Mixed vs. monospecific mountain forests in response to climate change: structural and growth perspectives of Norway spruce and European beech

•Positive effect of species mixing on stand production, diversity and tree growth.•Higher production potential of mixed stands compared to monospecifics.•Decreasing resilience of tree species to climatic extremes and air pollution with its increasing share.•Increasing radial growth of beech and spruce in mountain areas.•Higher ecological and economic benefits of mixture in conifer-broadleaved stands.