Uncovering growth dynamics in Scots pine through the detection of the onset of height growth using near-daily terrestrial laser scanning time series

Understanding when trees initiate growth each season is fundamental to linking forest productivity with changing environmental conditions. Yet, capturing this timing at high temporal resolution remains a challenge in forest ecology. Here, we use near-daily close-range laser scanning observations from a permanent laser scanning (PLS) system installed on a flux tower to detect the onset timing and magnitude of height growth in 106 Scots pine individuals within the same forest stand in Southern Finland. We were able to detect the onset of tree height growth at individual tree scale with daily precision by using a break detection method applied to height time series from the PLS observations. We found up to 27 days of variability in the timing of growth onset (132–159 Day of the Year) and up to 33 cm total absolute tree height growth variability (7–40 cm) among the Scots pine during the growing period of 2021. By studying various biotic and abiotic factors that could explain differences in growth dynamics, we found that light availability and microclimate, indicated by competition, local species richness, topography, and elevation, were the most important drivers of height growth onset timing (adj. R 2 = 0.10 in linear regression model and adj. R 2 = 0.14 in generalized additive model – GAM) while the relative height growth during the season was most impacted by the onset timing and microclimate, which were able to better explain the magnitude of growth in both the linear mixed-effects model (marginal R 2 = 0.31) and in the GAM (adj. R 2 = 0.50). Consistent with previous findings, our results suggest that variations within forest structure influence tree height growth dynamics. In this study, high spatiotemporal resolution PLS enabled the quantification of conventionally challenging tree functioning variables, such as the height growth onset, thereby offering quantitative evidence to better understand the tree functioning variabilities and the drivers of such variabilities in the context of intelligent forest management under changing climatic conditions. • Height growth onset timing among individuals in a stand varied by up to 27 days. • Local species richness, lighting, and microclimate were the main drivers of onset timing. • Earlier onset led to more relative height growth in a growing season. • High spatiotemporal laser scanning observations revealed unique tree growth dynamics.