Estimation Of Vegetation Productivity Of Chinese Terrestrial Ecosystem From1985to2006

Terrestrial ecosystem carbon cycle, as an important part of the global carbon cycle, plays a vitally significant role in global changes. It has also constantly been the focus on the study of global changes. With the development of terrestrial ecosystem carbon cycle model, the understanding of the terrestrial ecosystem carbon fluxes has been largely promoted, and the adoption of various models on the productivity of ecosystem has been one of the key contents in ecological research. In order to estimate net primary productivity of terrestrial ecosystems in China and the spatiotemporal pattern and uncertainty of net ecosystem productivity, this thesis used the Markov-chain Monte Carlo method to optimize the key parameter of the CASA model-the maximum light use efficiency based on the ChinaFLUX eddy flux data. The optimized CASA model was used to simulate China’s net primary productivity of terrestrial ecosystem and net ecosystem productivity from1985to2006, and conducted a quantitative analysis of the impact of the parameter uncertainty and the simulation of equilibrium on modeled productivity results. The conclusions obtained from this research are listed as follows.(1) The result of the sensitive analysis to CASA model parameters using a local sensitive analysis show that the most sensitive parameters of model are: the maximum light use efficiency, maximum NDVI, the leaf partition ratio with constant stem partition ratio and the root partition ratio with constant stem partition ratio.(2) The posterior estimation of the maximum light use efficiency using the Markov Chain Monte Carlo method in multiple ecological systems follow approximately normally distributions. Optimized values of the maximum light use efficiency for forest, cropland and grassland is0.60±0.05-0.81±0.05gCMJ-1,1.43±0.13gCMJ-1,0.20±0.03gCMJ-1, respectively. Then the optimized values of maximum light use efficiency were used to simulate the primary productivity of each ecosystem from2005to2006. The results using the optimized value were closer to the observed values compared with that using the default value, which significantly improved the underestimation of the ecosystem primary productivity modeld by the original model.(3) The simulation of China’s net primary productivity in terrestrial ecosystems and net ecosystem productivity from1985to2006was conducted based on the optimized maximum light use efficiency. The average value of China’s net primary productivity in terrestrial ecosystems in1985-2006is2.94Pg C a-1, increasing by53.4%compared with the modeled value (1.93Pg C a-1) using the default value. The average value of net ecosystem productivity is0.088Pg C a-1,76%higher than the result before parameter optimization.(4) The uncertainties of the simulation results of China’s terrestrial ecosystem productivity induced by parameter uncertainty and equilibrium modeling uncertainty were quantified. By comparing the results and the spin-up time, the model simulation results tend to be more reasonable when the driving model of the long standing average climate data is utilized and the iterations are set to3000times. The ecosystem which has the highest estimates of productivity also has the largest posteriori estimation uncertainty. More studies need to be done in estimating heterotrophic respiration parameters to to improve the accuracy of the model simulation.