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

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.

[1]  S. Bai,et al.  Effects of shade-tree species and spacing on soil and leaf nutrient concentrations in cocoa plantations at 8 years after establishment , 2017 .

[2]  R. Asare,et al.  INFLUENCES OF SHADING AND FERTILIZATION ON ON-FARM YIELDS OF COCOA IN GHANA , 2016, Experimental Agriculture.

[3]  B. Kyereh,et al.  Farmers’ perspectives on climate change manifestations in smallholder cocoa farms and shifts in cropping systems in the forest-savannah transitional zone of Ghana , 2017 .

[4]  J. Six,et al.  Shade trees have limited benefits for soil fertility in cocoa agroforests , 2017 .

[5]  R. Asare,et al.  Evaluating Farmers’ Knowledge of Shade Trees in Different Cocoa Agro-Ecological Zones in Ghana , 2017 .

[6]  Wenjie Liu,et al.  Can intercropping with the world's three major beverage plants help improve the water use of rubber trees? , 2016 .

[7]  Edward Yaw Kyere.  Farmers’ perception on climate change its manifestations in smallholder cocoa systems and shifts in cropping pattern in the forest-savannah transitional zone of Ghana , 2016 .

[8]  B. Sultan,et al.  Agriculture in West Africa in the Twenty-First Century: Climate Change and Impacts Scenarios, and Potential for Adaptation , 2016, Front. Plant Sci..

[9]  G. Schroth,et al.  Vulnerability to climate change of cocoa in West Africa: Patterns, opportunities and limits to adaptation. , 2016, The Science of the total environment.

[10]  N. Buchmann,et al.  Legumes are different: Leaf nitrogen, photosynthesis, and water use efficiency , 2016, Proceedings of the National Academy of Sciences.

[11]  G. Schroth,et al.  From site-level to regional adaptation planning for tropical commodities: cocoa in West Africa , 2016, Mitigation and Adaptation Strategies for Global Change.

[12]  Wenjie Liu,et al.  Below-ground interspecific competition for water in a rubber agroforestry system may enhance water utilization in plants , 2016, Scientific Reports.

[13]  B. Rapidel,et al.  Root distribution and water use in coffee shaded with Tabebuia rosea Bertol. and Simarouba glauca DC. compared to full sun coffee in sub-optimal environmental conditions , 2015, Agroforestry Systems.

[14]  E. Fischer,et al.  Anthropogenic contribution to global occurrence of heavy-precipitation and high-temperature extremes , 2015 .

[15]  E. Somarriba,et al.  Trade-offs between crop intensification and ecosystem services: the role of agroforestry in cocoa cultivation , 2014, Agroforestry Systems.

[16]  Jianping Huang,et al.  Combined effects of the Pacific Decadal Oscillation and El Niño-Southern Oscillation on Global Land Dry–Wet Changes , 2014, Scientific Reports.

[17]  A. Challinor,et al.  Climate variability and vulnerability to climate change: a review , 2014, Global change biology.

[18]  Kira A. Borden,et al.  Intraspecific root plasticity in agroforestry systems across edaphic conditions , 2014 .

[19]  A. Timmermann,et al.  Increasing frequency of extreme El Niño events due to greenhouse warming , 2014 .

[20]  Francis K. Dwomoh,et al.  Sustaining protected areas: Identifying and controlling deforestation and forest degradation drivers in the Ankasa Conservation Area, Ghana , 2013 .

[21]  G. Schroth,et al.  Predicting the future climatic suitability for cocoa farming of the world’s leading producer countries, Ghana and Côte d’Ivoire , 2013, Climatic Change.

[22]  D. Lobell,et al.  The critical role of extreme heat for maize production in the United States , 2013 .

[23]  P. Hadley,et al.  PHOTOSYNTHETIC ACTIVITY AND EARLY GROWTH OF FOUR CACAO GENOTYPES AS INFLUENCED BY DIFFERENT SHADE REGIMES UNDER WEST AFRICAN DRY AND WET SEASON CONDITIONS , 2012, Experimental Agriculture.

