Retrospective Analysis of a Large-Scale Gypsy Moth Outbreak in Hungary Combining Multi-Source Satellite and In Situ Data

Gypsy (or spongy) moth (Lymantria dispar) outbreaks have imposed significant threats to European forests for centuries. While traditional field-based research has provided detailed insights, it remains time-consuming, labour-intensive, and spatially limited. With the advancement of Earth observation satellite technology, forest monitoring has become more efficient and flexible. This study examined the impact of the most extensive gypsy moth outbreak (2003–2006) on the forest dynamics in Hungary using Moderate Resolution Imaging Spectroradiometer (MODIS)-derived indices: the Normalised Difference Vegetation Index (NDVI), Standardised NDVI (Z NDVI), and Leaf Area Index (LAI). Our results show that while the gypsy moth population in Hungary peaked in 2004, based on light trap data, and in 2005, according to field damage reports, the most severe defoliation occurred in 2005 and 2006, as detected by satellite-based decreases in the NDVI and LAI. MODIS-based vegetation indices proved effective in quantifying the extent and severity of defoliation, showing temporal and spatial patterns that aligned with ground observations. The LAI and NDVI metrics also captured varying degrees of defoliation and partial recovery. These findings underscore the value of integrating satellite data with field observations to improve early warning systems and enhance the forecasting and management of gypsy moth outbreaks.