Influence of early re-spacing on Sitka spruce branch structure

Abstract

The frequency, size, and insertion angle of primary branches are important determinants of wood quality and can be significantly influenced by silvicultural activities. This study quantified the long-term influence of early re-spacing on the branching characteristics of mature Sitka spruce [Picea sitchensis (Bong.) Carr.] trees growing in Northern Ireland, UK. The primary aim was to investigate whether any residual effect of stand density on branch attributes remained once the effect of changes in tree size variables had been considered, while a secondary objective was to test the performance of existing Sitka spruce branch models using the current dataset. Re-spacing treatments had corresponding stand densities of 2,858, 1,452, 725, 477, and 320 stems ha−1. Twenty-four trees were sampled when the stand was 57 years old and branch frequency, size, and insertion angle were recorded for model development. Maximum branch diameter, insertion angle, and branch frequency were significantly influenced by re-spacing, while no effect was found for relative branch diameter distribution. Residual re-spacing effects were most noticeable on branch size, with only small differences between treatments for branch frequency and insertion angle. Existing models performed well despite the wider range of stand densities examined in the present study. The results indicate that early re-spacing from 1.9 m2 to wider than 2.6 m2 will result in branch attributes that are detrimental to Sitka spruce sawn timber quality.