Canopy cover loss in Germany’s forests after the 2018-2020 drought years

Abstract

Central Europe was hit by several unusually strong periods of drought and heat between 2018 and 2020. These droughts affected forest ecosystems. While the annual tree crown condition assessments report generally rather bad conditions of the four dominant tree species in Germany, namely spruce, pine, beech and oak, many other tree species also show signs of severe damage. Cascading effects of drought and heat with insect infestations were fatal to vast forest areas in Germany, particularly in spruce stands. We present a first assessment of canopy cover loss in Germany since January 2018. Our approach makes use of dense Sentinel-2 and Landat-8 time series. We computed the disturbance index (DI) from the Tasseled Cap components brightness, greenness, and wetness. Using quantiles, we generated monthly DI composites and calculated anomalies to a reference period (2017). After applying a threshold, we were able to determine the date of canopy cover loss for all pixels where anomalies were recorded until the end of the observation period. From the resulting map, we calculated canopy cover loss statistics for administrative entities. Our results show canopy cover loss of more than 400,000 ha for Germany from 2018-2020 with large regional differences. However, clear-cutting of damaged trees continued in 2021 at exceptional high rates and reached 500,000 ha already in April 2021. The losses were largest in central Germany and reach up to two thirds of coniferous forest loss in some districts. Our map has high spatial (10 m) and temporal (monthly) resolution.