Using Prescribed Fire in Freshwater Marshes

There are many uncertainties in the use of prescribed fire in marshes.

Basin Marsh Burning

• Uncertainties with regard to knowing natural fire frequencies pose management challenges.
• If one believes that lightning was the “natural” ignition source for fire in marshes, it seems likely that many marshes only burned extensively under drought regimes. Using prescribed fires under drought regimes is generally not a feasible operational exercise due to fire control and smoke management issues. However, fire effects likely differ and are less severe with prescribed fire than drought regime fire.
• In lieu of burning under a springtime drought regime, managers often burn in fall and winter after killing frosts because increased flammability of marsh vegetation.
• Many marshes have organic soils that can ignite at certain moisture levels. Though ground fires are important ecological processes in marshes that function to maintain a mosaic of plant communities by removing peat and offsetting community change due to peat-building processes (Gunderson 1994), ground fires are difficult to manage. This is particularly true in urban interface areas. Despite acknowledgement of the ecological importance of ground fires, some managing agencies implement policies aimed at avoiding ignition of ground fires and attempt to suppress ground fires where they do ignite (Miller et al. 1998).
• Eutrophication of marshes likely causes plant response to fire to differ from the response under a natural nutrient regime. Fire could promote the expansion of unwanted plants via reducing competition and via liberation of nutrients. Cattail expansion has become a management problem in Florida marshes that have been altered through increased nutrient inputs. Peat fires that create slightly deeper water and liberate phosphorus may promote cattail expansion (Smith and Newman 2001, See Everglades Fire Effects for more detail). However, prescribed fires have also been observed to increase the rate of cattail expansion (Miller et al. 1998).
• Lack of information on the response of rare animals to marsh fires also poses management challenges.

• Reduced sedimentation rates in Gulf coastal marshes resulting from water management along with rising sea levels call the desirability of reducing fuel loads into question. Fires remove biomass and thus slow soil building processes (vertical accretion). In marshes along the Gulf coast where subsidence rates and sea level rise are causing the loss of marsh, reducing vertical accretion may not be desirable. Though more research is needed to fully understand the interaction of these processes (Nyman and Chabreck 1995).
• Maintenance of natural communities in the perceived natural state with the use of fire may not be feasible under altered hydrologic regimes. It seems clear that fire is important for control of some species of woody vegetation in marshes but it may not be effective in all situations. For example: controlling willow encroachment in altered Florida marshes with fire has been relatively unsuccessful. Contrary to traditional perception that fires control woody vegetation, evidence suggests that prolonged hydroperiods are more important in limiting willow than fire (Miller et al. 1998 and references therein).
• Managers will use fire in the absence of high water for control of woody vegetation. Burn frequencies to achieve control of woody vegetation are at the most frequent end of that reported as natural in the literature (FLDEP 2002).
• Some authors have questioned the usefulness of fire for controlling sawgrass fuel loads because biomass was greater in the burned than unburned plot 1 year following a burn (Lee et al. 1995). Knowledge of vegetation recovery rates is important to determine if prescribed fire is useful in reducing fuel loads in marshes.