Variation in timber strength of fast grown unthinned Sitka spruce in Northern Ireland.

Abstract

Timber from six unthinned stands of Sitka spruce (Picea sitchensis (Bong.) Carr.), of general yield classes ranging from 20 to 24 m3/ha/year, and established at spacings of 1·5-2·0 metres, was machine stress graded to determine the amount of timber sawn to structural sizes that attained BS 5268 Strength Classes (SC) 3 and 4. The stands were derived from seed from at least two North American sources. Although there were some differences between stands related to provenance, none was statistically significant. Within the range of conditions tested, yields of SC4 structural timber obtained varied between 24% and 57% of battens tested, the differences being primarily related to local yield class. Yields obtained of SC3 timber ranged from 36% to 69% of battens tested, and between 3% and 9% of battens did not meet the machine grading requirements of SC3 or SC4.