Estimating NEP by micrometeorological and biometric methods in a larch forest in Hokkaido, Japan

We report comparison of NEP of a temperate larch forest between micrometeorological and biometric methods. The study site is a Japanese larch plantation in Hokkaido, Japan (42°44'N, 141°31'E). The canopy height was approximately 15 m and tree age was about 45 years old. Canopy LAI reached the maximum at 5.5m2 m-2 in July. We measured NEE (-NEP) using eddy covariance method with open- and closed-path systems. We estimated biometric NEP from biomass increment, litter fall of overstory and understory, and heterotrophic respiration measured by chamber method. However, Biometric NEP should have a large uncertainty, because we neglect a fine root production. Daytime NEE tended to be slightly negative for open-path than for closed-path. In contrast, nighttime NEE tended to be slightly less positive for open-path than for closed-path. Consequently, the small difference of half-hourly NEE between from open- and closed-pass provided the large annual bias. High frequency loss corrections using Bandpass covariance method or experimental transfer function improved the daytime bias. However, they made the nighttime bias large. The annual NEPs obtained from open- and closed-path systems were compared with that estimated by the biometric method. NEP estimated by biometric method was close to that estimated by closed-path system.