Abiotic environmental factors and the composition of biotic neighbours collectively influence tree growth. The reaction of tree growth to the composition of these biotic neighbours largely depends on the availability of resources. However, it is still unclear how the effects of neighbourhood composition—including conspecific neighbour density and genetic and phylogenetic relatedness—on tree performance vary across different resource levels.

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.

In a long-term study in the Nabanhe 20-ha tropical seasonal rainforest dynamics plot in Xishuangbanna, Yunnan Province, researchers investigated how the growth of an ecologically dominant canopy tree species, Pometia pinnata, was influenced by the density dependence as well as the effects of within- and among-species relatedness in the neighbourhood.

They revealed that the growth of the dominant trees was significantly influenced by environmental factors and the density of conspecific neighbours. It was observed that the inhibitory effect of conspecific neighbours on tree growth was amplified with increased levels of light and soil moisture availability.

In addition, researchers found that the phylogenetic relatedness between the dominant trees and heterospecific neighbours transitioned from a positive to a negative impact on individual growth as the soil phosphorus content increased. Conversely, an increase in soil potassium content led to a shift from a negative to a positive genetic relatedness between and dominant trees and conspecific neighbours, affecting the growth of the target individuals.

The study highlights the necessity of taking into account various abiotic environmental factors, the composition of both intra- and interspecific biotic neighbours, 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 neighbourhood composition and resource levels,” said LIN Luxiang, the corresponding author of this study.