## 3 Results
### Measured vs. Simulated Daily and Monthly CO\({}_{2}\) Exchange Fluxes  
#### 3.3.1 Comparison of Model Performances for the Calibration and Evaluation Periods  
The application of site-specific and multi-site parameters improved simulation results for GPP and NEE on average by 27% and 38%, respectively, as compared to _a priori_ parameter sets (data not shown). For the calibration period \(r^{2}\) values for the comparison of measured and simulated daily CO\({}_{2}\) exchange fluxes are in between 0.51 to 0.90, model efficiency (ME) ranges from 0.48 to 0.85 and RMSPEn from 0.39 to 0.72. As can be expected, model performance criteria were slightly less good for the evaluation period in most cases (see Table 5; a comparison of simulated and measured C fluxes separated by forest sites for both periods are also illustrated in Figure 1). Looking at the slope of the relationship between simulations and measurements, simulations generally underestimate GPP and NEE, which is more expressed with multi-site parametrization than with the site-specific parameters (except GPP for the evaluation period; see Figure 1). The following result and discussion sections only refer to the sequences of data corresponding to the evaluation period.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Tree Species**} & \multirow{2}{*}{**Site**} & \multirow{2}{*}{**CO\({}_{2}\) Flux**} & \multicolumn{2}{c}{\(r^{2}\)} & \multicolumn{2}{c}{**ME**} & \multicolumn{2}{c}{**RPMSE\({}_{n}\)**} \\ \cline{3-8}  & & & **CP** & **EP** & **CP** & **EP** & **CP** & **EP** \\ \hline \multirow{8}{*}{**Pinus sylvestris**} & **FI-Hyy** & **GPP** & 0.85 & 0.86 & 0.85 & 0.81 & 0.39 & 0.44 \\  & **NEE** & 0.65 & 0.71 & 0.61 & 0.63 & 0.62 & 0.61 \\ \cline{2-8}  & **BE-Bra** & **GPP** & 0.85 & 0.80 & 0.83 & 0.73 & 0.41 & 0.52 \\  & **NEE** & 0.70 & 0.70 & 0.64 & 0.63 & 0.60 & 0.61 \\ \cline{2-8}  & **NL-Lo0** & **GPP** & 0.90 & 0.71 & 0.84 & 0.65 & 0.39 & 0.59 \\  & **NEE** & 0.74 & 0.51 & 0.70 & 0.47 & 0.55 & 0.72 \\ \cline{2-8}  & **FI-Sod** & **GPP** & 0.78 & 0.68 & 0.78 & 0.34 & 0.47 & 0.81 \\  & **NEE** & 0.64 & 0.35 & 0.63 & 0.22 & 0.61 & 0.88 \\ \hline \multirow{8}{*}{**Picea abies**} & **DE-Hoeg** & **GPP** & 0.67 & - & 0.62 & - & 0.61 & - \\  & **NEE** & 0.51 & - & 0.48 & - & 0.72 & - \\ \cline{2-8}  & **DE-Tha** & **GPP** & 0.85 & 0.80 & 0.85 & 0.79 & 0.39 & 0.45 \\  & **NEE** & 0.65 & 0.65 & 0.61 & 0.60 & 0.62 & 0.63 \\ \cline{2-8}  & **DE-Wet** & **GPP** & 0.85 & 0.79 & 0.83 & 0.77 & 0.41 & 0.48 \\  & **NEE** & 0.70 & 0.56 & 0.64 & 0.54 & 0.60 & 0.68 \\ \hline \multirow{8}{*}{**Fagus sylvatica**} & **IT-Col** & **GPP** & 0.79 & 0.66 & 0.77 & 0.63 & 0.48 & 0.60 \\  & **NEE** & 0.70 & 0.57 & 0.70 & 0.55 & 0.55 & 0.67 \\ \cline{1-1} \cline{2-8}  & **DK-Sor** & **GPP** & 0.84 & 0.85 & 0.81 & 0.83 & 0.43 & 0.42 \\ \cline{1-1}  & **NEE** & 0.67 & 0.69 & 0.64 & 0.67 & 0.60 & 0.57 \\ \cline{1-1} \cline{2-8}  & **FR-Hes** & **GPP** & 0.83 & 0.87 & 0.71 & 0.84 & 0.54 & 0.40 \\ \cline{1-1}  & **NEE** & 0.72 & 0.73 & 0.69 & 0.70 & 0.56 & 0.55 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of model evaluation criteria for daily CO\({}_{2}\) exchange fluxes with site-specific parameters during the calibration period (CP) and evaluation period (EP).