## 3 Results
### Comparison of Vegetation Indexes at Different Preset Points  
The ROI of the trees was extracted from six colors of vegetation indices, demonstrating that the ratio greenness index (GGR), green chromatic coordinate (GCC), green red vegetation index (GRVI), and green excess index (GEI) were able to reflect the whole process of growth and withering, as indicated in Figure 7.  
Figure 7 shows that the entire growth process corresponds to five stages of vegetation phenology: The first stage is the leaf bud expansion stage, and the corresponding GGR, GCC, GRVI, and GEI all show a gentle recursion trend; the second stage is the leaf bud blossom stage, and the corresponding GGR, GCC, GRVI, and GEI all show a rapidly rising trend; the third stage is the leaf spreading period, and the corresponding GGR, GCC, GRVI, and GEI all gradually reach the peak trend; the fourth stage is the leaf discoloration period, and the vegetation index remains relatively stable and only fluctuates slightly, representing  
Figure 7: Vegetation index analysis of different irrigation methods.  
a healthy growth trend; the fifth stage is the abscission period, which corresponds to the period when GGR, GCC, GRVI, and GEI begin to drop significantly to the lowest value. When the above four vegetation indexes are at their lowest value, the (RCC) shows the opposite trend. HUE was generally stable throughout the year.  
Partial Enlargement of the Same Vegetation Index at Different Preset Points  
The overall curves of RCC and HUE remained stable, indicating that the normal growth of _P. tometosa_ B301 in the stand was not severely damaged by the natural environment. To observe the growth trend, GGR, GCC, GRVI, GEI and four vegetation indices with distinct trend characteristics were selected for enlarged observation and analysis, as shown in Figure 8.  
Figure 8: Partial enlargement of vegetation index: (**a**) GGR-local enlarged view during growth, (**b**) GGR-Detail enlarged view during defoliation, (**c**) GCC-local enlarged view during growth, (**d**) GCC-Detail enlarged view during defoliation, (**e**) GEI-local enlarged view during growth, (**f**) GEI-Detail enlarged view during defoliation, (**g**) GRVI-local enlarged view during growth, (**h**) GRVI- Detail enlarged view during defoliation.  
In Figure 8, the ROIs of the three methods of cultivation are shown, revealing significant changes in GGR, GCC, GRVI, and GEI. The start of growing season was set as the shooting time (for reference only). Rain fed (preset point 1) reached its growth peak (MOE) 2 days earlier than DIFI (preset point 3) and BIFI (preset point 5) GGR, whereas leaves withered and fell (EOS) almost 6 days before DIFI and BIFI for CK (preset point 1), according to the GRVI. The GCC was used to define the peak time (MOE) of the three groups.  
Figure 8 shows that different irrigation methods and irrigation volumes affect the growth and withering of _P. tometosa_ B301, indirectly reflecting that different irrigation methods in the same forest stand cause different micro-ecological environments and increase the severity of diseases and insect pests in the area around the trees, corresponding to the differences in withering speed and color of planted forests.