Considerations for Grading Species Combinations. The Example of Douglas Fir With Larch in Ireland and Uk

Abstract

This paper examines the grading of Douglas fir (Pseudotsuga menziesii) and larch (Larix spp.) as a strength grading species combination for the growth area formed by Ireland and the UK. The two genera produce higher timber quality than Sitka spruce (Picea sitchensis), the main commercial timber species in the two countries. Developing this species combination may increase the volume of timber available for the market, making these species more commercially attractive to sawmills, particularly if there are common settings that can be used for either species whether mixed in production or not. Simultaneously, the paper examines the challenges of mixed species grading within the framework of the European standard EN14081 for machine control grading, as the requirements for combining species are not clearly defined. More than 1600 pieces are used for this study. The results found that the ranges of modulus of elasticity, strength and density of both species are similar, but special considerations are required to ensure the safe grading of the timber.