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Environmental filtering of dense-wooded species controls above-ground biomass stored in African moist forests

Authors

  • Sylvie Gourlet-Fleury,

    Corresponding author
    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
      Correspondence author. E-mail: sylvie.gourlet-fleury@cirad.fr
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  • Vivien Rossi,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Maxime Rejou-Mechain,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Vincent Freycon,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Adeline Fayolle,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Laurent Saint-André,

    1. UMR Eco&Sols, Ecologie Fonctionnelle & Biogéochimie des Sols & Agroécosystèmes, Montpellier SupAgro/CIRAD/INRA/IRD, 2 Place Viala, Bât 12, F-34060, Montpellier, France
    2. Inra, UR BEF, Biogéochimie des Ecosystèmes Forestiers, F-54280, Champenoux, France
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  • Guillaume Cornu,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Jean Gérard,

    1. UR Production et valorisation des bois tropicaux et méditerranéens, TA B-40, F-34398, Montpellier, France
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  • Jean-Michel Sarrailh,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Olivier Flores,

    1. UMR PVBMT, Université de la Réunion/CIRAD, 7 chemin de l’IRAT, F-97410, Saint-Pierre, France
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  • Fidèle Baya,

    1. MEFCP/ICRA, BP 830, Bangui, République centrafricaine
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  • Alain Billand,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Nicolas Fauvet,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Michel Gally,

    1. FRM, 60 Rue Henri Fabre, F-34130 Mauguio, France
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  • Matieu Henry,

    1. UMR Eco&Sols, Ecologie Fonctionnelle & Biogéochimie des Sols & Agroécosystèmes, Montpellier SupAgro/CIRAD/INRA/IRD, 2 Place Viala, Bât 12, F-34060, Montpellier, France
    2. GEEFT, AgroParisTech, F-34086, Montpellier, France
    3. Laboratorio di Ecologia Forestale, Università degli Studi della Tuscia, 01100 Viterbo, Italy
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  • Didier Hubert,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Alexandra Pasquier,

    1. Cirad, UR B&SEF, Biens et Services des Ecosystèmes Forestiers tropicaux, Campus International de Baillarguet, TA C-105/D, F-34398, Montpellier, France
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  • Nicolas Picard

    1. CIRAD, BP 4035, Libreville, Gabon
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Correspondence author. E-mail: sylvie.gourlet-fleury@cirad.fr

Summary

1. Regional above-ground biomass estimates for tropical moist forests remain highly inaccurate mostly because they are based on extrapolations from a few plots scattered across a limited range of soils and other environmental conditions. When such conditions impact biomass, the estimation is biased. The effect of soil types on biomass has especially yielded controversial results.

2. We investigated the relationship between above-ground biomass and soil type in undisturbed moist forests in the Central African Republic. We tested the effects of soil texture, as a surrogate for soil resources availability and physical constraints (soil depth and hydromorphy) on biomass. Forest inventory data were collected for trees ≥20 cm stem diameter in 2754 0.5 ha plots scattered over 4888 km2. The plots contained 224 taxons, of which 209 were identified to species. Soil types were characterized from a 1:1 000 000 scale soil map. Species-specific values for wood density were extracted from the CIRAD’s data base of wood technological properties.

3. We found that basal area and biomass differ in their responses to soil type, ranging from 17.8 m2 ha−1 (217.5 t ha−1) to 22.3 m2 ha−1 (273.3 t ha−1). While shallow and hydromorphic soils support forests with both low stem basal area and low biomass, forests on deep resource-poor soils are typically low in basal area but as high in biomass as forests on deep resource-rich soils. We demonstrated that the environmental filtering of slow growing dense-wooded species on resource-poor soils compensates for the low basal area, and we discuss whether this filtering effect is due to low fertility or to low water reserve.

4.Synthesis. We showed that soil physical conditions constrained the amount of biomass stored in tropical moist forests. Contrary to previous reports, our results suggest that biomass is similar on resource-poor and resource-rich soils. This finding highlights both the importance of taking into account soil characteristics and species wood density when trying to predict regional patterns of biomass. Our findings have implications for the evaluation of biomass stocks in tropical forests, in the context of the international negotiations on climate change.

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