Methane fluxes at upland forests in Japan based on the micrometeorological and chamber methods

Characterizing methane fluxes at upland forests are important to understand the global methane budget. We continuously measured methane fluxes based on the hyperbolic relaxed eddy accumulation (HREA) and automated dynamic closed chamber methods at three temperature forests: a mature larch plantation on a volcanic soil (FHK) since 2011, a young larch plantation on a Gambisol (TSE) since 2013, and deciduous broadleaf forest on an immature soil (YMS) since 2014. According to the chamber measurements, the three forests acted as a methane sink in the warm periods when the chamber measurements were conducted. In contrast, canopy-scale methane fluxes by the HREA often showed emission signals except FHK; in summer months, canopy-scale methane fluxes showed emissions in TSE and YMS, although those by chambers showed uptake. Consequently, missing sources at the canopy-scale were suggested in the measurements. In FHK at the uniform volcanic dry soil, both the HREA and chamber measurements showed a sink with similar magnitudes; the forest consumed methane except the winter. Canopy-scale annual methane budgets were a sink of 810 mg m-2 yr-1 for FHK, source of 190 mg m-2 yr-1 for TSE, and sink of 90 mg m-2 yr-1 for YMS.