## 3 Results
### Modeling of Daily Net Ecosystem Exchange
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multicolumn{4}{c}{**CA-Obs**} & \multicolumn{4}{c}{**CA-Oas**} & \multicolumn{4}{c}{**CA-Gro**} \\ \cline{2-13}  & \(\mathbf{R^{2}}\) & **NSE** & **Bias** & **RMSE** & \(\mathbf{R^{2}}\) & **NSE** & **Bias** & **RMSE** & \(\mathbf{R^{2}}\) & **NSE** & **Bias** & **RMSE** \\ \hline ANN1 & 0.502 & 0.438 & 0.313 & 0.998 & 0.553 & 0.536 & 0.165 & 1.782 & 0.387 & 0.310 & 0.358 & 1.321 \\ ANN2 & 0.514 & 0.465 & 0.222 & 0.974 & 0.376 & 0.362 & \(-\)0.151 & 2.090 & 0.507 & 0.475 & 0.250 & 1.152 \\ ANN3 & 0.054 & 0.026 & \(-\)0.073 & 1.314 & 0.067 & 0.064 & 0.065 & 2.532 & 0.107 & 0.098 & 0.126 & 1.510 \\ ANN4 & 0.423 & 0.332 & 0.382 & 1.088 & 0.614 & 0.614 & 0.026 & 1.625 & 0.412 & 0.333 & 0.301 & 1.299 \\ ANN5 & 0.736 & 0.701 & 0.207 & 0.728 & 0.638 & 0.636 & 0.039 & 1.580 & 0.605 & 0.559 & 0.315 & 1.056 \\ ANN6 & 0.775 & 0.719 & 0.270 & 0.705 & 0.744 & 0.744 & 0.004 & 1.325 & 0.674 & 0.631 & 0.301 & 0.966 \\
**ANN7** & **0.830** & **0.785** & **0.232** & **0.618** & **0.817** & **0.815** & **-0.073** & **1.125** & **0.719** & **0.663** & **0.322** & **0.923** \\ GRNN1 & 0.515 & 0.433 & 0.330 & 1.003 & 0.558 & 0.538 & 0.134 & 1.779 & 0.402 & 0.346 & 0.276 & 1.286 \\ GRNN2 & 0.528 & 0.464 & 0.271 & 0.975 & 0.376 & 0.352 & \(-\)0.387 & 2.106 & 0.507 & 0.481 & 0.249 & 1.146 \\ GRNN3 & 0.050 & 0.035 & 0.124 & 1.309 & 0.073 & 0.066 & 0.034 & 2.529 & 0.107 & 0.067 & \(-\)0.311 & 1.537 \\ GRNN4 & 0.368 & 0.297 & 0.313 & 1.117 & 0.685 & 0.627 & \(-\)0.557 & 1.597 & 0.420 & 0.337 & 0.344 & 1.295 \\ GRNN5 & 0.739 & 0.685 & 0.235 & 0.748 & 0.637 & 0.606 & \(-\)0.344 & 1.642 & 0.614 & 0.274 & 0.927 & 1.355 \\ GRNN6 & 0.779 & 0.725 & 0.079 & 0.699 & 0.714 & 0.694 & \(-\)0.339 & 1.447 & 0.661 & 0.554 & 0.436 & 1.062 \\
**GRNN7** & **0.805** & **0.766** & **0.055** & **0.644** & **0.787** & **0.755** & **-0.353** & **1.294** & **0.718** & **0.672** & **0.246** & **0.911** \\ ANFIS1 & 0.510 & 0.438 & 0.327 & 0.998 & 0.535 & 0.525 & 0.147 & 1.803 & 0.396 & 0.335 & 0.304 & 1.296 \\ ANFIS2 & 0.531 & 0.482 & 0.193 & 0.959 & 0.354 & 0.345 & \(-\)0.106 & 2.117 & 0.510 & 0.468 & 0.304 & 1.160 \\ ANFIS3 & 0.052 & 0.038 & \(-\)0.008 & 1.307 & 0.071 & 0.066 & 0.067 & 2.529 & 0.129 & 0.109 & 0.223 & 1.501 \\ ANFIS4 & 0.338 & 0.281 & 0.297 & 1.130 & 0.694 & 0.692 & 0.026 & 1.453 & 0.433 & 0.336 & 0.377 & 1.296 \\ ANFIS5 & 0.732 & 0.678 & 0.240 & 0.756 & 0.640 & 0.639 & \(-\)0.028 & 1.572 & 0.609 & 0.565 & 0.304 & 1.049 \\ ANFIS6 & 0.804 & 0.739 & 0.281 & 0.681 & 0.761 & 0.759 & 0.032 & 1.285 & 0.683 & 0.628 & 0.322 & 0.970 \\
**ANFIS7** & **0.808** & **0.758** & **0.264** & **0.655** & **0.830** & **0.824** & **-0.158** & **1.097** & **0.716** & **0.670** & **0.289** & **0.914** \\ SVM1 & 0.490 & 0.449 & 0.262 & 0.988 & 0.552 & 0.539 & 0.184 & 1.776 & 0.424 & 0.348 & 0.336 & 1.284 \\ SVM2 & 0.539 & 0.482 & 0.253 & 0.958 & 0.315 & 0.241 & \(-\)0.289 & 2.279 & 0.493 & 0.413 & 0.388 & 1.218 \\ SVM3 & 0.031 & \(-\)0.063 & 0.137 & 1.373 & 0.012 & \(-\)0.192 & 1.178 & 2.857 & 0.078 & \(-\)0.058 & 0.583 & 1.636 \\On the other hand, the over- and under-estimation of the best model in predicting the daily NEE for the three sites among the training, validation and testing periods are illustrated in Figure 6. It is clear that most of the estimated values closely follow the corresponding observed values in the three stands. In the growing season, however, the NEE values simulated by the GRNN model at CA-Gro site fail to well match the corresponding measured values. Figure 5: Comparisons of measured and simulated daily net ecosystem exchange (NEE) in the testing period in the three boreal forest stands. (**a–e**) For CA-Obs stand; (**f–j**) for CA-Oas stand; and (**k–o**) for CA-Gro stand.