Reduction of oak lace bug-related NDVI signals in 2025 following nearly a decade of persistence: legacy effects of extreme heat & drought in 2024 or subsequent winter conditions?

Since its spread across Central Europe, the Oak lace bug (Corythucha arcuata, Say 1832), an invasive species rapidly spreading since 2012, has caused persistent and spatially extensive canopy stress in oak-dominated forests, clearly detectable in satellite-derived vegetation indices. Between 2016 and 2024, characteristic NDVI declines associated with repeated infestations were consistently observed during the late summer, indicating chronic biotic stress superimposed on background climatic variability. During this period, the oak lace bug after establishment in an area showed only a weak interannual variability, but no signs of retreating.

Unexpectedly, in 2025 these biotic stress signals were largely absent across the affected regions. NDVI time series in 2025 showed substantially reduced late summer declines compared to previous years both in Hungary and Croatia, suggesting a sudden weakening of the oak lace bug-related canopy impacts. This abrupt change raises the question of which climatic mechanisms may have contributed to the apparent collapse of remotely sensed infestation signals. Two non-exclusive hypotheses are considered: (i) legacy effects of the extreme heat and drought conditions in August 2024, which caused widespread deterioration of oak canopy condition and may have disrupted host–insect interactions, and (ii) adverse winter conditions following the 2024 growing season, potentially affecting overwintering survival of the insect.

Using multi-year satellite time series (Harmonised Landsat-Sentinel-2, MODIS, VIIRS) and meteorological data (FORESEE), we investigated the changes in canopy greenness dynamics in relation to the preceding thermal, hydrological and seasonal weather extremes. Our analysis reveals a striking shift in the detectability of biotic stress signals and discusses possible climate-related controls on their persistence. The results demonstrate the value of satellite-based monitoring for capturing not only the emergence and spread of forest pests, but also their sudden decline, emphasizing the importance of considering compound and lagged climate effects when interpreting vegetation stress signals.

Keywords: Space-borne remote sensing, Vegetation indices, MODIS, Harmonized Landsat-Sentinel-2 dataset, invasive pest detection, extreme weather

Funding: The research has been supported by the Hungarian Scientific Research Fund (NKFIH FK-146600). This work has been implemented by the National Multidisciplinary Laboratory for Climate Change (RRF-2.3.1-21-2022-00014) project within the framework of Hungary's National Recovery and Resilience Plan, supported by the Recovery and Resilience Facility of the European Union. The study was supported by the EU NextGenerationEU through the Recovery and Resilience Plan for Croatia under the project Dendro-Carbon (No. 400-01/23-01/6-2).