Effects of Clumping Index and Maximum Carboxylation Rate on Vegetation Productivity Estimation Based on Remote Sensing Data
[Objective]This study aims to investigate the effect of clumping index(CI)and maximum carboxylation rate(Vcmax)from remote sensing products on estimation of vegetation productivity with the boreal ecosystem productivity simulator(BEPS)model.[Method]The FLUXNET and ChinaFLUX data were used to analyze the sensitivities of CI and Vcmax in BEPS model,and compare the effects of CI and Vcmax on Gross Primary Productivity(GPP)estimation.On this basis,the vegetation productivity of terrestrial ecosystems in China in 2012 was estimated.By comparing with the estimated results of the default value,we determined the impact of the spatio-temporal changes of CI and Vcmax on the model performance.[Result]1)The results showed that CI and Vcmax had high sensitivities in the BEPS model.They were positively correlated with vegetation productivity,and the sensitivity of Vcmax was higher than that of CI in different vegetation types.2)When CI and Vcmax remote sensing products(NDHD-CI and SIF-Vcmax)were used simultaneously,the simulation results had the smallest error and the highest accuracy.The root mean square error(RMSE)of GPP decreased from 665.60 g·m-2a-1 to 584.71 g·m-2a-1,and the mean absolute error(MAE)and mean relative error(MRE)were the lowest in the four simulation cases.3)In 2012,the total GPP and Net Primary Productivity(NPP)of terrestrial ecosystems in China were 5.21 Pg·a-1 and 2.49 Pg·a-1.respectively.Affected by the spatio-temporal dynamics in the CI and Vcmax,the GPP and NPP estimates were 3.06％and 4.72％lower than the default results of the model,respectively.[Conclusion]Our results have demonstrated that NDHD-CI and SIF-Vcmax can improve the accuracy of BEPS models in estimating vegetation productivity,and other high-sensitivity parameters and model mechanisms can be optimized and improved in the future.Affected by the temporal and spatial changes of CI and Vcmax,the estimation results of vegetation productivity are slightly lower than the default situation.The effect of Vcmax on vegetation productivity estimation is higher than that of CI.
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