Extractives in Norwegian-Grown and North American-Grown Western Redcedar and Their Relation to Durability
R Stirling, P O Flæte, G Alfredsen, P I Morris
The extractives responsible for the natural durability of western redcedar (WRC) are not well understood. Recent work by the Norwegian Institute of Wood Technology and the Norwegian Forest and Landscape Institute has evaluated the natural durability of Norwegian wood species and reference species, including Norwegian-grown WRC and North American-grown WRC, in a series of decay tests. The availability of retained samples from these tests presented an excellent opportunity to compare the extractives contents of North American and Norwegian grown-WRC, and to correlate field test decay data and extractives content. The North American-grown WRC contained much greater concentrations of extractives than the Norwegian-grown WRC evaluated in this test. However, despite these differences, performance in the EN 252 stake test in Sørkedalen was only marginally better for North American-grown WRC. Both sets of samples were comparatively low in an as yet uncharacterized compound previously associated with decay resistance. However, there were not enough data to thoroughly examine the correlations between extractives and durability data in this material.
Keywords: decay testing, extractives, natural durability, Thuja plicata, western red cedar