Estimating Timber Volume in a Standing Tree
Measuring an Individual Tree
The first step is to measure the Diameter of the tree at Breast Height, usually abbreviated as DBH. This is important for both classification purposes and determining volume of the tree. Measurement can be done using a Biltmore Stick, calipers, Standard Tape, or diameter tape. We prefer to use diameter tape, also sometimes called a pi tape. Standard tape is a ruler tape that would be used to measure circumference such as used by tailors to measure waistlines. Diameter tapes are similar but measure directly in diameter instead of circumference. You can use a standard tape and divide by pi ( 3.14 ) to achieve the same result but diameter tapes save you the conversion problem.
The DBH is used to classify the tree according to its potential uses.
Classification of Trees by size
Generally trees have different markets depending on how they will be used. Below are general classifications of common timber types. In evaluating a given tree it should be placed in the proper category.
Pulpwood: 6-9” DBH. Pulpwood trees are chipped into small pieces, chemically treated, and made into paper. Pulpwood is measured in tons or standard cords.
Superpulp: This is an unofficial designation used to describe pulpwood-sized pine trees from which at least one 2 x 4 board could be cut. Superpulp is more valuable than regular pulpwood, but markets for this product are not always available. Another name for superpulp is “canterwood.”
Palletwood: This is an unofficial designation for low-quality hardwood timber that is not good enough for lumber, but can be sawed into slats for pallet-making. Palletwood is sometimes called “skrag.”
Chip-n-saw: 10-13” DBH. By using a combination of techniques, these mid-sized trees produce chips for pulpwood as well as small dimension lumber. Chip-n-saw is measured in tons or standard cords. Value is heavily dependent on tree quality.
Sawtimber: 14”+ DBH. Trees are cut into lumber. Waste material is converted into chips for fuel or paper production. Sawtimber is measured in tons or board feet. Value is heavily dependent on tree quality.
Veneer: 16”+ DBH. By means of a large lathe, the tree is converted into continuous sheets of thin wood. This is used in the manufacture of plywood and furniture, depending on the type of tree. Veneer is measured in tons or board feet. Value is heavily dependent on tree quality.
Pole Logs: 16″+ DBH. These trees are used in the manufacture of power and telephone poles. They are usually high quality pine trees that are tall with limited knots and weak spots.
The further use of the DBH measurement is used in conjunction with the usable height of the tree to give us a meaningful measure of the timber volume contained in the one tree. Timber volume can be expressed in many different ways. Common measurements include:
Board feet Doyle Scale
Board feet Scribner Scale
Board feet International Scale
Unfortunately no single standard exists for measuring timber volumes and this adds to confusion. The choice of measurement units varies by industry and by the final use of the product. We will attempt to have all calculations come to a single unit of measurement — Tonnage. The reason for the choice is that while in some cases it has its weaknesses, it is easily measured. Trees arriving by truck at the mill can be weighed as they arrive and this is readily verifiable.
Measurement of the height of the tree is a little more difficult than measuring DBH. Eyeballing can give a crude approximaton but is not sufficient for most purposes. While the measurement of a felled tree is easy, stumpage or standing trees is a bit more difficult. While there are numerous instruments that can help, the usual ones are a Biltmore stick, or more commonly, a clinometer. Clinometers are used to measure the angle from level, that is incline in a positive or negative direction. Normally this is expressed in degrees, however most forestry clinometers have a 66′ foot scale that reads directly in feet if you are standing 66′ from the object being measured. See the diagram below.
You could measure the distance of 66′ by a tape measure, but the easiest way is to have a measured pace. For example my pace is 26 steps for 66′. This pace is different for each person. To measure your pace set out a known 100′ distance and step it off naturally and count the number of paces. Take 2/3 of the number of paces for a 66′ distance.
In reading the clinometer you should come up with two numbers, distance in feet above horizontal and distance below horizontal. The distance above should be from horizontal to the usable height of the tree. This is normally to approximately 4″ for pulp wood and 6″ for sawtimber. Note that if there is a major division of the branches of the tree, then your measurement should stop there. The distance below the horizontal should be measured to the point at which the log should be cut, usually about 4″ above the dirt.
Adding the two heights will give you the usable measurement of the height of the tree. Once the species of the tree, the usable height of the tree, and the classification of the tree are known, you can use tables to determine the volume in the tree.
Next, determining the volume of timber by tables and charts from your measurements. Look for Timber Cruising for Laymen, Part III, coming soon.