Spatial-temporal dependence of the neighborhood interaction in regulating tree growth in a tropical rainforest

The intensity of interactions among tree individuals in forests is regulated by distance and time. However, few studies have considered the variability of neighborhood competition with varying spatial and temporal scales simultaneously. Based on census data of a 50-ha plot on Barro Colorado Island (BCI) during 1981–2015, we analyzed the variation in the relationship between the neighborhood interaction, represented as the neighborhood competition index (NCI), and the tree growth rate of 41,965 individuals from 211 species along a gradient of the neighborhood radius and over time. The results showed that the neighborhood interaction negatively impacted tree growth, especially for smaller trees, across spatial and temporal scales. The strength of the NCI–growth relationship was scale- and time-dependent. This relationship intensified initially with the increasing neighborhood radius and then plateaued at an average of about 20 m from the target trees, indicating the strong influence from neighbors could be detected at a distance up to 50 m or even 100 m. The intensifying tendency of the NCI–growth relationship over time probably results from the warming trend in recent years or the continuous radial growth of the BCI forest. We emphasize the importance of individual interactions in dynamic forest growth, and that an appropriate radius and forest age should be considered for the neighborhood analysis.