Do fire and flood interact to determine forest islet structure and diversity in a Neotropical wetland?

Flood and fire act as ecological filters which can interact to shape forest structure and species composition. Our objective was to investigate how the interaction between fire and flood influences richness, abundance, basal area and species composition of the tree community and the monodominant belts of Attalea phalerata Mart. in forest islets of the Pantanal wetland. We used satellite images to find 12 forest islets without fire events from 1998 to 2014, and 12 forest islets burned only once in the same period in a fire event in 2009. In these forest islets, we set up a transect with 10 to 14 contiguous 5 × 10 m plots and sampled all trees with a diameter at breast height of ≥ 4.7 cm. We also measured the watermark height. Flooding influenced species richness and abundance, increased toward wetter areas of the forest islet flood gradient. In contrast, the interaction between fire and flood inverted that trend, with richness and abundance increasing in flood-free areas. Total basal area increases in the more flooded areas of the gradient. The fire or the interaction between fire and flooding did not influence the basal area. The relative abundance of A. phalerata increased with flood level and even more under the fire-flood interaction. We conclude that the interaction between fire and flood influences forest islet structure and species composition; moreover, it favors A. phalerata monodominance.