Flooding and fire frequency promotes beta diversity in tree and non-tree species in tropical wetlands

Abstract

The interaction between high fire frequency and long flooding seasons maintains open vegetation in floodplains, while low fire frequency and no flooding can lead to forest development. In the Kadiwéu Indigenous Territory (IT), in the ecotone between the Cerrado and the Pantanal biomes in Brazil, the diversified spatio-temporal patterns of fire activity affect the diversity of floral functional traits and plant phenological strategies. Given this scenario, we sampled tree and non-tree species abundance data in 156 plots subject to different flood levels and fire frequencies in the Kadiwéu IT. Based on flooding regimes and fire frequency data series from 2001 to 2021, we classify the sample sites as floodable or flood-free areas under high (annual or biennial burn), moderate (three-yearly burn), or low (burning at four-year intervals or more) fire frequency. We analyzed the effects of flooding and fire frequency on plant species richness, abundance, and beta diversity (β). In general, tree density did not affect non-tree species richness. The species richness on the patches with different fire frequency category was generally similar, especially regarding the tree species. However, the combined effect of fire and flooding shifted the species composition. Variability in fire frequency across the landscapes support β-diversity maintenance in ecotonal vegetation between tropical wetlands and savannas. Furthermore, the similarity in species composition between floodable and flood-free areas at the same fire frequency category is low due to differences in abundance and species replacement. As part of adaptive fire management, we suggest maintaining a heterogeneous mosaic of fire frequencies in the landscape.