Changes in soil CH4 fluxes from the conversion of tropical peat swamp forests: a meta-analysis

Currently, 25% of all deforestation in insular Southeast Asia occurs in peat swamp forests. When peatlands are deforested, drainage ditches are often constructed to lower the ground-water level, which may result in changes in peat methane (CH4) fluxes. Our aim was to evaluate how tropical peat swamp forest conversion affected these fluxes. Average CH4 fluxes, water table depths and the relationship between both were established for common land uses (LU) of Southeast Asia. We also compared peat CH4 fluxes before and after land-use change (LUC) using a meta-analysis. Average soil CH4 emissions amounted to 28.6 ± 9.7 and 107.6 ± 60.2 kg C ha-1 y-1 in virgin peat swamp forests and rice fields, respectively. In the other land uses the emissions (9.5 ± 6.1 kg C ha-1 y-1) were significantly lower. Methane fluxes displayed an exponential response to water table depth changes across LU ranging from dry-drained to wet-undrained situations. The significant overall effect size of LUC on CH4 emissions (-0.4 ± 0.2) indicated a small decrease of CH4 emissions with peat swamp forests conversion to another land use, including rice cultivation. It's important to stress, however, that the overall decrease in CH4 emission from peat swamp forests conversion would never offset the simultaneous increase in soil CO2 emissions due to accelerated peat decomposition.