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Estimating Merchantable Tree Height

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Merchantable tree height, the usable length of the tree, is the distance between stump height (generally one foot) and the limit of utilization in the tree. The limit of utilization may occur at a main fork, at a serious defect such as a hollow or a point of decay, where excess limbs or forks occur, or at a minimum usable top diameter. Merchantable tree height is measured in eight-foot lengths, called half-logs or bolts. For pulpwood, bolts are often referred to as sticks.

Merchantable product height depends on the product to be made from the tree (Figure 3). Local market opportunities may limit production of all products; for example, in northern Minnesota most timber is marketed as pulpwood.³

The usual minimum top diameter (inside bark) for sawlogs and pulpwood is the larger of 50 percent of tree DBH or eight inches for sawlogs and four inches for pulpwood. Veneer trees must have a top diameter (inside bark) of at least 10 inches. When estimating top diameters, it is helpful to picture the bottom of a pail as representing the approximate top diameter for sawlogs and the bottom of an oil can as the approximate top diameter for pulpwood.

You can estimate merchantable heights using a stick or piece of lath with markings at four-inch intervals (Figure 4). Each mark represents one eight-foot bolt when the stick is used as follows:

1. Stand 50 feet from the tree center such that the tree does not lean toward or away from you.
   
   
2. With the stick in hand, extend your arm out 25 inches from your eye. Hold the stick in line with the trunk of the tree being measured.
   
   
3. Determine the point where utilization is limited in the tree.
   
   
4. Sight along the bottom of the stick to stump height (i.e., one foot). Move your eyes, not your head, and read the stick measurement that corresponds to the limit of utilization point. Record the number of bolts between the stump and the merchantable height.

If you are unable to get a good sight on the tree from a distance of 50 feet, stand 25 feet from the tree and divide the resulting height measurement in half.

Sample forms for recording DBH and merchantable height for pulpwood and sawlog trees are contained in Tables 1 and 2.

As an example, a dot indicating one sample tree would be placed in the upper left-hand comer of Table 1 for a tree with a DBH of five inches and one eight-foot bolt of merchantable height. Separate tally forms are frequently used for each species and sample plot.