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Dryad

Flooding drives tropical dry forest tree community assembly in southeast Brazil

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Oct 17, 2023 version files 303.61 KB

Abstract

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 (i) characterize the vegetation structure and quantify community compositional differences among landforms and (ii) 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 (coordinates 14º 54’ 38’’ S 43º 42’ 53’’ W). We allocated six plots in each landform sampled from wettest to driest sites: (i) Marginal Dike (RF – Riparian Forest), (ii) Upper terrace (RWF – Riparian Wetland Forest), (iii) Lower Terrace (WF – Wetland Forest), (iv) Lower Plain (OFF – Occasionally Flooded Forest), and (v) Upper Plain (UF - Unflooded Forest). We conducted multivariate analyses (non-metric multidimensional scaling and Principal component analyses) to determine if the five sampled environments formed distinct floristic and environmental groups across the flooding gradient. We used ANOVA and Tukey post-hoc tests to assess soil variable differences among vegetation types (where relationships between edaphic variations and tree communities' floristic-structural patterns are the purpose of each analysis). 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.