Biogeographical Districts of the Caatinga Dominion: A Proposal Based on Geomorphology and Endemism

The Caatinga Dominion in Northeastern Brazil represents the largest semiarid phytogeographical area in South America. It was understudied during the twentieth century and was considered an area of lesser importance for conservation. But an increase in biodiversity studies in the last decades is showing that it is richer and more complex than previously thought. We compile here information from a range of sources to propose a new biogeographical regionalization for the semiarid Caatinga, splitting the area into biogeographical districts for which we provide new nomenclature. We show that each proposed Caatinga district is related to landscape units representing areas of Caatinga with contrasting edaphic features (stony and shallow, sandy and nutrient poor or nutrient rich soils, derived from crystalline, sedimentary or karstic landscapes, respectively). We also discuss the enclaves of other biomes embedded within the Caatinga Dominion and the ecotones with surrounding biomes and provide a new geomorphological and biogeographical map for the whole Dominion.