Fire Effects in Freshwater Marshes

Basin Marsh Burning

Fire is important in marshes to limit invasion of some species of woody plants (Kushlan 1990). Fires top kill many woody plants (Wade et al. 2000, Miller et al. 1998) and fire may eliminate the more fire sensitive hardwood species such as red maple (Acer rubrum), saltbush (Baccharis spp.), and wax myrtle (Myrica cerifera) (Miller et al. 1998). However, fire may only prune other more fire resistant species such as willow (Salix caroliniana) (Miller et al. 1998). Fire reduced height for willow for at least one year post-burn, but increased sprout number (Miller et al. 1998). Loveless (1959) stated that willow was unaffected by fire unless peat was burned. Willow may be more affected by hydrologic regime than fire regime (Miller et al. 1998).

In some cases, fire in marshes may be important in determining herbaceous species composition, while having little effect in others. In south Florida marshes, fire has been proposed as the factor determining whether sawgrass or maidencane is dominant (Lowe 1986). While topographic relief and thus hydroperiod controls the distribution of most plant communities in Florida marshes, Lowe (1986) hypothesizes that where fire kills sawgrass (severe peat consuming fires or rapid flood following a surface fire) maidencane rapidly colonizes the site becoming dominant. Sawgrass is thought to reclaim the site as a slowly moving vegetative front. Sawgrass is thought to out compete maidencane on relatively drier sites. Burning is cited as decreasing dominance by large species and increasing species diversity in coastal tidal marshes in North Carolina (Schafale and Weakley 1990). Further, fire has been cited as being important in regulating species composition in fresh and oligohaline marshes (Frost 1995), though little detail is given. Species dominance in Gulf coast marshes is affected by fire, with fire shifting dominance away from Spartina patens toward other marsh species (Ford and Grace 1998). Conversely, several studies have documented little change in species composition or diversity in marshes following fire (Lee et al. 1995, Van Arman and Goodrick 1979, Schmalzer et al. 1991). Further study is needed to determine if there are generalizations regarding the role of fire in maintenance of diversity in marshes.

Fires are thought to be important in marshes for limiting peat accumulation. Fires remove organic matter that would otherwise accumulate as peat. Occasionally, severe fires will remove peat. These fires are important in maintaining deeper water habitats in marshes (Kushlan 1990).

The availability of nutrients following marsh fires is variable. Soil phosphorus, often a limiting nutrient in marshes, has been shown to increase following fire (Miller et al. 1998, Smith et al. 2001) and to decrease following fire (Loveless 1959). Phosphorus in Spartina bakerii tissues has been shown to increase 1 year following fire (Schmalzer and Hinkle 1993). Though work by Smith et al. (2001) has shown that the type of fire (peat vs. surface) affects nutrient availability after fires (See Everglades Fire Effects).

Animals

Fires in marshes have been observed to cause some direct mortality of animals that utilize marshes. In a 1973 study, amphibians and reptiles were the only taxa directly killed by fire (Vogl 1973), though other taxa have been observed to die as a result of fire in the Everglades. Black rail mortality has occurred due to fires where fires were intense and complete. Rails were able to survive fires that were patchy and are believed to have used unburned vegetation as refuge (Legare et al. 1998).

Fires can modify habitat changing animal use patterns. Removal of vegetation by a fire increased use of a lakeside marsh by wading birds, but decreased use by birds preferring cover such as sparrows until vegetation recovered (Vogl 1973). Deeper water habitats within sawgrass marsh created by peat fires are used by wading birds for foraging (Hoffman et al. 1994). Though little is known about the Federally listed snail kite response to fire, snail kites prefer to forage in more open water areas, which are created by severe fires, as opposed to dense sawgrass (USFWS 1999). Burning has also been found to increase the abundance and richness of invertebrates. This increase in productivity is thought to be important for creating food sources for fish and wildlife (Van Arman and Goodrick 1979).

The effects of fire on other marsh dependent species, even listed species are unclear at best. The effects of fire on the preferred food of snail kites, the apple snail, and the round-tailed muskrat are unknown.