A trial of "sour" felling to prevent bluestain by depletion of sapwood nutrients
A Byrne, A Uzunovic, D Minchin, C Breuil
Discoloration of conifer wood caused by bluestain causes large economic losses in Canada. Most deep stain develops in the log stage during storage or transport. In a search for control strategies that will not disrupt woodlands productivity we tested "sour" felling, termed "hagarashi" in Japan. The practice involves delaying the delimbing of freshly harvested trees. The tree continues to transpire and to respire. This could result in partial drying of the wood and/or faster depletion of sapwood nutrients needed for the growth of bluestain fungi. Field experiments were done compared sour-felled trees with ones immediately processed by a harvester/delimber. We examined the development of stain and also analyzed sapwood nutrients. The latter included lipophilic extractives, phenolics, soluble sugars, starch and total nitrogen. There was no stain in both sets of trees, attributable to unfavourably cool weather. The viability of ray parenchyma cells and the moisture content remained similar in both sets of trees. Despite being unable to show a benefit in reduced stain this work provided baseline data for the levels of the extractives in fresh and stored lodgepole pine trees. Starch was depleted to 20-30% of its original amount over the six week period, presumably as it was used by the dying tree.