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Aim and hypothesis This study aims to disentangle the direct and indirect roles of space, climate, edaphic, and biodiversity effects on aboveground biomass in natural tropical forests, thereby evaluating the relative effects and contribution of abiotic and biotic factors on aboveground biomass. We hypothesized that the space effect drives the longitudinal, latitudinal, and elevational patterns in climatic and edaphic factors, thereby directly and indirectly determining the relationships between biodiversity and aboveground biomass in natural tropical forests. Methods We used structural equation modelling for linking spatial, climatic, edaphic, and biotic factors of aboveground biomass, using data from 247,691 trees across 907 tropical forest plots (total sampling area of 145.23 ha) of Hainan Island in Southern China. Results Aboveground biomass increased directly with functional dominance, individual tree size inequality, and climatic water availability but decreased directly with space and edaphic effects. However, space effect increased aboveground biomass indirectly via simultaneously differential direct changes (positive, negative, and non-significant) in climatic, edaphic, and biotic factors. As such, indirect effects of mean annual temperature and climatic water availability decreased aboveground biomass through differential direct changes in biotic factors, but opposite was true for soil fertility. Conclusions We argue that, despite the high relative contribution of biodiversity to aboveground biomass, the direct and indirect roles of space, climatic, and edaphic effects are also important for explaining biotic factors and aboveground biomass under the predictions of several abiotic-based hypotheses. Hence, conserving biodiversity across space is important for forest management and land development under climate change.