitation theory.

Severe fires that consume peat in any of these communities can result in an herbaceous community (Hungerford et al. 1998). The magnitude of soil consumption required for the development of an herbaceous community is unknown and likewise weather it is soil consumption per se that is the cause is unknown.

The prolonged absence of fire in communities except the most nutrient limited (high and low pocosin of large domed peatlands) is thought to promote succession toward bay forests (Weakley and Schafale 1991). Within the landscape mosaic, bay forests are situated where, by chance fire frequency has been lowest, or where landscape features create areas that are not likely to burn, for instance along drainage ways that develop at the edges of domed peatlands (McKevlin 1996). Most bay forest species are known to resprout so after some non-severe burns bay forests may regenerate themselves rather than becoming either Atlantic white cedar forests, or pond pine woodland or an herbaceous community (Schafale and Weakley 1990).

Many possible successional pathways have been suggested for each of these communities (reviewed in McKevlin 1996). It seems that the successional pathway a community takes is dependent on the frequency, intensity and severity of fires along with soil fertility and hydrologic conditions during and after the fire (McKevlin 1996, Frost 1995). Hydroperiod may be very important because of its effects on fire frequency and peat build-up. Peat build-up in turn affects nutrient status. Fire reduces peat formation and also creates a temporarily more fertile environment by releasing nutrients stored in organic matter. Water table depth during a fire contributes to depth of peat consumption.

These communities may be perpetuated by fire or may become other community types because of fire. With more study, these relationships may become clearer. Current research mapping community types with remote sensing technology (Bucher and High 2000) coupled with mapping of fire footprints and other parameters related to fire frequency, intensity and severity may help reveal more information on successional relationships of these communities.

Recent Anthropogenic Use of Fire

The historic fire regime of pocosins are not completely understood, but it is clear that changes in the natural fire regime, coupled with other anthropogenic disturbance (drainage, timber harvests) have changed the spatial footprint of various peatland communities including high and low pocosin. For instance Atlantic white cedar forests were once much more widespread than presently, and human disturbance of hydrology and concurrent changes in fire regime have resulted in pocosin vegetation where Atlantic white cedar forests once stood (Christensen 1981).

Fires are less frequent in pocosins today than historically (Bucher and High 2000). Fire suppression and conversion of lands surrounding pocosins have likely contributed to this decreased fire frequency. In fact many managing agencies do not routinely burn pocosins as part of management due to operational difficulties (see Prescribed Fire in Pocosins and Large Shrub Bogs). One ecological consequence attributed to fire suppression within pocosins is the decline in extent of canebrakes (Frost 2000).

Natural Regime/Fire Adaptations

Pocosin vegetation is inextricably linked to fire although it’s exact role in the development and perpetuation of pocosin and related vegetation is not clear (see: Successional Relationships of Peatland Communities). Christensen et al. (1981) assert that fire in pocosin vegetation is inevitable. The vegetation characteristics guarantee that fire will occur at some point, and that pocosins perpetuate themselves because of these characteristics (see: Plants of Pocosins and Shrub Bogs: Adaptations to Fire).

Fires in pocosins are infrequent. Various fire frequencies have been cited for pocosins. For instance Frost (1995) suggests that fires occur in low pocosin every 13 to 50 years, and in high pocosin every 25- 50 years. Bucher and High (2000) suggest a return interval of 5 to 30 years. Fires can be severe if ground fires are ignited. Severe fires in this system, however, are likely a natural part of creating heterogeneity within the system, which is important in maintaining plant diversity in pocosins (Christensen et al. 1981).

Fires in pocosins are typically intense due to high fuel loads. Typical fuel loads of 22.4 – 34 mt/ha (10-15 tons/acre) have been reported for pocosins (Sharitz and Gresham 1998, Bramlett 1990) and where fire suppression has lengthened the return interval to 50+ years, fuel loads can reach 15-25 tons/acre (Bucher and High 2000). Fuel loads for low pocosin have been reported as 6.4 tons/acre (Wade and Ward 1973).

Natural fire season in pocosins is not well understood. Wildfires in pocosin fuels are common in spring, but have occurred in all seasons (Wade and Ward 1973). Early spring is a hospitable time for fires in pocosins because drought commonly occurs in early spring and because live fuel moisture in pocosin shrubs is lowest in early spring, directly proceeding new growth (Blackmarr and Flanner 1968).

Despite characteristics that make vegetation flammable, pocosins are wet enough that they are not flammable until drought conditions occur. Under drought conditions, fires in large peatlands were large in extent.

Pocosin and shrub bog plants are adapted to fire and have adaptations that allow them to perpetuate themselves following fires and even depend on fire to complete their life cycle. Virtually all shrub species in pocosins have underground organs that allow them to resprout following fires (see Plant resistance to fire).

Pocosin and shrub bog plants have characteristics that promote fire. Many shrub bog and pocosin shrubs have sclerophyllus (tough leathery) leaves that are high in lignin. One result of this leaf character is that leaves do not decompose readily so they contribute to fuel buildup. Further, a number of shrub species like gallberry (Ilex glabra) and red bay (Persea borbonia) have large amounts of secondary chemicals in leaves. These chemicals, like sclerophylly, are theorized to deter herbivory. Another end result is that many of these secondary chemicals are volatile, which leads to very flammable leaves (Christensen et al 1981). All of these characters lead to high levels of available fuel.

