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Land-use intensification in the tropics plays an important role in meeting global demand for agricultural commodities but generates high environmental costs. Here, we synthesize the impacts of rainforest conversion to tree plantations of increasing management intensity on carbon stocks and dynamics. Rainforests in Sumatra converted to jungle rubber, rubber, and oil palm monocultures lost 116 Mg C ha−1, 159 Mg C ha−1, and 174 Mg C ha−1, respectively. Up to 21% of these carbon losses originated from belowground pools, where soil organic matter still decreases a decade after conversion. Oil palm cultivation leads to the highest carbon losses but it is the most efficient land use, providing the lowest ratio between ecosystem carbon storage loss or net primary production (NPP) decrease and yield. The imbalanced sharing of NPP between short-term human needs and maintenance of long-term ecosystem functions could compromise the ability of plantations to provide ecosystem services regulating climate, soil fertility, water, and nutrient cycles [ABSTRACT FROM AUTHOR]

• Flooding in riparian areas counters the effects of land use change on C storage. • C preservation due to oxygen-limited mineralization under anaerobic conditions. • δ13C values represent changing environmental conditions. Progressive conversion of tropical rainforests to agricultural monocultures in South East Asia increasingly affects landscape types such as riparian areas. The impacts of conversions on soil organic matter (SOM) vary with changing landforms. However, this was often not accounted for in previous studies where SOM in soils in riparian areas was combined with SOM from well-drained adjacent slopes. Because riparian areas have a high carbon (C) storage potential, our objectives were i) to assess their C stocks after conversion to rubber and oil palm plantations in Sumatra (Indonesia) and ii) to compare the impacts of land use conversion on C stocks between riparian and well-drained areas. Average soil C stock losses from the top 30 cm were about 14% and 4% following conversion of riparian forest to rubber and oil palm plantations, respectively, indicating a high resistance of C to mineralization. C losses from well-drained areas were twice as high as from riparian areas after the respective conversion. δ13C values from riparian areas showed clear heterogeneity down soil profiles that was explained i) by alternating oxic and anoxic conditions, leading to reduced SOM and litter decomposition in riparian areas and ii) by mineral sediments and organic matter deposition and accumulation by erosion from adjacent slopes covered by plantations. We conclude that riparian areas are more resilient in terms of soil C storage towards land-use change than well-drained areas because of sediment deposition and reduced oxygen availability. On this basis, we developed a conceptual model of the effects of land-use change and various ecotone characteristics on SOM mineralization in the top- and subsoil of riparian areas. [ABSTRACT FROM AUTHOR]