Thinning strategies impact the productivity, perpetuity and profitability of mixed stands

In southern Sweden, there is possibility for growing spruce-birch mixed stands. However, the required knowledge to manage these stands effectively, i.e. optimal thinning strategies, is limited. Thus, we utilized data from young mixed-forest experiments in southern Sweden to simulate different thinning strategies. Moreover, we compared results from the mixed stands to spruce and birch monocultures. The regeneration was characterized by soil scarification, natural regeneration of birch and high-density planting of Norway spruce seedlings. Pre-commercial thinning (PCT) was carried out to create spruce-dominated mixed stands, birch-dominated mixed stands, and spruce and birch monocultures. The first commercial thinning strategy in the mixed stands was to retain the initial mixture proportions until final felling, while the other was thinning from below, which prioritized removal of the smallest trees of either species. At the end of the rotation, similar growth (9.6-10.2 m3 ha-1 yr-1) and better economy (ca. 13-28% more) was observed in spruce-dominated mixed stands compared to spruce monoculture. It was possible with the appropriate thinning strategy to maintain birch proportion in the mixed stand when the initial stand at PCT is birch-dominated. However, tradeoff exists between retaining a high birch basal area, sustaining productivity and obtaining a good economy.