A new study published in Ecology Letters reveals that, as forests age, neighbourhood tree diversity increasingly alleviates competitive pressure on tree growth by enhancing niche differentiation among neighbouring trees.

Led by Prof. LIU Xiaojuan from the Institute of Botany, the Chinese Academy of Sciences (IBCAS), the researchers integrated 14 years of growth measurements from 15,877 individual trees across 516 plots from a large forest biodiversity experiment in southeast China.

According to the corresponding author Prof. LIU, "this study links community-level diversity to individual tree growth through neighbourhood interactions and reveals how competition and niche differentiation jointly shape tree growth and forest productivity over time".

The researchers found that neighbourhood species richness influenced individual tree growth through increasing neighbourhood basal area and niche difference. The effect of neighbourhood basal area shifted from positive to negative over time, indicating a transition from facilitation to competition among neighbouring trees. However, increasingly positive effects of niche difference between focal trees and their neighbours progressively offset this negative effect. As a result, neighbourhood species richness had a weak but overall positive effect on individual tree growth. In addition, focal trees with acquisitive traits responded more strongly to competition and niche differentiation. The positive effects of neighbourhood richness on growth were stronger in drier years.

This study shows that niche differentiation can counterbalance intensified competition in more diverse forests, helping maintain higher forest biomass. These findings provide a scientific basis for the development and restoration of climate-resilient forests.

Figure 1. Overview of the study experiment (BEF-China) and individual trees within experiment plots (Image by LI Shan & CHEN Chen)

Figure 2. Temporal dynamics of neighborhood diversity effects on tree growth (Image by YANG Zhuo)