400 trees per hectare, following which they would grow unaffected by competition‐induced mortality and reach the target diameter in a total of only 70 years. Although the overall harvest would be smaller, getting a commercial return 20 years earlier will often make perfect economic sense. Understanding both the principles and the details of Norway spruce self‐thinning helps the forest managers achieve this.
Figure 5.40 A density management diagram (DMD) for Norway spruce in central‐southern European montane regions, based on observed combinations of stand density and average tree size (calculated as the quadratic mean diameter – the square root of the mean of the squared diameters), both plotted on log scales. Alternative trajectories over time are plotted from an initial population of 2600 10 cm diameter trees per hectare (bottom right, red circle). Unmanaged self‐thinning would give rise to a population of c. 650 40 cm diameter trees per hectare in 90 years. Managed precommercial thinning would give rise to a population of c. 400 40 cm diameter trees per hectare in 70 years.
Source: After Vacchiano et al. (2013).
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