Cocoa agroforestry is less resilient to sub-optimal and extreme climate than cocoa in full sun

Abdulai Issaka, Vaast Philippe, Hoffmann Munir P., Asare Richard, Jassogne Laurence, Van Asten Piet J.A., Rötter Reimund P., Graefe Sophie. 2018. Cocoa agroforestry is less resilient to sub-optimal and extreme climate than cocoa in full sun. Global Change Biology, 24 (1) : 273-286.

Quartile : Outlier, Sujet : BIODIVERSITY CONSERVATION / Quartile : Outlier, Sujet : ENVIRONMENTAL SCIENCES / Quartile : Outlier, Sujet : ECOLOGY

Résumé : Cocoa agroforestry is perceived as potential adaptation strategy to sub-optimal or adverse environmental conditions such as drought. We tested this strategy over wet, dry and extremely dry periods comparing cocoa in full sun with agroforestry systems: shaded by (i) a leguminous tree species, Albizia ferruginea and (ii) Antiaris toxicaria, the most common shade tree species in the region. We monitored micro-climate, sap flux density, throughfall, and soil water content from November 2014 to March 2016 at the forest-savannah transition zone of Ghana with climate and drought events during the study period serving as proxy for projected future climatic conditions in marginal cocoa cultivation areas of West Africa. Combined transpiration of cocoa and shade trees was significantly higher than cocoa in full sun during wet and dry periods. During wet period, transpiration rate of cocoa plants shaded by A. ferruginea was significantly lower than cocoa under A. toxicaria and full sun. During the extreme drought of 2015/16, all cocoa plants under A. ferruginea died. Cocoa plants under A. toxicaria suffered 77% mortality and massive stress with significantly reduced sap flux density of 115 g cm−2 day−1, whereas cocoa in full sun maintained higher sap flux density of 170 g cm−2 day−1. Moreover, cocoa sap flux recovery after the extreme drought was significantly higher in full sun (163 g cm−2 day−1) than under A. toxicaria (37 g cm−2 day−1). Soil water content in full sun was higher than in shaded systems suggesting that cocoa mortality in the shaded systems was linked to strong competition for soil water. The present results have major implications for cocoa cultivation under climate change. Promoting shade cocoa agroforestry as drought resilient system especially under climate change needs to be carefully reconsidered as shade tree species such as the recommended leguminous A. ferruginea constitute major risk to cocoa functioning under extended severe drought.

Mots-clés Agrovoc : agroforesterie, Theobroma cacao, besoin en eau, saison sèche, résistance à la sécheresse, arbre d'ombrage, compétition biologique, compétition végétale, évapotranspiration, Albizia, Antiaris, changement climatique

Mots-clés géographiques Agrovoc : Ghana, Afrique occidentale

Mots-clés complémentaires : Albizia ferruginea, Antiaris toxicaria

Classification Agris : F08 - Systèmes et modes de culture
K10 - Production forestière
F60 - Physiologie et biochimie végétale
P40 - Météorologie et climatologie

Champ stratégique Cirad : Axe 1 (2014-2018) - Agriculture écologiquement intensive

Auteurs et affiliations

• Abdulai Issaka, Georg-August University of Göttingen (DEU)
• Vaast Philippe, CIRAD-PERSYST-UMR Eco&Sols (FRA)
• Hoffmann Munir P., Georg-August University of Göttingen (DEU)
• Asare Richard, IITA (GHA)
• Jassogne Laurence, IITA (UGA)
• Van Asten Piet J.A., IITA (UGA)
• Rötter Reimund P., Georg-August University of Göttingen (DEU) - auteur correspondant
• Graefe Sophie, Georg-August University of Göttingen (DEU)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/587265/)

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