Drought and frost resistance of trees: a comparison of four species at different sites and altitudes

Drought and frost resistances are key factors for the survival and distribution of tree species. In this study, the vulnerability to drought-induced embolism and frost resistance of four species were analysed, whereby different sites and altitudes were compared and seasonal variation was considered. Fagus sylvatica L., Sorbus aucuparia L., Picea abies L. Karst and Larix decidua Mill samples were harvested at high and low altitude sites in France and Austria, respectively, and sampling occurred in winter and summer. Pressure at 50% loss of conductivity (P (50)), specific hydraulic conductivity (k (s)) and temperature lethal for 50% of cells (LT50) were determined, and soluble carbohydrate and starch content were quantified. No site-, altitude- or season-specific trend in P (50) was observed, except for S. aucuparia, which showed P (50) to decrease with altitude. Within regions, k (s) tended to decrease with altitudes. LT50 was between -48.4A degrees C (winter) and -9.4A degrees C (summer) and more negative in Tyrolean trees. Starch content was overall lower and carbohydrate content higher in winter than in summer, no site-specific or altitudinal trend was observed. Studied species obviously differed in their strategies to withstand to frost and drought, so that site-related, altitudinal and seasonal patterns varied.