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The persistence of carbon in the African forest understory

Nature Plants 5, 133–140 (2019) | Download Citation

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Abstract

Quantifying carbon dynamics in forests is critical for understanding their role in long-term climate regulation1,2,3,4. Yet little is known about tree longevity in tropical forests3,5,6,7,8, a factor that is vital for estimating carbon persistence3,4. Here we calculate mean carbon age (the period that carbon is fixed in trees7) in different strata of African tropical forests using (1) growth-ring records with a unique timestamp accurately demarcating 66 years of growth in one site and (2) measurements of diameter increments from the African Tropical Rainforest Observation Network (23 sites). We find that in spite of their much smaller size, in understory trees mean carbon age (74 years) is greater than in sub-canopy (54 years) and canopy (57 years) trees and similar to carbon age in emergent trees (66 years). The remarkable carbon longevity in the understory results from slow and aperiodic growth as an adaptation to limited resource availability9,10,11. Our analysis also reveals that while the understory represents a small share (11%) of the carbon stock12,13, it contributes disproportionally to the forest carbon sink (20%). We conclude that accounting for the diversity of carbon age and carbon sequestration among different forest strata is critical for effective conservation management14,15,16 and for accurate modelling of carbon cycling4.

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Data availability

The input data and R-scripts to generate the figures and tables are available for download using the following private link: https://figshare.com/s/06c793575d3b52ef5574. Images of wood cores are available using the following link: https://figshare.com/s/e6101fe7d330f8ea140a. This folder also contains all annotation documents needed to visualize growth ring boundaries on the wood samples (please consult the README document for guidelines). Wood samples used to conduct this analysis are stored in the Tervuren xylarium (http://www.africamuseum.be/collections/browsecollections/naturalsciences/earth/xylarium). These samples may be studied, within the Tervuren xylarium, on request addressed to the curator H.B. (hans.beeckman@africamuseum.be) or the corresponding author W.H. (whubau@gmail.com).

Additional information

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                            Acknowledgements

                            Nkulapark: W.H. and T.D.M. were both funded by the Brain programme of the Belgian Federal Government (BR/132/A1/AFRIFORD and BR/143/A3/HERBAXYLAREDD). The PhD project of T.D.M and the tenure track of J.V.d.B. were supported by Ghent University Special Research Fund (BOF). Fieldwork was sponsored by the King Leopold III fund for nature exploration and conservation. B.A.I. is supported by the Institut National pour l’Étude et la Recherche Agronomiques en R.D.Congo (INERA- RDC- Luki) and the École Régionale Postuniversitaire d’Aménagement et de Gestion intégrés des Forêts et Territoires tropicaux (ERAIFT Kinshasa). We thank WWF-RDC (G. Lejeune), INERA and ERAIFT for facilitating fieldwork in the Luki Reserve. We thank the INERA employees (J.-B. Ndunga, J.-M., F. Mbungu Phaka, L. Ngoma, P. Noble), the WWF ecoguards and the students of the Universities of Kinshasa (UNIKIN) and Boma for assistance in the field. For assistance with datasets we thank M. De Groot, K. Lievens, P. Dekeyser, S. Willen and J. Kempenaers. The 23 permanent inventory plots: This paper is also a product of the AfriTRON network, for which we are indebted to hundreds of institutions, field assistants and local communities for establishing and maintaining the plots. This network has been supported by the European Research Council (291585, ‘T-FORCES’ – Tropical Forests in the Changing Earth System, Advanced Grant to O.L.P. and S.L.L.), the Gordon and Betty Moore Foundation, the David and Lucile Packard Foundation, the European Union’s Seventh Framework Programme (no. 283080, ‘GEOCARBON’) and Natural Environment Research Council (NERC) Consortium Grant ‘TROBIT’ (no. NE/D005590/1), ‘BIO-RED’ (no. NE/N012542/1) and a NERC New Investigators Grant, the Royal Society, the Centre for International Forestry (CIFOR) and Gabon’s National Parks Agency (ANPN). We are indebted to the University of Yaounde I, the National Herbarium of Yaounde, Rougier-Gabon, the Marien Ngouabi University of Brazzaville, WCS-Congo, Salonga National Park, WCS-D.R.Congo and the University of Kisangani for logistical support in Africa.

