Tree Volume

To estimate the wood volume of a tree?fs stem, your forester will measure the tree diameter and merchantable height, then find the corresponding volume in a table.

Sawtimber and Veneer Trees
Trees that are large enough and of high enough quality to produce logs that can be sawed into lumber are referred to as sawtimber. To qualify as sawtimber, trees should have at least one 8-foot bolt, be at least 10 inches DBH, and have a top diameter inside bark (DIB) that is the larger of either 8 inches or 50 percent of DBH. For example, to be a sawlog, a tree of 20 inches DBH should have a minimum top DIB of 10 inches. These specifications are typical, but individual buyers may have different specifications. Sawtimber trees must not contain too many defects that reduce wood volume such as decay, scars, cracks, bulges, bark distortions, holes, branch stubs, or crook.

Individual trees of many species (such as black walnut, white ash, sugar maple, red oak, white oak) that are of exceptional quality, have at least one 8-foot bolt, are at least 16 inches DBH, and contain bolts that have a top DIB of at least 10 inches often can be sold as veneer trees. Logs harvested from these trees will be sliced or peeled into thin sheets. Such trees are more valuable than sawtimber.

The basic unit for estimating wood volume for both sawtimber and veneer trees is the board foot. A board foot is a piece of wood of any shape that contains 144 cubic inches of wood (for example, 12 inches by 12 inches by 1 inch, or 6 inches by 6 inches by 4 inches). Timber value is often described in dollars per thousand board feet (MBF).

Formulas called log and tree rules have been developed to estimate the number of board feet in a tree or log. A tree rule refers to a table that estimates wood volume in a standing tree. A log rule refers to a table that estimates wood volume in a cut log.

These rules differ in their assumptions about factors such as tree taper, board thickness, kerf (saw thickness), and minimum and maximum board width. They are never totally accurate, because:

The Scribner rule (see Table 2-1 below) is used most often in the Lake States. For example, a tree with a DBH of 22 inches and four bolts (32 feet) of merchantable height will yield about 286 board feet. If the tree had a 10 percent defect then the total tree volume would be reduced to 257 board feet.

Table 2-1. Tree volume in board feet (Scribner rule).