Carbon-focused climate mitigation strategies are becoming increasingly important in forests. However, with ongoing biodiversity declines, we require better knowledge of how much such strategies account for biodiversity. We particularly lack information across multiple trophic levels and on established forests, where the interplay between carbon stocks, stand age and tree diversity might influence carbon–biodiversity relationships. Using a large dataset (>4,000 heterotrophic species of 23 taxonomic groups) from secondary, subtropical forests, we tested how multitrophic diversity and diversity within trophic groups relate to aboveground, belowground, and total carbon stocks at different levels of tree species richness and stand age. Our study revealed that aboveground carbon, the key component of climate-based management, was largely unrelated to multitrophic diversity. By contrast, total carbon stocks—i.e. including belowground carbon—emerged as a significant predictor of multitrophic diversity. Relationships were non-linear and strongest for lower trophic levels, but non-significant for higher trophic level diversity. Tree species richness and stand age moderated these relationships, suggesting long-term regeneration of forests may be particularly effective in reconciling carbon and biodiversity targets. Our findings highlight that the biodiversity benefits of climate-oriented management need to be evaluated carefully, and only maximizing aboveground carbon may fail to account for biodiversity conservation requirements.

Full details on measurements and estimation methods for all carbon components are provided in Liu et al. (2018). We used tree species richness and woody plant diversity as key predictors of heterotrophic biodiversity and carbon stocks. Woody plant diversity was completely inventoried in 2008 quantified as the number of tree and shrub species > 1 m height per plot. We assessed heterotrophic biodiversity for seven groups of organisms that aggregated data for a total of 23 taxa of aboveground arthropods, soil fungi, and bacteria. The sampling of heterotrophs was conducted between 2008 and 2012 with a set of methods that cover the wide range of habitat use and activity patterns of arthropods and microorganisms and that were best suited to assess the focal taxa. Further information is provided in Schuldt et al. (2015) Nature Communications. Carbon stocks were quantified for aboveground, forest-floor, and belowground carbon in Mg C ha-¹. Full details on measurements and estimation methods for all carbon components are provided in Liu et al. (2018) Proceedings B.