## 5 Conclusions  
With respect to _P. tomentosa_ B301, our research results show that all six vegetation indices were able to reflect the phenological growth law, but there were slight differences among them. To represent the growth conditions objectively in the process of phenological analysis, GCC and GEI were selected to show the seasonal changes in the vegetation. However, the amplitude of variation in GCC is relatively large, so it was deemed to be more suitable for accurately studying _P. tomentosa_ B301. Under sufficient water conditions, the overall vegetation index of _P. tomentosa_ B301 under DIFI (preset point 1) was higher, and the withering process was relatively short. BIFI (preset point 5) performed rapidly in the early stage and gradually slowed during the later stage. The amplitude of variation of the vegetation value was large. This indicates that the irrigation results of DIFI were better than those of BIFI, and that DIFI was more conducive to the growth of _P. tomentosa_ B301 after reducing the waste of water resources. Additionally, the irrigation methods exert different degrees of damage due to diseases and insect pests on _P. tomentosa_ B301. Furthermore, this indicates that sufficient water is more conducive to the growth and development of planted forests than rain fed (preset point 1). In the rainy season, the high precipitation could improve the growth rate of _P. tomentosa_ B301 in the BIFI area, but the growth rate decreased for this tree species in the DIFI area. Conversely, low precipitation was able to increase the growth rate of _P. tomentosa_ B301 in the DIFI area. In view of the irregular follow-up and low precipitation, the tree species under CK (preset point 1) had better development, indicating that vegetation with rain-fed irrigation (preset point 1) was better able to adapt to changes in the environment. Overall, precipitation had different impacts on _P. tomentosa_ B301 in the DIFI and BIFI areas. From the perspective of long-term development, monitoring forest phenology using near-earth remote sensing images using scientific cultivation modes could improve productivity.  
This study provides corresponding scientific measurements for precision irrigation, nutrient supply and pest prevention, forms an information system while reducing material waste and financial cost, provides a feasible way to study the relationship between seasonal changes in vegetation communities and different health factors, and provides an effective means to diagnose the seasonal evolution characteristics of artificial forests and the rapid response of ecosystems to climate change on local, regional and global scales.  
Conceptualization, P.G.; methodology, P.G. and L.Z.; formal analysis, P.G.; investigation, P.G., Y.L., Y.G. and Y.W.; writing--original draft preparation, P.G.; writing--review and editing, P.G., Y.Z., B.X. and G.L.; supervision, Y.Z. All authors have read and agreed to the published version of the manuscript. This work is supported by The National Key Research and Development Program of China (2021 YFD2201203) and The Fundamental Research Funds for the Central Universities (2021 ZY74). All data will be available on request. The authors declare no conflict of interest.