Abstract: Aims The phenology of tree growth is a key research priority in the field of forest carbon sequestration within the context of global change. However, up until now, due to challenges in observation, the majority of studies have focused on the radial growth dynamics of trees, and the study of height growth patterns still lacks comprehensive coverage. Additionally, few studies employ high-frequency monitoring techniques, which limited utilization of high-frequency measurements hinders our understanding of the underlying phenological drivers. The use of canopy color indices to infer tree growth dynamics is also becoming a trend. Methods Here, we have employed area array solid-state lidar for continuous, high frequency measurements of saplings Cunninghamia lanceolata and Castanopsis carlesii height growth dynamics in a experimental mesocosm. Furthermore, we acquired RGB-converted canopy color indices from visible time-lapse photographs and integrated them with environmental factors monitored via a multi-meteorological factors observation system. The objective was to investigate the phenology of saplings height growth and their climate drives. Important findings The results indicated that the growing seasons of Castanopsis carlesii and Cunninghamia lanceolata started at similar times, but the growing season of Castanopsis carlesii ended significantly earlier than that of Cunninghamia lanceolata. Additionally, Cunninghamia lanceolata had a significantly longer growing season and a greater cumulative annual growth in tree height compared to Castanopsis carlesii. The daily growth rate of Castanopsis carlesii was significantly positively correlated with soil moisture content. In contrast, the daily growth rate of Cunninghamia lanceolata was significantly negatively correlated with air temperature and soil water content, while showing a significant positive correlation with soil temperature and vapor pressure deficit (VPD). Notable differences in canopy color indices were observed between the two species: the daily growth rate of Cunninghamia lanceolata were significantly positively correlated with the Green Excess Index (ExG), Green Chromatic Coordinate (Gcc), and Green Red Vegetation Index (GRVI), while Castanopsis carlesii showed significant correlation with GRVI only. In summary, this study employed systematic phenological observation instruments to analyze the height growth phenology and its influencing factors in trees. Additionally, it utilized canopy color indices to infer tree growth, providing important theoretical evidence for forest carbon sequestration research.

Key words: tree height growth, phenology, laser radar altimetry, canopy color index