Greater methane uptake in deciduous forest soils than in coniferous plantation soils along an elevational gradient in a cool-temperate mountainous region of Japan

Forest soils are an important sink for atmospheric methane (CH4), yet the factors controlling spatial variability of CH4 uptake among forest types remain insufficiently understood. In this study, CH4 fluxes were measured along an elevational transect within a geographically limited mountainous region of Takayama, central Japan. Eleven sites representing deciduous broadleaf forests and evergreen coniferous stands, including cedar and cypress plantations, were investigated using manual chamber measurements during six campaigns over two growing seasons. Despite a mean temperature range of approximately 10－22°C during measurements, CH4 fluxes did not exhibit a clear seasonal pattern. No significant correlation in CH4 uptake was obtained along the elevational gradient itself. In contrast, deciduous broadleaf forests showed significantly greater CH4 uptake than adjacent evergreen conifer forests. Soil pH, carbon and nitrogen contents, porosity, and soil moisture were similar between forest types. However, C:N ratios tended to be higher in coniferous forests, whereas soil respiration tended to be higher in deciduous forests. Estimated annual CH4 uptake based on growing-season measurements was within the range previously reported for Japanese forest soils. Within this landscape, forest type appeared to exert a stronger influence on CH4 uptake than elevation.