Tree rings in tree species of a seasonal semi-deciduous forest in southern Brazil: wood anatomical markers, annual formation and radial growth dynamic

Abstract

Tree rings provide valid predictions regarding species age and growth rates and, therefore, they can contribute to understand forest dynamics and ecology. In this work, we evaluated the tree rings of eight tree species from different successional groups that show distinct degrees of deciduousness in a seasonal semi-deciduous forest located in a transition zone between subtropical and the tropical climates in southern Brazil. We focused on wood anatomical markers, the annual nature of tree-ring formation, the description of false rings, a cross-dating analyses and an interpretation of the radial increment dynamics of the species. We sampled increment cores at breast height, performed cambial wounding and measured tree-ring widths. Annual tree rings were found in seven species, which were confirmed by cambium wounding. Differences in fiber wall thickness between latewood and earlywood and the marginal parenchyma were the main anatomical markers observed. Deciduous species had better distinction of tree ring boundaries, while the evergreen species had slightly distinct tree ring boundaries. False rings were characterized by variations in wood density and axial parenchyma bands of different widths within true tree rings. The annual tree ring confirmation and the anatomical description of the true and false rings are useful for future dendroecological research in the area. Considering the cross-dating analyses and tree-ring distinctiveness, Chrysophyllum gonocarpum is a recommended species. Regarding radial growth, the early secondary species had higher growth rates than the late secondary species. Assessing the growth trajectories over time, distinct patterns were observed among the species: a constant growth, an initial increase followed by a reduction, and oscillations of the growth were observed. As no consistent pattern of the growth trajectories was observed among species that belong to the same successional groups, they contribute to the explanation of the particular life history of these individuals in the seasonal semi-deciduous forest.