Development of single oak trees in a mixed coniferous stand

Abstract: Pedunculate oak (Quercus robur) and sessile oak (Quercus petraea) are important tree species in the southern half of Sweden. Oak trees house a large biological fauna and can have high value timber. Managing oaks in pure stands is common but a large portion of oak is found in admixed in coniferous stands. The aim of the study was to investigate the growth of single oaks in a multi-layered, conifer-dominated mixed stand in relation to thinning method, competing trees and age. The study was conducted in Tönnersjöheden experimental forest in southern Sweden on 100-year old pine stand with naturally regenerated spruce and oak. The area was divided into different target diameter harvest treatments and thinned 2008-2009. 90 oaks were sampled for the single tree analyses, 30 trees for the age analyses and data from long-term study was used for thinning comparison. Results revealed that oak trees in the thinned stands grew significantly more than the control. The difference between various thinning treatments was not significant. Oaks with a higher number of neighbouring Norway spruce grew less than oaks with few or no neighbouring spruce trees. Any effect on growth of the distance to or size of the neighbouring tree was not found. The age of the measured trees was 38-68 years and the age had a positive relation to DBH and tree height. Due to the light demanding nature of oak, thinning is essential for sufficient growth of suppressed oak trees. How the thinning is conducted was found to be less important in this study. The effect on growth by neighbour trees of different species was noticed while the size or distance to neighbours was not, implying that a focus on the tree species (in this case Norway spruce) is important when thinning to promote oak growth.