Multi-temporal UAV monitoring of pine processionary moth impacts in Pinus nigra stands

Pine processionary moth (PPM, Thaumetopoea pityocampa) is the most important biotic disturbance affecting Mediterranean pine forests. This endemic insect causes outbreaks that can lead to severe winter defoliations, reducing tree growth and forest productivity. Despite its ecological importance, canopy responses throughout the complete PPM feeding cycle remain poorly understood. We aim to assess the potential of monthly UAV-derived multispectral and thermal data to characterize temporal dynamics related to PPM defoliations on Black pine (Pinus nigra ssp. salzmannii) forests at individual tree scale in Soria (Spain). Preliminary results show statistically significant differences among defoliation severity classes. A consistent seasonal pattern was observed, with NDVI declining during winter and spring due to PPM feeding activity and reaching minimum values in April-May, followed by recovery during summer-autumn. In addition, the integration of multispectral and thermal information enabled the development of a composite stress index that reflects a progressive increase throughout the PPM defoliation period. A strong intra-annual seasonal signal driven by the PPM cycle was detected, highlighting the capacity of UAV-based monitoring to capture both defoliation impacts and post-defoliation recovery processes in Pinus nigra. This study represents an initial step toward the development of a multi-sensor UAV framework for tree-level assessment and monitoring of PPM-induced forest stress.