Too many years ago, I served on a timber industry committee charged, among other things, with figuring out whether it was better to advocate the calculation of “allowable sale quantities” in board or cubic feet. Board foot measure estimates how much lumber can be sawn from a log, with allowances for saw blade width (“kerf”), slabs (the left-overs after squaring off a round log), and sawing strategy. Cubic foot measure is the geometry-based volume of a log.
Ceteris paribus, the number of board feet equivalent to one cubic foot is proportional directly to log diameter. For example, a small-diameter log has a bf/cf ratio of about 4, while a large-diameter log’s ratio is about 6.
Today, almost all serious measures of timber are made in cubic feet, except for pulpwood and biomass, which are measured by weight. That’s because cubic foot measure is widely regarded as a more accurate representation of total wood volume, less subject to the vagaries of milling technology and scaling judgment.
Which measure one chooses makes a difference in how one sees the world of wood production and supply. “Everyone” knows that Oregon’s timber harvest has dropped precipitously since the early 1990s. And, so it has, measured in board feet (the blue-line curve).
But a funny thing happens when Oregon’s harvest is measured in cubic feet (the red-line curve). Not nearly so dramatic a decline. The reason is pretty simple. Oregon’s plantation forests grow a whole lot of wood, producing much more growth annually than the old forests the plantations replaced. Cubic foot measure, which is much less sensitive to tree diameter, more accurately captures that volume than does board foot measure.