Quantifying Variation in Canopy Height from LiDAR Data as a Function of Altitude Along Alpine Treeline Ecotone in Indian Himalaya

Canopy height is a key physiognomic parameter of biodiversity, productivity and other ecosystem functions in high-elevation alpine ecosystems. However, little is known as to how altitude influences canopy height in these ecosystems. This study makes use of an open-access global forest canopy height map with a spatial resolution of 30 m that integrates Global Ecosystem Dynamics Investigation (GEDI) Light Detection and Ranging (LiDAR) data (April October 2019) and Landsat analysis -ready time-series data (year 2019). The variation in canopy height was quantified for each 100 m elevation band starting 500 metres below the alpine treeline ecotone at 3780 masl and extending up to 500 m above the alpine treeline ecotone. The global forest height map was compared to the in situ data (root-mean-square error [RMSE] = 6.6 m; mean absolute error [MAE] = 4.45 m). We observed a strong negative correlation (R-2 = 0.96) between altitude and LiDAR-estimated canopy height. The altitude alone explained 96% of the variation in canopy height (p < 0.001). This chapter provides the first of its kind landscape-level quantification of the rate at which canopy height decreases with the increase in altitudinal gradient across the Indian Himalayan treeline.