Effect of neighbouring perennials on cocoa tree pod production in complex agroforestry systems in Cameroon

Abstract

Agroforestry systems (AFS) are gaining major interest in cocoa producing countries. However, the analysis of competition effects in multispecific complex agricultural systems remains a key lock-in preventing both (i) a thorough understanding of resource partitioning, and (ii) the co-design of spatial patterns and management of cocoa AFS (cAFS) minimising competition. We sampled 48 cAFS 1000 m² plots in Central Cameroon and used an individual based approach to analyse the effect neighbouring tree community composition had on coca tree pod production. First, we determined the distance up to which each neighbouring tree influenced the production of a given cocoa tree and checked for the significance and the magnitude of this effect. We then explored the trade-offs between cocoa tree production and the abundance of associated trees. Our results first underline a significant intra-specific competition within the cocoa tree populations studied, which would need to be thinned down to 800–1100 individuals per ha. We also found a general negative effect of associated trees kept or grown for their fruits (e.g. mango, traditional species, citrus trees). Those effects were stronger when the trees were positioned between 6 and 11 m away from the cocoa trees. These trees clearly impaired pod production, especially for small diameter cocoa trees. Palm trees, however, had a positive effect on cocoa pod production, with suitable densities modelled ranging from 0 to 240 individuals per ha. Finally, we found both positive and negative effects of associated forest trees on cocoa pod production, which varied with the distance separating them from the cocoa trees and the size of the cocoa trees. Overall, our analyses show that cocoa production in complex cAFS is influenced both by intra- and inter-specific interactions while it remains difficult to distinguish between potential intertwined effects and resource limitations.