Associations between mycorrhizal dominance and woody species diversity shift with stand development and climate across subtropical and tropical forests in Taiwan

Abstract

Mycorrhizal symbioses influence woody species diversity, but whether this association shifts with forest stand development remains underexplored. Using forest inventory data across subtropical and tropical forests in Taiwan, we found that woody species diversity was lower in ectomycorrhizal (EM)-dominated than in arbuscular mycorrhizal (AM)-dominated forests, while forests with mixed mycorrhizal strategies supported the highest woody species diversity. However, these associations were strongest in early development stands and tended to converge towards high diversity in late development stands despite differences in mycorrhizal dominance. These results are consistent with stronger conspecific negative density dependence in AM-dominated forests and niche partitioning among mycorrhizal strategies at early developmental stages, while alternative recruitment dynamics associated with AM- and EM-dominated canopies may promote high woody species diversity at late developmental stages. Climate modulated these patterns, with the negative association between EM dominance and woody species diversity strongest in cold regions, while the diversity peak in mixed AM–EM forests was most pronounced in median climates and diminished towards warm and cold climates. In addition, woody species evenness was more consistently highest in forests with mixed mycorrhizal strategies across stand development stages compared to woody species richness, suggesting that mycorrhizal coexistence promotes more equal species abundances. These findings highlight that associations between mycorrhizal strategies and woody species diversity depend on forest developmental stage, underpinning new understanding of subtropical and tropical forest recovery under global change.