Central African Republic; competition indices; Democratic Republic of the Congo; distance-dependent tree growth models; Republic of Congo; soil nutrients; wood density; Ecology, Evolution, Behavior and Systematics; Ecology; Plant Science
Abstract :
[en] Identifying and quantifying factors that influence tree growth are crucial issues to ensure sustainable forest management, particularly in moist tropical forests. Tree growth depends on several factors comprising ontogenic stage, competition by neighbours and environmental conditions. Several studies have focused on one or two of them, but very few have considered all three, especially in Central Africa. We investigated the effects of diameter and competition on tree growth, in four Central African sites characterized by their soil physicochemical properties, at both tree community and population levels. We calibrated growth models using diameter data collected on 29,741 trees between 2015 and 2018, on twelve 4 or 9-ha plots spread over the four sites. These models included diameter, wood density, competition indices and site effect as explainable variables at the community level and excluded wood density at the population level. At the community level, the best models explained 11% of growth variability with a decreasing effect of species wood density, diameter, site and competition. Our results show that even if low, site effect can result from different soil nutrients depending on both tree size and species wood density. We observed higher tree growth on sites with (i) high exchangeable K, organic C, total N and total P for low wood density species; (ii) high available P and C:N for small trees, high exchangeable Ca and Mg for medium to large trees, all belonging to medium and hard wood density species. At the population level, the best models explained between 0 to 43% of growth variability, with significant competition effect (resp. site effect) for 21 (resp. 9) of the 43 species studied. Site ranking varied greatly between the 9 species concerned, probably reflecting different sensitivities to the scarcity of particular soil nutrients. Synthesis. Our study provides original results on the factors influencing tree growth in Central Africa, showing that the potential effect of soil nutrients depends on tree size and species wood density. Remaining highly unpredictable at the population level, this effect makes it essential to increase the number of dynamics monitoring systems in logging concessions.
Gourlet-Fleury, Sylvie ; Forêts et Sociétés, Université de Montpellier, Cirad Montpellier, France ; Cirad Forêts et Sociétés, Montpellier, France
Rossi, Vivien ; Cirad Forêts et Sociétés, Montpellier, France ; Cirad Forêts et Sociétés, Yaoundé, Cameroon ; Plant Systematic and Ecology Laboratory (LaBosystE), Department of Biology, Higher Teachs' Training College, University of Yaoundé I, Yaoundé, Cameroon
Forni, Eric; Forêts et Sociétés, Université de Montpellier, Cirad Montpellier, France ; Cirad Forêts et Sociétés, Montpellier, France
Fayolle, Adeline ; Université de Liège - ULiège > TERRA Research Centre > Gestion des ressources forestières
Ligot, Gauthier ; Université de Liège - ULiège > TERRA Research Centre > Gestion des ressources forestières
Allah-Barem, Félix; Institut Centrafricain de la Recherche Agronomique, Bangui, Central African Republic
Baya, Fidèle; Institut Centrafricain de la Recherche Agronomique, Bangui, Central African Republic
Bénédet, Fabrice; Forêts et Sociétés, Université de Montpellier, Cirad Montpellier, France ; Cirad Forêts et Sociétés, Montpellier, France
Boyemba, Faustin; Laboratoire d'Ecologie et Aménagement Forestier Durable (LECAFOR), Université de Kisangani, Kisangani, Democratic Republic Congo
Cornu, Guillaume ; Forêts et Sociétés, Université de Montpellier, Cirad Montpellier, France ; Cirad Forêts et Sociétés, Montpellier, France
Doucet, Jean-Louis ; Université de Liège - ULiège > TERRA Research Centre > Gestion des ressources forestières
Gillet, Jean-François ; Université de Liège - ULiège > Département GxABT > Gestion des ressources forestières ; Nature Forest Environment, Porcheresse/Daverdisse, Belgium
Mazengue, Mathurin; Mokabi SA, Impfondo, Democratic Republic Congo
Mbasi Mbula, Michel; Laboratoire d'Ecologie et Aménagement Forestier Durable (LECAFOR), Université de Kisangani, Kisangani, Democratic Republic Congo ; Institut Supérieur d'Etudes Agronomiques de Bengamisa (ISEA-Bengamisa), Bengamisa, Democratic Republic Congo
Van Hoef, Yorick; Forêts et Sociétés, Université de Montpellier, Cirad Montpellier, France ; Cirad Forêts et Sociétés, Montpellier, France
AFD - Agence Française de Développement [FR] FFEM - Fonds Français pour l'Environnement Mondial [FR]
Funding text :
This work was supported by FFEM (« Fonds Français pour l'Environnement Mondial ») and AFD (‘Agence Française de Développement’), DynAfFor Project, convention CZZ1636.01D and CZZ1636.02D, and the P3FAC Project, convention CZZ 2101.01 R). We thank the ARF Project and its seven partners: AFD, CIRAD, ICRA, SCAC/MAE, University of Bangui and the logging company SCAD for providing access to the M'Baïki site and to its database; the logging companies CIB‐Olam and Mokabi SA (Rougier Group) for their logistical organization, which enabled the settlement and monitoring of the Loundoungou and Mokabi sites in the best conditions; and the University of Kisangani and the R&SD project which, under both UE and FFEM fundings, settled and monitored the Yoko site. We would also like to thank all the members of the field teams who spared no effort to carry out the work with seriousness and good humour. We have a special thought for one of them, Issa Mogbaya, who died during the work period. We thank Jacques Beauchene and Kevin Candelier for sharing their expertise on the properties of tropical woods. Finally, we would like to express our gratitude to anonymous reviewers for their valuable comments.
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