Variation in natural durability of British grown Douglas fir ((Pseudotsuga menziesii (Mirb.) Franco). Part II. Effect of extractive contents and taxifolin
S Akhter, M D C Hale
The previous paper (Part I: Effect of density and growth rate) described the variation in natural durability of 4 Douglas fir (DF) seed origins (Darrington, J. Landing, Naselle and Hawkinsville) in a pure culture decay test and fungal cellar test. The pure culture tests were performed against two brown rot fungi (Coniophora puteana and Postia placenta). In the fungal cellar test soft rot was the predominant decay type because of the high moisture content. The paper showed that significant variation in natural durability occurred between the seed origins and between trees within the seed origins. Furthermore density partly explained the variation in the natural durability of 3, of the 4 seed origins.
Extractives are often considered to be the major reason for heartwood durability. This paper has determined the variation in extractive contents between different seed origins and has examined the effect of extractive contents and taxifolin, the main component of acetone extracts on the decay resistance of 26 year old DF trees from different seed origins.
Keywords: Natural durability, Douglas fir, extractives, taxifolin