Abstract
Recent studies show that several tree species are spreading to higher latitudes and elevations due to climate change. European beech, presently dominating from the colline to the subalpine vegetation belt, is already present in upper montane subalpine forests and has a high potential to further advance to higher elevations in European mountain forests, where the temperature is predicted to further increase in the near future. Although essential for adaptive silviculture, it remains unknown whether the upward shift of beech could be assisted when it is mixed with Norway spruce or silver fr compared with mono-specifc stands, as the species interactions under such conditions are hardly known. In this study, we posed the general hypotheses that the growth depending on age of European beech in mountain forests was similar in mono-specifc and mixed-species stands and remained stable over time and space in the last two centuries. The scrutiny of these hypotheses was based on increment coring of 1240 dominant beech trees in 45 plots in mono-specifc stands of beech and in 46 mixed mountain forests. We found that (i) on average, mean tree diameter increased linearly with age. The age trend was linear in both forest types, but the slope of the age–growth relationship was higher in mono-specifc than in mixed mountain forests. (ii) Beech growth in mono-specifc stands was stronger reduced with increasing elevation than that in mixed-species stands. (iii) Beech growth in mono-specifc stands was on average higher than beech growth in mixed stands. However, at elevations>1200 m, growth of beech in mixed stands was higher than that in mono-specifc stands. Diferences in the growth patterns among elevation zones are less pronounced now than in the past, in both mono-specifc and mixed stands. As the higher and longer persisting growth rates extend the fexibility of suitable ages or size for tree harvest and removal, the longer-lasting growth may be of special relevance for multi-aged silviculture concepts. On top of their function for structure and habitat improvement, the remaining old trees may grow more in mass and value than assumed so far.