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 decreased methane (CH4) production and increased CH4 consumption by peat soils. Our aim was to evaluate how tropical peat swamp forest conversion affected soil CH4 emissions. Average CH4 fluxes and associated water table depths and correlation between both were calculated from the literature for common land use treatments. In addition, we used a meta-analysis statistical approach to compare soil CH4 fluxes before and after land-use change. Mean rates of soil CH4 emissions amounted to average values of 28.5 ± 9.7 kg C ha-1 y-1 and 155.1 ± 82.4 kg C ha-1 y-1 in virgin peat swamp forests and rice fields, respectively; whereas in the other land uses, mean soil CH4 fluxes (9.9 ± 5.4 kg C ha-1 y-1) were significantly lower. Methane fluxes were positively correlated (r = 0.54; P = 0.0149) with the water table depth. The significant overall effect size of land-use change on emissions of CH4 was -0.4 ± 0.2 indicating a small decrease of CH4 emissions with the conversion of virgin peat swamp forests to another land use, including rice cultivation. A similar analysis would be required on soil emissions of N2O. 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 decomposition of the peat.