Merchantable Height
Merchantable height refers to the length of the usable tree and is measured from a 1-foot stump height to the cutoff (merchantable height) point in the top of the tree. The cutoff height will vary with locality, with the product being produced, and with excessive limbs, a major fork or other types of internal/external defects. Unless there are obvious, outward signs of defect in the trunk (logs), hardwood (deciduous or broadleaf) trees are normally measured to the first major fork in the trunk unless the upper (smaller) trunk diameter limit (determined by the processing mill) is reached before the fork in the trunk. Larger limbs do not necessarily cause a problem if they do not create a "Y" fork in the trunk. Side limbs will be cut off flush with the trunk when the tree is felled. Limbs do, however, create knots, which are considered defects, so the quality of the wood will not be as good when the tree has many branches along the trunk.
Other types of defects in the trunk that affect a tree's merchantable height include crook or sweep (bend) in the trunk or outward signs of rot and decay such as a conk (fungus fruiting body), swelling or bulge on the side of the trunk, or a cavity hole. The cutoff (merchantable height) point will be at a point below any of these defects for trees exhibiting such defects. Pictures of these defects can be found here.
Conifers (evergreen, cone-bearing trees) normally grow with one central stem and rarely fork unless there is a double top. Unless there are internal or external defects, merchantable height in conifers is frequently determined by the smaller diameter limit in the top log. This smaller diameter limit is established by the processing mill.
For the Invitational's Tree Measurement and Forest Evaluation contest events, the diameter limit for the top log cannot be less than 8 inches in diameter. If the tree you are measuring has no major defects and no forks, you are to measure merchantable height to a point in the top of the tree where the trunk diameter equals 8 inches.
Your tree scale stick has been calibrated so that if you stand 66 feet away from the tree being measured and hold the stick the correct distance from your eye (either 20-, 23- or 25-inches depending on the stick's calibration) in an upright, vertical position, the number of merchantable logs can be read from the stick's right-hand margin (see photo 6). It is important to make sure the stick is held vertical and not at an angle (see photo 7). Holding the stick so it tilts toward or away from you will yield a wrong measurement. Do not move the stick or your head when taking a measurement. Tilt your head back slightly so you do not have to move it when taking the height measurement. If you are wearing a hat, you should tilt the hat back on your head so it does not impair your vision. Moving your head changes angles and will result in an incorrect measurement.
Before you pace away from the tree to take the height measurement, walk around the tree and look up to inspect its entire trunk for signs of defect. Determine where the cutoff (merchantable height) point is before moving away from the tree.
Now, pace out or measure a distance 66 feet away from the tree. Make sure you walk away from the tree on the level or contour. When you turn and face the tree, the base of the tree should be at the same height as your feet. Do not walk uphill or downhill from the tree to take its height measurement. Doing so will yield an incorrect measurement.
When you reach the 66 foot distance, turn and face the tree. Hold the scale stick vertical and the required distance from your eye. Line the zero end of the scale stick up with the a point on the tree's trunk that is 1-foot above the ground (see photo 8). Loggers frequently do not cut trees off flush with the ground so allowing for a 1-foot high stump is important in measuring the tree for merchantable height. If you place a clipboard with a white piece of paper at the base of the tree before you pace away from it, the top of the clipboard will equal a 1-foot high stump and will be easy for you to see at the 66 foot distance. Now without moving your head, look up (move only your eyes) into the tree and determine where the cutoff (merchantable height) point intercepts the scale stick. Read this measurement to the nearest full half-log (see photo 9).
To determine the tree's board-foot volume, use the International 1/4 volume table in the Invitational Handbook. A similar volume table is also printed on the tree scale stick. Find the tree's diameter measurement on the stick. Below this measurement are four or five numbers. These numbers represent the board-foot volumes for a tree that would contain either 1, 2, 3, 4 or 5, 16-foot logs. Knowing the diameter of the tree and its merchantable height in 16-foot logs, you should be able to determine the board-foot volume of the tree from the volume table in the Invitational Handbook or printed on the scale stick.
The board-foot volume you have determined is called the gross board-foot volume. No deduction has been made for defect in tree. If a deduction for defect were made, the resulting board-foot volume would be the net volume. For the Invitational Tree Measurement and Forest Evaluation contest events, you are only required to determine gross board-foot volume of the contest trees.
It is essential for accuracy in measuring diameter and height that the stick be held the correct distance from your eye and that you position yourself 66 feet away from the tree to determine its merchantable height. For more information, please contact either of the Invitational Co-Chairmen.
