The influence of planting density on modulus of elasticity of structural timber from Irish-grown Sitka Spruce

Abstract

As Europe moves towards more sustainable construction, there is an increasing demand for structural timber. The purpose of this research is to explore new forestry management strategies, which will produce an optimum balance of the quantity and quality of structural timber over a minimum period of time. The focus is on timber from Sitka spruce, which is the most important Irish commercial forest tree species. Planting density is an important factor affecting both structural timber quantity and quality. Trees with wider spacing get more light and grow faster, which affects annual ring width and knot size. These, in turn, affect the bending strength, modulus of elasticity and density of timber, which are the grade determining properties according to EN 338:2003. The current standard planting density in Ireland is 2500 stems/ha and the timber produced meets the requirements for the C16 strength class. For Irish-grown Sitka spruce timber, modulus of elasticity is the critical grade determining property, which dictates the strength class. This study has two aims, first to explore the possibilities of improving the strength class by increasing the planting density and second, to explore the possibility of keeping the same class while increasing the quantity of structural timber by reducing the planting density. The effects of different planting densities, ranging from 1550 to 3700 stems per hectare, on the structural properties of Sitka spruce timber originated from a forest in County Leitrim are examined. Overall, 72 trees were felled and cut into logs. Logs were non-destructively tested using acoustic tools and subsequently processed into structural timber. The timber boards were then tested using three different types of strength graders in order to examine the difference in timber modulus of elasticity between different planting densities. The results showed statistically significant effects of different planting densities on the variation in timber modulus of elasticity.

Predicting structural timber grade-determining properties using acoustic and density measurements on young Sitka spruce trees and logs

“…The plantation was established in 1992 and the trees were planted at different planting densities, ranging between 1550 and 3700 stems ha −1 , which appeared to be arbitrarily located within the site. In a parallel study (Simic et al 2017), the influence of planting D on timber MOE measured using NDTs was studied. Twelve plots were selected from the forest.…”

The effect of thinning on mechanical properties of Douglas fir, Norway spruce, and Sitka spruce

“…With regard to the effects of other silvicultural interventions, several aspects are already well documented (Zobel and van Buijtenen 1989). For example, genetics (Dungey et al 2006;Roth et al 2007;Lasserre et al 2009), fertilizers (Jaakkola et al 2006), initial spacing (Rais et al 2014Aslezaeim 2016;Johansson 1993;Lasserre et al 2005;Simic et al 2017), pruning (Makinen et al 2014), and respacing and thinning all affect wood properties to a varying degree (Brazier 1977;Macdonald 2002;Cameron 2002;Eriksson et al 2006;Savill and Sandels 1983;Cameron et al 2015;Pape 1999b). The size of the effect varies between the species and throughout the lifetime of an individual tree.…”

The influence of crown and stem characteristics on timber quality in softwoods

“…Several other factors can also have an effect on the mechanical properties, both directly and indirectly. Starting with stand formation, initial planting density (Rais et al, 2014;Simic et al, 2017;Aslezaeim, 2016;Johansson, 1993;Lasserre et al, 2005) or the genetic makeup (Dungey et al, 2006;Lasserre et al, 2009) can all have a profound effect on timber quality. The influence of both early respacing and thinning was confirmed across various species (Cameron, 2002;Eriksson et al, 2006;Savill & Sandels, 1983;Cameron et al, 2015;Pape, 1999;Moore et al, 2009), as was the effect of site (Macdonald, 2002;Kimberley et al, 2015Kimberley et al, , 2017Lasserre et al, 2008) .…”