The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide1,2. The role of tropical forests is critical because they are carbon-dense and highly productive3,4. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades5,6,7, 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 networks9,10. 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 area6,7, 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 Asia5,6,11 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 models2,10,15 predict.
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We thank the villagers from Oban (Nigeria), Prince Town, Baneekurom and Dadieso (Ghana), Somolomo, Mekas, Lomie and Alat Makay (Cameroon) and Ekobakoba (Gabon) for hosting our fieldwork, and A. Moungazi, S. Mbadinga, H. Bourobou, L. N. Banak, T. Nzebi, K. Jeffery, SEGC/CIRMF/WCS Research Station Lopé, K. Ntim, K. Opoku, Forestry Commission of Ghana, T. Tafoek, Federal University of Agriculture, Abeokuta, Nigeria, ECOFAC-Cameroon, Cameroon Ministry Scientific Research and Innovation, Cameroon Ministry of Forests and Fauna (MINFOF), Forest Development Authority (Liberia), S. Grahame, R. Lowe, L. Banin and K. C. Nguembou for field assistance and logistical support. We thank R. Condit for helping access the Edoro and Lenda data sets, C. Chatelain for providing data from the African Flowering Plants database to standardize our species identifications, J. Chave for providing allometric data, L. Poorter for providing gap size-frequency data, B. Nelson for providing large-scale blow-down data, D. Appleyard for assistance with the plot map, and the Network for Vegetation Function (Nation Evolutionary Synthesis Center and ARC-NZ) for providing some wood mass density data. This work was supported by the Royal Society and the Natural Environment Research Council (UK).
Author Contributions S.L.L., O.L.P. and Y.M. conceived the experiment. S.L.L. designed the experiment. All authors except T.R.B., M.G., G.L-G., Y.M. and J.P. contributed materials. S.L.L., T.R.B., M.G., G.L-G. O.L.P. and J.P. provided analysis tools. S.L.L., G.L-G. and M.G analysed data. S.L.L. wrote the paper. All authors commented on the analysis and presentation of the data.
This file contains Supplementary Notes, Supplementary Tables S1- S5, Supplementary Figures S1-S16 with Legends and Supplementary References