Estimation of Individual Tree-Level Structural and Biochemical Traits for Seabuckthorn Forests in Lhasa Valley Plain by Coupling UAV-Based LiDAR and Multispectral Images with N-PROSAIL Model

The accurate and efficient extraction of individual tree phenotypic traits for seabuckthorn (Hippophae rhamnoides L.) in natural forests is crucial for germplasm exploration, precision silviculture, and ecological restoration. This study extracted structural and biochemical traits of seabuckthorn in Tibet’s Lhasa valley using Unmanned aerial vehicle (UAV) LiDAR, multispectral imagery, and the N-PROSAIL model. Firstly, building on a classification conducted through multi-scale spatial analysis and hierarchical clustering with dynamic thresholds, shrub interference was effectively reduced, thereby improving the accuracy of individual tree segmentation. Tree height and crown width were derived from the segmentation results, and a DBH estimation model was developed using handheld LiDAR data. Finally, leaf nitrogen content was mapped within canopies using random forest combined with the N-PROSAIL model and nitrogen reference data. The results demonstrated that the optimized segmentation method successfully extracted structural traits (F1 = 84.21%). Tree height was accurately estimated (R2 = 0.814, RMSE = 0.580 m), and the DBH prediction model performed satisfactorily (R2 = 0.779, RMSE = 1.725 cm). The random forest model also effectively estimated leaf nitrogen content (R2 = 0.680, RMSE = 2.074 mg/g).