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

Abstract

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 À2 day À1 , whereas cocoa in full sun maintained higher sap flux density of 170 g cm À2 day À1 . Moreover, cocoa sap flux recovery after the extreme drought was significantly higher in full sun (163 g cm À2 day À1 ) than under A. toxicaria (37 g cm À2 day À1 ). 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. K E Y W O R D Sagroforestry, extreme heat and drought, sap flux density, shade tree species, soil water deficit, by 2020 (Carr & Lockwood, 2011;ICCO, 2016; World Cocoa Foundation, 2014 (Fountain & H€ utz-Adams, 2015;Lambert, 2014). Increasing income from cocoa is therefore a major pathway for smallholders to escape poverty in the region. However, farmers livelihoods are highly threatened by the vulnerability of their agricultural production systems to increases in the frequency and severity of extreme weather such as heat-waves and drought (Coumou & Rahmstorf, 2012;Sheffield & Wood, 2008;Sultan & Gaetani, 2016;Thornton, Ericksen, Herrero, & Challinor, 2014 Schroth, & Doffangui, 2015). Such response is currently not feasible anymore as forest land is limited and deforestation related to cocoa farming under strict control due to international commitments to prevent deforestation to reduce global warming and loss of biodiversity (Asante, Acheampong, Kyereh, & Kyereh, 2016;Damnyag et al., 2013;Ruf et al., 2015). Cocoa production therefore needs to beco...

The physiological responses of cacao to the environment and the implications for climate change resilience. A review

“…Daily maximum temperatures much higher than the maximum monthly temperature have been reported. For example, daily maximum temperatures between 35°C and 40°C and as high as 44°C have been reported in regions of Ghana (Asare et al 2017;Abdulai et al 2018a). The monthly average maximum and minimum temperatures, which are often quoted, do not necessarily reflect absolute extremes of the temperature experienced.…”

Governance of zero deforestation cocoa in West Africa: New forms of public–private interaction

“…Further studies estimate that cocoa production accounted for 57% of agriculture-driven deforestation in Sub-Saharan Africa from 2000 to 2013, and cocoa witnessed the highest expansion rate as compared with other exportoriented crops (Ordway et al, 2017). 3 In terms of underlying drivers of deforestation (Geist & Lambin, 2002), cocoa from West Africa is a cash crop destined almost exclusively for export markets (domestic consumption of chocolate in West Africa is minimal), explaining how deforestation is partly attributed to increasing global demand for cocoa and chocolate (Abdulai et al, 2018;Li & Mo, 2016).…”

“…Cocoa from this region is grown primarily on small, family-owned farms; the West African cocoa belt comprises about 2 million smallholders who depend on cocoa sales for food and income security (Kroeger, Bakhtary, et al, 2017;Schroth et al, 2016). A high proportion of these cocoa farmers are suffering from severe poverty, defined as per capita income of less than USD 1.90 per day (Abdulai et al, 2018). Poverty is often attributed to low productivity of cocoa farms.…”

Climate Change Sensitivity of Multi-Species Afforestation in Semi-Arid Benin

“…Tree growth sensitivity to drought may be substantial in West African semi-arid zones, where water availability is one of the most limiting factors of plant growth, e.g., [11], and where extreme drought events are projected to become more frequent [12][13][14]. In this region, extreme drought events are associated with extended dry spells, low air humidity, high atmospheric evaporative demand, and high air temperatures [15], potentially increasing water stress in trees [13].…”

“…For example, Abdulai et al [14] revealed drought vulnerability in a cocoa-based system in the forest-savanna transition zones of West Africa, despite the availability of subsoil water below a depth of 75 cm. This observation suggests that drought vulnerability may be related to trees' ability to develop sufficiently deep root systems [21].…”