Prescribed Burning of Coastal Marsh

Authored By: S. Hermann

Prescribed burning is a common and often-preferred management tool used in coastal marsh ecosystems of the southeastern U.S. The need to reduce fuel and so to minimize severe wildfires in southeastern coastal salt marshes has been recognized for over a century (reviewed by Nyman and Chabreck 1995). Even so, few studies have evaluated the effectiveness of different seasons and frequencies of burning. This is especially puzzling given that issues of fuel reduction and ecological effects related to season of burn are being studied more and more in inland Coastal Plain pine forests. However, most research and adaptive management to date in coastal salt marshes has been directed at comparing long-unburned areas with sites recently burned in the dormant season. In these ecosystems, dormant-season burning has been the standard technique for fuel reduction for decades despite the general acceptance that, prior to European settlement, fire in both Coastal Plain inland pine forests and coastal marshes occurred primarily in the growing season. Twenty-five years ago, Hoffpauer (1968) estimated that 300,000 to 400,000 ha of Louisiana coastal marsh were burned annually. In recent years, USFWS Region IV has burned more than 70,000 ha of salt marsh annually during the dormant season. The U.S. Park Service, numerous state agencies, and some private owners manage additional land in a similar manner.

The ecological significance of season of burn was not recognized until the last quarter of the century. Acceptance of alternative months for prescribed burning was probably related, in part, to documentation that such fires did little or no harm to resident animal species in the short term and in the long term created desirable habitat structure. Recent studies have also demonstrated that growing-season burns may increase the availability of insects, a resource important for nesting success of many bird species.

Although reintroduction of natural processes may be impractical, use of growing-season burns in Coastal Plains pine forests provides many significant benefits when compared to dormant-season fires. Some of the positive effects include:

increases in flowering and/or seed production of some plant species,
decreases in the number of stems of encroaching hardwoods,
shifts in vegetation structure for many animals, and
increases in numbers of acceptable burn days each year, giving managers more opportunities for fuel reduction.

It is unknown if similar benefits would be realized by applying alternative types of prescribed fires to coastal salt marshes, but continued lack of knowledge may well hamper fuel reduction and conservation efforts for these ecosystems and associated species of special concern.

There is very little published information on specific environmental conditions that result in successful prescribed burns in coastal salt and brackish marshes. Some managers have commented that low relative humidity, light wind and continuous dead litter are required before Juncus marsh will burn cleanly. Zontek (1966) noted that in north Florida an accumulation of 3 or more years of fuel is necessary before a coastal marsh is expected to burn cleanly. Wade (1991) provides one of the few descriptions of fire weather for a fire in a southeastern coastal marsh. For a September burn in Spartina bakerii on a barrier island off the coast of Southwestern Florida, he reported that conditions at time of ignition (10 AM) were: