Successional agroforestry promotes biomass carbon storage in cocoa production systems: results from a long-term system comparison experiment on organic and conventional systems

Agroforestry systems are perceived as an effective approach to store carbon in agroecosystems by building tree biomass and raising soil organic carbon (SOC) stocks. This is especially evident in the tropics, where the cultivation of cash crops such as cacao in agroforestry systems is increasingly used. Among agroforestry systems, organic management, which avoids synthetic inputs for crop protection and fertilization, and the concept of successional agroforestry (SA), which aims to increase carbon storage by using high initial tree densities and intensive pruning without external inputs, have gained interest as alternatives to monocultures with less environmental impact. To assess the temporal development of carbon storage of differently managed agroforestry systems, we revisited a 14-year field experiment located in the Alto Beni Region of Bolivia to quantify biomass and SOC stocks in five distinct cocoa production systems. The field experiment includes SA as well as organic and conventional monocultures (OM and CM) and agroforestry systems (OA and CA). We found that all agroforestry systems increased carbon stocks in the biomass and the soil, especially in the particulate organic matter fraction. No significant effect of organic management practices was observed. After 14 years, the highest biomass carbon was observed in the SA system and topsoil SOC stocks increased significantly in SA and CA. Our findings emphasize the potential to enhance carbon accumulation in agroforestry systems with high initial tree density and rigorous pruning, even without additional fertilizer or synthetic plant protection inputs. • Agroforestry enhances soil and biomass carbon stocks compared to cacao monocultures • No effect of organic management on soil and biomass carbon within agroforestry systems. • Greatest gains of biomass carbon in successional agroforestry systems