Darwinian spreading and quality thinning in even-aged boreal forest stands

Darwinian spreading of vigor, in addition to quality distribution, is introduced in a tree growth model. The size of any tree, within an even-aged stand, is taken as a measure of an inherited productive capacity, and then combined with quality thinning. For sparse cultivation density, the result is forestry without commercial thinnings; large trees cannot be removed since they are the most productive, neither small trees because the unit price of harvesting would be large. For large cultivation density, thinning from above becomes combined with quality thinning of large trees. Darwinian spreading of growth rate may correlate with quality. Quality thinning may enhance growth rate. Such effects combined, large trees still become removed but quality thinning becomes implemented in almost all diameter classes. At financial maturity, Darwinian spreading treated with quality thinning, the weighted mean breast height diameter is in the vicinity of 20 cm within stands of high planting density, and somewhat higher with low planting density. Quality correlating with Darwinian spreading of growth, and growth rate correlating with observed quality, trees grow bigger, the maturity size becoming closer to 25 cm - bigger than in earlier studies without tree-size - dependency of vigor.