Natural recovery of plant species diversity in secondary forests in Eastern Amazonia: contributions to passive forest restoration

Abstract

Natural regeneration is important in the context of the strategies to recover native vegetation in Brazil and of the international commitments of forest restoration undertaken by the country. However, trajectories of recovery can be highly variable and context-dependent, demanding studies to foster the use of secondary forests in restoration. Here, we describe the natural recovery of plant diversity in a chronosequence (5–21 years old) and how it is influenced by age of the regenerating forests. For this, we sampled the floristic composition and structure in 20 fragments of secondary forest in Southeast Para in 2014 and 2015. Transects of either 10 × 250 m or 20 × 125 m (0.25 ha) were delimited in each forest fragment, and subdivided into 25 subplots of 10 × 10 m, where plants of the upper stratum (DBH ≥ 10 cm) were sampled. The lower stratum (DBH < 10 cm) was sampled in five 5 × 20 m subplots that were nested in the 0.25-ha transects. We recorded 5509 individuals of 282 species and 61 families in the 20 transects evaluated. The species diversity recovery occured rapidly in the first few decades of ecological succession. Floristic composition of the upper stratum was correlated with forest age. Species diversity metrics were predicted by the age and basal area of secondary forests, demonstrating their importance as indicators of successional stages in secondary forests. Our results reinforce the relevance of using secondary forest in restoration programmes across the Amazonian region.