                            Author information

                            1. These authors contributed equally: W. Hubau, T. De Mil.

                            Affiliations

                            1. Service of Wood Biology, Royal Museum for Central Africa, Tervuren, Belgium

                              • Wannes Hubau
                              • , Tom De Mil
                              • , Bhély Angoboy Ilondea
                              • , Laurent Nsenga
                              • , Benjamin Toirambe
                              • , Camille Couralet
                              • , Nils Bourland
                              • , Sofie Dierickx
                              • , Emmanuel Kasongo Yakusu
                              • , Mélissa Rousseau
                              • , John Tshibamba Mukendi
                              •  & Hans Beeckman

                            2. UGent-Woodlab, Laboratory of Wood Technology, Department of Environment, Ghent University, Ghent, Belgium

                              • Wannes Hubau
                              • , Tom De Mil
                              • , Jan Van den Bulcke
                              • , Joris Van Acker
                              • , Victor Deklerck
                              •  & Emmanuel Kasongo Yakusu

                            3. School of Geography, University of Leeds, Leeds, UK

                              • Wannes Hubau
                              • , Oliver L. Phillips
                              • , Martin J. P. Sullivan
                              • , Serge K. Begne
                              • , Timothy R. Baker
                              • , Martin Gilpin
                              • , Gabriela Lopez-Gonzalez
                              • , Georgia Pickavance
                              • , Joey Talbot
                              •  & Simon L. Lewis

                            4. Centre for X-ray Tomography , Ghent University, Ghent, Belgium

                              • Jan Van den Bulcke
                              • , Joris Van Acker
                              •  & Victor Deklerck

                            5. Institut National pour l’Étude et la Recherche Agronomique, Kinshasa, Democratic Republic of the Congo

                              • Bhély Angoboy Ilondea

                            6. École Régionale Postuniversitaire d’Aménagement et de Gestion intégrés des Forêts et Territoires tropicaux , Kinshasa, Democratic Republic of the Congo

                              • Bhély Angoboy Ilondea

                            7. Centre for Ecology and Hydrology, Penicuik, UK

                              • Lindsay F. Banin

                            8. Plant Systematic and Ecology Laboratory, Higher Teachers’ Training College, University of Yaounde, Yaounde, Cameroon

                              • Serge K. Begne
                              • , Marie-Noel D. Kamdem
                              • , Bonaventure Sonké
                              • , Hermann Taedoumg
                              •  & Lise Zemagho

                            9. CIFOR, Bogor, Indonesia

                              • Nils Bourland
                              •  & Terry Sunderland

                            10. Forest Resources Management, Gembloux Agro-Bio Tech, University of Liège, Liège, Belgium

                              • Nils Bourland
                              •  & Jean-Louis Doucet

                            11. Resources and Synergies Development, Singapore, Singapore

                              • Nils Bourland
                              •  & Mélissa Rousseau

                            12. Rougier-Gabon, Libreville, Gabon

                              • Eric Chezeaux

                            13. Nicholas School of the Environment, Duke University, Durham, NC, USA

                              • Connie J. Clark
                              •  & John R. Poulsen

                            14. Grantham Research Institute on Climate Change and the Environment, London, UK

                              • Murray Collins

                            15. Inventory and Monitoring Program, National Park Service, Fredericksburg, VA, USA

                              • James A. Comiskey

                            16. Smithsonian Institution, Washington, DC, USA

                              • James A. Comiskey

                            17. Department of Geography, University College London, London, UK

                              • Aida Cuni-Sanchez
                              •  & Simon L. Lewis

                            18. Department of Geography and Environment, University of York, York, UK

                              • Aida Cuni-Sanchez

                            19. Wildlife Conservation Society-DR Congo, Kinshasa I, Democratic Republic of the Congo

                              • Corneille E. N. Ewango
                              • , Jean-Remy Makana
                              •  & Jacques Mukinzi

