Fire Regime of Pond Cypress Wetlands

There is widespread recognition that cypress dominated forests are tied to fire (citations in Ewel and Mitsch 1978 and Wade et al. 1980). Because these systems are isolated wetlands within a matrix of other fire adapted community types such as pine flatwoods, wet prairies, pine savannahs or marshes, fires periodically spread from the upland pyric communities into wetlands especially in the dry season (Ewel and Mitsch 1978, Kirkman 1995). Fire frequencies in these isolated, pond cypress dominated wetlands appear to be on the order of decades (every 10-50 years) rather than centuries as for bald cypress dominated wetlands (Ewel 1990).

Different types of pond cypress wetlands and different portions of wetlands likely experienced different fire frequencies. The actual historical frequency of fires in these systems is not well understood. The frequency of fire is likely inversely related to the length of hydroperiod and depth of flooding in the wet season (Ewel 1998, Kirkman et al. 2000). Historically, the margins of these isolated wetlands may have experienced a higher fire frequency than the entire wetland as fires from the uplands spread down into wetlands before reaching non-flammable vegetation or saturated soils (FNAI 1990). For dome swamps the outer edge may have burned as frequently as the surrounding natural community (every 3-5 yrs; FNAI 1990), where the centers of domes, especially large domes, may have burned only every 100-150 years (FNAI 1990). A frequency of one burn in 20+ years is cited for domes by Sutter and Kral (1994). Cypress ponds and cypress gum ponds with mineral or organic soils burned infrequently, every 20 to 50 years (Sutter and Kral 1994). Cypress savannahs likely burned more frequently than domes, once per decade (Wade et al. 1980). Cypress strands are thought to have burned less frequently than domes (Wade et al. 1980). In the absence of fire, hardwoods out compete cypress and cypress dominated wetlands are thought to succeed to hardwood swamps (Ewel 1998, literature cited therein). Shrub invasion has been documented where dome hydrology was altered due to ditching and where fires were excluded (Marois and Ewel 1983).

The natural fire season of cypress wetlands was likely the early lightning season, before the onset of the summer rainy season when wetlands were likely to be dry, increasing the probability that they would burn with the surrounding communities (Robertson et al. 1998).

Pond cypress wetlands with extensive peat accumulation (i.e., deeper basins) may be susceptible to infrequent, severe ground fires. These fires can consume soil killing much or all of the vegetation rooted therein. Drained cypress domes and strands are likely at a greater risk of severe ground fires (Marios and Ewel 1983). Observations suggest that severely burned cypress domes and strands are invaded by shrubs such as Carolina willow (Salix caroliniana) in south Florida (Wade et al. 1980), tupelo and titi farther north (Ewel 1995, Marios and Ewel 1983) or may become herbaceous wetlands or aquatic sites such as the open water at the center of cypress domes. This process of severe fire during drought is important in maintaining characteristics of Carolina Bays (a wetland of specific geologic origin, in which pond cypress can occur) (Schalles et al. 1989).

Anthropogenic Alterations of the Fire Regime

Fire is rarely applied directly to forested wetlands, aside from silvicultural applications (Brandt and Ewel 1989). Much of the surrounding habitats have routinely been prescribe burned in the dormant season. This shift in season of burn for surrounding communities, i.e., burning in the dormant season as opposed to the natural lightning season, has likely inadvertently lead to a decrease in fire frequencies within cypress wetlands. Wetlands typically hold more water in winter, thus are less likely to carry fire in winter than in droughty spring periods (Kirkman et al. 2000). In addition, many wetlands are “protected” from fire by plowed firebreaks (Kirkman et al. 2000).