[24]  Stefan Rahmstorf,et al.  A decade of weather extremes , 2012 .

[25]  S. Adjei-Nsiah,et al.  Climate change and shift in cropping system: from cocoa to maize-based cropping system in Wenchi area of Ghana , 2012 .

[26]  H. Breuning‐madsen,et al.  Origin of Harmattan dust settled in Northern Ghana — Long transported or local dust? , 2011 .

[27]  Yann Clough,et al.  Multifunctional shade‐tree management in tropical agroforestry landscapes – a review , 2011 .

[28]  G. Lockwood,et al.  THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF COCOA (THEOBROMA CACAO L.): A REVIEW , 2011, Experimental Agriculture.

[29]  E. Dreyer,et al.  Agroforestry associating coffee and Inga densiflora results in complementarity for water uptake and decreases deep drainage in Costa Rica , 2011 .

[30]  E. Dreyer,et al.  Rainfall partitioning into throughfall, stemflow and interception loss in a coffee (Coffea arabica L.) monoculture compared to an agroforestry system with Inga densiflora. , 2010 .

[31]  L. Schwendenmann,et al.  Throughfall reduction in a cacao agroforest: tree water use and soil water budgeting , 2010 .

[32]  E. Veldkamp,et al.  Effects of an experimental drought on the functioning of a cacao agroforestry system, Sulawesi, Indonesia , 2010 .

[33]  D. Hertel,et al.  Response of cocoa trees (Theobroma cacao) to a 13-month desiccation period in Sulawesi, Indonesia , 2010, Agroforestry Systems.

[34]  P. Waylen,et al.  Trends in spatio‐temporal variability in annual rainfall in Ghana (1951‐2000) , 2009 .

[35]  J. Bunce,et al.  Photosynthetic photon flux density, carbon dioxide concentration, and vapor pressure deficit effects on photosynthesis in cacao seedlings , 2008, Photosynthetica.

[36]  E. Wood,et al.  Projected changes in drought occurrence under future global warming from multi-model, multi-scenario, IPCC AR4 simulations , 2008 .

[37]  Brenda B. Lin,et al.  Agroforestry management as an adaptive strategy against potential microclimate extremes in coffee agriculture , 2007 .

[38]  W. Rawls,et al.  Soil Water Characteristic Estimates by Texture and Organic Matter for Hydrologic Solutions , 2006 .

[39]  N. Anten,et al.  A physiological production model for cocoa (Theobroma cacao): model presentation validation and application , 2005 .

[40]  P. Hadley,et al.  The effects of temperature and light integral on early vegetative growth and chlorophyll fluorescence of four contrasting genotypes of cacao (Theobroma cacao) , 2004 .

[41]  C. S. Holling,et al.  Resilience and Sustainable Development: Building Adaptive Capacity in a World of Transformations , 2002, Ambio.

[42]  W. Smith,et al.  SAP FLUX OF CO-OCCURRING SPECIES IN A WESTERN SUBALPINE FOREST DURING SEASONAL SOIL DROUGHT , 2000 .

[43]  A. Granier,et al.  Evaluation of transpiration in a Douglas-fir stand by means of sap flow measurements. , 1987, Tree physiology.

[44]  G. Schroth,et al.  Climate change, cocoa migrations and deforestation in West Africa: What does the past tell us about the future? , 2014, Sustainability Science.

[45]  D. Hölscher,et al.  The influence of emergent trees on rainfall distribution in a cacao agroforest (Sulawesi, Indonesia) , 2009 .

[46]  L. S. Pereira,et al.  Crop evapotranspiration : guidelines for computing crop water requirements , 1998 .

[47]  Agriculture in West Africa: Prof. John Phillips , 1951, Nature.