Georgia 4-H Forestry Field Day Manual

Lonnie E. Varnedoe, Public Service Assistant, The University of Georgia
Kim D. Coder, Professor of Forestry, The University of Georgia
David J. Moorhead, Professor of Forestry, The University of Georgia

The University of Georgia, Extension Forest Resources, Bulletin FOR96-029, 1996, 52 pp.

Contest Events:
2. Tree Measurement Estimation:

Participants will estimate the sawtimber volume in up to five (5) designated trees to an eight (8) inch top diameter (outside the bark).

Contestants may use an official cruise or scale stick with no modifications. Diameter tapes, calipers, and other instruments will not be allowed. The person obtaining the total volume closest to that calculated by the judges will be the individual winner. The amount that each team member missed the correct volume will be determined. The team with the lowest total for its best three participants will be the winner.

Allow only one contestant at each tree at the same time. When they have calculated the total volume in all trees, an appropriate expansion factor should be applied to yield a per acre estimate of sawtimber volume. The finial answer should be circled and the sheet turned in.

Contest Rules:

1. Merchantable heights will be determined to the nearest full half-log for sawtimber. A half-log is defined as being 8 feet long. The minimum basal log will be 10 inches D.B.H., one log merchantable length, and have a minimum top diameter of 8 inches. See the following section on tree measures for details.
    
2. Contestants must determine diameter and associated volume to the nearest one inch class.
    
3. Record sawlog volumes as found in the standard International 1/4 (rule) tree scale volume table (Form class 78) provided by the contest judge (see page 13). Do not use the volume table found on the tree scale stick.
    
4. Contestants must be able to compute volumes on a per acre basis from 1/10, 1/5, or 1/4 acre sample plots. Foresters seldom measure every tree when estimating volumes per acre. The concept of an expansion factor should be emphasized during contestant training.

Practice Preparation:

Select and number five to ten sawtimber sized trees (10 inches DBH and larger). If possible, measure diameters with a diameter tape and merchantable height with an altimeter or clinometer. Careful "stick" measurements are acceptable. Avoid borderline trees, that is, those trees with a diameter or height that might easily be thrown one inch larger or smaller or one-half log higher or shorter. Give each contestant a scale stick and a sheet numbered with spaces for DBH, height, and volume. The following example may be used.

Sawtimber Volume Estimation Sample Plot

For each tree, diameter breast height (DBH) and merchantable height in 16 foot logs (to the full half log) is measured and entered on the table. Then board foot volume for each tree is determined using the Tree Volume Table. The volume for the five trees is added together for the sub-total. Multiply by the appropriate number to bring the value to a per acre basis.

Sawtimber Volume Estimation Form

Measurement of Standing Trees:

Purpose: Standing trees are measured to obtain an estimate of the amounts of various forest products which might be cut from the tree. These measurements to estimate volume are important because most timber sales are based on volume. In order to make decisions on managing a forest stand, estimates of total tree volume, volume per acre, and volume by product are necessary.

Forest Products: The volume of products such as poles, piling, sawlogs, veneer logs, pulpwood and fence posts can be determined from tree measurements.

Method: Since all tree stems are basically a part of a cylinder, they have a diameter and height which may be measured. Diameter of standing trees are measured, by time-honored custom, at 4 1/2 feet above ground on the uphill side of the tree. This is termed "diameter breast height" and is abbreviated as DBH. Height of a standing tree might be measured as total (the entire height from ground line to the top) or merchantable. Merchantable height varies, depending on the product which might be cut. Trees which will produce sawlogs will have different merchantable height criteria than pulpwood trees. The minimum top diameter is fixed by certain product specifications. If a tree is to be cut into logs, the lengths cut will vary, depending upon the demand of the mill to which the logs will go. This is true of sawlogs as well as veneer logs. As a result, total merchantable length will vary.

Tools: The tree scale stick is used to measure diameter and height in the 4-H Forestry Contest. Figure 1. depicts how the tree scale stick is used to find the diameter.

Figure 1. – Method of using tree scale stick to obtain tree diameter as view from above.

DO NOT MOVE HEAD, JUST EYE.

Figure 1. – Method of using tree scale stick to obtain tree diameter.

Use the flat side of the stick, indicated "Diameter of Tree (in inches)." Hold the stick level at 25 inches from the eye, against the tree, at a height of 4-1/2 feet above ground perpendicular to the line of sight. Practice is needed to find both the 4 ½ foot point in relation to your height, and the 25-inch distance to your eye. When the stick is placed against a tree, close one eye, sight at the left or zero end. The stick and the tree bark should be in the same line of sight.

Now - DO NOT MOVE YOUR HEAD - Just move your eye across the stick to the right hand edge of the tree. Read the tree diameter to the nearest inch. Hold the stick perpendicular to the tree.

Height is measured as follows, pace out 66 feet from the base of the tree to a point where the entire tree can be seen. Hold the stick up right so that the "Number of 16 foot logs" side faces you. The zero end should point toward the ground. Plumb the stick at 25 inches from the eye. Sight the zero end to appear to rest at a one (1) foot stump height. DO NOT MOVE YOUR HEAD OR THE STICK. Look up the stick to the point where the top of the last merchantable cut would be made in the tree.

Figure 2. - Method of using tree scale t obtain tree height.

DO NOT MOVE HEAD, JUST EYE

Merchantable tree cut height for conifers in this contest is eight inches (8 inches) top diameter outside the bark OR the first major fork (a major fork is where a stem/branch is larger than 1/3 the diameter of the main stem and the crotch is "V-shaped ").

Merchantable tree height for hardwoods in this contest is eight inches (8 inches) top diameter outside the bark OR the first major fork (a major fork is where a stem/branch is larger than 1/3 the diameter of the main stem and the crotch is "V-shaped ") OR a major structural defect OR first major branch.

Read sawlogs to the full one-half log. Do not make a log longer than it actually is. For example, record a 2 3/4 log tree as 2 ½, not as a 3 log tree. Do not add length that is not present.

Practice on pacing is needed to find the 66 foot point. The 25 inch distance from eye to stick is the same as in measuring tree diameter.

Volume Tables

These are a composite of actual volumes on an average basis. Once the tree measurement is determined, enter the appropriate table from the left with the tree diameter (D.B.H.). Move across to the right to the column containing tree merchantable height at the top. At the intersection of these two points will be that tree's volume. Read and record each tree volume directly and separately. For contest purposes do not use the volume table on the tree scale stick.

Tree Volume in Board Feet (International ¼)
Number of useable 16-foot logs

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