A simulation study to analyse the relations between crown condition and drought in Switzerland

Drought stress is assumed to be one of the major factors limiting forest health. This study investigates statistical correlations between site-specific estimations of drought and observed crown defoliation in Switzerland. For this, ecophysiologically based drought indices were computed using the model WAWAHAMO that simulates hydrological and ecophysiological processes in forested ecosystems. Correlation coefficients were calculated for spatial and temporal relationships. No meaningful spatial correlations were found. In the case of temporal relations, significant impacts of drought were detected for all deciduous tree species under consideration, i.e. F. sylvatica, Abies species, F. excelsior, and Quercus species. Weak correlations were found for the coniferous tree species P. abies and no relations were found for the tree species A. alba and P. sylvestris. The limitations of such studies are discussed in view of various aspects.