Drought episodes are predicted to increase their intensity and frequency in Central Europe, which will have a particular impact on forest vitality, productivity, and species distribution. In addition, changes in drought response may change with tree ontogeny. The impact of tree species interaction on forest vulnerability to drought is limited. The aim of this study is to find out how deciduous saplings react to the severe drought of 2018 and whether tree species diversity buffer the impact of drought stress on saplings. Based on field measurement of crown transparency, species richness and the Sentinel-2 normalized difference vegetation index (NDVI) for adult trees, the vulnerability and recovery from drought and the species interaction were analyzed. Field work was carried out in Central Eastern Germany in 2018 during the vegetation season and repeated in 2019. 10 random saplings were measured in 218 plots (15 × 15 m), with 2149 individuals in total.
Results/Conclusions
Preliminary results show: (1) forest stands with high species diversity are more exposed to drought stress than stands with low species diversity (p < 0.001); (2) 65% of the recorded saplings species experienced defoliation during the drought episode of 2018, with Fagus sylvatica L. and Betula pendula Roth. saplings being less affected (< 55%) than Carpinus betulus L., Sorbus aucuparia L. and, Frangula alnus Mill. (≥ 85%); (3) C. betulus and S. aucuparia recovered faster than F. sylvatica, B. pendula, Quercus spp. and Crataegus spp., F. alnus, Sambucus nigra L., Acer platanoides L. and, Corylus avellana L., species (p < 0.001); (4) The NDVI for the adult tree species showed a non-significant correlation with sapling defoliation 2018 (p > 0.05). Our results suggest that tree diversity can increase the drought vulnerability of saplings. Although there was less precipitation in 2018 than in 2003, F. sylvatica saplings seem to be capable of withstanding and surviving extreme drought, however they may face a slow recovery. Saplings and adult trees exhibited a different response to drought stress, which is essential to consider for implementing adaptive forest management strategies to mitigate the impact of climate change.