Net primary productivity and carbon allocation along secondary succession in a central African tropical forest

Carbon (C) uptake in regrowing secondary forests increasingly dominates landscape-scale C dynamics in the tropics. Understanding the recovery trajectories of net primary productivity (NPP) and C allocation, along with the underlying demographic and functional drivers of biomass recovery, is therefore critical. Using a space-for-time setup spanning five successional stages, we showed that - for forests in the Yoko reserve, in central Africa - C fluxes related to recruitment and mortality decreased along succession, alongside a gradual transition from a forest with high stem density and acquisitive species to one with lower stem density and more conservative species. In the first decade of succession, NPP allocation shifted from being dominated by woody productivity to canopy productivity. Higher tree mortality in early succession counterbalanced the higher woody NPP, producing a relatively constant net woody C sink along succession. While being positive, this woody C sink was small, suggesting a slow but steady recovery to old-growth aboveground C stocks ranging between 171 and 238 Mg C ha^-1. Overall, our findings demonstrate the potential of secondary forests in the Congo basin to mitigate climate change, but also emphasize the need to conserve old-growth forest C stocks and expand long-term observational data to better constrain regional C recovery dynamics.