## 5 Conclusions  
Based on the primary satellite-based SIF (GOME-2 SIF), the modeled SIF (GOSIF), the vegetation index EVI2 (MCD12Q2), FLUX datasets, PEP725 datasets, climate data, and MODIS land cover data, we investigated the differences and consistencies of spring phenology of GOME-2 SIF, GOSIF, and EVI2 (MCD12Q2) across boreal forests. Despite a slight difference, our results confirmed that the spring phenology onset dates based on GOME-2 SIF, GOSIF, and EVI2 (MCD12Q2) were entirely reasonable. This was supported by analyzing the phenology onset dates across different coniferous vegetation types and the corresponding temperatures at the onset date. Furthermore, remote sensing datasets exhibited strong correlations with FLUX-GPP and PEP725 in comparative analyses of spring phenology and its relationship with climate factors. Hence, this study enriched the available remote sensing data sources for large-scale spring phenology and phenology-climate relationship research. Conceptualization, D.S. and Y.J. ; methodology, D.S. ; writing--original draft preparation, D.S. ; writing--review and editing, Y.J., M.C., M.G., X.X. and M.K. ; visualization, D.S. ;supervision, YJ. ; project administration, YJ. ; funding acquisition, YJ. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was supported by the National Natural Science Foundation of China (Grant No. 42471057 and Grant No. 42171049). **Data Availability Statement:** The datasets are available online at websites as follows: GOME-2 SIF dataset ([[https://avdc.gsfc.nasa.gov/](https://avdc.gsfc.nasa.gov/)]([https://avdc.gsfc.nasa.gov/](https://avdc.gsfc.nasa.gov/))) accessed on 1 June 2020, the GOSIF product ([[http://globalecology.unh.edu](http://globalecology.unh.edu)]([http://globalecology.unh.edu](http://globalecology.unh.edu))) accessed on 1 March 2020, the MODIS data ([[https://lpdaac.usgs.gov/](https://lpdaac.usgs.gov/)]([https://lpdaac.usgs.gov/](https://lpdaac.usgs.gov/))) accessed on 1 July 2020, FLUXNET data ([[https://fluxnet.fluxdata.org/](https://fluxnet.fluxdata.org/)]([https://fluxnet.fluxdata.org/](https://fluxnet.fluxdata.org/))) accessed on 1 November 2019, and PEP725 data ([[http://www.pep725.eu/](http://www.pep725.eu/)]([http://www.pep725.eu/](http://www.pep725.eu/))) accessed on 1 June 2023. **Acknowledgments:** We would like to gratefully acknowledge all contributors of the remote sensing data and ground observation data. **Conflicts of Interest:** The authors declare no conflicts of interest. **Abbreviations**  
GOME-2 SIF Global Ozone Monitoring Experiment-2 Solar-induced Chlorophyll Fluorescence OCO-2 SIF The Orbiting Carbon Observatory-2 SIF  
GOSIF A new global 'OCO-2' SIF dataset based on a data-driven approach  
EVI2 Two-band Enhanced Vegetation Index  
FLUX-GPP Gross primary productivity data in flux datasets  
PEP725 The Pan European Phenology network  
SOS Start of growing season  
Pcor Partial correlation coefficients  
TMAX Daily maximum air temperature  
TMIN Daily minimum air temperature  
P Cumulative precipitation  
R Surface solar radiation downwardsFigure 11: Comparison between SOSs of boreal forests derived from GOME-2 SIF, GOSIF, EVI2, and FLUX-GPP and their non-parametric tests at different scale grids centered on the sites. (**a**) Consistency of SOSs estimated from GOME-2 SIF, GOSIF, and EVI2 at their optimal spatial resolution in detecting phenology, i.e., 3.5\({}^{\circ}\) (GOME-2 SIF), 0.05\({}^{\circ}\) (GOSIF), and 0.005\({}^{\circ}\) (EVI2). (**b**) Non-parametric tests of SOSs from remote sensing datasets and FLUX-GPP. Different letters in (**b**) denote significant differences (\(p<0.05\)).