Thinning responses of individual trees in mixed stands of Norway spruce and Scots pine

Abstract

ABSTRACT Effects of species composition on the growth of Norway spruce – Scots pine mixtures had earlier only been studied in unthinned stands. Individual-tree thinning responses in mixed stands were studied to test for the presence of mixture effects in more open stands. Data were collected from 28 temporary sample plots with varying species proportions in 7 thinned spruce-pine stands on medium fertile sites in Eastern Norway. Effects of neighborhood species composition on the individual-tree basal area growth before and after thinning were tested for to detect mixture effects. Spatially-explicit competition indices were used to describe release during thinning in the growth models. Neighborhood species composition only had a minor effect on the thinning response of spruce. Growth before thinning of both species and the thinning response of pine were not affected by species composition. Release had a strong effect on the thinning response of both species. Low density of the studied stands and the more dominant position of pine compared to spruce in mixture, even after the thinning from below, explained some of the observed effects.