Effect of fire on the soil seed bank of neotropical grasslands in the pantanal wetland

Abstract

Research reports have suggested that the soil seed banks can have seedling recruitment favoured by fire, especially in grassy plant communities prone to this environmental factor. We examine effects of fire on the soil seed bank of grasslands in the Neotropical wetland Pantanal (hyperseasonal savanna). Our hypothesis was of negative effect, given the contrasting traits associated to seed-seedling tolerance to fire or flooding in addition to the strength of flood as the main ecological driver in floodable areas. Soil samples were collected before and immediately after a prescribed burn in floodable savanna grasslands, at different depths (2 cm layers down to the 10 cm depth), plus litter. The soil samples were taken to a greenhouse for censuses of seedling emergence, to assess the species composition of the seed bank. We recorded a density of 7404 seeds/m2 and 49 morphospecies, mostly aquatic plants (63%). Among the analysed ecological parameters, the species richness and composition did not change significantly between the pre and postfire conditions; yet the abundance was significantly lower only in the first 2 cm layer of the burned soil. Both abundance and richness decrease with soil depth. This apparent fire tolerance of the soil seed bank of floodable savanna grasslands is here proposed as a clue to understand fire as another ecological driver, as well as flood, but further long-term studies are needed.