A review of the effects of silviculture on timber quality of Sitka spruce

Abstract

This review focuses on timber quality with a particular emphasis on Sitka spruce and sawlog production, although issues pertaining to pulp and panel quality are also dealt with. The review is split into three broad areas. The first covers the factors controlling wood quality that operate within the timber itself and also at the whole-tree scale. These include knots, grain angle, wood density, tracheid length, microfibril angle, juvenile wood and compression wood, tree/log size, growth rate, stem straightness and stem taper. The second section reviews the link between silviculture, site and genetics on these controlling factors and the consequences for wood quality for different end-uses. The silvicultural factors reviewed are rotation length, initial spacing, respacing before canopy closure, thinning after canopy closure, nursing mixtures, pruning, cultivation, weed suppression and fertilizer use. Site factors include site quality, wind, slope, and snow and ice. There is a brief section on the role of genetic improvement on timber quality. Finally, the review provides conclusions and recommends that stands should be identified as being suitable for sawlogs or fibre products and then managed consistently throughout the rotation with a strong focus on the final wood product. For Sitka spruce, the objective of maximizing volume yield appears to be compromising batten performance and buyers should consider premiums for stands where quality has been provided rather than quantity. Long-term forest plans and certification could play an increasing role in providing the assurance that good consistent silvicultural practice had been undertaken throughout the rotation, hence creating the possibility of offering clear premiums for high grade timber.