Abstract: At the site level, the authors used the Century plant-soil ecosystem model and Landsat remote sensing to estimate the aboveground biomass of Aneurolepidium chinense steppe and Stipa grandis steppe in the Xilin river basin, Inner Mongolia China. The results of century simulation matched well in terms of the seasonal and yearly change of biomass, with those of field moniforing. The results of field monitoring replicated well were about 142.45～144.37 g/m2 and 210. 38~227.44 g/m2 on S. grandis and A. chinense steppe, respectvely, whereas the simulation results were 127. 04～156. 23 g/m2 and 189.25~193.98 g/m2, respectively. Simulated soil organic matter was around ±–25% of the observed data. Normalized differnce vegetation index derived aboveground biomass was around ±25 % of the observed field biomass on the A. chinence and S. grandis steppe, using Landsat TM imagecries on July 31, 1987 and August 11, 1991. The effect of global climate change and elevated CO2 on these steppe was examined, using the climate fields from Global Change Models of Canadian Climate Center and Geophysics Flow Dynamics Laboratory under 1 × CO2 (350 X 10-6) and 2 × CO2 (700 X 10-6) sceneries. Climate change resulted in considerable decrease of primary productivity and soil organic matter of A. chinense and S. grandis steppe, the former being more sensitive to climate change.

Key words: Biomass, Aneurolepidium chinese steppe, Stipa grandis steppe, Ecosystem model, Normalized differnce vegetation index