Increasing carbon storage in intact African tropical forests

Abstract

The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide^1,2. The role of tropical forests is critical because they are carbon-dense and highly productive^3,4. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades^5,6,7, but the response of one-third of the world’s tropical forests in Africa⁸ is largely unknown owing to an absence of spatially extensive observation networks^9,10. Here we report data from a ten-country network of long-term monitoring plots in African tropical forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha^-1 yr^-1 between 1968 and 2007 (95% confidence interval (CI), 0.22–0.94; mean interval, 1987–96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr^-1 (CI, 0.15–0.43). These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area^6,7, providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon. Indeed, combining all standardized inventory data from this study and from tropical America and Asia^5,6,11 together yields a comparable figure of 0.49 Mg C ha^-1 yr^-1 (n = 156; 562 ha; CI, 0.29–0.66; mean interval, 1987–97). This indicates a carbon sink of 1.3 Pg C yr^-1 (CI, 0.8–1.6) across all tropical forests during recent decades. Taxon-specific analyses of African inventory and other data¹² suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks¹³, as some theory¹⁴ and models^2,10,15 predict.