Thinning effects on stand formation and modifications of a young pine/birch forest: a boreal zone case study

Thinning of young forests attracts the attention of scientists despite the long-term commercial effect. However, these researches are scarce. Therefore, it is important to study experiments with a long history. The aim of our study is to investigate the impact of thinning carried out in young pine/birch boreal forests on stand formation, natural regeneration, ground cover and properties of the soil layers in stands. We investigated three types of thinning in young pine/birch forests. In one plot of the initial stand, thinning was performed in two stages with a time interval of 27 years; in the first stage, thinning intensity was 75% of stems, while in the second stage, thinning intensity was 30%. In two other plots, thinning was performed in one stage at a stand age of 13 years, with thinning intensities of 76 and 84%. At the stand age of 72 years (2017), integrated studies of the silvicultural and ecological states were carried out. All thinned plots had developed into pure pine stands with 28–53% thicker stems, 12–18% higher trees and a growing stock 55–92% higher compared to the un-thinned reference stand. The most pronounced differences were observed for Option 1. With thinning, forest type changed to red whortleberry type, while the un-thinned reference site developed into a blueberry type forest. Thinning in young pine/birch stands results in the formation of pure pine stands. The associated modification of environmental properties changed the composition and density of the ground cover and some properties of the upper soil layers. Two-stage thinning had the least impacts; this approach can be used to produce stands with high commercial value. It is especially recommended for young pine/birch forests in the northern taiga.