Competition explains tropical tree species coexistence and abundance

Abstract The numerous tree species co-occurring in tropical forests presents a challenging puzzle1. Conventional competition models suggest that such coexistence is improbable2–7, but this study offers a novel solution. By modelling interspecific competition as both competitive intensity and susceptibility, we provide conditions for stable coexistence of multiple species8. We test how well our model captures the aboveground biomass dynamics of a Malaysian rainforest tree community. We use estimated leaf biomass per species as a proxy for competitive intensity and derive model parameters from repeated measurements. Our model predicts that 370 out of the 486 tree species assessed coexist stably. This coexistence hinges on that the species’ susceptibility to conspecific competitive intensity, which we refer to as the conspecific negative biomass dependence (CNBD), is greater than their susceptibility to heterospecific competitive intensity. The modelled equilibrium biomass of the forest, and that of most species, align closely with empirical observations, suggesting the reliability of our approximations. Notably, strong CNBD corresponds to the decline of relative tree growth rates as tree size increases. Our study provides an unexpectedly simple and coherent explanation for the stable coexistence of numerous tree species, resolves the long-standing diversity-stability paradox, and challenges previous interpretations of competitive coexistence.