The magnet effect of fire on herbivores affects plant community structure in a forested system

Abstract

Fire plays an important role in plant community structure in many terrestrial ecosystems. However, most studies assume responses of plant communities to fire are primarily generated by direct effects. That is, studies often assume the net effects of fire on plant communities are primarily driven by fire consuming existing plant biomass, resetting succession, and stimulating new seed germination. Far less attention has been paid to indirect effects of fire on plant communities as mediated by food web interactions. Here we demonstrated in a series of experiments in a loblolly pine (Pinus taeda) forest that the net effects of fire on plant community heterogeneity are indirectly mediated through changes in herbivore behavior. First, we demonstrated that fire causes a magnet effect for herbivores resulting in a 3-fold strengthening of herbivore use. Then in another experiment using a replicated before-after control-impact design with four treatments, we demonstrated that combining fire and herbivory has a non-additive positive effect on plant community heterogeneity. The shifts in the plant community were sustained post-fire through the plant dormancy period. These results highlight the need to conserve the fire-herbivory interaction rather than either force independently.