Density dependence of tree growth varies with temperature gradient and mycorrhizal type

Abstract Conspecific negative density dependence (CNDD) plays a key role in maintaining species coexistence and theoretically contributes to large‐scale diversity patterns. However, the effect of CNDD on large‐scale tree diversity patterns remains debated, particularly for long‐lived tree species. In this study, we collected decadal dynamic tree growth data from 50 forest plots across eastern China. We evaluated density‐dependent tree growth responses to conspecific versus heterospecific neighbours along the temperature gradient. Specifically, we compared the stabilizing CNDD effect that was calculated as the difference between conspecific and heterospecific density effects on tree growth between arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) tree species. Our results revealed that the strength of both CNDD and stabilizing CNDD in AM tree species became more negative with increasing temperature, while remaining constant in EM tree species along the temperature gradient. The observed CNDD patterns correspond well with climatic patterns of local tree species richness, where the increase in species richness along the temperature gradient is mainly attributed to AM tree species. Furthermore, we found stronger conspecific limitation on tree growth in AM trees compared to EM trees in warm forests. Synthesis. Our results support a close link between the strength of CNDD and local tree species richness patterns along the temperature gradient. These findings highlight the critical role of mycorrhizal symbiosis in mediating CNDD processes and shaping large‐scale tree diversity patterns.