Contribution of agroforests to landscape carbon storage

While many studies have measured the carbon (C) stocks of traditional agroforests at the plot level, their contribution to overall landscape C storage has rarely been quantified. Here we demonstrate the significant contribution that traditional agroforests with shaded tree crops can make to landscape C storage, and thus climate change mitigation, focusing on the cocoa (Theobroma cacao) agroforests (locally known as cabrucas) of southern Bahia, Brazil. Using published allometric relationships and tree inventories of 55 shaded cocoa farms, 6 mature forests, 8 disturbed forests and 7 fallows, we calculate average aboveground C stocks of 87 and 46 Mg ha⁻¹ in traditional and intensified cocoa agroforests, respectively, 183 Mg ha⁻¹ in old-growth forests, 102 Mg ha⁻¹ in disturbed forests and 33 Mg ha⁻¹ in fallows. Based on the most recent land cover data available, we estimate that cocoa agroforests hold 59 % of the total aboveground C stocks of the tree dominated vegetation in this landscape, while forests hold 32 % and fallows hold 9 %. Carbon stocks of intensified cocoa agroforestry systems were only little over one-half of those of traditional agroforests, indicating a threat to landscape C stocks from current land use trends. We show that in agroforests as in natural forests, C stocks are highly concentrated in the largest trees. This suggests that the intensification of traditional agroforests, which generally involves increasing the density of cocoa and other tree crops and reducing the density of shade trees, is possible without greatly affecting their C storage if large trees are conserved. In order to conserve the climate stabilizing effect of traditional agroforests and steer necessary intensification measures towards climate-friendly solutions, we suggest that biodiversity and C-rich traditional agroforests should be included in current discussions about Reducing Emissions from Deforestation and Forest Degradation (REDD+) and/or their owners be rewarded for their environmental services through other incentive mechanisms.