Biomass and carbon stocks of organic and conventional cocoa agroforests, Ghana

Abstract

Cocoa production is a globally important commodity that has been a major driver of deforestation in humid tropical areas. Cocoa agroforestry systems have been credited for storing significant stocks of carbon potentially mitigating some of the negative impacts of cocoa production on ecosystem services but the impact of organic management on this potential is unclear, especially in Africa. We quantified cocoa and shade tree biomass, above and below ground and soil carbon stocks of 42 organic and 42 conventional cocoa agroforestry systems in Ghana (a globally important cocoa producing country) across three cocoa-age groups; young (≤ 15 years), mature (16–30 years) and old (≥ 31). We used the carbon stocks data to estimate the monetary value of the stored carbon in the two systems. Mean aboveground biomass C (Org. 41.3 ± 3.62 vs. Con. 22.9 ± 2.60 Mg C ha−1), belowground biomass C (Org. 7.8 ± 0.67 vs. Con. 4.2 ± 0.66 Mg C ha−1) and soil C stocks (Org. 59.7 ± 3.36 vs. Con. 49.7 ± 3.33 Mg C ha−1) were higher on organic farms compared to conventional farms. The dominant shade tree species on both organic (15 spp.) and conventional (15 spp.) stored more than 70 % of vegetation carbon stocks on both farm types. The estimated monetary value of the rate of CO2 equivalent of stored carbon by organic cocoa systems ranged from 74.58 US$ ha−1 yr−1 in old farms to 208.07 US$ ha−1 yr−1 in young farms compared to a range of 39.08 US$ ha−1 yr−1 in old farms to 99.60 US$ ha−1 yr−1 in young farms on conventional cocoa farms. The results show that organic cocoa agroforestry systems in our study area hold a greater potential to accumulate carbon and in addition benefit from carbon schemes than conventional cocoa agroforestry systems. Organic farms had higher shade tree diversity and richness which reflected the willingness of organic farmers to maintain/plant agroforestry trees. This indicate organic cocoa agroforestry system can help retain important ecosystem services within the cocoa production areas while providing some additional income to small holder cocoa farmers.