ABSTRACT
The Middle São Francisco River valley is a vast territorial area with marked seasonal change and diversity of lithology, landscapes, soil, and vegetation. However, the relationships between soil characteristics and plant communities are poorly known. In this study, we show the relationships between key soil properties that determine the establishment of savanna-steppe, wooded savanna-steppe, savanna, semideciduous forest, and deciduous forest in this region through analysis of 166 soil profiles. In general, savanna soils are much more leached, Al-saturated, and sandier, and they are located in the highlands of the regional landscape. Savanna-steppe soils are eutrophic, yet sodic or solodic and shallow, always associated with lowlands. The semideciduous forests are highly variable in terms of soil properties, and their distribution seems to be controlled by water availability. There is great similarity between wooded savanna-steppe soils and deciduous forest soils, which are overall eutrophic, alkaline, and well developed, so that phytophisiognomy is the main difference between these two formations. The semiarid phytogeography of this ecotonal zone is highly influenced by soil properties, with great soil contrasts between savanna (Cerrado) and savanna-steppe (Caatinga), which are very similar to their respective core reference areas. In comparison to the neighboring Caatinga and Cerrado, the deciduous forests have highly contrasting soil properties, highlighting them as a separate phytogeographic entity.
phytogeography; geobotany; soil-vegetation relationships; Brazilian semiarid region
