## Materials and Methods
### Validation of The Biome-BGC Model  
In this study, the simulation results of the Biome-BGC model were validated through comparative analysis of observed values and simulated values, combined with relevant literature findings. The observed values of NPP were derived from the analytic-tree fitted biomass model, obtained from a sample-plot survey based on the sub-compartment data of forest resource inventory and planning projects in 2003 and 2013 [41,42]. The carbon content in various plant organs, litters, and A and B layers of soil are determined by experiment, and the observed values of carbon density were estimated according to the carbon storage obtained from the biomass and the area data [43]. [PERSON] et al. used the CBM-CFS3 model as the basic platform and simulated annual NPP values (2.20-5.08 Mg C hm\({}^{-2}\) year\({}^{-1}\)) and carbon densities of various forest types in the Three Gorges Reservoir area by plotting age-harvest growth curves for the major forest types [44]. [PERSON] et al., based on forest resources inventory data from three periods (6, 7, and 8), used the forest stock volume (increment) extension method to estimate average NPP values of forests in the Three Gorges Reservoir area; NPP ranged between 2.85 and 6.19 Mg C hm\({}^{-2}\) year\({}^{-1}\)[45]. The comparison results are shown in Tables 3 and 4. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No** & **Parameters** & **Unit** & **ENF** & **DBF** & **EBF** & **SHRUB** \\ \hline P14 & C:N of dead wood & KgC/KgN & 729.0 & 109.9 & 300.0 & 730 \\ P15 & Leaf litter labile proportion & DIM & 0.31 & 0.39 & 0.32 & 0.48 \\ P16 & Leaf litter cellulose proportion & DIM & 0.45 & 0.44 & 0.44 & 0.37 \\ P17 & Leaf litter lignin proportion & DIM & 0.24 & 0.17 & 0.24 & 0.15 \\ P18 & Fine root labile proportion & DIM & 0.34 & 0.29 & 0.30 & 0.41 \\ P19 & Fine root cellulose proportion & DIM & 0.44 & 0.18 & 0.45 & 0.37 \\ P20 & Fine root lignin proportion & DIM & 0.22 & 0.53 & 0.25 & 0.22 \\ P21 & Dead wood cellulose proportion & DIM & 0.71 & 0.66 & 0.76 & 0.71 \\ P22 & Dead wood lignin proportion & DIM & 0.29 & 0.34 & 0.24 & 0.29 \\ P23 & Canopy water interception coefficient & \(1/\text{LAI}/\text{day}\) & 0.045 & 0.021 & 0.041 & 0.045 \\ P24 & Canopy light extinction coefficient & DIM & 0.5 & 0.7 & 0.7 & 0.55 \\ P25 & All-sided to projected leaf area ratio & DIM & 2.6 & 2.0 & 2.0 & 2.3 \\ P26 & Specific leaf area & m\({}^{2}/\text{KgC}\) & 8.1 & 20.0 & 12.0 & 17.5 \\ P27 & Ratio of shaded SLA:sunlit SLA & DIM & 2.0 & 2.0 & 2 & 2 \\ P28 & Fraction of leaf N in Rubisco & DIM & 0.08 & 0.085 & 0.06 & 0.04 \\ P29 & Maximum stomatal conductance & m/s & 0.006 & 0.005 & 0.005 & 0.006 \\ P30 & Cuticular conductance & m/s & 0.0006 & 0.00001 & 0.00001 & 0.00006 \\ P31 & Boundary layer conductance & m/s & 0.09 & 0.01 & 0.01 & 0.02 \\ P32 & Leaf water potential: start of & MPa & \(-\)0.65 & \(-\)0.6 & \(-\)0.6 & \(-\)0.81 \\  & conductance reduction & MPa & \(-\)2.5 & \(-\)2.3 & \(-\)3.9 & \(-\)4.2 \\ P33 & Vapor pressure deficit: start of & Pa & 610 & 930.0 & 1800.0 & 970 \\  & conductance reduction & Pa & 3100 & 4100 & 4100.0 & 4100 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._ \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Vegetation Type** & \begin{tabular}{c} **Observed NPP Value** \\ **(Mg C hm\({}^{-2}\) year\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Simulated NPP Value** \\ **(Mg C hm\({}^{-2}\) year\({}^{-1}\))** \\ \end{tabular} &
\begin{tabular}{c} **NPP Values from the Literature** \\ **(Mg C hm\({}^{-2}\) year\({}^{-1}\))** \\ \end{tabular} \\ \hline ENF & 3.60 & 5.53 & Average NPP of various \\ Mixed & 3.22 & 4.94 & forest types \\ DBF & 3.28 & 4.35 & 2.20–5.08 [44] \\ EBF & 4.55 & 4.41 & 2.85–6.19 [45] \\ Shrub & 2.81 & 2.86 & 2.85–6.19 [45] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison between measured and simulated NPP values in the TGRA.