Validation and Adaptability Evaluation of Grass Ecosystem Model CENTURY in Inner Mongolia

Inner Mongolia grassland is one of the most important grazing lands in China.Grassland area of Inner Mongolia is about 87 million hm2,accounts for 67.5% of land area of Inner Mongolia and 25% of national grassland area of China.It is very important for sustainable utilization of grassland and the prevention of grassland desertification to study the impact of climate changes on grassland ecosystem.Grassland ecosystem models have been widely used as tools to analyze the impact of climate change on grassland productivity.At present,grassland ecosystem model(CENTURY) has been validated in a single grassland type of Inner Mongolia.However,few studies evaluated the adaptability of CENTURY model in different grassland types within Inner Mongolia.Therefore,there is lack of parameters for applying CENTURY model over different grassland types of Inner Mongolia.In this paper,Ergun Right Banner(N50.25°,E120.18°),Xianghuang Banner(N42.23°,E113.83°),Wushen Banner(N38.60°,E108.83°) and Sunit Left Banner(N43.85°,E113.72°) were selected to represent four main grassland types including meadow steppe,typical steppe,desert steppe and steppe desert in Inner Mongolia.The long-term observation data of grassland biomass from the livestock meteorological experiment stations were used to calibrate and validate the grassland ecosystem model(CENTURY 4.6).CENTURY model was a process-based ecosystem model comprising the sub-models of plant production,soil organic matter and soil water movement.Monthly meteorological data(maximum temperature,minimum temperature,and precipitation) for the study sites were used as the driving variables of CENTURY model.Management measures and soil datawere also used as the inputs of the model.The calibration and validation results showed that there was a close consistency between the simulated and measured aboveground biomass of meadow steppe,typical steppe,desert steppe and steppe desert.The determination coefficients(R2) were 0.60,0.60,0.65 and 0.59(P0.05).Relative mean square roots(RMSE) were 29.65,31.45,25.51 and 7.90 g C·m-2.CENTURY model could be used to simulate the response of aboveground biomass of different grassland types to climate change and climate variability and thereafter study the impact of climate change on grass productivity.Sensitivity analyses showed that the sensitive parameters of grassland aboveground biomass were the optimum growth temperature,the maximum growth temperature and the coefficient for calculating potential grassland productivity.Accurate determinations of these parameters are the key in applying CENTURY model.The sensitivity analysis of CENTURY model to driving variables showed that grassland aboveground biomass was more sensitive to monthly precipitation and monthly maximal temperature than monthly minimum temperature.The changes of accumulated aboveground biomass of four main grassland types was simulated during the past 50 years(1961-2010) based on CENTURY model.The simulation results displayed that the accumulated aboveground biomass during the last 50 years increased in Ergun Right Banner and Wushen Banner and decreased in Xianghuang Banner and Sunit Left Banner,but there was no significant difference at 95% level.These results were consistent with existing studies.