The impacts of oil palm expansion on the terrestrial carbon cycle in Southeast Asia

Rising demand for palm oil has driven rapid expansion of oil palm plantations in Southeast Asia over the past decades, yet their impacts on the regional carbon budget remain poorly constrained due to complex interactions between oil palm ecosystems and climate change, stand age, soils, and management. Here, we develop a diagnostic terrestrial biosphere model that incorporates key processes of oil palm carbon cycles, driven by high-resolution remote-sensing products and meteorological forcings. We validate our model using extensive observational data, including 31 site-years of carbon flux observations from eddy covariance sites and 360 sub-national yield records, and then simulate the carbon dynamics from 2001 to 2020 across Indonesia and Malaysia. Our model reproduces the observed carbon fluxes well, with R² > 0.90 and RMSE < 502 gC/m²/year against eddy covariance measurements. We find oil palm plantations initially (yrs < 10 years) act as strong carbon sources, with annual net ecosystem exchange (excluding harvested fruits) exceeding 2,000 gC/m²/year. The plantations approach carbon neutrality and can become net sinks on mineral soils after maturity (yrs > 10 years), whereas those on peat soils remain net sources in their lifetime. Our study reveals the controlling factors of oil palm carbon fluxes and provides a spatially explicit estimate of carbon fluxes across oil palm plantations, offering insight into their contribution to the regional carbon budget.