The effect of neighbor species’ phylogenetic and trait difference on tree growth in subtropical forests

To comprehensively understand ecological dynamics within a forest
ecosystem, it is vital to explore how surrounding trees influence the
growth of individual trees in a community. Biotic interactions have a
significant potential impacts on individual tree growth and their effects
can be evaluated through trait and phylogenetic-based approaches. This
study investigates the relative importance of biotic interactions on tree
growth by examining several metrics and considering three classes of
intrinsic growth rates among the focal individuals: slower, intermediate
and faster-growing trees. The metrics include hierarchical and absolute
trait differences of focal trees to neighbors, neighborhood crowding
index, phylogenetic distance, and trait community metrics. Our results
indicated that the phylogenetic distance between the focal tree and its
neighbors positively impacted the growth of all classes, whereas different
traits have distinct effects on slower and faster-growing trees. Specific
leaf area (SLA) and leaf area (LA) showed hierarchical importance to tree
growth. Trees surrounded by neighbors with higher SLA and LA than
themselves grow better, particularly for slower-growing trees. Higher
levels of wood density difference between the focal trees and their
neighbors positively impacts slower and faster-growing trees, while height
difference negatively impacts faster-growing trees. We conclude that the
interactions between trees are mediated by their ecological differences,
but the performance and responses to surrounding competitors vary along
with their growth class within a community. This study has revealed that
the tree's intrinsic growth rate mediates the effect of traits and
phylogeny of surrounding trees on individual tree growth.