Water and nutrients mediate tree communities in the driest region of Caatinga

[Display omitted] •Twelve vegetation plots and soil profiles were analyzed in dry forest sites.•Surface horizon properties are crucial to vegetation parameters.•Richness diversity reduces soil capacity to support life.•Soil organic matter influences tree communities.•Wilting point is crucial for survival of species. The abundance and diversity of plant species in rainforests are related to soil fertility. Caatinga is one of the most diverse dry forests on Earth. However, the response of plant communities to edaphic factors is poorly known. In this study, we aimed to investigate the influence of soil properties on the structure and composition of tree communities in the driest region in Caatinga. Twelve sites were selected to represent vegetation and soil diversity. Vegetation plots of 20 × 50 m were delimited in these sites. All individuals in these plots with height ≥1 m and diameter at ground level ≥3 cm were identified. Soil samples were collected for physico-chemical analysis in each vegetation plot. Among the 3276 individuals identified in all sites, 2491 were alive, and 785 were dead. They belonged to 15 families and 28 species. According to the structure and composition of the vegetation, the sites were grouped into Brown and Green groups by NMDS. The Green group had higher diversity, biomass, mean height, number of families, and exclusive families than the Brown group. Soils were moderately acid to moderately alkaline, eutrophic, and dominantly loamy. The C, N, and P soil contents were positively correlated to community diversity and richness. The correlation between the wilting point and the number of dead individuals indicates that the duration of drought stress was more relevant than its frequency. The surface horizon properties were more relevant to vegetation parameters than those in deeper horizons. The decrease in tree diversity and richness and the increase of generalist species number reduce soil capacity to support life. Biogeochemical interactions between plants and soil are crucial to Caatinga.