Fire Lines and Forested Wetlands

Fire managers have a history of protecting forested wetlands from fire. Wetlands commonly “protected” from fire include pond cypress wetlands, streamhead and small basin shrub bogs, swamps, and isolated bay forests. The effects of fire suppression due to fire lines have repercussions in plant communities notably increases in woody plant dominance and canopy closure. These changes in turn affect plant and animal communities. Changes in hydrology caused by fire lines have also been implicated in changes in plant and animal communities.

Vegetation Structure and Composition

Ecotones of wetlands are often where fire lines are constructed and where many of the detrimental effects of fire lines are seen. The ecotone of many forested wetlands has a zone that is herb dominated, likely maintained by a combination of hydrologic conditions and frequent fire (Robertson et al. 1998). Construction of fire lines in the ecotone can lead to the elimination of this herb-dominated zone. Where fire is excluded in areas down slope from fire lines, shrubs invade. Shrubs often out compete herbs, thus eliminating the herbaceous ecotone between forested wetlands and surrounding fire maintained communities. Subsequent fire lines are often constructed up slope from the last thus exacerbating the shrub expansion problem (Frost, Walker and Peet 1986).

Wetland ecotones are noted as the habitat for a number of rare plant species (Harper et al 1998, Hart and Newman 1995, Robertson et al.1998, Chafin 2000, Edwards and Weakley 2001). Many of these rare plants utilizing these habitats are non-woody (Walker 1993, Edwards and Weakley 2001). Invasion of shrubs into these ecotones threatens these rare non –woody plants that tend to decrease in abundance as shrubs increase (Harcombe et al. 1993, Peet and Allard 1993). Plowing lines in this zone can also physically destroy some of these plants (Frost, Walker and Peet 1986).

Several rare amphibian species including the flatwoods salamander, striped newt, gopher frog and Pine Barrens tree frog, are also depend on herbaceous wetland ecotones for completion of their life cycle (Palis 1996, USFWS 1999, Harper et al. 1998). Changes in habitat structure (i.e., elimination of open herb and grass dominated areas) due to fire suppression are implicated in the degradation of gopher frog and flatwoods salamander breeding sites (USFWS 1999). Pine barrens tree frogs also utilize the interface between shrubby areas and open pools (Harper et al. 1998). (See: Fire Ecology of Pond Cypress Wetlands)

Hydrology

In addition to changes in vegetation structure, plowed lines can change hydrology of isolated wetlands (Bacchus 1995).

• Plowed lines can make connections to adjacent permanent water wetlands (Harper et al. 1998)
• They can alter hydroperiod (Palis 1996).
• Fire lines have been implicated in altering seepage hydrology by channeling water away from the site (Bacchus 1995, Hermann 1995).
• Erosion can also become a problem where fire lines are constructed in wetlands with topographic change such as streamheads (Robertson et al. 1998, FNAI 1990, Frost Walker and Peet 1986).

Some of effects of theses hydrologic changes are as follows:

• Hydrologic changes to wetlands are known as causes of floral and faunal changes in wetlands (Ewel 1990, Harris and Vickers 1984).
• Direct effects of fire line construction include plowed lines ponding water, which amphibians use as breeding sites. These sites are often unsuitable because they are isolated and falling water levels strand and kill amphibians in the aquatic phase of their lifecycle (Harper et al. 1998).
• Fire lines that connect isolated wetlands to permanent water bodies can allow colonization by predatory fish. This process is detrimental to amphibian populations whose larval stages can then fall prey to predatory fish (Palis 1996).

Management Guidelines

Fire is important in forested wetlands for maintenance of vegetation structure and composition and for maintaining plant and animal habitat. Fire managers have created firebreaks in wetland ecotones in part to widen the hydrologic window under which adjacent communities can be burned (excluding wetlands due to risk of ground fire). Some managers feel that hard firebreaks separating wetlands are necessary to meet management targets with respect to burn season, frequency and fire effects in the surrounding natural communities. The negative ecological effects of plowed fire lines should be weighed with operational needs.

The following guidelines should be considered in management of forested wetlands embedded within fire type communities:

• Do not place plowed lines in ecotones.
• Allow fire to burn through wetlands or allow fire to penetrate into wetlands.
• Determine the necessity of protecting wetlands:
  • Is organic soil actually present?
  • Under what moisture regime and organic matter content might soils ignite?
  • Is it possible to allow organic soils to ignite from smoke management, containment, and legal perspectives? Many local and state governments have implemented laws and rules that effectively prohibit smoldering ground fires (see organic soils).
• Utilize alternatives to plowed lines when not allowing fires into wetlands.
• Burn under conditions of high moisture when wetlands are not likely to burn.
• Utilize mowed breaks rather than plowed lines.