The interactive effects of herbivory and fire on an oligohaline marsh, Little Lake, Louisiana, USA

Herbivory and fire have been shown to affect the structure and composition of marsh communities. Because fire may alter plant species composition and cover, and these alterations may have an effect on herbivore populations or foraging patterns, an interactive effect of herbivory and fire may be expected. In this study, the effects of fire and vertebrate herbivory in a Louisiana oligohaline marsh were studied using small, controlled burns and animal exclosures. Mean total biomass was nearly 2 times greater in the plots protected from herbivory than in the plots subject to natural herbivory. Additionally, mean total biomass was over 1.5 times greater in the plots that remained unburned than in those that were burned. Two dominant perennial species, Spartina patens and Scirpus olneyi, were negatively affected by herbivory, but two annual sedges, Cyperus flavescens and Cyperus odorata, were positively affected. Burning reduced the aboveground biomass of Spartina patens and Bacopa monnieri. No species increased in biomass as a result of fire. No significant differences were found in species richness between herbivory treatments or between fire treatments. Although both herbivory and fire were found to cause significant changes in the vegetation, the interaction between herbivory and fire was not found to produce any significant effects in any test conducted.