See: Pond Pine: Intense Fire Adaptations.

Plants

Shrubs within pocosins resprout following fires; however, shrub dominance varies with time since fire. Observations indicate that Zenobia dominates soon after fires, but looses dominance to Lyonia and Cyrilla within approximately 5 years (Christensen 1981). Species diversity is highest in pocosins soon after fires when herbaceous vegetation becomes more abundant (Weakley and Schafale 1991).

Ground fires in organic soils are important in the maintenance of plant diversity. Most herbaceous plants are restricted to areas where fire was severe, soils were burned and shrubs were subsequently killed. This is particularly important for rare plants that utilize these habitats in pocosins. Low pocosin has been converted to grassland where 1.5 to 2 feet of soil was consumed (Hungerford et al. 1998). The microtopographic changes created when soils are burned are thought to be important for seedling establishment. Low spots are though to have a more favorable moisture regime than higher surrounding peat, which may stay dry for longer and be less hospitable for seedling establishment (Christensen 1981).

Pocosin above ground biomass often recovers quickly following fire. Burned areas can have up to 25% of the original aboveground biomass within 1 year of the fire (Christensen 1981). This response may be due in part to the increased availability of nutrients released by fire that is otherwise bound up in plant materials (Christensen 1981).

Animals

Almost no information is available on the direct effects of fire on pocosin animals. Intense fires in pocosins may lead to the direct mortality of some animals such as white tailed deer or perhaps small mammals (Wade and Ward 1973). Injuries such as burns on the legs of white tailed deer from falling through a crust of organic soil into a ground fire have also been noted.

Studies on effects of fire on animals within community types other than pocosin indicate that long-term changes in vegetation structure due to fire may affect animals more than other fire-related short-term changes. For instance, a severe fire that creates an herbaceous community from a shrub dominated community, or an intense fire that removes canopy species will affect animal species composition more than fires that change vegetation structure for short periods of time. Animal use of pocosins likely change with time as vegetation recovers, and because pocosins often burn in a mosaic pattern of intensity and severity, spatial patterns of use also likely change. The importance of variable intensity fires and mosaic burn patterns may be important for perpetuation of populations of relatively non-mobile vertebrate species such as mice, rats, shrews and rabbits. More research is needed to understand fire and animal relationships within pocosins.

Prescribed fire is used in pocosins for fuel management and for the maintenance of biodiversity and natural processes (Bucher and High 2000). It is also used for silvicultural purposes such as site improvement, pond pine seedling establishment, and for fire hazard reduction during early pine growth (Christensen 1981, Taylor and Wendel 1964).

Implementing a prescribed fire program in large tracts of pocosin vegetation is more difficult than in many other plant communities. Domed peatlands are large in extent, with very high fuel loads situated on organic soils where access is difficult. Several key operational issues emerge in burning pocosins:

1. Burning large blocks of vegetation is rarely feasible due to fire control issues and restrictions on smoke production, particularly in a community type that only sustains fire under droughty conditions. Thus, blocks need to be broken up into manageable units.
2. When creating firebreaks in wetlands, wetland permits must be sought from appropriate local, state and federal agencies. Pocosins are regulated under Section 404 of the Clean Water Act and activities within pocosins require permits from the Army Corps of Engineers. The ecological effects of ditched firebreaks must also be considered.
3. The width of firebreaks required to control fires in pocosins is also larger than in most other community types. Firebreak widths of 1.5 to 2.5 times the flame length are recommended by National Wildfire Coordinating Group, which result in firebreak widths of 15-60 ft wide depending on conditions.
4. There is uncertainty in using prescribed fires in areas with organic soils because
   • Igniting a ground fire, though sometimes desirable from an ecological perspective, can be hazardous because of excessive production of smoke resulting from smoldering ground fires.
   • Factors that determine ignition and sustained burning of organic soils have only recently received intensive study and in the past, literature was often confusing regarding safe conditions under which burning could be conducted.
   • Smoldering ground fires are often hard to extinguish, can go on for long periods and create potential for fires to re-ignite and for escapes. Some of these concerns may be ameliorated where water control structures are present such that the water table may be manipulated to assist in extinguishing ground fires as needed.

Several of these factors make fire practitioners uncomfortable using fire in pocosins but, despite these challenges prescribed fires have been safely applied to pocosin vegetation (Hungerford et al.1998, Bucher and High 2000).

In addition to operational considerations, ecological factors to consider in burning pocosin vegetation include:

1. Planning for ground fires that promote openings that support not only herbaceous species but also rare plant species is important to maintain diversity.
2. Maintenance of diversity involves considerations of frequency and the patch mosaic in which past fires have burned, because plant diversity is highest soon after fires (Christensen 1981).
• Robertson et al. (1998) have recommend, as an approximation, burning low pocosin every 20 years and that the need for burning can be assessed by the extent of herbaceous openings.
• The same authors suggest burning high pocosin on 5 to 8 year intervals. This fire return interval is at the more frequent end of the cited historical return interval because the authors were promoting the restoration of canebrake communities. Managing for pure canebrake communities may promote a less diverse community because of the often monotypic stands of cane that can develop in pocosins under a frequent fire regime (Frost 1995). When setting a target fire return interval, consider objectives with regard to diversity.
3. The presence of rare plants may necessitate a particular fire regime and depending on the plant, different regimes may be prescribed (Robertson et al. 1998). Life history information on the species of concern should be consulted when it is available.