Tropical Plant Production and Agricultural Systems Modelling (TROPAGS), University of Goettingen, Göttingen, Germany.
UMR Eco&Sols, Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), Montpellier, France.
Glob Chang Biol. 2018 Jan;24(1):273-286. doi: 10.1111/gcb.13885. Epub 2017 Sep 28.
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 day , whereas cocoa in full sun maintained higher sap flux density of 170 g cm day . Moreover, cocoa sap flux recovery after the extreme drought was significantly higher in full sun (163 g cm day ) than under A. toxicaria (37 g cm day ). 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.
可可农林业被认为是适应不利环境条件（如干旱）的潜在策略。我们在湿润、干燥和极干燥期进行了这项策略的测试，将全日照下的可可与农林系统进行了比较：（i）由豆科 Albizia ferruginea 和（ii）该地区最常见的遮荫树种 Antiaris toxicaria 遮荫。我们从 2014 年 11 月到 2016 年 3 月在加纳的森林-热带稀树草原过渡带监测微气候、液流密度、穿透雨和土壤水分，研究期间的气候和干旱事件作为未来在西非边缘可可种植区的预测气候条件的代表。在湿润和干燥期，可可和遮荫树的总蒸腾量明显高于全日照下的可可。在湿润期，A. ferruginea 遮荫下的可可蒸腾速率明显低于 A. toxicaria 和全日照下的可可。在 2015/16 年的极端干旱期间，所有的 A. ferruginea 遮荫下的可可植物都死了。A. toxicaria 遮荫下的可可植物死亡率为 77%，受到严重胁迫，液流密度显著降低至 115 g cm 天，而全日照下的可可植物维持较高的液流密度 170 g cm 天。此外，在极端干旱后，全日照下的可可液流恢复速度（163 g cm 天）明显高于 A. toxicaria 遮荫下的可可（37 g cm 天）。全日照下的土壤水分含量高于遮荫系统，表明遮荫系统中的可可死亡与对土壤水分的强烈竞争有关。目前的结果对气候变化下的可可种植具有重要意义。促进作为抗旱系统的遮荫可可农林业，特别是在气候变化下，需要重新仔细考虑，因为建议的豆科 A. ferruginea 等遮荫树种在延长严重干旱下对可可的功能构成重大风险。
