## 3 Results
### GPP Response to Limiting Factors Per Land Cover Class: Statistical Analysis
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & \multicolumn{2}{c}{**Grasslands**} & \multicolumn{4}{c}{**Croplands**} & \multicolumn{4}{c}{**Croplands/Natural**} \\  & **2000** & **2007** & **2010** & **2000** & **2007** & **2010** & **2000** & **2007** & **2010** \\ \hline
**N deposition** & 67.7\% & 63.7\% & 66.0\% & 44.1\% & 37.9\% & 34.6\% & 16.9\% & 14.1\% & 14.2\% \\
**Precipitation** & 8.1\% & 9.5\% & 13.6\% & 2.7\% & Excl. & 5.0\% & 2.1\% & 1.4\% & 1.0\% \\
**Sunshine** & 0.5\% & 0.1\% & 0.3\% & 0.2\% & Excl. & 0.7\% & Excl. & 0.3\% & 2.9\% \\
**Temperature** & 0.2\% & 1.4\% & 0.2\% & Excl. & 2.4\% & 0.6\% & Excl. & 0.5\% & Excl. \\ \hline \end{tabular}
\end{table} 
Table 3: Coefficient of determination (R2) change per variable (alphabetically ordered) that the stepwise regression model selected for grasslands, croplands, and croplands/natural vegetation mosaics. Excl: Excluded. Natural logarithms of N deposition used for grasslands in all the years and for croplands in 2000. In grasslands, standardized residuals were normally distributed in all the cases. D-W values from 1.9 to 2 indicated independence of residuals, and the B-P test showed residuals with heteroscedasticity that were statistically significant. The leave-one-out cross-validation resulted in SR R\({}^{2}\) values ca. 0.9 for all the years. The regression coefficients to build the model for statistical inference are shown in Table 7. In croplands, standardized residuals were normally distributed for all the datasets. D-W values were ca. 1.9, revealing independence of errors. The B-P test showed heteroscedasticity that was statistically significant. The leave-one-out cross-validation resulted in SR R\({}^{2}\) values ca. 0.6 for all the years. The regression coefficients to create the model for statistical inference are shown in Table 8. In croplands/natural vegetation mosaics, standardized residuals were not normally distributed in all the samples. D-W values ca. 1.8 showed independence of errors. The K test indicated heteroscedasticity that was statistically significant. The leave-one-out cross-validation resulted in SR R\({}^{2}\) values ca. 0.4 for all the years. The regression coefficients to generate the model for statistical inference are shown in Table 9. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & \multicolumn{2}{c}{**2000**} & \multicolumn{4}{c}{**2007**} & \multicolumn{4}{c}{**2010**} \\ \hline \multirow{2}{*}{**Order**} & **Adjusted** & \multirow{2}{*}{**RMSE**} & \multirow{2}{*}{**Order**} & **Adjusted** & \multirow{2}{*}{**RMSE**} & **Order** & **Adjusted** & \multirow{2}{*}{**RMSE**} \\  & **R\({}^{2}\)** & & & & & & & \\ \hline
**N dep** & 0.169 *** & 0.228 & N dep & 0.141 *** & 0.247 & N dep & 0.142 *** & 0.238 \\
**Precip** & 0.189 *** & 0.225 & Temp & 0.146 *** & 0.246 & Sunsh & 0.171 *** & 0.234 \\
**Sunsh** & Excl & & Precip & 0.160 *** & 0.244 & Precip & 0.181 *** & 0.232 \\
**Temp** & Excl & & Sunsh & 0.163 *** & 0.243 & Temp & Excl & \\ \hline \end{tabular}
\end{table} 
Table 6: Order of variables entered into the model and adjusted R\({}^{2}\) for croplands/natural vegetation mosaics according to the addition of a new variable to the model: N deposition: N dep, Temp: Temperature, Precip: Precipitation, and Sunsh: Sunshine. Excl: Variable excluded from the model. *** Statistically significant \(p<0.001\).