Stem and leaf functional traits allow successional classification in six pioneer and non-pioneer tree species in Tropical Moist Broadleaved Forests

摘要

More than half of the tropical forests are secondary forests that are undergoing a highly dynamic interplay of forest succession of uncertain outcome. Vegetation models can help predict forest trajectory but require simplifying the high biodiversity of these forests into a few distinct classes of functional or successional groups. The classification of tree species by successional groups has traditionally relied on qualitative criteria such as life span, or on parameters that are difficult to measure on mature trees in the field, like photosynthetic activity, in particular in tropical forests. Hence, quantitative traits that can be easily measured in a number of species may provide more accurate classification thresholds. The present study identifies quantitative anatomical and biochemical traits of leaf and stem of six species that are useful for classification of successional groups in the Tropical Moist Broadleaved Forest (TMBF) of south-eastern Brazil. Consistent with assumed fast growth and high light requirements of pioneers the investigated pioneer species presented higher stem glucose content (600%), larger vessel elements (162%), greater stomatal density (72%) and higher chloroplastic pigments concentrations (90%) than non-pioneer species. By contrast, non-pioneers were characterized by larger mesophyll cells (70%) and higher cell wall polymers concentrations (65-100%) in leaf and stem. The biggest differences between pioneer and non-pioneer species were observed in leaf blade thickness, followed by vessel lumen diameter, and stem lignin. We provide research laboratories a variety of different tools that they can use as a guideline to accurately assess the successional class of tree species in the TMBF of south-eastern Brazil.