Evaluating soil CO₂ fluxes during the transition from peat swamp forest to an oil palm plantation.

Conversion of peat swamp forests to oil palm plantations has significant implications for soil CO2 emissions, but the magnitude of this impact remains highly uncertain. To evaluate the effects of this conversion on soil CO₂ fluxes, monthly measurements of soil CO₂ flux, environmental conditions, and soil chemical properties were conducted in a peat swamp forest undergoing conversion to an oil palm plantation. The study covered three land use phases: peat swamp forest (January 2016-February 2017), land preparation (March 2017-April 2018), and oil palm plantation (May 2018-April 2023). Despite a reduction in groundwater level (GWL) and an increase in soil temperature during land preparation, soil CO₂ emissions (1768-2135 g C m-2 yr-1) did not differ significantly from those in peat swamp forest (1402-1430 g C m-2 yr-1). Soil CO₂ emissions increased during the first three years after oil palm plantation establishment (2606-3119 g C m-2 yr-1) and subsequently declined during the fourth and fifth years (1858-2348 g C m-2 yr-1). This decline was probably driven by multiple factors, including the accumulation of recalcitrant C, indicated by an increase in the pyrophosphate solubility index; an increase in GWL due to improved water management; and increased shading due to the development of the oil palm canopy. Continued monitoring beyond the first five years is needed to assess whether the declining trend persists as the plantation matures. Overall, these results highlight the need to protect remaining peat swamp forests to mitigate further carbon losses.