GEDI reveals decline in overstorey and increase in understorey canopy cover of protected forests in Central Europe since 2019

Drought and insect disturbances have resulted in widespread forest dieback in the forests of Central Europe since 2018. However, the implications of these changes in forest cover on the vertical structure, such as the canopy cover of the overstorey and understorey, have yet to be investigated at a large scale. By making use of the Global Ecosystem Dynamic Investigation (GEDI) spaceborne waveform lidar, we show here that overstorey canopy cover has declined and understorey canopy cover has increased in both coniferous and broadleaved protected forests in Central Europe since 2019. The observed loss of overstorey canopy cover is consistent with results from other remote sensing-based forest monitoring products. However, only GEDI has the capability to detect the increase in understorey canopy cover. For example, in Harz Mountains in Germany, overstorey canopy cover decreases by approximately 4.45 % per year in coniferous forests and by approximately 1.57 % per year in broadleaved forests, while understorey canopy cover increases by approximately 1.18 % and 0.59 %, respectively. For coniferous forests, we find that changes in overstorey canopy cover have a significant negative correlation (r = – 0.78, p < 0.01) with changes in understorey canopy cover. However, this relationship is not significant for broadleaved forests. This implies that canopy mortality in coniferous forests is more likely to trigger succession in the understorey than in broadleaved forests. This study demonstrates a new perspective for monitoring the dynamics of forest overstorey and understorey using spaceborne lidar, which can help improve understanding of feedbacks between forests and climate. • Monitoring the change of forest vertical canopy cover with GEDI. • Decrease in overstorey and increase in understorey canopy cover of protected forests in Central Europe. • Understorey growth rises as overstorey canopy cover declines in coniferous forests.