The role of mountains as refugia for biodiversity in Brazilian Caatinga: Conservationist implications

Abstract

The relationship between how humans and altitude influence the structure of plant communities has been poorly investigated and particularly so in semiarid ecosystems. Understanding the processes that affect plant community structure is essential for sustaining the biodiversity found in altitudinal refugia of the Brazilian Caatinga. In this study, we investigated the influence of altitudinal gradients and human impacts on floristic composition and structure of a shrubby-arboreal community in northeastern Brazil. We recorded a total of 68 tree species in 45 randomly sampled 4×50m plots in three different altitudinal levels (Level 1, Level 2, and Level 3). The species clearly separated among the altitudes studied when the abundance data were analyzed (Bray–Curtis, Nonmetric Multidimensional Scaling). Whittaker plots indicated that Level 3 (highest) had more species and greater evenness and thus greater diversity. On the other hand, Level 1 (lowest) had lower diversity with greater dominance of a few pioneer species. Our results indicated that higher altitudes appear to function as refugia for many plant species (unique species and species shared with Atlantic Forest), which results in greater specie richness. However, high levels of human disturbance at lower altitudinal levels contribute to lower diversity due to the competitive abilities and dominance of pioneer tree species. The maintenance of these altitudinal Caatinga refugia is important and should be a priority for the implementation of new protected areas in the semiarid region of Brazil.