Shade canopy density variables in cocoa and coffee agroforestry systems

Résumé fourni par la source

Abstract An estimated 3.41 million hectares of cocoa and 8.08 million hectares of coffee are cultivated under shade trees i.e. in agroforestry systems. Shade canopies are usually characterized in terms of tree density (N, trees ha-1), tree basal area (G, m2 ha-1) and percent canopy cover (%C). This article shows that these variables have cross-compensation effects that reduce their capacity to inform on the shading conditions in the understory. Density and basal area are not directly related to canopy cover (and hence to shading) and need additional assumptions about both tree size and species-specific allometric relationships between stem diameter and crown diameter. This article explores the compensatory effects between these variables and uses simulations with the software ShadeMotion (www.shademotion.net) to show how 24 different, simple, even-sized, mono-layered, Cordia alliodora shade canopies with constant N, G and %C display significantly different shade levels and temporal patterns of shading depending on tree stem and crown diameters, tree height, spatial planting configurations (square, random and alleys) and leaf fall patterns. A minimum set of variables capable of providing a more informative description of the shading characteristics of a cocoa or coffee shade canopy is proposed. Findings in this study can shed light on the current, heated debate on the pros and cons of definitions of cocoa agroforestry used by chocolate companies, governments, certification companies, NGOs, and donors, especially in West and Central Africa. In this article, emphasis is given to cocoa, but the analysis, results and conclusions are equally applicable to coffee agroforestry systems.

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