Comparison between the quadratic mean diameter d_q in mixed and pure stand. Mean diameter of (a) Norway spruce and (b) European beech in the mixed stand plotted over the diameter in the neighbouring pure stand. Means (rhombi) for Norway spruce amount to 30.4 cm and 34.0 cm in the pure and mixed stand, respectively. European beech achieves 23.1 in pure and 21.9 in mixed stands.