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To produce charcoal and prevent the deforestation around Kinshasa (Gond et al., 2017), 7,700 ha of Acacia auriculiformis were planted on savannah ecosystems, in 1987 (Bateke Plateau, DR Congo). Since 1995, the plantation was managed using the rotational woodlot system alternating agricultural and charcoal production on the same area (Kimaro et al., 2007). The 7,700 ha produced a large amounts of charcoal, cassava and maize during many years (Bisiaux et al., 2009). However, farmers have observed for a while a decline in wood and crop productivity. The aim of this study was to compare chemical properties of soils in six acacia stands in two farms having undergone different agroforestry trajectories: - one 22-year-old acacia stand, never-harvested; 4 stands in their 2nd rotation after 1 cropping cycle; and 1 stand in its 3rd rotation after 2 cropping cycles - and soils in the native control savannah. Compared to the original savannah, all acacia stands showed an increase in soil C, N and N-NO3- contents, but a decline in soil pH and exchangeable cations, and an increase in exchangeable Al and CEC (Fig 1). To maintain the sustainability of the system, we recommend different practices in order to improve the nutrient balance and decrease the soil acidity. Such practices are the debarking of tree stems before carbonization, the restitution of small branches and charcoal residues to the soil, and the supply of natural rock phosphate (Dubiez et al., 2018).

Recent studies based on remote sensing showed a gradual expansion of tree cover over savannah and agricultural land in the forest-savannah transition zone of Cameroon1, part of this expansion is actually due to shaded cocoa. Despite unfavourable conditions in herbaceous savannah (low soil fertility, weed competition and risk of bush fire), farmers have proven that afforestation is achievable using cocoa and specific technics to build up an associated tree canopy2. Full-grown cocoa agroforestry systems created on savannah (S-cAFS) and in forest (F-cAFS) seem to exhibit comparable multi-strata structure. Nevertheless, previous land uses and related canopy structures may have contrasted impacts on production and other ecosystem services over time. We selected 1 to 70 year-old S-cAFS and F-cAFS, and we used forest and savannah patches as controls3. By combining measurements of cocoa production, litter fall and cycling, soil quality, carbon storage and tree species diversity along this age gradient, we showed that those variables in S- and F-cAFS generally tended to comparable levels after several decades. Results also emphasized the ability of S-cAFS to increase most of the ecosystem services (ES) although the time needed to reach levels found in F-cAFS varied strongly amongst variables (Fig 1). Results also showed the positive contribution of associated plants to ES, particularly C storage and nutrient cycling contributing to REDD+ 4 and sustainability of the cropping system.