Seasonal and interannual variation in net ecosystem production of an evergreen needleleaf forest in Japan

Carbon dioxide (CO2) flux was measured above the forest at the Fujiyoshida site on the northern slope of Mount Fuji in Japan in 2000-2008 using an eddy covariance technique. The forest mainly consists of Japanese red pine () and Japanese holly (). The 9-year average of monthly mean net ecosystem production (NEP) ranged from -0.1 g C m(-2) day(-1) in January to 2.5 g C m(-2) day(-1) in May. The maximum net uptake was observed in May, although gross primary production (GPP) was highest in July. Variation in the leaf amount did not notably affect seasonal variation in GPP. This site was characterized by carbon uptake even in winter, if the meteorological conditions were conducive for photosynthesis and a resulting long period of carbon uptake. The 9-year averages of annual NEP, GPP, and ecosystem respiration (RE) were 388, 1,802, and 1,413 g C m(-2) year(-1), respectively. The annual NEP was lowest in 2003 and highest in 2004 over the 9 years. Year-to-year variability of NEP mainly depended on air temperature and photosynthetically active radiation in summer, and the dependence of the deviation of annual NEP on that of GPP was greater than that of RE. Long-term observational data indicated that the carbon uptake ability at the study site was at a moderate level in comparison with other temperate humid evergreen forests around the world. These data also indicated that the site had a high carbon uptake ability compared with other deciduous forests in Japan because of the duration of carbon uptake.