Mixed mountain forests of European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst), and silver fir (Abies alba Mill.) cover a total area of more than 10 million hectares in Europe. Due to altitudinal zoning, these forests are particularly vulnerable to climate change. However, as little is known about the long-term development of the productivity and the adaptation and mitigation potential of these forest systems in Europe, reliable information on productivity is required for sustainable forest management. Using generalized additive mixed models this study investigated 60 long-term experimental plots and provides information about the productivity of mixed mountain forests across a variety of European mountain areas in a standardized way for the first time. The average periodic annual volume increment (PAI) of these forests amounts to 9.3 m3ha−1y−1. Despite a significant increase in annual mean temperature the PAI has not changed significantly over the last 30 years. However, at the species level, we found significant changes in the growth dynamics. While beech had a PAI of 8.2 m3ha−1y−1 over the entire period (1980–2010), the PAI of spruce dropped significantly from 14.2 to 10.8 m3ha−1y−1, and the PAI of fir rose significantly from 7.2 to 11.3 m3ha−1y−1. Consequently, we observed stable stand volume increments in relation to climate change.

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Abstract& Key message In Abies alba Mill. stands and mixed stands of A. alba and Picea abies L. (H. Karst), microsites neighbouring the trunks of adult trees were more conducive to A. alba regeneration. Although at the stand level, the effect of Fagus sylvatica L. was positive; the local effect of the adult F. sylvatica neighbourhood was insignificant. Hence, forming mixed stands with a fine-grained mosaic of admixed species might better facilitate natural regeneration of A. alba than monospecific stands.

The little-leaf linden stand, investigated in this study, is a relict of the Atlantic period. On three permanent sample plots, situated in a strictly protected reserve, trees were measured and classed in 1990 and 2000. Stands in these areas represented the growing up stage in transition to the optimum stage (Obrożyska 1), the optimum stage (Obrożyska 2), and the growing up stage, the selection structure phase (Obrożyska 3). In 2000 the percentage of linden by volume was 97% in Obrożyska 1 and 2, and 77% in Obrożyska 3, while the stand volume was 768, 861, and 761 m³/ha, and basal area 60, 62, and 55 m²/ha,respectively. These stands have the highest per hectare volume among stands of primeval character in the Polish part of the Carpathians.