Integrated effects of neighborhood composition and resource levels on growth of a dominant tree species in a tropical forest

Abiotic environments and biotic neighborhoods interact to influence plant growth and community assembly. However, the nature of this interaction depends very much on how biotic neighborhoods are measured, including their relatedness to focal plants. In a tropical seasonal rainforest, we examine the growth of a dominant canopy species in response to environmental factors, the densities and relatedness of conspecific and heterospecific neighbors, and their interactions. We find significant environmental effects and conspecific negative density dependence on growth. Furthermore, conspecific neighbor density has stronger negative effects on growth under high light and soil water resource levels, but weaker negative effects under low light and soil water resource levels. In addition, more closely related heterospecifics in the neighborhood have negative effects on growth under high soil phosphorus availability, but positive effects under low soil phosphorus availability. In contrast, more closely related conspecifics in the neighborhood have negative effects on growth under low soil potassium availability, but positive effects under high soil potassium availability. Our study emphasizes the importance of both intra- and inter-specific neighborhood composition and their interactions with resource levels for understanding tree growth. This enhances our understanding of the complex processes in community assembly and species coexistence within forest communities.