Seasonal and inter-annual variation of CO2 flux between a temperate forest and the atmosphere in Japan

The objective of this research is to elucidate the seasonal and inter-annual variations of CO 2 exchanges between the atmosphere and a temperate deciduous forest in Japan and to elucidate their relation to meteorological conditions. The uptake rates of CO 2 from October 1993 to December 1996 were estimated from field measurements of CO 2 concentrations and meteorological conditions using a tower. Net of uptake rate of CO 2 was positive (uptake by forest ecosystems) from June to September and negative (release to the air) from October to April. Averages of integrated uptake rates of CO 2 were 840, − 450 and 390 gCO 2 /m 2 /year (2.3, − 1.2 and 1.1 tC/ha/year) for daytime, night and whole day (net), but they had notable inter-annual variation due to the differences of averaged insolation and temperature each summer of 1994 to 1996. The errors of CO 2 flux due to topographical conditions were investigated through comparison with heat budgets. CO 2 uptake rate estimated by tower measurement might be underestimation of 40%, therefore, above net-uptake value, 1.1 tC/ha/year became 1.8. This value of uptake rate was smaller than the results obtained in other temperate deciduous forests. The causes of this are partially in the difference of the height of the site and the short active period of the present forest. According to the CO 2 flux measurements in several forests including the present one, the forest ecosystems could be a large sink of CO 2 , however, more data of the CO 2 flux is needed at the various forests and latitudes to reduce the uncertainty of estimation of CO 2 uptake on a global scale. DOI: 10.1034/j.1600-0889.1999.00020.x