The effect of processor debarking on wood quality deterioration during the interim storage of Norway spruce logs

Abstract

Deterioration of post-harvest timber quality and the consequent devaluation of sawlogs result in significant financial losses for the forest-based industries. The present study investigates the effect of processor debarking on the wood quality deterioration of Norway spruce sawlogs due to insect infestation and sap-staining during interim storage. Experiments were conducted in the Austrian Alps in 2022 and 2023, comparing processor debarked logs with conventionally processed logs. A total of 96 logs were analysed, with 24 logs in each treatment group per year. The study evaluated the colonisation by bark- and wood-infesting insects, the development of visible blue-stain and the effect of meteorological parameters on wood quality development. The results showed that debarking significantly reduced colonisation by wood boring insects, which cause technical damage and bark beetles, which are important vectors of blue-stain fungi, and thereby mitigated sapwood discolouration. A regression model obtained showed a significant effect of debarking on sap-stain compared to conventional processing, within the first few weeks after harvest. In addition, the temperature-dependent growth rate of blue-stain fungi, the moisture content of the logs and the number of Ips typographus galleries were positively correlated with the percentage of blue-stained sapwood area on the cross sections of the logs. The model showed a coefficient of determination (R²) of 0.50 after cross validation. The results suggest that debarking can extend the potential duration of interim storage without degradation by 13 days. This research highlights the potential of debarking as a practical measure to mitigate insect infestation and delay timber devaluation.