Resprouting drives successional pathways and the resilience of Caatinga dry forest in human-modified landscapes

Tropical forest regeneration has gained renewed interest in recent years as secondary forests have being considered biodiversity repositories and a key source for globally relevant ecosystem services as climate regulation and carbon sequestration and storage. Here, we address the regeneration of a Caatinga dry forest in the context of slash-and-burn agriculture and chronic anthropogenic disturbance by examining forest regeneration mechanisms and a comprehensive set of community-level plant diversity measures (i.e., taxonomic, functional, and phylogenetic) in regenerating (4 to 70-yr old) and old-growth forest stands. Resprouting from root suckers was the predominant regeneration mechanism across recently abandoned crop fields. Overall, regenerating forests were similar to old-growth forests in terms of taxonomic and functional composition, and functional and phylogenetic diversity. Moreover, except for the taxonomic diversity, community-level plant diversity measures were not related to forest age or soil properties. Our results suggest that Caatinga dry forest covering sandy soils is particularly resilient due to regeneration driven by resprouting. The same set of plant species dominates the entire regeneration process, including old-growth forest stands. Accordingly, Caatinga dry forest regeneration may follow an initial composition model, rather than following a directional and deterministic trajectory associated with species replacements. This initial composition model probably results from a combination of three factors: (1) early regeneration driven by resprouting rather than seed arrival and seedling recruitment; (2) biomass accumulation mostly due to growth by early colonizers and by those species able to resprout after chronic anthropogenic disturbance and during forest regeneration; and (3) the co-occurrence of functionally distinct plant species. Accordingly, resprouting can guarantee some level of resilience, and hence, the services provided by secondary forests. Nevertheless, forest dynamics in landscapes inhabited by forest-dependent people are affected to a great extent by the nature of the imposed pressures and the ecological profile of the remaining flora.