Linking Lumber Quality and Knot Proximity

The southeastern United States is home to millions of acres of southern yellow pine forests. These trees are worth billions of dollars when harvested and sold as lumber. Their value, however, is affected by their quality, and their quality can be affected by multiple knots in close proximity on a board.

Multiple knots in close proximity in southern yellow pine lumber.

Knots derive from tree branches, and because the grain of a knot runs more or less perpendicular to the length of the board, it weakens the board. Multiple knots near each other on a board weaken it even further, but lumber grading rules used to assess knot groupings are somewhat subjective.

Forest Products Laboratory researchers are studying southern pine lumber to quantify the effects of different kinds of knot groupings. The study is expected to reveal what kind of knot patterns affect strength, stiffness, and the ultimate performance of lumber the most. In addition to helping improve lumber valuation practices, this work will also help foresters modify silvicultrual practices to reduce the occurrence of knots in close proximity in the first place.

For more on the details of this study, see the Research In Progress report.