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The effect of mountain pine beetle killed wood on pulp fibre quality : an exploratory study Woo, Kathy L.

Abstract

Lodgepole pine stands harbour a major commercial significance in British Columbia. The lodgepole pine forests not only make up half of the British Columbia Interior annual harvest, but are also highly utilized and acceptable for lumber and pulp production. Unfortunately, mature lodgepole pine stands have been surmounted by outbreaks of mountain pine beetle, which is the most destructive insect to pine. In addition, mountain pine beetle epidemic outbreaks can last for numerous years depending on climatic factors; damaging vast areas of lodgepole pine forests and making long term planning for timber supply and integrated resource management arduous. Currently, the loss of lodgepole pine due to mountain pine beetle infestation is substantial, and as an attempt to battle the crisis, abundant volumes have been harvested. However, previous work has concurred that wood from dead trees affect product quality, which is the primary concern for the pulp and paper industry. Currently, there is a lack of information on the mechanism and effects of mountain pine beetle on pulp fibre quality. In order to fully utilize the mountain pine beetle killed resource, it is crucial to understand how the pine beetle impacts fibre quality. As a result, the present investigation evaluates the effects of mountain pine beetle killed wood on wood morphology, chemistry and pulping properties. Prior to experimental analysis, a dead (infested by mountain pine beetle) and sound standing lodgepole pine tree were harvested from the same site and segregated into sapwood and heartwood at different positions of the tree. Moisture content and density analysis demonstrated that infested sapwood and heartwood exhibited significantly reduced moisture content and lowered density, as tree height increased. The chemical analysis indicated that infested sapwood contained less extractives, lignin and carbohydrates when compared to sound sapwood. These results are likely due to the mountain pine beetle and subsequent blue stain fungi infestation. Extractive content typically increased with tree height whereas, the carbohydrate content tended to decrease. In general, no clear trend was apparent for the heartwood chemical analysis. Consequently, the permeability analysis demonstrated that infested sapwood was more permeable than sound sapwood; while sound heartwood was more permeable than infested heartwood. These results are likely due to the fact that fungal hyphae were present in infested sapwood and numerous aspirated pits were found in infested heartwood as observed from the microscopic analysis. Moreover, the chip quality analysis revealed that the infested wood typically generated more fines than sound wood; however, tree height did not appear to affect chip quality. Similarly, the pulp quality analysis demonstrated that the infested wood had a lower kappa number, generated a higher pulp yield and consumed less alkali compared to sound wood. The changes in pulp quality can be attributed to the changes in wood chemistry. Additionally, paper quality analyses revealed that paper from the infested wood had lower burst and tensile indices and higher tear strengths. Paper quality from the infested wood was also more porous, less smooth and less dense. The fibre quality analysis suggest that differences in paper quality made from infested wood may be due to the original fibre attributes rather than the effect of pine beetle or blue stain fungi, in that the results indicated that the infested wood fibres were longer and coarser. Clearly, mountain pine beetle infested wood affects wood quality, however, the differences between sound and infested wood are not so significant that the beetle killed resource cannot be utilized.

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