Fire Regimes of Pocosins and Large Shrub Bogs

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.