Identification of tree species poses the biggest obstacle. Many field and identification guides to trees exist and can be purchased from local bookstores. A computerized interactive twig identification key can be downloaded from the internet at Illinois State University (http://www.bio.ilstu.edu/Armstrong/biolab/eled/twigkey/twigkey. htm). The key can be used to identify the genus of trees native to Illinois (maple, oak, ash, etc.) using winter condition twigs (no leaves). A field guide can be used to determine the particular species. In many cases the owner will know the identity of a particular tree.

How to measure and score a tree

Step 1: On the worksheet include the tree species, date, class, school, location of the tree, and name of the owner. The registry is public and many curious people may wish to see the tree. If the tree is on private property it is important to get the owner's permission to measure and nominate the tree. Tree registration will not give people permission to tresspass. Trees must be viewed just from the street or sidewalk unless the owner gives permission. If the big tree is not visible from the street then people must obtain permission of the owner to visit the tree. You will not need permission to measure trees along streets, on school grounds, and in parks. Perhaps some of the students will have a large tree in their yard.

Step 2: The circumference is measured in inches at 4 1/2 feet above the ground with a measuring tape. It is important to take the measurement at this fixed point so it can be remeasured. If the trunk forks or a branch grows at this point, the measurement should be taken just below these obstacles. The circumference is recorded on the worksheet. If the tree consists of two or more distinct trunks at this height, the circumference of only the largest trunk is measured.  The circumference receives 1 point for each inch of circumference.

Step 3: The height is measured in feet with a tangent height gauge (figure two). The tangent height gauge is used by holding it parallel to the ground and viewing the top of the tree through the two guide holes. The person holding the tangent guide should move forward or backward until the very top of the tree in seen through both of the holes. Once the approximate distance from the tree is found, it may be useful for another person to assist in making certain the gauge is being held level by using the level bubble parallel. Experienced users can level the gauge by watching the leveling bubble in the mirror. After the tangent guide is level it may be necessary to move forward or backward some more to view the tree's top through the two holes. Once the bubble is level, and the top of the tree is in view, two measurements can be taken, the distance from the tip of the height gauge (next to your eye) to the ground, and the distance from the tip of the height gauge to the trunk of the tree. The tree height is equal to the sum of these two measurements, distance from the tree to the gauge plus height of the gauge from the ground.  A tree receives 1 point for each foot in height.  

Step 4: Crown spread is determined by the spread of the branches and they give the tree its shape (figure one).  The crown spread is measured as the average of the crown width in two dimensions at right angles, e.g., (north-south spread + east-west spread) divided by 2. 

Stand directly under the outermost branches of the tree.  Place a marker.   Then walk to the opposite side and repeat.  Measure the distance between the two markers.  Now repeat measuring the crown width at right angles to the first measurement.  The average crown spread is then divided by four and recorded on the worksheet.

Step 5: The tree's score is determined by adding the three measurements, circumference in inches, height in feet, and one-fourth of the crown spread. This score is recorded on the worksheet.

How to submit your nominations

Once the worksheet is complete, send it to the Fell Arboretum Big Tree Project, Don Schmidt, Campus Box 4120, Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120. Representatives of the Fell Arboretum Society will verify the identification and scoring of the five largest trees of each species on a yearly basis. Each class will receive a certificate of their nomination.

What tools do you need?

You need a tape measure, tangent height gauge, two people, and a Big Tree register Worksheet.

If you would like to borrow a tree height gauge for use in your class, please contact us (Don Schmidt, J. E. Armstrong). 

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