## 2 Experimental Section
### Statistics  
The coefficient of variation (CV) is used to show variations of model parameters. All temperature-related parameters _i.e._, PSNTMAX, PSNTOPT and PSNTMIN (see Table 2 for description), were converted to Kelvin. Model performance was evaluated using the coefficient of determination (\(r^{2}\)), model efficiency (ME) and normalized root mean square prediction error (RMSPEn) [40,44,45]. Model performance criteria were calculated for daily as well as for monthly aggregated values. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c} \hline \hline  & & & & \multicolumn{6}{c}{**Average Annual**} & & & & & & & & & & & & & & & \\
**Site** & **Shortcut** & **Tree Species** & **Latitude** & \multicolumn{2}{c}{**Ciminate Conditions**} & \multicolumn{2}{c}{**Stand**} & \multicolumn{2}{c}{**N Dep.**} & \multicolumn{2}{c}{**Organic Layer**} & \multicolumn{2}{c}{**Soil (First 5 cm)**} \\  & & & & & **Ciminate** & \multicolumn{2}{c}{**Ciminating Age**} & \multicolumn{2}{c}{**(kg N & & & & & & & & & & \\  & & & & & **T (C)** & **P (mm)** & & & & & & & & & & & & & \\ \cline{1-19}  & & & & & **T (C)** & **P (mm)** & & & & & & & & & & & & & \\ \cline{1-19}  & & & & & & & & & & & & & & & & & & \\ \hline Hyyūlas—Finland * & FI-Hyp & _Pinus sybusters_ & \(N\,61^{\circ}50^{\prime}\) & 4.0 & 614 & 56 & 4 & MODER & 32 & 39 & \begin{tabular}{} \end{tabular} & 8–13 & 3.4 & 31 & 4.6 \\ Brasschast—Belgium & Be-Bra & _Pinus sybusters_ & \(N\,51^{\circ}18^{\prime}\) & 10.8 & 825 & 87 & 40 & MODER & 44 & 28 & \begin{tabular}{} \end{tabular} & 1–4 & 5.0 & 23 & 3.8 \\ Lobobos—Netherlands & NL-Loop & _Pinus sybusters_ & \(N\,52^{\circ}10^{\prime}\) & 10.1 & 788 & 106 & 50 & MODER & 44 * & 27 & \begin{tabular}{} \end{tabular} & 2–9 & 8.5 & 17 & 3.4 \\ Sodankyla—Finland & F1-Sod & _Pinus sybusters_ & \(N\,67^{\circ}21^{\prime}\) & 0.8 & 500 & 60–154 & 2 & MODER & 32 & 29 *** & sand & 2–9 & 2.2 & 29 *** & 3.3 \\ Hoglwald—Germany & DE-Hoog & _Pleac abies_ & \(N\,50^{\circ}30^{\prime}\) & 8.7 & 856 & 109 & 30 & MODER & 35 & 30 & \begin{tabular}{} \end{tabular} & 5–25 & 4.2 & 19 & 3.6 \\ Thrand—Germany * & DE-Tha & _Pleac abies_ & \(N\,50^{\circ}57^{\prime}\) & 8.9 & 860 & 125 & 30 & MODER & 41 & 24 & \begin{tabular}{} \end{tabular} & 13–16 & 6.3 & 20 & 3.9 \\ Wetzstein—Germany & DE-Wet & _Pleac abies_ & \(N\,50^{\circ}27^{\prime}\) & 6.5 & 865 & 61 & 21 & MODER & 36 & 26 & \begin{tabular}{} \end{tabular} & 7–11 & 7.0 & 10 & 3.7 \\ Collelongo—Italy & IT-Col & _Fagus sybusters_ & \(N\,46^{\circ}35^{\prime}\) & 4.7 & 830 & 47 & 12 & MODER & 38 & 33 & \begin{tabular}{} \end{tabular} & 25–27 & 9.0 & 13 & 4.1 \\ Sorce—Denmark & DK-Sor & _Fagus sybractica_ & \(N\,55^{\circ}29^{\prime}\) & 8.6 & 752 & 95 & 27 & MODER & 45 *** & 22 *** & \
\begin{tabular}{} \end{tabular} & 22–26 & 2.5 & 15 & 4.6 \\ Hesse—France ** & FR-Hes & _Fagus sybractica_ & \(N\,48^{\circ}40^{\prime}\) & 10.2 & 965 & 46 & 16 & MULL & 41 & 41 &
\begin{tabular}{} \end{tabular} & 22–29 & 3.9 & 15 & 4.6 \\ \hline \hline \multicolumn{12}{c}{**FI-Hyp: [36,46,47], European fluxes database cluster; **BE-Bra:** [48,49], European fluxes database cluster; **NL-Loop** [50, 51, 52], European fluxes database cluster; **FI-Sod**: European fluxes database cluster; **DE-Hoog:** [53, 54, 55, 56]; **DE-Tha:** [41,52,57, 58, 59], European fluxes database cluster; **DE-Wet:** [59,60], European fluxes database cluster; **IT-Ren:** [61], European fluxes database cluster; **DE-Sor**: [13,62, 63, 65], European fluxes database cluster; **FR-Hes:** [41,62,63], European fluxes database cluster; **FT-Hes:** [41,62,63], European fluxes database cluster; **Thinning event 2002; **Thinning event 2005; *** Model default value.**} \\ \end{tabular}
\end{table} 
Table 1: Site characteristics of investigated forest ecosystems (soil type is arranged according FAO classification).