Growth of European beech across altitudinal and climatic gradients: Experiences from Slovenia

Studies on the long-term growth dynamics of tree species under global warming have yielded varying or even contradictory results, including for European beech. We studied the response of the basal area growth of European beech to 30-year climate averages (mean temperature, annual precipitation sum and mean diurnal range) across an altitudinal range of 78–1629 m a.s.l. Our analysis was based on an extensive dataset of 331,965 beech trees from 54,403 plots under diverse site and stand conditions. We found a non-linear response of beech basal area growth to temperature, precipitation sum and elevation. Separate analyses conducted for 400 m elevation belts revealed significant differences in growth responses. A unimodal response to temperature was observed along the entire elevation gradient; however, in the lowest and the highest elevation belts, the relationship was linear, negative in the lowest, and positive in the highest. Across the entire elevation range, growth showed a plateaued unimodal relationship with annual precipitation, while at elevations ≤400 m a.s.l., a positive linear response was observed. Significant differences in growth responses between stand canopies were also observed, with dominant trees being more sensitive to most predictors. Our results suggest that changes in growth rate due to rising temperatures should be interpreted relative to the current mean temperature. The varying responses of stand canopies to climatic variables, and the predominant impact of tree and stand variables on growth rate, underscore the importance of considering forest stand dynamics in climate-growth studies.