Dataset for: Seasonal changes in tree stem and soil methane fluxes along a soil moisture gradient in a subtropical Australian rainforest

Tree stem and soil CH4 fluxes showed a significant positive correlation with soil moisture. Valley floor soil CH4 fluxes transitioned between a CH4 sink (end dry season: -151 µmol soil m-2 d-1) to a source (end wet season: 830 µmol soil m-2 d-1). Drier soils of the slope plots acted as a net CH4 sink year-round, with average soil CH4 fluxes of -135 µmol soil m-2 d-1 (lower slope) and -156 µmol soil m-2 d-1 (upper slope).

In the sloped plots, tree stems emitted negligible CH4, except for two “high-emitting” trees, featuring CH4 fluxes 200 and 300-fold higher than the adjacent trees. In the valley floor at the end of the wet season, tree stem emission contributed an extra 27 % to the soil CH4 source, while in the slope plots, tree CH4 emissions offset < 1 % of soil CH4 uptake. This study adds to the limited knowledge of high temporal and spatial heterogeneity of upland tree and soil CH4 fluxes, and it highlights the importance of rainforest soils as important global CH4 sink.