Abiotic environmental factors and the composition of biotic neighbors collectively influence tree growth. The reaction of tree growth to the composition of these biotic neighbors largely depends on the availability of resources. However, it is still unclear how the effects of neighborhood composition—including conspecific neighbor density and genetic and phylogenetic relatedness—on tree performance might vary across different levels of resources.
In a study published in Proceedings of the Royal Society B, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences (CAS) underscored the pivotal role of environmental and neighbourhood effects in shaping the growth of a dominant canopy species, Pometia pinnata, in tropical forest.
The researchers investigated how the growth of an ecologically dominant canopy tree species, Pometia pinnata, is influenced by density dependence, as well as the effects of within- and among-species relatedness in the neighbourhood, in a long-term study in the Nabanhe 20-ha tropical seasonal rainforest dynamics plot in Xishuangbanna, Yunnan, SW China.
The researchers specifically scrutinized the roles of various neighborhood types, such as species richness and tree size distribution, in addition to resource levels like light, water, and soil nutrients. They evaluated these factors on the growth rate and health status of the dominant canopy tree species while also investigating the potential interactions amongst these parameters.
The study revealed that the growth of the dominant trees was significantly influenced by environmental factors and the density of conspecific neighbors. It was observed that the inhibitory effect of conspecific neighbors on tree growth was amplified with increased levels of light and soil moisture availability.
Additionally, as the soil phosphorus content increased, the phylogenetic relatedness between heterospecific neighbors and the dominant trees transitioned from a positive to a negative impact on individual growth. Conversely, an increase in soil potassium content led to a shift from a negative to a positive genetic relatedness between conspecific neighbors and dominant trees, affecting the growth of the target individuals.
The study underscored the necessity of taking into account various abiotic environmental factors, the composition of both intra- and interspecific biotic neighbors, and their interactions, in order to fully understand the mechanisms driving tree growth.
"In the management and conservation of tropical forests, it is imperative to consider both neighborhood composition and resource levels” said LIN Luxiang, the corresponding author of the study.
First Published: 19 February 2025
