Mapping Alpine Treeline Ecotones in the Tungnath Himalaya Using Terrestrial Laser Scanning and GEDI LiDAR

Alpine treeline ecotones are extremely vulnerable to climate change, making them important early warning systems in climate research. Advanced remote sensing tools, such as Light Detection and Ranging (LiDAR), enable detailed mapping and monitoring of these high-altitude zones, offering critical baseline data for future change detection. This study combines ground-based Terrestrial Laser Scanning (TLS) and space borne Global Ecosystem Dynamics Investigation (GEDI)- LiDAR data to analyze the structural attributes and delineate the position of alpine treelines in the Tungnath Himalaya, India, located at elevations between 3252 and 3,590 meters above mean sea level (a.m.s.l).  TLS provided high-resolution three-dimensional data on alpine vegetation, including tree height, diameter at breast height (DBH), and canopy structure. Using an automated algorithm, 84.84% of individual trees were segmented from TLS data. TLS-derived tree height and DBH estimates achieved root mean square errors of 44.74 cm and 78.45 cm, respectively, compared to field-measured values. A semi-automated method using GEDI LiDAR identified trees taller than 3 meters to delineate the treeline, achieving a positional accuracy of ~ ±40 m a.m.s.l when validated against TLS-derived data.  The results show that combining TLS with GEDI provides a non-destructive and effective method for assessing treeline structure and location in the Indian Himalaya. Future research might use multi-temporal LiDAR datasets to track treeline movements and obtain a better understanding of the long-term effects of climate change on alpine ecosystems.