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<p>Accurately Crown asymmetry is a common morphological response to heterogeneous environmental pressures, and this asymmetry directly influences the physiological processes of tree growth. Advances in UAV-Lidar technology have facilitated the acquisition of high-precision crown data, providing new pathways to characterize crown structural variations and investigate their impacts on tree growth. In this study, we propose a novel crown asymmetry index (I<sub><i>hctsa</i></sub>), based on UAV-LiDAR data and time-series tool, to characterize crown asymmetry. Using a <i>Cunninghamia lanceolata</i> plantation in southeastern China as a case study, we analyzed the size-dependent effects of crown asymmetry on tree growth. The results revealed a significant reversal in the effect of crown asymmetry as tree size increased. Specifically, crown asymmetry exhibited a significant negative effect on the growth of small DBH trees, whereas it showed a significant positive effect on the growth of large DBH trees. Compared to the traditional Mean Circularity Index (I<sub>MC</sub>), the I<sub><i>hctsa</i></sub> index captures the structural characteristics of crown variations and can determine the DBH threshold value (≈ 19.77&#xa0;cm) for growth response at which transition from negative to positive. Furthermore, the LiDAR-based crown overlap index (CI2) demonstrated superior methodological suitability for separating thinning effects compared to the classic Hegyi index (CI1). This study demonstrates the feasibility and effectiveness of utilizing LiDAR for spatial competition analysis, providing a new methodological reference for forest ecology research.</p>

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Assessing the size-dependent effect of crown asymmetry on tree growth: a novel approach using UAV-LiDAR and time-series analysis

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • Zhaoting Zhu,
  • Yujun Sun,
  • Xiaolei Qiu,
  • Xueli Ma,
  • Yifu Wang

摘要

Accurately Crown asymmetry is a common morphological response to heterogeneous environmental pressures, and this asymmetry directly influences the physiological processes of tree growth. Advances in UAV-Lidar technology have facilitated the acquisition of high-precision crown data, providing new pathways to characterize crown structural variations and investigate their impacts on tree growth. In this study, we propose a novel crown asymmetry index (Ihctsa), based on UAV-LiDAR data and time-series tool, to characterize crown asymmetry. Using a Cunninghamia lanceolata plantation in southeastern China as a case study, we analyzed the size-dependent effects of crown asymmetry on tree growth. The results revealed a significant reversal in the effect of crown asymmetry as tree size increased. Specifically, crown asymmetry exhibited a significant negative effect on the growth of small DBH trees, whereas it showed a significant positive effect on the growth of large DBH trees. Compared to the traditional Mean Circularity Index (IMC), the Ihctsa index captures the structural characteristics of crown variations and can determine the DBH threshold value (≈ 19.77 cm) for growth response at which transition from negative to positive. Furthermore, the LiDAR-based crown overlap index (CI2) demonstrated superior methodological suitability for separating thinning effects compared to the classic Hegyi index (CI1). This study demonstrates the feasibility and effectiveness of utilizing LiDAR for spatial competition analysis, providing a new methodological reference for forest ecology research.