Quick qualitative and quantitative changes in reproductive efforts in an open cerrado community: An explorative study of fire-stimulated species

Abstract

Cerrado is a tropical savanna hotspot that is impacted by frequent wildfires, but where many effects of fire still are poorly understood. This is especially true for the herbaceous strata at the community level, in which reproductive efforts are deeply affected by fire. The objectives of this study were the following: evaluate if fire qualitatively and/or quantitatively affects the production of sexual reproductive structures in an open cerrado community; describe fire-stimulated or fire-inhibited flowering and fruiting species; and evaluate the influence of water availability on flowering and fruiting. The number of species with flowers and fruits/m2 and the number of reproductive units/m2 were sampled in eight 20×20 m2 plots in Chapada Diamantina, Brazil. After the first sampling in the beginning of the rainy season (November 2009), the vegetation in four plots was burned and then the eight plots were resampled over five months. Indexes of fire-stimulated and fire-inhibited flowering and fruiting species were calculated. Non-metric multidimensional scaling and cross-correlation analyses were calculated and differences between the burnt and unburnt plots were compared with an analysis of variance. Sexual reproduction was deeply affected by fire, which changed the composition of reproducing species. Profuse reproduction of graminoids (Poaceae) and geophytic herbs classified as fire-stimulated flowering and/or fire-stimulated fruiting species concomitantly occurred with a high increase of water in the burnt soil compared to the unburnt soil in the first two months after the fires. The sexual reproduction of shrubby species was inhibited by fire. In an objective way, 21 species stimulated or inhibited by fire were recorded. Fire also changed the influence of rainfall on reproductive efforts. This study shows quick qualitative and quantitative effects of fire on open cerrado functioning and highlights the necessity of fire management for biodiversity conservation in savannas.