摘要：
Aims Functional traits have emerged as an important tool to evaluate plant performance. However, the environmental conditions and ecological pressures that plants face change with their size, and the relationship between traits and plant performance should therefore be size-dependent, which has rarely been tested.
Methods Here, we evaluated over a broad range of tree sizes the interspecific relationship between tree growth and mortality and eight functional stem, leaf and seed traits. We did so across 59 tree species in Brazilian dry forests and evaluated whether the relationships found for wet forest types in the literature also hold for dry forests, where water rather than light might limit tree performance.
Important findings We indeed found a strong size-dependent relationship between demographic rates and functional traits. At small sizes, when trees are in the shaded understory, species with functional trait values that enhance light capture or shade tolerance (i.e. higher maximum adult stature, taller heights, wider crowns, higher seed mass) have higher growth and/or lower mortality rates (MR). This relationship disappears at larger sizes when trees attain better light conditions in the canopy. Drought adaptations play only a role at larger tree sizes; once trees are in the dry and exposed canopy, species with higher wood density (an indicator of cavitation resistance) have lower MRs. Our study shows that both drought and shade adaptations are important in this dry forest, and that the relationships between functional traits and plant performance changes with plant size. Plant size should therefore explicitly be included as an axis of variation in functional analyses, to better understand the relationship between functional traits and demographic rates.
