Carbon dioxide balance of an oil palm plantation established on tropical peat

Abstract

Oil palm plantations have been expanding in recent decades in Indonesia and Malaysia. Carbon-rich tropical peat swamp forest has not been excluded from this expansion, because it was the last frontier suitable for industrial agriculture and more accessible than other undeveloped areas. Carbon dioxide (CO2) emission through accelerated peat decomposition is one of the main environmental concerns in the conversion of peatlands into plantations, which undergo drainage to increase palm growth rates and production. Changes in aboveground biomass might also significantly alter the CO2 exchange dynamics of the ecosystem. Despite the potential changes in CO2 balance due to land conversion, so far no study has been conducted using the eddy covariance technique about the CO2 balance of oil palm plantations established on peat. We have monitored the eddy CO2 flux above an oil palm plantation on peat in Sarawak, Malaysia since 2011. During the period from 2011 to 2014 (four years), the plantation at 7–10 years of age was a large stable CO2 source with an annual net ecosystem CO2 exchange (NEE) of 994 ± 158 g C m−2 yr−1. The NEE was much more positive than that of a peat swamp forest (-136 ± 51 g C m−2 yr−1) in the same region during the same period. The large positive NEE was caused mainly by its relatively small gross primary production (GPP) (2529 ± 125 g C m−2 yr−1) due to low leaf area index resulting from high palm mortality. In addition, a large amount of plant debris left in the plantation probably contributed to the large NEE through decomposition, especially under the many canopy gaps due to high palm mortality mainly caused by toppling on poorly compacted peat. Adequate peat compaction is essential to reduce the mortality rate.