Efeitos das perturbações antrópicas crônicas e da aridez na montagem e funcionamento da flora lenhosa da caatinga: implicações para a conservação

Abstract

Tropical forests play a prominent role in retaining biodiversity and providing ecosystem goods and services on a local to global scale but are increasingly threatened by the expansion of anthropogenic landscapes. In addition, these forests are affected by severe and continuous drought events, which, together with chronic anthropic disturbances, are conditioning forces for the assembly of plant communities. In order to act efficiently towards “biodiversity-friendly anthropic landscapes”, we need to understand the impact and magnitude of the changes caused by these selective forces. Adaptive, or morpho-physiological traits (i.e., functional traits) reflect how plants respond to environmental changes and their potential effects on ecosystem processes. As opposed to traditional taxonomic approaches in ecology, functional approaches allow elucidating mechanisms underlying vegetational changes and generate predictive models of community and ecosystem responses to potential environmental changes. In this perspective, I explore in this study the effects of aridity and chronic anthropogenic disturbances (i.e., collection of wood and non-timber forest products, extensive grazing, hunting, and damage caused to vegetation by the introduction of exotic species that occur in areas remaining of the forest) on the taxonomic, functional and phylogenetic diversity of the woody flora of the Caatinga. The results suggest that (1) the predictors tested here generally had negative effects on plant diversity, with aridity and human and animal occupation pressure being the most important predictors of these effects; (2) these forests decrease species richness in more arid environments, in addition, the species composition in the disturbed areas was different, being little represented by the abundance of dense wood species in the most disturbed areas; (3) arid and disturbed environments are functionally and phylogenetically poorer, (4) communities in drier and more disturbed sites tend to contain species with more conservative trait combinations - short plants with small leaves - and communities with more stress-tolerant strategies and ruderals. The results of this study demonstrate that chronic anthropic disturbances in the Caatinga cannot be neglected, as they confer important negative effects on the taxonomic, functional, and phylogenetic diversity of the woody flora. Therefore, management strategies that reconcile the use of these forests and the maintenance of Caatinga biodiversity are urgent.