You Know Biltmore Stick. Do You Know Biltmore Pachymeter?

By Nilesh Timilsina, Robert Beanblossom, and Kavi Raj Awasthi 

June 21, 2023 
Originally published in The Forestry Source - May 2023 issue 

In any introductory forestry course, one of the most basic tools a forester first learns to use is a Biltmore Stick. It was invented by Dr. Carl A. Schenck, the founder of the Biltmore Forest School: the very first professional school of forestry in America. The school was located on the present-day site of the Cradle of Forestry in America on the Pisgah National Forest in western North Carolina and operated from 1898 through 1913. When Dr. Schenck closed the doors to the school in late October 1913, 70% of all foresters in the United States at the time had graduated from there – a remarkable achievement. 

The first Biltmore sticks were made simply by carving notches on the handle of an ax. Later, Dr. Schenck required each student to make their own. Today, most foresters still carry one in the woods for rough cruising, marking a plot center, as a walking stick, or simply to move snakes from our path. All foresters are aware of a Biltmore stick; however, few have heard of a Biltmore pachymeter, a device invented by a graduate of the Biltmore Forest School to measure the upper stem diameter of a tree.  

Biltmore Pachymeter Invention
Lesser known is the “Biltmore Pachymeter,” a simple device designed to measure the upper stem diameter of a tree. It was the creation of a bright, promising student by the name of Ralph Getman Burton, a native of Pittsfield, Massachusetts.

Born on March 27, 1884, he entered the Biltmore Forest School immediately following graduation from high school. This was unusual since most students of Dr. Schenck had some college, with many having attained undergraduate degrees in various fields before studying forestry. Burton, as young as he was, excelled at school. He obtained a bachelor of forestry degree, a bachelor of forest engineering degree (the equivalent of today’s master’s degree) with high honors, and after graduation became an assistant professor of forestry at the school under Dr. Schenck. Later, he joined forces with fellow student Taft Reed and formed one of the first forestry consulting firms in the US. 

Biltmore Pachymeter Construction

The Biltmore Pachymeter is used along with a measurement scale placed at a convenient height on the base of a tree trunk (Burton 1906, Chapman 1924). The instrument uses the principle of similar triangles (Figure 1). This principle considers two triangles of the same shape, which may or may not be the same size but have equal and/or congruent corresponding angles. When these criteria are met, the principle states that the triangles’ corresponding sides have an equal ratio.

Although any stick or wood with parallel edges can be used as a pachymeter, Burton (1906) describes his instrument as a piece of metal that is 18 inches long and 1.5 inches wide. It has a longitudinal slot that is 0.25 inches wide and 17 inches long. The top (d1) and bottom (d2) edges of the slots should be parallel to each other (Figure 1a). As shown in Figure 1a, a diameter measurement scale (D2) is placed at a convenient height on the base of a tree trunk. An observer (A) holds the pachymeter in his outstretched hand vertically and parallel to the tree. The observer (A) moves backward or forward with the pachymeter until a desired diameter is read, through the bottom slot of the pachymeter (d2), on the scale (D2) placed at the base of the tree trunk. From the exact location, the observer’s sight moves upward. It looks through the upper slot of the pachymeter, wherever the pachymeter cuts off even with the upper diameter (D1), giving the upper diameter reading equal to the diameter read at the bottom scale (D2).

Biltmore pachymeter uses two sets of similar triangles (Burton 1906, Chapman 1924; Figure 1b). The first set of similar triangles is used to determine the height of the upper diameter to be measured, and the second set of similar triangles is used to determine the diameter. In Figure 1a, the upper set of similar triangles for height to upper diameter is given by the triangles formed by A and d1 and A and D1, respectively. Similarly, another set of triangles for diameter reading is formed by A and d2 and A and D2, respectively.

Again according to principles of similar triangle

here,

·         l and L are the distances from A to d1 and D1, respectively

·         e and E are distances from A to d2 and D2, respectively

 

since d1 and d2 are equal, D1 (upper diameter) will be equal to D2 (lower diameter read on the scale placed at the bottom of the tree trunk).


Biltmore Pachymeter Legacy
Some of the many tributes paid to Burton included this memorable one, “Ralph was often called in consultation on important matters requiring a thorough knowledge of forestry, and he wrote for publication many articles of a technical character. All such articles were regarded as authoritative. He had a graceful and interesting style that appealed not only to those of a scientific mind but to the layman as well. He was a fine young man with a career of exceptional promise.”
 
Photo Credit
Image 1: Dr. Carl A. Schneck, inventor of the Biltmore Stick; North Carolina State University Libraries. 
Image 2: Illustration of the use of Biltmore pachymeter. The figure shows two sets of similar triangles. Society of American Foresters. 

References
Burton, Ralph G. 1906. “The Biltmore Pachymeter.”, Forestry Quarterly 4, no. 1:8-9. 
Chapman, Herman Haupt. 1924. Forest Mensuration. John Wiley & Sons, Inc.

Nilesh Timilsina is an associate professor of forest biometrics at Clemson University. Robert Beanblossom is the volunteer caretaker at the Cradle of Forestry. Kavi Raj Awasthi is a graduate student in the department of forestry and environmental conservation at Clemson University.