Fire drives the reproductive responses of herbaceous plants in a Neotropical swamp

Palm swamps (veredas) are unique and diverse plant communities associated with the headwaters of streams in central Brazil, and they are frequently subjected to fires. We evaluated the effect of fire and the role of different fire-related cues on inducing reproduction by palm swamp vegetation. We compared the responses of species in burned plots, in plots in which the aboveground vegetation was clipped and then removed, and in unburned and unclipped control plots. Both the number of reproductive species and the total number of flowers/fruits produced by all species monthly were significantly greater in the burned than in the clipped and control plots, and greater in the clipped than in the control plots. For 34 of the 48 individual species analyzed the number of flowers/fruits produced per m(2)/month was greater in the burned than in the control plots, whereas the clipping treatment significantly increased the reproductive rate of only six species. This indicates that increased light availability was not the only factor inducing plant reproduction. Most likely, plant reproduction was also stimulated by the availability of soil nutrients whose concentrations increased significantly after burning. Although our results indicate that most plant species that occur in palm swamps are fire-recruiters, care must be taken in using fire as management tool, especially as the frequency of human-induced fires in palm swamps have increased dramatically in recent years.