Development of bluestain in logs prevents the Canadian forest industry from producing maximum-value products from a considerable proportion of the resource every year. When considering bluestain-control strategies that could be implemented without disrupting woodlands or mill productivity one of the most promising is sour felling. This involves felling the trees and leaving the foliage on for about a month before delimbing. Sour felling has been proposed as a method of reducing the moisture content and transportation costs of trees. However, due to continued respiration and transpiration the sapwood nutrients are also expected to be somewhat depleted during the period in which delimbing is delayed. These nutrients would then not be available for staining fungi. Passing comment is made in the literature to bluestain development sometimes being less in sour-felled logs, particularly in pine. We therefore focused on sour felling as a possible control measure for stain in lodgepole pine. Sour-felling is industrially feasible for companies using a feller/buncher for the initial cutting and delimbers to remove the branches. This is the most common harvesting method used in the BC interior and Alberta.
The objective of the test was to determine if sour felling can reduce the wood nutrient status and/or incidence of bluestain in lodgepole pine roundwood. In late August 1999, near Edson, Alberta, 57 lodgepole pine (Pinus contorta Dougl.) trees were mechanically felled. Of these, 20 were mechanically delimbed controls and 30 were left with their limbs intact (sour-felled). Discs were taken from trees growing alongside for chemical analyses of wood extractives in the laboratory. In October, the test site was revisited and a second set of samples (six-week samples) taken from the logs. As no bluestain had occurred in the logs after six weeks (probably a result of the coolness of the weather) trees from both the delimbed and sour-felled piles were removed and sampled as the original sample trees (time-0) had been, in order to determine the effect of storage on nutrient status of the sapwood. Chemical analyses were done for lipophilic extractives, phenolics, soluble sugars, starch and total nitrogen concentrations.
Because the conditions were not suitable for the formation of stain in the delimbed logs the study was unable to determine whether sour felling had any effect on the prevention of bluestain during the fall of 1999. However, the project did provide baseline data on the levels of extractives known to be nutrients for staining fungi. For trees felled in August 1999, those extractives occurred in the following order of abundance: lipophilic extractives (24 g/kg); soluble sugars (1.6 g/kg); starch (1.3 g/kg); and nitrogenous compounds such as elemental nitrogen (0.45 g/kg). Generally, the viability of ray parenchyma cells, the sapwood moisture content and the amounts of nutrients present in the sapwood remained at the same level over the six-week storage period, irrespective of whether the logs were from trees that had been delimbed or whether the trees sampled had been left in their full lengths with their limbs and foliage intact. Only one nutrient, starch, was depleted to 20-30% its original amount over the six-week storage period. Pinosylvin, pinobanskin and pinocembrin, which are some of the compounds thought to prevent fungal attack of heartwood, were below detectable levels in most logs sampled. However, some stored logs had small amounts of these extractives present, possibly a response to wounding.
It is recommended that the test be repeated in a hot summer to determine the maximum possible effect that sour felling might have on the prevention of bluestain.
Stains - Fungal - Control
Pinus contorta Dougl. var. latifolia - Stains, Fungal