Fungal spoilage of kiln dried Sitka spruce at Scottish sawmills
Within close packed kiln dried Sitka spruce timber a disfiguring sapwood stain, caused by Ophiostoma piceae, frequently developed. Spoilage was investigated through research into nutritional status, moisture content and wettability of Sitka spruce timber, physical conditions within stacks of timber, moisture and nutritional requirements of O. piceae and infection of timber by O. piceae. Recommendations to minimise spoilage of kiln dried timber were made. Carbon and nitrogen compounds abundant in softwood did not result in greater growth than others. Cellulose and lignin were not degraded; O. piceae was unable to grow into wood. Saturated atmospheres of monoterpenes reduced growth rate, pigmentation and coremia formation on agar. Kiln dried batten surfaces contained 18% glucose, 8 times higher than green or air dried timber. However, growth was not nutritionally limited on air dried compared to kiln dried wood. The carbon/nitrogen ratio of kiln dried battens (4500:1) was 3 times higher than green timber and 9 times higher than air dried timber. The minimum relative humidity for growth of O. piceae was 93%, at which the moisture content of Sitka spruce sapwood was 21%. Stain coverage increased from zero at a batten moisture content of 15%, to 10% cover at 25% moisture content. Partially air dried timber developed greater stain coverage than kiln dried timber stored in similar pack types. Stain development was greater in summer than winter, when it was limited by temperature. Maximum mean batten stain cover (32%) developed in close packed wrapped partially air dried timber during warm and wet weather conditions. Kiln dried stickered timber only developed a lower mean batten surface moisture content than close packed timber during the summer. Moisture content of individual rows of battens within packs stored in the sawmill yard developed different moisture contents and stain coverage. Greater staining developed on rows with higher moisture content, which tended to be located toward the upper surfaces of packs exposed to percolating rainwater.