Specific leaf area explains differences in leaf traits between congeneric savanna and forest trees

Abstract

Summary Leaf traits are commonly associated with the life history, distribution and resource requirements of a species. To improve our understanding of the ecological and physiological differences between tropical savanna and forest trees, we compared leaf traits of species native to savanna and gallery (riverine) forests in the Cerrado region of central Brazil. Congeneric species pairs from 14 different taxonomic families were studied, each with a savanna species and a forest species present at the study site. Only individuals growing in savanna conditions under full sun were studied. We measured foliar nutrients, δ13C, δ15N and specific leaf area (SLA: leaf area per unit leaf mass). We used phylogenetically independent contrasts to compare savanna and forest species and to test for correlations among species traits. Overall, leaves of forest species had 17% higher N concentration, 32% higher P concentration, and 37% higher K concentration, despite growing in similar soils. Concentrations of all three elements were strongly and positively correlated with SLA. Forest species had 52% greater SLA, on average, than savanna species, which accounts for the higher foliar nutrient concentrations of these species. Savanna species had higher δ13C values than forest species, indicating higher water‐use efficiency. The SLA was negatively correlated with δ13C, suggesting that SLA may also account for the higher water‐use efficiency of savanna species. There was no difference in foliar δ15N between savanna and forest species, but foliar δ15N was negatively correlated with soil pH. These results contribute to recent studies showing that tropical savanna and forest species represent two distinct functional types, with large differences in ecology and physiology, that have important consequences for the dynamics of savanna–forest boundaries.