1. Anonymous 1994 . Nordiskt trä. Sorteringsregler för sågat virke av furu och gran . [Nordic timber. Sorting rules for sawn timber from pine and spruce.] , Stockholm : Arbor publishing . (In Swedish.)
2. External knot size and frequency in black spruce trees from an initial spacing trial in Thunder Bay, Ontario
3. The interior knot structure of Pinus sylvestris stems