                            20. Centre de Formation et de Recherche en Conservation Forestière , Epulu, Democratic Republic of the Congo

                              • Corneille E. N. Ewango

                            21. Faculté de Gestion de Ressources Naturelles Renouvelables, Université de Kisangani, Kisangani, Democratic Republic of the Congo

                              • Corneille E. N. Ewango
                              • , Emmanuel Kasongo Yakusu
                              • , Faustin M. Mbayu
                              •  & John Tshibamba Mukendi

                            22. Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, UK

                              • Ted R. Feldpausch

                            23. National Herbarium, Yaounde, Cameroon

                              • Christelle Gonmadje

                            24. ForestGEO, Smithsonian Tropical Research Institute, Panamá, Republic of Panama

                              • Jefferson S. Hall

                            25. Royal Botanic Garden Edinburgh, Edinburgh, UK

                              • David J. Harris

                            26. Service d’Évolution Biologique et écologie, Faculté des Sciences, Université Libre de Bruxelles, Brussels, Belgium

                              • Olivier J. Hardy
                              •  & Jason Vleminckx

                            27. Faculty of Science, Department of Botany and Plant Physiology, University of Buea, Buea, Cameroon

                              • Marie-Noel D. Kamdem

                            28. Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK

                              • Yadvinder Malhi
                              •  & Sam Moore

                            29. Salonga National Park, Kinshasa I, Democratic Republic of the Congo

                              • Jacques Mukinzi

                            30. Bureau Waardenburg, Culemborg, the Netherlands

                              • Jan Reitsma

                            31. Faculty of Forestry, University of British Columbia, Vancouver, Canada

                              • Terry Sunderland

                            32. Faculté des Sciences Appliquées, Université de Mbujimayi, Mbujimayi, Democratic Republic of the Congo

                              • John Tshibamba Mukendi

                            33. Yale School of Forestry and Environmental Studies, New Haven, CT, USA

                              • Peter M. Umunay

                            34. Department of Biological Sciences, Florida International University, Miami, FL, USA

                              • Jason Vleminckx

                            35. Agence Nationale des Parcs Nationaux, Libreville, Gabon

                              • Lee J. T. White

                            36. Institut de Recherche en Écologie Tropicale, Libreville, Gabon

                              • Lee J. T. White

                            37. School of Natural Sciences, University of Stirling, Stirling, UK

                              • Lee J. T. White

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                            Contributions

                            W.H., T.D.M., J.V.d.B., J.V.A. and H.B. conceived and designed the Nkulapark study and S.L.L. conceived the AfriTRON plot network. T.D.M. and B.A.I. coordinated collection of Nkulapark data and wood cores. T.D.M. and J.V.d.B. measured growth ring series. W.H. carried out the data analysis and wrote the paper. S.L.L., O.L.P., T.R.B. and Y.M. conceived the ForestPlots.net database, and most co-authors helped collecting AfriTRON forest census data. S.L.L., B.S., S.K.B., A.C.S., W.H., T.S., T.R.F., T.S., C.E.N.E. and L.W.W. coordinated forest plots data collection. M.J.P.S., G.L.G., S.L.L., O.L.P., T.R.B. and G.P. contributed tools to analyse and curate data. All co-authors commented on or approved the manuscript.

                            Competing interests

                            The authors declare no competing interests.

                            Corresponding author

                            Correspondence to Wannes Hubau.

                            Supplementary information

                            1. Supplementary Information

                              Supplementary Figures 1–4

                            2. Reporting Summary

                            3. Supplementary Table 1

                              Number of growth rings, growth-ring formation rate, tree age and mean carbon age of all 55 Nkulapark trees with 1,948 nail traces used for this analysis

                            4. Supplementary Table 2

                              List of all 23 plots included in this analysis, with geographic coordinates, plot size, dates of first and last census, and the main researchers for each plot

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                            DOI

                            https://doi.org/10.1038/s41477-018-0316-5