We describe the population dynamics, growth of dominant species and plant biomass production in an ecosystem undergoing succession from Pinus densiflora dominance to Quercus mongolica ssp. crispula dominance. The diameter at breast height (DBH) was recorded for a period of 31 years. As DBH increased, the tree density decreased. We estimated the net biomass production of the canopy trees, the biomass of the understory and the average amount of litter. These results suggest that the biomass production of an ecosystem depends on its species composition. In order to estimate future ecosystem productivity, it is necessary to predict temporal changes in species composition.