An analysis of crown condition of Picea, Fagus and Abies in relation to environment in Switzerland

The health of Swiss forests is now being monitored at some 160permanent sites at 8 km intervals on a square grid. Data onthe conditions of the tree crowns in 1993 and on the soil, climate,and topography have been analysed to determine the extent towhich crown condition depends on these factors. Transparencywas the only widespread symptom of ill health or lack of vigour,and it was common in only three species, Picea abies (L.) Karst.,Abies alba Mill., and Fagus sylvatica L. Relations between transparencyand the environmental variables recorded were weak, and forFagus too weak to be of consequence. The strongest relationsare with the soil water holding capacity for Picea, and withwater holding capacity and carbonate content for Abies. It seemsthat the loss of leaves is the trees' natural physiologicalresponse to lack of water in the soil: drought is a sufficientexplanation for the observed crown condition. The results andinterpretation accord with those elsewhere in Europe in 1993.