The role of tree crown on the performance of trees at individual and community levels: whole-phenotypic context matters

Abstract

Functional traits offer insights into plant performance. However, linking traits to individual tree performance requires considering the overall phenotypic context and utilizing traits measured at the individual level. Tree growth rates are informative metrics about performance, however how it is measured provides different information on tree or community growth dynamics and structure and can alter the relationships or their strength with functional traits and individual phenotypes. Moreover, at the community level, trees can adjust their crown shapes and sizes to optimize canopy space utilization, and a high level of canopy packing can enhance the individual to community-level growth rate. In this study, we assessed the crown area of 1144 individual trees, a simple trait measured at the individual level, and the leaf mass per area (LMA), a common functional trait, to test trait-growth relationships, considering absolute and relative growth rate. The observed total photosynthetic mass (integrating crown area and LMA) positively explained absolute tree growth rates, interacting with tree height. As higher the trees, more intense was the effect. Importantly, this effect was not solely based on LMA or crown size. This implies that LMA’s predictive power could improve by integrating leaf-level traits with whole-plant allocation to leaf area. These variables, however, failed to predict the tree’s relative growth rates. Additionally, our study found that increased canopy packing levels raised the community-level growth rate within our plots. This overall community growth seems be facilitated by denser tree arrangements and efficient light interception in the forest due to the higher canopy packing level. We highlight the importance of considering crown area as a critical variable to be measured during floristic inventories and in studies focused on tree performance.