Interactions between soil and other environmental variables modulate forest expansion and ecotone dynamics in humid savannas of Central Africa
2024
Sagang, Le, Bienfaiteur Takougoum | Tcheferi, Imma | Ploton, Pierre | Libalah, Moses | Simo-Droissart, Murielle | Sirri, Nelly | Dauby, Gilles | Ngansop, Eric | Bissek, Jean, Pierre | Kamdem, Narcisse | Mofack, Gislain, I I | Zebaze, Donatien | Leblanc, Hugo | Djonko, Fabrice | Sonké, Bonaventure | Barbier, Nicolas | Couteron, Pierre | University of California (UC) | University of Yaoundé 1 = Université de Yaoundé I | Institut de Recherche Agricole pour le Développement [Yaoundé] (IRAD) | Université de Yaoundé I (UY1) | Botanique et Modélisation de l'Architecture des Plantes et des Végétations (UMR AMAP) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [Occitanie])-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université de Montpellier (UM) | ANR-17-EGAS-0001,CEDERS,Capturing Effects of Diet on Emissions from Ruminant Systems(2017) | European Project: 3DForMod
International audience
Afficher plus [+] Moins [-]anglais. 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.
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