## 5 Conclusions  
In this study, we assessed the potential to jointly use near-infrared-enabled digital repeat photography and eddy covariance data for monitoring structural and physiological phenology in seasonally dry Mediterranean tree-grass ecosystems. We analyzed 9 site-years using four PhenoCam-based vegetation indices (GCC, CamNDVI, CamNIRv, and CamRVI) and GPP, and we compared the phenological transition dates (PTDs) and growing season length (GSL) derived from the different data streams. We show that, in Mediterranean tree-grass ecosystem, meteorology plays an important role in governing seasonal variation of vegetation indices and GPP, though the importance of water availability and temperature vary across seasons. We show the PTDs derived from VIs differ from each other. For the widely used GCC and CamNDVI, the PTDs extracted from CamNDVI are delayed compared to the ones derived from the GCC, which is likely attributed to GCC, and is more sensitive to color changes, while CamNDVI is more sensitive to LAI and biomass. CamNIRv is best at representing the PTDs of GPP at the Green-up period, while CamNDVI is the best proxy to represent the PTDs of GPP at the Dry-down period. CamNIRv performs best regarding the representation of the GSL of GPP. In summary, we show that it is possible to determine crucial PTDs of structural and physiological phenology through using near-infrared-enabled digital cameras. GPP could be well represented when combining the use of different VIs for this purpose. Conceptualization, M.M., M.R., C.R., and Y.L. ; Methodology, Y.L., G.F., X.M., and M.M. ; Formal Analysis, Y.L., and T.S.E.-M.; Supervision, M.M., M.R., C.R., and X.M., Investigation, B.A., R.G.-C., T.W.H., G.M., and M.P.M. ; Data Curation, T.S.E.-M., R.G.-C., M.P.M., G.M., and T.W.H. ; Writing-Original Draft Preparation, Y.L., Writing-Review & Editing, all coauthors. The authors acknowledge the Alexander von Humboldt Foundation for supporting this research with the Max-Planck Prize to [PERSON]. Y.L. and M.M. gratefully acknowledge financial support from the China Scholarship Council. We are also thankful for financial support from the Spanish Ministry of Economy and Competitiveness through the FLUXPEC project \"Monitoring changes in water and carbon fluxes from remote and proximal sensing in a Mediterranean dehesa ecosystem\" (CGL2012-34383). The development of PhenoCam has been supported by the Northeastern States Research Cooperative, NSF's Macrosystems Biology program (award EF-1065029 and EF-1702697), DOE's Regional and Global Climate Modeling program (award DE-SC0016011), and the US National Park Service Inventory and Monitoring Program and the USA National Phenology Network (grant number G10 AP00129 from the United States Geological Survey). The authors thank [PERSON] for relevant technical assistance and comments on graphics. The authors thank two anonymous reviewers and the editor for constructive comments to improve the earlier manuscript. The authors thank [PERSON] for final proofreading for English. The authors declare no conflict of interest. Figure 11: Comparison between _max_([PERSON] et al., 2012) and _max_density_ methods for their performance of filtering the PhenoCam-based vegetation indexes like near-infrared reflectance of vegetation index (NIRv). The black points are original half-hourly NIRv data, while red points stand for the filtered daily NIRv data retrieved by using _max_ or _max_density_ method. Figure 14: Scatter plots between monthly mean air temperature (Ta), monthly sum of precipitation (Prec) and green chromatic coordinate (GCC) during day time of (**a**) autumn, (**b**) winter, (**c**) spring, and (**d**) summer in hydrological year 2014 to 2016 in four Mediterranean tree–grass ecosystem in Spain. The data in hydrological years of 2014, 2015 and 2016 are colored with green, red and blue color, respectively. The regression line and the formula are shown if the linear regression is statistically significant (\(p\)-value: \(p<0.05\)). The gray area represents 95% confidence interval.