[en] Forest expansion into savanna is a pervasive phenomenon in West and Central Africa, warranting comparative studies under diverse environmental conditions. We collected vegetation data from the woody and grassy components within 73 plots of 0.16 ha distributed along a successional gradient from humid savanna to forest in Central Africa. We associated spatially collocated edaphic parameters and fire frequency derived from remote sensing to investigate their combined influence on the vegetation. Soil texture was more influential in shaping savanna structure and species distribution than soil fertility, with clay-rich soils promoting higher grass productivity and fire frequency. Savanna featuring woody aboveground biomass surpassing 40 Mg ha-1 could escape the grass-fire feedback loop, by depressing grass biomass below 4 Mg ha-1. This thicker woody layer also favoured the establishment of fire-tolerant forest pioneers, which synergically contributed to the expansion of forests. Conversely, savannas below this fire suppression threshold sustained a balance between trees and grasses through the grass-fire feedback mechanism. This hysteresis loop, particularly pronounced on clayey soils, suggests that the contrast between grassy savanna and young forests might represent alternative ecosystem states, although savannas with low woody biomass remained vulnerable to forest edge encroachment.
Sagang, Le Bienfaiteur Takougoum ; Institute of the Environment and Sustainability, University of California, Los Angeles, CA 90095, USA ; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon ; IRAD-Njombé Research Station, P.O. Box 13, Njombé, Cameroon
Tcheferi, Imma; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon
Ploton, Pierre; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon ; AMAP, Univ Montpellier, IRD, CNRS, INRAE, CIRAD, Montpellier 34394, France
Libalah, Moses; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon ; Department of Plant Biology, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
Simo-Droissart, Murielle; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon
Sirri, Nelly; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon
Dauby, Gilles; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon ; AMAP, Univ Montpellier, IRD, CNRS, INRAE, CIRAD, Montpellier 34394, France
Ngansop, Eric; IRAD-Njombé Research Station, P.O. Box 13, Njombé, Cameroon ; IRAD-National Herbarium of Cameroun, P.O. Box 1601, Yaoundé, Cameroon
Bissek, Jean Pierre; Ministry of Forestry and Wildlife, Mpem & Djim National Parc, P.O. Box 05, Ntui, Cameroon
Kamdem, Narcisse; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon
Mofack, Gislain I I; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon
Zebaze Dongmo, Donatien ; Université de Liège - ULiège > TERRA Research Centre ; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon
Leblanc, Hugo; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon ; AMAP, Univ Montpellier, IRD, CNRS, INRAE, CIRAD, Montpellier 34394, France
Djonko, Fabrice; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon
Sonké, Bonaventure; Department of Biology, Plant Systematics and Ecology Laboratory, Higher Teachers' Training College, University of Yaoundé I, P.O. Box 047, Yaoundé, Cameroon ; International Joint Laboratory DYCOFAC, IRD-UYI-IRGM, P.O Box 1857, Yaoundé, Cameroon
ANR - Agence Nationale de la Recherche NHPC - Nachtigal Hydro Power Company
Funding text :
This work was financially supported by the Nachtigal Hydropower Company (NHPC, Contract no. C006C007-DES-2017) under the
environmental impact study associated to the construction of a hydroelectric dam on the Sanaga river in the center region of Cameroon.This
study is also part of the 3DForMod project (ANR-17-EGAS-0002-01) funded by the framework of the JPI FACCE ERA-GAS call under the
European Union’s Horizon 2020 research and innovation program (grant agreement no. 696356). L.B.T.S. benefited from the 'Allocations de
recherche pour une thèse au Sud (ARTS)' grant programme to fund research stays in France.
