Aboveground carbon stocks in Madagascar’s vanilla production landscape – exploring rehabilitation through agroforestry in the light of land-use history

Forests and tree-dominated land uses store large amounts of carbon stocks in plant biomass. However, anthropogenic changes in land use and land cover decrease tree cover and associated carbon stocks. Agroforestry has the potential to maintain or restore carbon in plant biomass but the amount will be influenced by various factors that may include land-use history and management practices. However, few studies explicitly address how these factors determine aboveground carbon stocks. Therefore, our study estimates aboveground carbon stocks in different land-use types, across stem diameters and geographic origin of tree species, and its structural controls. We particularly focus on the importance of land-use history in agroforestry systems. We conducted the study in the mosaic landscape of north-eastern Madagascar in old-growth forests, forest fragments, woody fallows, and vanilla agroforests. The agroforests differed in land-use history and were either directly derived from a forest or a woody fallow after slash-and-burn shifting cultivation. Aboveground carbon stocks were highest in old-growth forests and lowest in woody fallows. Within vanilla agroforests, aboveground carbon stocks were highly variable: forest-derived agroforests stored significantly higher carbon stocks that were mainly stored in native and endemic species, whereas fallow-derived agroforests stored lower carbon stocks that were mainly provided by introduced species. Furthermore, aboveground carbon stocks were mainly controlled by stem density and stem diameter. In conclusion, forest-derived agroforests have the potential to maintain relatively high carbon stocks and a forest-like structure in the landscape, whereas fallow-derived agroforests contribute to converting historically forested open land into permanent tree-dominated land-use systems, thereby restoring carbon stocks. Thus, considering the land-use history of agroforests is important for conservation and restoration agendas.