Phytogeographical meta-analysis of the caatinga biome

Abstract

The caatingas are a complex of phytophysiognomies characterized by short, deciduous trees and shrubs in the Brazilian semi-arid region. For long time the caatingas have been considered as having little endemism and diversity in a flora subordinated to the Atlantic forest and/or Argentine Chaco. Although a synthesis about their flora is still missing, recent investigations have shown that the caatingas have a considerable richness in species and endemism even on genus level. Also, the caatingas seem to have two great nuclei of floristic diversity: one associated with cristalin terrains, the other with sedimentar terrains. Studies have suggested that the critalin nucleus is associated with the flora of the Seasonally Dry Tropical Forest (SDTF), which occupied large extension of the South American continent during the Pleistocene. Nowadays the SDTF occurs in disjunctions, one of them being the caatingas on cristalin terrains. On the other hand the flora of the caatingas on sedimentar terrains has been postulated to originate from the South American xeric flora. Our goal is to investigate whether the caatinga flora would be organized in distinct floristic nuclei or would follow gradients presided by environmental variables, such as climate, soil, reliev etc. We will build a databank from the available literature, including theses and monographies and apply multivariate analysis. If the species ordinate according to distinct floristic groups, we will investigate the similarity of the floras in cristalin and sedimentary terrains in order to know their affinities to the SDTF or xeric flora. If the caatinga flora ordinate according to gradients, we will apply other multivariate analyses in order to know the environmental variables that are associated with the species distribution. We intend to produce a large databank encompassing all studies so far done in the caatingas, which can support the understanding of biogeographic variables associated with species distribution. Also, we will have a thorough floristic list, which can allow us to assess how rich the caatinga woody flora is and how many the endemisms are.