Divergent herb communities in drier and chronically disturbed areas of the Brazilian Caatinga

Although the herbaceous plants concentrate the diversity of vascular plants in the largest dry forest of South America, the Brazilian Caatinga, their responses to environmental modifications are poorly known. We assessed the taxonomic, phylogenetic and functional responses of herb communities to independent gradients of annual rainfall (510-940 mm), chronic disturbance (0-100%), and local density of woody plants in 19 forest sites of the Catimbau National Park, Northeast Brazil. We expected that drier and more chronically disturbed stands with greater density of woody plants would support less-dense and impoverished herb communities. We recorded 6787 individuals belonging to 57 species and 53 genera, predominantly dicots. Rainfall reduction decreased herb density, benefited a small set of particular genera, increased phylogenetic clustering within terminal clades and favored species pollinated by birds and butterflies. Increased chronic disturbance did not affect herb density and richness, but benefited another set of herb genera, reduced phylogenetic clustering and favored dicot herbs pollinated by bees. The density of woody plants also affected different aspects of taxonomic, phylogenetic and functional dimensions. By shaping different components of herb diversity, rainfall reduction and increased chronic disturbance are likely to act synergistically and drive the Caatinga towards multiple successional pathways. (c) 2021 Associacao Brasileira de Ciencia Ecologica e Conservacao. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Automated summary

This study investigated the responses of herb communities in the Brazilian Caatinga to rainfall, disturbance, and woody plant density. The results showed that reduced rainfall led to decreased herb density but benefited certain genera, while increased chronic disturbance positively affected herb genera and woody plant density influenced various aspects of herb diversity.