Elevational and Thermal Drivers of Loss of Vigor by Pinus pseudostrobus Lindl. Revealed by UAV Multispectral and LiDAR Data

Climate change has increased the frequency of hotter droughts and forest decline processes, highlighting the need for monitoring methodologies capable of detecting loss of vigor on the individual-tree scale. Pinus pseudostrobus is an economically important species in the temperate forests of the indigenous community of Nuevo San Juan Parangaricutiro, Michoacán. The aim of this study was to evaluate the elevational and thermal factors associated with the spatial and temporal variability of P. pseudostrobus vigor by integrating multispectral, LiDAR, and land surface temperature (LST) data. Five multispectral flights were conducted using unmanned aerial vehicles (UAVs) between June 2023 and June 2024, along with one LiDAR flight in April 2024, across an elevational gradient ranging from 2150 to 2920 m. High-resolution orthomosaics, NDVI and LCI indices, a canopy height model, and an object-based classification using Random Forest were generated. LST was obtained from Landsat 8–9 imagery in Google Earth Engine using the Statistical Mono-Window algorithm. Spectral, thermal, and elevation values were extracted at the individual-tree level. The classification achieved an overall accuracy of 69.6% and enabled the identification of 28,585 P. pseudostrobus individuals. NDVI and LCI varied significantly among periods, elevations, and their interaction. The lowest values of vigor were recorded in lower elevation areas, particularly in June 2023, April 2024, and June 2024. In addition, both indices decreased as LST increased, showing strong negative relationships for NDVI (R2 = 0.96) and LCI (R2 = 0.86). Individuals located at the lower elevational limit showed greater vulnerability to thermal stress.