The dynamics of net primary productivity (NPP) and biomass of temperate forests Northeastern China was examined by comparing field data with simulation results from the ZELIG model. For broad-leaf/Korean pine mixed forests, biomass was estimated between 198 and 370 Mg ha −1 (dry weight), and NPP was estimated at 8–20 Mg ha −1 per year (dry weight). The simulation results indicate that NPP in mixed forests would discontinuously increase over the next 200–400 years, to a maximum value of 21 Mg ha −1 per year. Simulation of biomass dynamics suggests that it would peak in about 300 years at approximately 400 Mg ha −1, and then slowly decline. For oak forests, simulated NPP ranges from 5 to 13 Mg ha −1 per year, with biomass estimated at 120–310 Mg ha −1. In aspen–birch forests, maximum NPP and biomass values were 18 Mg ha −1 per year and 320 Mg ha −1, respectively, while minimum NPP and biomass values were 7 Mg ha −1 per year and 50 Mg ha −1, respectively. Larch forests were found to have lower values of NPP and biomass than other forest types, with NPP between 5 and 12 Mg ha −1 per year, and biomass between 50 and 275 Mg ha −1. Comparison of measured field data with ZELIG simulated values indicates only a 8–13% error, based on more than 50 independent plots, with a mean accuracy for simulated NPP between 88 and 93%.