From peat swamp forest to oil palm plantations: The stability of tropical peatland carbon

Abstract

Accurate assessment of tropical peatland carbon dynamics is important to (a) determine the size of the active carbon pool, (b) estimate the scale of transfers of peat-derived greenhouse gases (GHGs) to the atmosphere resulting from land use change, and (c) support carbon emissions reduction policies. To date, information on the quality of tropical peatland organic matter and its sensitivity to increases in global temperatures is limited, particularly in the context of land conversion. The aim of this work is therefore to determine peat quality and temperature response of potential GHG emissions under flooded conditions from tropical peatland sites. Whilst reflecting the process of conversion from forest to oil palm plantation. Four land use types that represent the stages of conversion from peat swamp forest to oil palm were chosen: (i) secondary ‘forest’, (ii) recently ‘drained’ but not cleared forest (iii) cleared and recently planted ‘young oil palm’ plantation and (iv) ‘mature oil palm’ plantation. Overall, surface peat carbon was more labile than deeper peats. The largest labile pool was measured at forest sites. In the later stages of land conversion, the labile carbon had been lost and the relative abundance of recalcitrant organic material increased. Potential GHG fluxes were greatest in surface peats compared to deeper peats and declined as labile carbon was depleted following land conversion. Higher temperatures resulted in higher potential GHG emissions at all stages of conversion, but the magnitude of the temperature response depended on organic matter lability. For CO 2 fluxes, the temperature response was most pronounced at forest sites. This reflects the greater peat lability at this land use. In contrast, for CH 4 emissions, there were increased emissions both at forest and converted land types with higher temperatures. This suggests that increasing temperatures in response to climate warming may drive higher CH 4 emissions from sites dominated by degraded organic matter. Collectively, this study demonstrates that during conversion from peat swamp forest to oil palm plantation, the enhanced decomposition and reduced litter input rates is reflected eventually in reduced potential gross CO 2 emissions from peat. Nonetheless higher temperature resulting from climate warming may maintain high GHG emissions at plantation sites. © 2019