A recent study published in Nature, led by Prof. WANG Xugao from the Institute of Applied Ecology, Chinese Academy of Sciences, in collaboration with international researchers, proposes a new biological hypothesis by integrating tree dispersal modes and mycorrhizal types to explore the latitudinal variation in forest biodiversity maintenance processes.

Forest ecosystems are crucial for biodiversity conservation, with the highest levels of forest biodiversity found in tropical biomes and relatively lower levels in subtropical and temperate biomes. Understanding the mechanisms that stabilize biodiversity from temperate to subtropical forests is urgent yet challenging, given the importance of the latitudinal gradient of forest biodiversity for future conservation efforts.

To address this, the researchers collected data on 720 tree species from 21 large forest dynamics plots (ranging from 16 to 50 hectares) located across tropical, subtropical, and temperate biomes. Employing advanced spatial analysis methods alongside this extensive observational dataset, the researchers discovered that abundant species are less spatially aggregated than rare species, indicating a negative aggregation–abundance relationship. This relationship was found to be stronger in temperate forests than in tropical forests.

Through spatially explicit simulation models combined with functional trait information, the researchers further demonstrated that animal seed dispersal and mycorrhizal associations together explain the negative aggregation–abundance relationship, contributing to biodiversity maintenance from temperate to tropical forests.

In tropical forests, where the aggregation–abundance relationship is weak (i.e., abundant species have more conspecific neighbors than rare species), simulation results indicate that the spatial distribution of recruits away from their parents—primarily observed in animal-dispersed species—can stabilize species coexistence. In contrast, in temperate forests, characterized by a strong negative aggregation–abundance relationship (i.e., abundant species have a similar number of conspecific neighbors as rare species), the maintenance of community diversity heavily depends on ectomycorrhizal associations. Ectomycorrhizal fungi protect host plants from pathogens and contribute to the observed clustering of recruits near conspecific adults in temperate forests.

“These findings suggest a novel dispersal-mycorrhiza perspective for understanding global forest biodiversity maintenance and highlight the distinct roles that animals and fungi play in temperate and tropical forests,” said WANG Xugao, the corresponding author of this study. “Additionally, this research provides a unified framework of analytical models to assist ecologists in integrating spatial information into future biodiversity studies.”