Carbon cycling in mature and regrowth forests globally

Abstract

Forests are major components of the global carbon (C) cycle and thereby strongly influence atmospheric carbon dioxide (CO₂) and climate. However, efforts to incorporate forests into climate models and CO₂ accounting frameworks have been constrained by a lack of accessible, global-scale synthesis on how C cycling varies across forest types and stand ages. Here, we draw from the Global Forest Carbon Database, ForC, to provide a macroscopic overview of C cycling in the world’s forests, giving special attention to stand age-related variation. Specifically, we use 11 923 ForC records for 34 C cycle variables from 865 geographic locations to characterize ensemble C budgets for four broad forest types—tropical broadleaf evergreen, temperate broadleaf, temperate conifer, and boreal. We calculate means and standard deviations for both mature and regrowth (age < 100 years) forests and quantify trends with stand age in regrowth forests for all variables with sufficient data. C cycling rates generally decreased from tropical to temperate to boreal in both mature and regrowth forests, whereas C stocks showed less directional variation. Mature forest net ecosystem production did not differ significantly among biomes. The majority of flux variables, together with most live biomass pools, increased significantly with the logarithm of stand age. As climate change accelerates, understanding and managing the carbon dynamics of forests is critical to forecasting, mitigation, and adaptation. This comprehensive and synthetic global overview of C stocks and fluxes across biomes and stand ages contributes to these efforts.