## 3 Results  
### Leaf Phenology Derived from Ground Observation and UAV Imagery  
A typical example of seasonal trajectories of leaf phenological metrics is shown in Figure 1. Although all the metrics showed similar trajectories in the spring, the summer to autumn trajectories were markedly different among the metrics; that is, crown leaf cover based on ground visual observation (CLC\({}_{\text{ground}}\)) and Hue had a long peak period, the green chromatic coordinate (GCC), and green excess index (GEI) showed a continuous decline over summer, and the green-red vegetation index (GRVI) had an intermediate pattern between Hue and GCC (Figure 1). These trends were common for all individuals, with several exceptions (e.g., the GEI for _Acer rufinterve_ Siebold & Zucc. in 2019 had a longer peak period than that of the GRVI, Figure 10).  
Figure 1: Seasonal trajectories of leaf phenological metrics for _Betula grossa_ Siebold & Zucc. measured in 2020, with a visual explanation of seasons (thin arrows in the upper part of the panel; spring, April–May; summer, June–September; autumn, October–November), phenophases (thick arrows below the panel), and phenological transition dates (symbols). Solid lines are the fitted results of double logistic models. All values are normalized to the scale from 0 to 1. The data points used for curve fitting and the other trees’ data are shown in Figure 10. Abbreviations: DOY, day of the year; CLC\({}_{\text{ground}}\). crown leaf cover based on the ground observation; GCC, green chromatic coordinate; GEI, green excess index; GRVI, green-red vegetation index.  
The phenological transition dates derived from \(\text{CLC}_{\text{ground}}\) showed large inter-species variations (Figure 2). The mean start and end dates of the spring rising phase (SOR and EOR, respectively) varied by 13.5 and 27 days across the species, respectively. In addition, the mean start and end dates of the decreasing period (SOD and EOD, respectively) varied by 55.5 and 35.5 days, respectively. The climatic conditions in 2020 were characterized by heavier precipitation in July and warmer winter temperature than that in 2019 (Figure A6). Although the influence of such inter-annual variations in climatic conditions was included in the intra-species variations in leaf phenology, the mean intra-species variations in SOR, EOR, SOD, and EOD were 5.4, 6.7, 14.9, and 8.0 days, respectively, which were smaller than the inter-species variations in SOR, EOR, SOD, and EOD.  
A comparison of the phenological transition dates derived from \(\text{CLC}_{\text{ground}}\) and the UAV metrics is shown in Figure 3. The transition dates derived from the UAV metrics were significantly correlated with those derived from \(\text{CLC}_{\text{ground}}\) throughout the spring rising phase irrespective of the type of UAV metric (Figure 3A-C), whereas the RMSE values of the correlations increased as the spring progressed. In contrast, during the decreasing phase, the correlations of the phenological transition dates differed markedly among the UAV metrics, that is, although the Hue-derived transition dates showed significant correlations with the \(\text{CLC}_{\text{ground}}\)-derived dates throughout the phase, the GCC and GEI-derived dates were considerably different from the \(\text{CLC}_{\text{ground}}\)-derived dates, except for EOD (Figure 3D-F). Regarding GRVI, significant correlations were found in the comparison of MOD and EOD, but not in the comparison of SOD.  
Figure 2: Inter-species variations in the phenological transition dates derived from crown leaf cover based on ground observations (\(\text{CLC}_{\text{ground}}\)) during the rising phase (**A**) and decreasing phase (**B**). Each data point represents the transition date of individual trees. The \(y\)-axis of each panel is sorted based on either SOR or SOD. Abbreviations: DOY, day of the year; SOR, start of the rising phase; EOR, end of the rising phase; SOD, start of the decreasing phase; EOD, end of the decreasing phase.