Fire Effects and Fire Ecology

Anthropogenic Alterations to the Fire Regime

Like most coastal plain fire communities, the natural fire regime of pond pine communities has been altered since pre-Columbian times (FNAI 1990, Schafale and Weakley 1990). Fires are less frequent today than in the pre-Columbian period. Though there is little published information specifically about pond pine communities, the general pattern is a shift from growing season fires to dormant season fires. Due to less frequent fires and increased fuel loads, many fires today may be more intense and more severe than historically. Further, the hydrology of many very wet sites has been altered (FNAI 1990, Richardson and Gibbons 1993) thus fire effects are likely changed.

Fire Regime

Fires in most pond pine communities are relatively infrequent. Because pond pine grows on wet sites, frequent fires of uplands and slightly drier flatwoods do not regularly penetrate into pond pine sites. Under the natural historical fire regime these sites burned under drought conditions. Depending on the community type in which pond pine grows it may experience fire only every 50-150 years in woody bogs or swamps or every 3 to 10 years in wet Flatwoods (FNAI 1990). In the extensive pond pine woodlands associated with pocosins, fires likely occurred every 10-20 years (Sutter and Kral 1994). There is variation in the frequencies reported for pond pine woodland likely due to the wide range of variations in this community type. Frost (1995) gave fire return frequencies of 13 – 50 years for communities that can be interpreted as pond pine woodland. Qualitative descriptions of pond pine woodland state that they likely burned slightly more frequently than high or low pocosin due to slightly drier sites on which pond pine woodland occurs (Schafale and Weakley 1990).

These infrequent fires are often intense due to the high understory fuel loads. Qualitative community descriptions describe pond pine woodland as having a more closed canopy and a taller shrub layer than high pocosin (Schafale and Weakley 1990), i.e., more fuel than high pocosin. Values reported for fuel loads in pocosin fuels probably include pond pine woodland. These values range from 10-25 tons per acre (Sharitz and Gresham 1998, Bramlett 1990, Bucher and High 2000, Wade and Ward 1973).

Pond pine communities are often considered intermediate successionally. On large peatlands, pocosins succeed to bay forest, or Atlantic white cedar forest (See Successional Relationships of Peatland Communities). On these same sites, too frequent or severe a fire may eliminate pond pines. On other soils, lack of fires produces bay forests or other swamp types (Abrahamson and Hartnett 1990). In fact some authors view pond pine flatwoods as burned out bay forests (Abrahamson and Hartnett 1990).

Where pond pine grows in association with herbaceous vegetation, as in some flatwoods or savannas, these sites generally experience frequent fires. Fires in these systems are likely on the order of every three years as opposed to once per decade (FNAI 1990).

Under a natural fire regime, edges of pond pine communities likely experienced more frequent fires than the entire community. Where these communities abut frequent fire communities such as mesic flatwoods or pine savanna frequent fires would sweep down slope from drier communities into pond pine communities until encountering a fuel moisture level that was too wet to support fire. This ecotone is often herb dominated and habitat for rare plants (Weakley and Schafale 1991). Thus, healthy pond pine woodland/pine savanna or wet flatwoods transition zones are herb dominated.

In pond pine woodlands that burn frequently (every 7-12 years), switch cane can become a dominant understory shrub (Frost 1995). Robertson et al. (1998) state that a frequency of 3-5 years promotes switch cane in pond pine woodlands and frequencies of 10-20 years promote shrubs. The rapid growth of cane promotes fuel build-up and its flammability may make cane-dominated pocosins more susceptible to fire more often than shrub dominated pocosins, thus perpetuating themselves (Schafale and Weakley 1990). Reductions in fire frequency have been implicated in the apparent historical decline of canebrake vegetation within pocosins (Frost 2000). Many sites that are now pond pine woodland may formerly have been canebrake communities (Schafale and Weakley 1990) when the natural fire regime was uninterrupted and frequent fires more common.

See the sections Slash pine understory plant response, Longleaf Pine understory plant response, Fire Effects in Shrub bogs and Fire Effects in Pocosins and Large Shrub Bogs for more information on associated plant and animal responses to fires.