Avoidance of tree-site mismatching of modelled cacao production systems across climatic zones: Roots for multifunctionality

CONTEXT Protective roles of shade trees for climate-resilient cacao appear to depend on tree-site matching. Agroforestry practices involve a wide range of context-specific management options, which can be complex and pose challenges due to tradeoffs. OBJECTIVE To assess the benefits and drawbacks, across a range of contexts, of various cacao-based land use systems on multifunctionality and economic performance. METHODS We used the process-based Water, Nutrient and Light Capture in agroforestry systems (WaNuLCAS) model to assess the performance of five cacao-based land use systems (cacao monoculture, cacao + annual crops, cacao + fruit tree, cacao + fast-growing tree, and cacao + slow-growing tree), in three climate regimes (tropical rainforest, monsoon, and savannah), two soil textures, and two sources of data for cacao root length density (W Africa and Indonesia, respectively). Several metrics quantified the performance of each land use system, including the Land Equivalent Ratio for production (LERP),multifunctionality (LERM), Net Present Value (NPV), Return to Labour (RtL), and Benefit-Cost Ratio (BCR). RESULTS AND CONCLUSIONS Simulated cacao production per tree, positively or negatively influenced by intercrops, responded to the number of days cacao grew under water-limited conditions. High cacao root density supported higher LERP values (an average of 1.15 versus 0.95 in other cases). In the savanna, the LERP difference between cacao with high root density and those with low root density became 0.27. Among agroforestry systems, cacao + annual crops had the highest LERP of 1.13, followed by cacao + slow-growing trees (1.09), while the lowest outcome (0.98) was for cacao + fruit trees. These values were higher in rainforest climates, and lowest for savanna. Soil texture had no effect on the average LERP across other main factors. Tree-based agroforestry had a higher time-averaged carbon stock than monocultures or systems with annual crops. However, their effects on other environmental performance aspects, averaged over a 20-year life cycle, were modest, and variation in LERM was small. Economic performance indicators diverged, with the highest NPV were for cacao + annual crops or cacao + fruit trees, the highest BCR was for cacao + fruit trees, and the highest RtL was for cacao + fruit trees followed by cacao + slow-growing trees. SIGNIFICANCE Our study highlights that the potential benefits of cacao-based agroforestry practices depend on strong root development by the cacao trees. In selecting for high yields in monocultures, the benefits of intercropping may be forfeited, especially in drier climates with the lower values for root length density measured in W Africa.