Temperature effect on size distributions in spruce-fir-beech mixed stands across Europe

•Species size distribution dynamics in mixed forests were explored using a matrix model.•Warming modifies species dynamics of mixed mountain spruce-fir-beech forests.•Warming positively effects stand basal area of fir but negatively effects beech.•Increasing temperature favors the size-dominance of fir over spruce and beech.•Size-dominant species identity influences stand basal area in spruce-fir-beech forests.