Can High-Quality Oak Be Produced at Lower Planting Densities? : a Study of Oak Group Planting Mixed with Birch

Sammanfattning

Climate change poses a severe risk to conventional coniferous monocultures in southern Sweden, requiring a management shift toward more resilient broadleaves like oaks (Quercus spp.) and birch (Betula spp.). However, traditional oak establishment is limited by high initial costs. Here group planting of oak in mixtures with birch offers a cost-effective alternative. Yet, long-term knowledge regarding stand and tree level growth in these mixtures and competitive dynamics remain limited in Scandinavia. This study evaluated how three management intensities affect oak and birch development in a group-planting system in southern Sweden. An experimental trial established in 2008 in Tönnersjöheden was inventoried in 2021 and 2025 (ages 16 and 20). Three treatments were compared: (T1) Unthinned control; (T2) pre-commercial/ crown thinning around oak crowns; and (T3) intensive value production thinning. Despite heavily reduced standing volume in the thinned plots and a slightly lower site productivity in T3, statistical analyses only showed some statistically significant differences in oak growth increment across the three treatments. Furthermore, T3 generally promoted larger birch trees and improved oak stem straightness. Overall, the results demonstrate that treatment effects depend on the production objective. The study highlights the potential of group planting of oaks within mixtures of birch as an alternative to traditional row planting, as initial growth and quality variables seem strong.