CO2 Absorption in Terrestrial Ecosystems and Global Environment

A five-year strategic project (S-1 project), which was organized to clarify the carbon dynamics of terrestrial ecosystems in East Asia was conducted from April 2002 to March 2007 with financial support from the Ministry of Environment, Japan. It had four themes. The first was a bottom-up approach using micrometeorological and ecological techniques to measure carbon dioxide fluxes at sixteen tower sites in Japan and East Asia. The second was a top-down approach using an inverse model based on atmospheric CO2 concentration data finely measured at six western Siberian sites. The third was a modeling approach driven by data-based quality-controlled data from the first theme and artificial satellite data. The fourth and final theme synthesized the results of the three themes mentioned above following a systems approach, which led to a comprehensive conclusion. The main results obtained by the many principal investigators of the S-1 project are summarized below. 1. Characteristic seasonal changes of Net Ecosystem Production (NEP) were obtained from ten tower flux sites including forest and grassland sites. 2. Annual NEP values obtained by micrometeorological and ecological techniques showed almost satisfactory agreement at the six forest sites, although those obtained by the micrometeorological technique were usually higher than ones obtained by the ecological technique. 3. A satisfactory agreement was obtained for seasonal changes of biomass at a paddy field site between results obtained by micrometeorological and ecological harvesting techniques. 4. Seasonal changes of NEP in western Siberia estimated by an inverse model showed a similar pattern to those of an ecological process-based model, Sim-CYCLE, but there was a fairly large difference between the estimated annual values of the two models. 5. Gross Primary Production (GPP) and Net Primary Production (NPP) maps of a spacially high resolution drawn by Sim-CYCLE revealed a characteristic pattern reflecting the diverse vegetation types in East Asia. This region was estimated to be a net carbon sink, with 57 Tg carbon on an annual average during the six years from 2000 to 2005, although annual values fluctuated greatly due to weather conditions.