The two measurements most commonly used to estimate the volume of wood in a tree or log are diameter and log length. Stem quality is also evaluated using a grading system that considers how large and straight a stem is and whether or not there are defects such as branches.
Measuring Tree Diameter
The convenient point of measurement is determined by a person's height. A standard point is 4 ½ feet
above the ground (above the ground on the uphill side if the tree is on a slope). Stem diameter measured in this manner is referred to as "diameter at breast height" and is abbreviated "dbh". Diameter is usually measured with a special diameter tape sold by forestry supply companies. However, many carpenter's tapes have a scale on the reverse side for measuring units of diameter. Or, you may use a regular cloth tape to measure around the tree and divide the reading by 3.14 to obtain the diameter. Measuring dbh to the nearest inch is adequate. Measuring Log Length
A tree may be thought of as a collection of logs and pulpwood
. Small trees with dbh's ranging from 5 to 11 inches are only suitable for pulpwood. Trees greater than 11 inches dbh are suitable for sawlogs, from which lumber is cut. Typically, pulpwood is measured in 8 foot lengths and sawlogs are measured in 16 foot lengths
your request for "How to Estimate the Value of Timber in Your Woodlot" Circular #148 January 1989 By Harry V. Wiant. Estimating Pulpwood and Log Volume
Pulpwood is often measured by weight at the point of delivery. A truck containing a load of pulpwood is weighed and the weight of wood is determined by subtracting the truck weight from the total weight. Sawlogs are the most valuable parts of the tree and accurate volume estimates are critical to receiving a fair price for you timber. Sawlog volumes are estimated in units of board feet. Simply, a board foot
is the amount of wood in a piece measuring 12 inches square and 1 inch thick.
By using stem diameters and log lengths, three different "log rules" or mathematical equations, have been developed for estimating the number of board feet in a log. Request the publication mentioned above for more details. The three log rules are called "Doyle," "Scribner," and "International." The landowner selling timber is advised to estimate the volume of their trees using Scribner or International. Because the Doyle log rule underestimates board feet volumes, most timber buyers prefer to use the Doyle log rule. If you, as a seller, are not aware of this difference, you may settle for much less money than your timber is worth. Try to negotiate a volume estimate using either the International or Scribner rules, otherwise, make sure you negotiate a selling price that is about 40% higher per thousand board feet. Note: All of the tree value estimates in the web page are based on volumes determined using the International Log Rule.
Estimating Log Grade and Defects
Defects on a tree stem, such as rot, splits, cracks, and curvy stems
can reduce the amount of lumber that can be obtained from a given log at the sawmill. Click on the pictures at the bottom of this page to see some examples of defects in standing trees as well as a high value sawlog. In addition to volume loss, the value of lumber that can be sawn from a given log depends on factors such as the presence or absence of knots (caused by branches). Trees can be graded according to a system that takes into account the amount of volume and the quality of the lumber that will be lost from the log when it is sawn. Logs given "Grades" where:
- Grade 1 logs are the straightest logs with little or no defects.
- Grade 2 logs have some defects.
- Grade 3 logs have the most defects and can also have somewhat curvy stems.
Logs that are too curvy to be sawn, or have too many defects, are typically sold as pulpwood. The value of trees is related to their grade and species, with Grade 1 trees being worth more than Grade 3. The highest value category of sawlog is called "veneer". This grade of log is typically peeled at the mill and used in the manufacture of fine furniture. For most species (except for black cherry), veneer logs tend to be larger in diameter than Grade 1 sawlogs and have no defects.
If a landowner selling timber is not familiar with how tree grade is related to tree value, they may not receive a fair price for their timber. A landowner can gain a fair appreciation of the quality of their trees using observation and common sense. If trees are large with few knots showing on the lower (larger) logs, and stems are straight with no damage or rot then the logs will tend to be of high value. If there is evidence of a lot of stem rot in lower logs and many branches and crooked stems, then the trees probably have lower value. Tree species is also a very important factor determining tree value.