Large-scale early-wilting response of Central European forests to the 2018 extreme drought

The combination of drought and heat affects forest ecosystems by deteriorating the health of trees, which can lead to large-scale die-offs with consequences on biodiversity, the carbon cycle, and wood production. It is thus crucial to understand how drought events affect tree health and which factors determine forest susceptibility and resilience. We analyze the response of Central European forests to the 2018 summer drought with 10 x 10 m satellite observations. By associating time-series statistics of the Normalized Difference Vegetation Index (NDVI) with visually classified observations of early wilting, we show that the drought led to early leaf-shedding across 21,500 +/- 2,800 km(2), in particular in central and eastern Germany and in the Czech Republic. High temperatures and low precipitation, especially in August, mostly explained these large-scale patterns, with small- to medium-sized trees, steep slopes, and shallow soils being important regional risk factors. Early wilting revealed a lasting impact on forest productivity, with affected trees showing reduced greenness in the following spring. Our approach reliably detects early wilting at the resolution of large individual crowns and links it to key environmental drivers. It provides a sound basis to monitor and forecast early-wilting responses that may follow the droughts of the coming decades.