Epsilon Archive for Student Projects

Abstract

Pedunculate oak (Quercus robur) is a prominent tree species in European temperate forests, providing many ecosystem services and habitat for a variety of species. Intensification of forest management during the 20th century and lack of disturbance in protected areas have led to denser canopies, which negatively impact natural regeneration of oak. Oak is a light demanding species and has historically mainly been found in semi-open areas with frequent disturbance. Dalby Söderskog national park, located in southern Sweden, is a formerly oak dominated temperate forest where a new oak regeneration has established after a recent increase in light availability due to the tree diseases Dutch elm disease and ash dieback. Earlier studies have found that crown size was positively related to stem diameter in young oaks in Dalby Söderskog. The purpose of this study was to examine how crown competition influences stem diameter growth of individual oaks over time. Additionally, the difference in stem diameter growth was examined in trees for which crown competition status remained the same and in trees for which crown competition increased. This was done by statistical analyses of the stem diameter growth and the change in crown competition status of 394 young oaks between 2021 and 2025. The basic hypothesis was that stem diameter increment decreases with increasing crown competition. The results confirm the hypothesis, showing that stem growth in pedunculate oak is negatively affected by higher crown competition. The general pattern is the same for all oaks, independent on if crown competition status has been constant or increased during the four years. The young oaks in Dalby Söderskog have a very high stem growth when they have sufficient light availability, but when the crown is almost or completely overgrown the stem growth is very low. The results also showed that already one to three years of increased shading will lead to a significantly lower stem growth compared to constant competition status, demonstrating rapid negative effects of increasing crown competition and stand density.