NIRE Annual Report 1996

NIRE Annual Report

1996

Research on the Modeling of the Carbon Budget in a Temperate Forest by the Field Measurements of CO₂ Flux

Objectives: Our objective was to elucidate the seasonal variation of CO₂ flux between air and biosphere in temperate deciduous forest in Japan. The fluxes of CO₂ between air and temperate forest were estimated by the field measurement of CO₂ concentration and meteorological conditions using a tower. The seasonal variation of fluxes, the relation between them and meteorological conditions were investigated.

Results: The fluxes of CO₂ were calculated according to the eddy correlation and aerodynamic methods. The values of CO₂ flux depend on the activities of vegetation including photosynthesis, respiration and the decomposition of organic matter which relate to the meteorological conditions. Figure 1 and Figure 2 show the relations between CO₂ flux ( daytime ) and insolation and between CO₂ flux(night) and air temperature. And, seasonal variation of CO₂ flux was investigated. Uptake rate of CO₂ in this temperate forest was positive ( uptake by vegetation ) from May to September and negative (release to the air) from October to April as shown in Figure 3. Annual net uptake was 460 g CO₂/m² from October 1993 to September 1994 and 210 g CO₂/m² from October 1994 to September 1995. The difference of uptake between two years was related to the differences of insolation and temperature in two summers.

1)	Airplane measurements of CO₂ distribution on Iriomote island in Japan. Atmospheric Environment 30, 1091-1097,1996.
2)	Seasonal variation of CO₂ flux between air and temperate forest, Proceeding of 10th World Clean Air Congress, Helsinki, Finland, 1995.

National Institute for Resources and Environment