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

The objective of this research is to Elucidate the seasonal and inter-annua l variations of CO2 exchanges between the atmosphere and a temperate decidu ous forest in Japan and to elucidate their relation to meteorological condi tions. The uptake rates of CO2 from October 1993 to December 1996 were esti mated from field measurements of CO2 concentrations and meteorological cond itions using-a tower. Net of uptake rate of CO2 was positive (uptake by for est ecosystems) from June to September and negative (release to the air) fr om October to April. Averages of integrated uptake rates of CO2 were 840, - 450 and 390 gCO(2)/m(2)/year (2.3, -1.2 and 1.1 tC/ha/year) for daytime, ni ght 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 CO2 flux due to topographical conditions were invest igated through comparison with heat budgets. CO2 uptake rate estimated by t ower measurement might be underestimation of 40%, therefore, above net-upta ke 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 s hort active period of the present Forest. According to the CO2 flux measure ments in several Forests including the present one, the forest ecosystems c ould be a large sink of CO2, however, more data of the CO2 flux is needed a t the various forests and latitudes to reduce the uncertainty of estimation of CO2 uptake on a global scale.