Carbon stocks in central African forests enhanced by elephant disturbance

Abstract

Large herbivores, such as elephants, can have important effects on ecosystems and biogeochemical cycles. Yet, the influence of elephants on the structure, productivity and carbon stocks in Africa’s rainforests remain largely unknown. Here, we quantify those effects by incorporating elephant disturbance in the Ecosystem Demography model, and verify the modelled effects by comparing them with forest inventory data from two lowland primary forests in Africa. We find that the reduction of forest stem density due to the presence of elephants leads to changes in the competition for light, water and space among trees. These changes favour the emergence of fewer and larger trees with higher wood density. Such a shift in African’s rainforest structure and species composition increases the long-term equilibrium of aboveground biomass. The shift also reduces the forest net primary productivity, given the trade-off between productivity and wood density. At a typical density of 0.5 to 1 animals per km2, elephant disturbances increase aboveground biomass by 26–60 t ha−1. Conversely, the extinction of forest elephants would result in a 7% decrease in the aboveground biomass in central African rainforests. These modelled results are confirmed by field inventory data. We speculate that the presence of forest elephants may have shaped the structure of Africa’s rainforests, which probably plays an important role in differentiating them from Amazonian rainforests.

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Fig. 1: Simulated stand-scale AGB and NPP in response to different elephant population densities in the Congo Basin.
Fig. 2: Stand-scale effect of elephant disturbance.
Fig. 3: Summary of the regional effect of elephant disturbance on AGB.

Data availability

Forest data are available for NF upon request to S.B. and for LK at www.forestplots.net. Central Africa forest data are available in the supplementary material of Lewis et al.12 and Slik et al.49 and in the main text of Poulsen et. al.48.

Code availability

The ED2 model code is available at https://github.com/fabeit/ED2/tree/master/ED/src.

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Acknowledgements

We would like to thank D. Papale, M. Zapparoli, L. Portoghesi, M. di Porcia e Brugnera, and H. Verbeeck for feedback that helped improve the manuscript. We thank the contributors to the AfriTRON network for making their data publicly available, J. Poulsen, G. van der Heijden and the TEAM Network in particular. We thank the Institut Congolais pour la Conservation de la Nature for granting permission to conduct research at LuiKotale, and Lompole villagers for granting permission to access the forest of their ancestors. We thank the government of the Republic of Congo for permission to study elephant ecology in the Ndoki forest and the Wildlife Conservation Society for invaluable support in the field. F.Berzaghi was funded by the CEA Enhanced Eurotalents Fellowship (a Marie Sklodowska-Curie Actions Programme) and the University of Tuscia doctoral programme. We thank the Centre de Calcul et Messageries, Pôle des Systèmes d’Information et des Usages du Numérique Université de Bourgogne for the assistance with and use of their cluster. Research at LuiKotale was supported by the Max-Planck-Society, the German Ministry of Education and Research and le Conseil Regional de Bourgogne. We thank the African Elephant Program of the United States Fish and Wildlife Service for supporting data collection in the Ndoki Forest and USAID for funding.

Author information

F. Berzaghi and C.E.D. conceived the study and S.V., M.L. and M.S. helped refine the design. F. Berzaghi led the writing with inputs from all co-authors. F. Berzaghi and M.L. developed the ED2 model. F. Berzaghi analysed data and created figures with inputs from P.C., C.E.D. and S.B.

Correspondence to Fabio Berzaghi.

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Supplementary descriptions, Supplementary Figs. 1–7 and Supplementary Tables 1–3.

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