How To Measure A Big Tree

Taking the Measurements

The circumference of the trunk is usually the easiest measurement to make.  A tape can be run around the trunk at 4.5 feet above the ground or a string can be used if a long tape is not available.  In situations where the tree grows on a steep slope there may be some uncertainty as to just where on the trunk 4.5 feet comes.  In these cases, it is best to measure the circumference at 4.5 feet on both the upslope and downslope sides and average them.  If a tree trunk branches below 4.5 feet, the circumference of only the largest branch should be measured.

The height is best determined by using an clinometer, Abney Hand Level, transit, laser range finder, or other instrument for measuring the angle formed by sighting the base and top of the tree.   If this angle is measured 100 feet from the tree, a table of tangents can be used to convert the number of degrees of the angle to the height of the tree if feet.  If, for instance, the angle is measured as 30 degrees, and you look up 30 degrees in a table of trigonometric functions, you will find that the tangent of 30 degrees is 0.577.   This number is then multiplied by 100 to give the height of the tree.   Therefore the height of the tree is 100 x 0.577 which equals 57.7 feet.

If instruments to measure the angle are not available, you can use a straight stick.   Hold the stick vertically at arm's length, making sure that the length of the stick above your hand equals the distance from your hand to your eye.  Back away from the tree on ground level with the base of the tree.  When you are far enough from the tree that you can sight over your hand to the base of the tree and over the top of the stick to the top of the tree, you are at a distance from the tree equal to the height of the tree.  

The average crown spread can be measured by examining the farthest extent of the crown on all sides of the tree.  You then measure the tip-to-tip distance across the largest crown length.  Do the same across the shortest tip-to-tip crown distance and average the two.  The average is known as the average crown spread.

Reporting the Big Tree

To report a big tree, first determine the identity of the tree.  It will not be sufficient to say "It is some kind of oak".  If there is uncertainty another identification might be necessary.  Send photos or leaves, twigs and acorns or fruit in with the measurements   Personnel from your County Extension Service or a nearby college or university should be consulted to help you confirm the identity of the tree.

Second, take the measurements as described above.  If this is not practical, at least measure the girth of the tree in inches at 4.5 feet above the ground.  

Finally send the name of the tree, its location, and measurements to Michigan's Big Tree Coordinator, Andy Sawyer, 1117 State St., St. Joseph, MI   (269)-930-9698  You can always find out the name of the big tree coordinator for any state in the country by contacting the Director, National Big Tree Program, The American Forestry Association, 910 Seventeenth St. NW., Washington, D.C. 20006.

Determination of State and National Champion Status

State and National Champion trees are determined by a point system, based on three measurements. The number of points is obtained by adding the circumference of the trunk, in inches, 4.5 feet above the ground to the height in feet and 1/4 of the average crown spread in feet.