In Ireland, most structural timber from Sitka spruce (Picea sitchensis[Bong.] Carr.) is machine graded into C16 strength class. However, timber from early thinnings is mostly used for non-structural applications. There is an increased demand for structural timber, and timber from young trees could contribute to wood supply. However, this timber has lower mechanical properties than mature timber. In order to pre-sort the resource for structural application of wood from thinning, the possibilities of acoustic and density (D) measurements on young trees and logs have been investigated. The stress wave velocity (SWV) and pin penetration depth (PD) were measured on standing trees, which were then felled and cut into 10-m-long logs and subsequently into 3-m-long logs. Fundamental frequency was measured on logs. Finally, the logs were processed into boards, which were tested in accordance with EN 408 to obtain modulus of elasticity (MOE) in bending, bending strength (BStr) and D. The results showed good relationships between timber properties and acoustic and D measurements. Models for predicting grade properties of timber from thinnings are presented. Pre-sorting of young Sitka spruce trees and logs helped obtain higher C16 yields.

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.

No abstract