## 3 Results
### Comparison of Spring Phenology in Boreal Forests at the Site Scale  
Comparative analysis with ground observations revealed significant correlations (\(p<\) 0.05) between spring phenology onset dates derived from GOME-2 SIF, GOSIF, and EVI2 and ground observations, both at 3.5\({}^{\circ}\) grids (Figure 5a, Table 3) and at their optimal spatial scales for phenology detection, i.e., 3.5\({}^{\circ}\) (GOME-2 SIF), 0.05\({}^{\circ}\) (GOSIF), and 0.005\({}^{\circ}\) (EVI2) (Figures A1 and A2, Tables A2 and A3), except at scales centered on PEP725 sites. In terms of absolute values, GOME-2 SIF and FLUX-GPP had an average difference of 8 days, while GOSIF and EVI2 differed from FLUX-GPP by 16 days and 12 days, respectively. Compared to PEP725, GOME-2 SIF had an average difference of 38 days, while GOSIF and EVI2 differed by 24 days and 23 days, respectively. On average, SOSs from remote \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{**T\({}_{\text{air}}\) at SOS (\({}^{\circ}\)C)**} & **MF** & **ENF** & **DNF** & **WS** & **S** & **OS** \\ \hline GOME-2 SIF & 6.6 \(\pm\) 3.8 & 4.6 \(\pm\) 4.0 & 7.1 \(\pm\) 2.8 & 5.3 \(\pm\) 4.1 & 5.0 \(\pm\) 3.4 & 3.5 \(\pm\) 2.9 \\ GOSIF & 9.0 \(\pm\) 2.9 & 7.5 \(\pm\) 2.8 & 7.8 \(\pm\) 2.3 & 7.6 \(\pm\) 3.0 & 6.2 \(\pm\) 3.0 & 4.2 \(\pm\) 2.3 \\ EVI2 & 8.1 \(\pm\) 2.5 & 7.4 \(\pm\) 2.2 & 7.9 \(\pm\) 2.3 & 7.5 \(\pm\) 2.5 & 6.3 \(\pm\) 3.1 & 3.4 \(\pm\) 3.3 \\ \hline \multicolumn{1}{c}{**LST at SOS (\({}^{\circ}\)C)**} & **MF** & **ENF** & **DNF** & **WS** & **S** & **OS** \\ \hline GOME-2 SIF & 7.8 \(\pm\) 4.0 & 5.7 \(\pm\) 4.2 & 8.6 \(\pm\) 3.1 & 6.5 \(\pm\) 4.4 & 6.2 \(\pm\) 3.9 & 4.5 \(\pm\) 3.5 \\ GOSIF & 10.3 \(\pm\) 3.4 & 8.6 \(\pm\) 3.0 & 9.4 \(\pm\) 2.6 & 8.8 \(\pm\) 3.4 & 7.5 \(\pm\) 3.4 & 5.4 \(\pm\) 2.6 \\ EVI2 & 9.7 \(\pm\) 3.2 & 8.5 \(\pm\) 2.6 & 9.4 \(\pm\) 2.7 & 8.8 \(\pm\) 3.2 & 7.6 \(\pm\) 3.6 & 4.8 \(\pm\) 3.8 \\ \hline \multicolumn{1}{c}{MF: Mixed Forests; ENF: Evergreen Needleleaf Forests; DNF: deciduous Needleleaf Forests; WS: Woody Savannas; S: Savannas; OS: Open Shrublands.} \\ \end{tabular}
\end{table} 
Table 2: Daily maximum temperature (T\({}_{\text{air}}\)) and daily maximum land surface temperature (LST, canopy temperature) at spring phenology onset date (SOS) of various coniferous vegetation types. Figure 4: Spring phenology onset dates and their non-parametric tests of various coniferous vegetation types. The white dots represent the mean value. MF: Mixed Forests; ENF: Evergreen Needleleaf Forests; DNF: Deciduous Needleleaf Forests; WS: Woody Savannas; S: Savannas; OS: Open Shrublands. Different letters denote significant differences (\(p<\) 0.05). Comparison of Relationships Between Spring Phenology and Climate Factors in Boreal Forests at the Site Scale  
At 3.5\({}^{\circ}\) grids centered on the sites, partial correlation analyses (Table A5) of SOS-climate relationships based on GOME-2 SIF, GOSIF, EVI2, and FLUX-GPP demonstrated that the correlation between GOME-2 SIF and FLUX-GPP was statistically significant (\(p<0.05\)) (Figure 6a). Consistent results were observed for spring phenology and climate factors at Eurasia flux sites (Figure A3, Tables A6 and A7). Notably, the SOS-climate relationship between GOME-2 SIF and GOSIF exhibited the strongest correlation (Figure 6b-d). Similarly, partial correlation analyses (Table A8) of GOME-2 SIF, GOSIF, EVI2, and PEP72 showed significant consistency (\(p<0.05\)) in the SOS-climate relationships between three remote sensing datasets and PEP725 (Figure 6e). In addition, the SOSs of GOSIF and EVI2 showed the strongest correlation with climate factors (Figure 6f-h). relationships for GOME-2 SIF, GOSIF, and EVI2 showed significant correlations (_p_ < 0.05) with ground observations. This demonstrated the complementary roles of the three remote sensing datasets in studying spring phenology and its relationship with climate in boreal forests, thereby enriching the available remote sensing data sources for phenological research in this region.