Growth response of five co-occurring conifers to drought across a wide climatic gradient in Central Europe.
Climate change projections indicate drier conditions and an increase in the frequency and duration of extreme drought events in the coming decades in Central Europe. However, it is not clear which tree species will be able to cope with drier climatic conditions and higher year-to-year climatic variability. We analyzed tree-growth responses of five co-occurring conifer species to past climatic variations and severe droughts across a wide climatic gradient in Central Europe, covering four distinct biogeographic regions: the northern Swiss Alps, the Swiss Plateau, the foothills of the Jura Mountains and the dry Central Alps. We studied three native tree species (Larix decidua Mill, Picea abies (L.) Karst. and Pinus sylvestris L.) and two non-native species (Pinus nigra Arn. and Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Tree-ring width was measured for 770 trees from 14 sites and species-specific site chronologies were established. Response-function analysis, Principal Component Analysis (PCA), linear regressions and Superposed Epoch Analysis were used to assess the species-specific growth sensitivity to climate and severe drought along the gradient. Irrespective of the species and site conditions, high temperatures and low precipitation amounts in summer and autumn of the year prior growth significantly reduced tree growth. When evaporative demand, precipitation and soil water holding capacity were considered together, low water availability in current summer strongly reduced growth. Overall, the growth-climate relationships of the species were not or only slightly related to the site water balance per se. However, when all species-specific growth response coefficients were introduced into a PCA, a clear separation of the populations of the Central Alps (driest sites) became apparent. At these sites, soil water deficits in previous autumn and current spring strongly reduced radial growth, whereas at moist and wet sites on the Swiss Plateau, in the Jura Mountains and northern Alps summer drought impeded growth. Along the gradient, the native P. abies, L. decidua and P. sylvestris were the most sensitive species to drought, implying that their long-term performance and survival on nowadays dry sites can be compromised under a drier climate in Central Europe.