5:15 PM - 7:15 PM
[BCG05-P01] Land use changes affect the strength of the soil methane sink: comparison of a forest, rubber plantation and oil palm plantation in southern Thailand
★Invited Papers
Keywords:Land Use Change, methane, CH4 flux, forest, rubber, oil palm
Southeast Asia has experienced large changes in land use in recent decades and tree plantations for economical purposes are becoming a major land use, particularly in Thailand where the forest area has decreased from 221,700 km2 in 1973 to 162,000 km2 in 2022 while rubber plantations now cover over 51,000 km2 and oil palm plantations more than 12,000 km2. Methane (CH4) is the second most important anthropogenic greenhouse gas and contributes more than 20% to the anthropogenic radiative forcing. Tropical soils contributed to more than half of the global methane sink and this ecosystem service must be preserved as it is an effective mechanism for atmospheric CH4 removal. Our objective was therefore to assess the consequences of the conversion of an upland tropical forest to oil palm and rubber plantations on the uptake of atmospheric CH4.
We measured net soil CH4 fluxes over several months in a natural tropical rainforest, a rubber plantation and an oil palm plantation in the South peninsular Thailand. We observed a large and significant reduction in net soil CH4 uptake between the forest and the two plantations. The plantation soils tended to be more humid with a higher apparent density than the forest soils, which can reduce gas diffusion into the soils and limit CH4 oxidation by methanotrophic bacteria. Moreover, the soil of the rubber plantations occasionally transitioned from a net CH4 sink to a net source during the rainy season, suggesting that land uses do not only decreased the methanotrophic activity but also stimulated methanogenic activities.
We also measured net soil CH4 fluxes twice, during the wet season and the dry season in rubber plantations located in the central plain and in the northeastern plateau and found that the magnitude of soil CH4 uptake during the dry season and soil CH4 emission during the rainy season differed notably over a 1000 km long geographic transect.
Our results show that land use changes strongly affect the strength of the soil methane sink in Southern Thailand. Given the areas under rubber and oil palm cultivation in Thailand and more broadly in Southeast Asia, these results highlight the need to extend this type of research to enable predictive mapping of soil CH4 uptake to the regional scale, across climatic and physiographic gradients.
We measured net soil CH4 fluxes over several months in a natural tropical rainforest, a rubber plantation and an oil palm plantation in the South peninsular Thailand. We observed a large and significant reduction in net soil CH4 uptake between the forest and the two plantations. The plantation soils tended to be more humid with a higher apparent density than the forest soils, which can reduce gas diffusion into the soils and limit CH4 oxidation by methanotrophic bacteria. Moreover, the soil of the rubber plantations occasionally transitioned from a net CH4 sink to a net source during the rainy season, suggesting that land uses do not only decreased the methanotrophic activity but also stimulated methanogenic activities.
We also measured net soil CH4 fluxes twice, during the wet season and the dry season in rubber plantations located in the central plain and in the northeastern plateau and found that the magnitude of soil CH4 uptake during the dry season and soil CH4 emission during the rainy season differed notably over a 1000 km long geographic transect.
Our results show that land use changes strongly affect the strength of the soil methane sink in Southern Thailand. Given the areas under rubber and oil palm cultivation in Thailand and more broadly in Southeast Asia, these results highlight the need to extend this type of research to enable predictive mapping of soil CH4 uptake to the regional scale, across climatic and physiographic gradients.