Growth rings in woody species of Ombrophilous Dense Forest: occurrence, anatomical features and ecological considerations

The objective of this study was to survey species of Ombrophilous Dense Forest (Atlantic Forest) in the Serra da Jiboia (Bahia), Brazil, which have growth rings, to characterize their growth zones anatomically, and on the basis of these data and others already published, to provide an answer to some questions which are relevant to understanding why growth rings occur in species of the Atlantic Forest. The wood anatomy of 111 species collected in Ombrophilous Dense Forest in Bahia and Rio de Janeiro, belonging to 77 genera and 37 families, was studied to discover the presence of growth rings and if so to characterize them. Growth rings were present in most species (79 %), and of these, the majority showed anatomical markers characterized by thick-walled and/ or radially flattened late wood fibres, although other markers may occur together with this one. The explanation for the occurrence of this marker in the growth rings of Atlantic Forest species may lie in historical-evolutionary factors. The absence of growth rings is positively related to the species collected in the Atlantic Forest compared to those of the Cerrado. However, the presence of poorly defined growth rings was shown to be negatively related to endemic species of the Ombrophilous Dense Forest, compared to those which occur in other vegetation types within the Atlantic Forest. Contrasting conditions of water availability and seasonality in these different habitats offer a theoretical basis to explain these patterns.