Fire Ecology of Pond Cypress Wetlands

Vegetation

Surface fires typically leave cypress unharmed (citations in Wade et al. 1980), especially where cypress can root at least partially in mineral soil or where peat soils do not ignite (Ewel and Mitsch 1978). Bald cypress is known to be very tolerant of fire with only longleaf pine, slash pine and loblolly being more tolerant given similar bark thickness (Hare 1965). Though fire tolerance of pond cypress was not systematically compared with bald cypress, the bark of pond cypress tends to be thicker and shaggier than that of bald cypress suggesting that it may be even more fire tolerant than bald cypress (Ewel 1998). Cypress is known to sprout epicormically when branches are killed by fire and coppice following cutting and burning where above ground stems were killed (Ewel and Mitsch 1978). Cypress coppice, however, are often killed by fire (Ewel 1995).

Severe ground fires can kill mature cypress trees particularly when growing on deep peat (Ewel and Mitsch 1978). If cypress is not killed by a severe ground fire, the tree can be wounded leading to fungal infection and heart rot (Ewel 1995). Heart rot may contribute to tree cavity development. Furthermore, some ground fires that do not cause direct mortality may contribute to secondary mortality from windthrow by consuming soil and roots that function to anchor trees.

There is some suggestion that fires may stimulate cone production in cypress, but further investigation is needed to confirm this (Ewel 1995).

A combination of fires and hydrologic regimes limits hardwoods within cypress wetlands. Hardwoods are generally recognized as being less tolerant of fire than cypress (Hare 1965). In one study, hardwoods suffered more mortality than cypress after a wild fire (Ewel and Mitsch 1978). This suggests that frequent fires play a role in limiting hardwoods within pond cypress wetlands.

Little research has been done specifically on the effects of fire frequency or season on shrubs in cypress wetlands. The role of fire frequency, season and intensity in controlling hardwoods and shrubs in upland systems is relatively well studied. In general, very frequent fires (annual) in the growing season are most effective at reducing hardwoods and shrubs in upland systems. Many of the shrubs and hardwoods studied in various upland systems such as flatwoods and pine savannahs are the same shrubs that occur in pond cypress wetlands. In addition, observations of fire practitioners suggest that frequent fires may be important in reducing shrubs in wetlands. For instance, Ferguson (1998) observed that growing season fires applied in the Apalachicola National Forest had the effect of reducing titi (Cyrilla racemiflora, Cyrilla parviflora and Cliftonia monophylla) and opening the transitions to wetlands. In examining aerial photography, Huffman and Blanchard (1991) observed that woody plants invaded wetlands after a period of fire suppression, and after reintroducing fires under droughty conditions, noted that hardwoods appeared to decrease. Literature on herbaceous bogs also suggests that frequent fire maintains them as such and the absence of fire promotes shrubby systems (reviewed in Harper et al. 1998). However, recent studies in shrub bogs and marshes suggests that fires do not decrease shrub density, but frequent fires can eliminate recruitment into new areas and thus maintaining shrub free zones (Olsen and Platt 1995, Drewa et al. 2002a, 2002b) and frequent or lightning season fires may decrease the cover of shrubs (Lee et al. in press, Lee et al. In prep)

Similar to upland systems, the abundance of herbaceous plants including many rare plants is dependent on fire regime. An open canopy in cypress domes has been correlated with greater abundance of grasses and sedges (Marios and Ewel 1983). Fire with the hydrologic regime are important in keeping canopies open and limiting shrub layers of cypress wetlands thus eliminating competition for herbaceous species. The number of rare plant species found there demonstrates the importance of fire in maintaining an herbaceous wetland margin. 

The process of frequent fire may have been important in limiting organic soil buildup and peat accumulation, especially in more shallow wetlands by removing plant debris that would otherwise accumulate as peat (Kirkman et al. 2000, Schalles et al. 1989).

Animals

There has been little study of the direct effects of fire on wildlife inhabiting domes; however, a growing body of literature is beginning to implicate the indirect effects of fire suppression on vegetation in and around wetlands in declines and changes animal populations, particularly amphibian populations (Russell et al. 2002).

Canopy closure due to invading hardwoods and an increase in shrub dominance in the absence of fire (see plant response) affects animal species composition and abundance. Wading birds appear to prefer permanent water, large diameter trees, sparse hardwoods and an open understory (Harris and Vickers 1984). Several amphibian species including the pig frog, striped newt and flatwoods salamander utilize seasonally flooded grassy ecotones for foraging or breeding (Hart and Newman 1995, Palis 1996, Franz and Smith 1999). Canopy closure of wetlands historically used by the federally endangered Mississippi gopher frog is one of the factors cited in many wetlands becoming unsuitable breeding sites (USFWS 2001). Canopy closure in wetlands has decreased the abundance of some species of amphibians and has been correlated with extinctions of others (Werner and Glennemeier 1999, Skelly et al. 1999).

Several Federally listed amphibians such as the flatwoods salamander and the Mississippi gopher frog; a candidate for listing, the striped newt; and regionally rare species such as the Dusky gopher frog and the Florida gopher frog utilize habitats maintained by frequent fires. All species utilize upland habitats in stages of their life cycles, but breed in small, ephemeral wetlands including cypress dominated wetlands (Johnson 2000, Palis 1996, Franz and Smith 1999). Habitat loss due to modification by agriculture, forestry operations or other uses is the largest threat cited for all species. However, where suitable habitat remains, much of it has been degraded by fire suppression in both uplands and wetlands (Palis 1996, USFWS 1999, USFWS 2001, Johnson 2000, Franz and Smith 1999).

The role of frequent fire in maintaining herbaceous plants is particularly important for these amphibian species. Grassy wetlands, with an open canopy are critical for flatwoods salamander and gopher frog reproduction. Gopher frogs use emergent vegetation for deposition of eggs and larval flatwoods salamanders utilize herbaceous vegetation for cover and for foraging (USFWS 2001, Palis 1996). Maintenance of the grassy nature of the wetland particularly the ecotone requires frequent early lightning season fires to prevent shrub invasion (USFWS 2001). Less is known of the biology of the striped newt; however, it tends to persist only in frequently burned habitats (Johnson 2001). It appears that herbaceous vegetation in wetlands and uplands is important in this species’ life cycle. Placement of firebreaks around wetlands can lead to detrimental changes in these species habitats.