Flooding drives tropical dry forest tree community assembly in Southeast Brazil

In this study, we characterized and compared vegetation types associated with geomorphological units susceptible to distinct flooding levels. Differences in vegetation are related to landform variations. We aimed to 1) characterize the vegetation structure and quantify community compositional differences among landforms and 2) compare landforms soil characteristics and how these correlate with the tree vegetation. The study area is located in the Brazilian Caatinga domain, near the Verde Grande river, a tributary of São Francisco river (14°54′38ʺS, 43°42′53ʺW). We allocated six plots in each of the five landforms sampled (from wettest to driest sites): 1) marginal dike (RF – riparian forest), 2) upper terrace (RWF – riparian wetland forest), 3) lower terrace (WF – wetland forest), 4) lower plain (OFF – occasionally flooded forest) and 5) upper plain (UF – unflooded forest). We ran a non-metric multidimensional scaling, produced a Venn diagram, and performed a principal component analysis (PCA) on the soil data (compared through a Tukey test at 5% significance after a significant ANOVA). A total of 1422 individuals, 26 families, 70 genera and 89 species were recorded. The NMDS revealed two distinct floristic groups: one group is associated with landforms with assumed higher flood frequency (RF, RWF, WF) and one with less frequently flooded landforms (OFF and UF). The RF, OFF, and UF landforms contained exclusive species (that only occurred in the plots of a particular landform). The species Geofroea spinosa (Fabaceae) was responsible for 70% of the total biomass recorded in the landforms RWF and WF. The soil analysis showed a gradient of soil acidity and fertility related to water saturation, whereby the most frequently flooded plots had the highest acidity values and highest fertility. We found that flood-related conditions significantly influence tree community structure and species distribution in this floodplain in the Brazilian Caatinga domain.