Carbon emissions from forest conversion by Kalimantan oil palm plantations

Oil palm supplies >30% of world vegetable oil production¹. Plantation expansion is occurring throughout the tropics, predominantly in Indonesia, where forests with heterogeneous carbon stocks undergo high conversion rates^2-4. Quantifying oil palm's contribution to global carbon budgets therefore requires refined spatio-temporal assessments of land cover converted to plantations^5,6. Here, we report oil palm development across Kalimantan (538,346 km²) from 1990 to 2010, and project expansion to 2020 within government-allocated leases. Using Landsat satellite analyses to discern multiple land covers, coupled with above- and below-ground carbon accounting, we develop the first high-resolution carbon flux estimates from Kalimantan plantations. From 1990 to 2010, 90% of lands converted to oil palm were forested (47% intact, 22% logged, 21% agroforests). By 2010, 87% of total oil palm area (31,640 km²) occurred on mineral soils, and these plantations contributed 61-73% of 1990-2010 net oil palm emissions (0.020-0.024 GtC yr^-1). Although oil palm expanded 278% from 2000 to 2010, 79% of allocated leases remained undeveloped. By 2020, full lease development would convert 93,844 km² (∼ 90% forested lands, including 41% intact forests). Oil palm would then occupy 34% of lowlands outside protected areas. Plantation expansion in Kalimantan alone is projected to contribute 18-22% (0.12-0.15 GtC yr^-1) of Indonesia's 2020 CO ₂ -equivalent emissions. Allocated oil palm leases represent a critical yet undocumented source of deforestation and carbon emissions.