A SIMULATION STUDY OF RESPONSES OF THE NORTHEAST CHINA TRANSECT TO ELEVATED CO2 AND CLIMATE-CHANGE

The spatiotemporal variations of vegetation biomass of the ecological transect in northeast China were simulated. Slate variables of the mod el included green biomass and nongreen biomass of 12 vegetation catego ries and water contents of three soil layers. The simulated monthly gr een biomass was converted into NDVI, or Normalized Differential Vegeta tion Index of AVHRR (Advanced Very High Resolution Radiometry). A comp arison between the modeled and the observed NDVI was made at 10' spati al resolution, Atmospheric CO2 concentration and montiiiy precipitatio n were used as two driving variables for global change simulation. Eff ects of precipitation increments on percentage sunshine, relative humi dity, radiation, evapotranspiration, and eventually soil water and pla nt growth, were considered, Two levers of CO2 concentration (present, doubled) and seven levels of precipitation increments (0, 0.05, 0.1, 0 .15, 0.2, 0.25, and 0.30) were prescribed for a total of 14 simulation runs. A steady-state solution was obtained for each simulation run. T he results of simulation showed that with the present climate conditio ns, doubling atmospheric CO2 concentration led approximately to a 20.3 % increase in green biomass, 11.0% increase in nongreen biomass, 19,0% increase in green NPP, 12.8% increase in nongreen NPP, and 24.9% incr ease in overall average NPP at steady state, These increases go, respe ctively, to 32.9, 13.9, 30.0, 20.1, and 23.4% when a 30% precipitation increase was superimposed on the doubled CO2 concentration.