Interannual radial growth sensitivity to climatic variations and extreme events in mixed and pure stands of silver fir and beech in the Italian Peninsula

Climate change is increasingly favoring the occurrence of extreme weather events, affecting species distribution and tree growth. It has been proposed that mixed forests are more resistant to extreme drought and heat that corresponding monocultures. For this reason, we sampled tree cores in nine stands along a latitudinal gradient of the Italian Peninsula (Trentino - Alto Adige, Molise, Calabria), considering mixed forests and corresponding monocultures of silver fir and beech. The objectives of the study were to identify differences between mixed and pure stands of beech and silver fir to climatic patterns and extreme events. Pointer years, and correlation and response functions, were analysed to evaluate the climate-growth relationships between mixed and pure stands. Results showed a clinal variation in radial growth traits of beech and silver fir, in both mixture and monoculture. In particular, beech and silver fir in mixture were both positively affected by high summer water availability. In Trentino - Alto Adige and Molise, positive correlations were observed with winter temperatures, for silver fir; positive (Trentino - Alto Adige) and negative (Molise) correlations were detected with spring temperatures, for beech. Pointer years showed a clear grouping of climate variables in Trentino - Alto Adige and Calabria, which influenced both species, in mixture and monoculture. On the other hand, grouping was relatively vague in Molise, especially for silver fir in pure and mixed stands. Complementarity in resource uptake and use between beech and silver fir was not always advantageous for both species.