Vegetation structure and productivity in cocoa-based agroforestry systems in Talamanca, Costa Rica
Résumé
In the humid tropics, the remaining forest patches are increasingly isolated within an expanding agricultural matrix. There, a significant area consists of complex agroforestry systems with high structural and functional plant diversity. These anthropogenic habitats are gaining increasing conservation value as deforestation progresses. Cocoa-based agroforests provide habitats for some forest dependent species and play a largely undocumented role in providing other ecosystem services. The high variability of their botanical composition and structure is poorly described and its relevancy in assessing ecosystem services has not yet been investigated. We characterized the structure and productivity of 36 cocoa agroforests in Talamanca, Costa Rica. These agroforestry systems (AFS) were chosen to maximize contrasts in terms of biophysical context, botanical composition and management practices. Results showed significant differences in the vegetation structure that enabled us to distinguish four main clusters: complex and high density canopy AFS, high cocoa density AFS, high Musa density AFS and complex and low density canopy AFS. Changes in vegetation structure reflected differences in the farmers' strategies but did not affect the overall cocoa yield (136 kg ha?1 year?1) or the aboveground fresh plant volume (400 m3 ha?1). Cocoa yield per tree in the high Musa density AFS cluster was 454.5 g per cocoa tree, which was significantly twice as much as in lower cocoa density clusters, suggesting that structure affects productivity through spatial distribution more than through botanical composition. These results open new perspectives to improve cocoa orchards' structural complexity and their relative ecosystem services without affecting their overall productivity. Further investigations and additional samplings are needed to fully understand the mechanisms involved.