Illinois Big Tree Register

Illinois Big Tree Logo

The Illinois Department of Natural Resources initiated the Illinois Big Tree Register in 1962 to appreciate, discover, and record the largest native tree species in the state. The Illinois Big Tree Register is part of a cooperative effort between the University of Illinois at Urbana-Champaign, the Illinois Department of Natural Resources, and the National Register of Big Trees sponsored by American Forests® and The Davey Tree Expert Company. The University of Illinois, in cooperation with the Illinois Department of Natural Resources, would like to encourage every citizen of this great state to search our forests, parks, and front yards for future Big Tree champions. We hope that in searching for these trees, citizens will become more aware of the vital importance of Illinois’ rural and community forest resource.

Intrigued? Want to get involved? The Illinois Big Tree Register is always looking for volunteers to inspect, measure, and certify nominations and current champions. Contact us today to learn how to become involved in the Big Tree program!

Big Tree Guidelines


Everyone is encouraged to submit their nominations to the Illinois Big Tree Register. Please note, the Illinois Big Tree Register only accepts nominations native to Illinois as listed in Robert H. Mohlenbrock’s Vascular Flora of Illinois. Hybrids and minor varieties are currently excluded from the Register. Botanical nomenclature follows Deadline for submitting nominations is August 1. Nominations received after this date will be kept on file and evaluated the following year.

To nominate a tree, please fill out an Illinois Big Tree nomination form and return it to the Illinois Big Tree Program coordinator. All nominations must be verified by a certified inspector prior to placement on the Register. Both the nominator and the owner of the certified Big Tree will receive a certificate of recognition. A nomination that comes within 5 points of a current champion will be listed as a co-champion. However, only the top two scores for that species will be listed. Certified nominations that come within 30 points of the champion will be kept on file as “contenders” should the current champion fall. Big Tree champions must be re-measured every ten years. Beginning in 2008, all trees listed on the Register that have not been re-measured within the last ten years will be dethroned in lieu of a recently measured contender. Please contact the Big Tree coordinator if there is any change in status or condition of a Big Tree.


The “biggest” tree of each native species is determined by a point system devised by American Forests®. Scoring is based on the sum of three required tree measurements:

Circumference (inches) + Total Height (feet) + ¼ Ave. Crown Width (feet) = Total Score

Definition of a Tree

A tree is a woody plant with an erect, perennial stem at least 9.5 inches in circumference at a point 4.5 feet above ground; a well-defined crown of foliage; and a total vertical height of at least 13 feet (Little 1979.) Nominations that do not meet this definition are ineligible for the Illinois Big Tree Register.

Information Required for Each Big Tree Nomination

  1. Correct common and scientific name (
  2. Circumference of the tree at 4.5 feet, measured in inches
  3. Total vertical height, measured to the nearest foot
  4. Average crown spread, measured to the nearest foot
  5. Date measurements were taken and by whom
  6. Map location, detailed directions, and GPS coordinates
  7. High quality, digital color photographs; uncompressed TIFF formats preferred. Photos should show as much crown and main stem as possible. Please include an additional photo for scale and identification.

*All nomination forms become property of the University of Illinois and will not be returned. By submitting photos, you hereby grant the University of Illinois permission to post the image on the web and use the image for the promotion of the Register without compensation.

National Register of Big Trees

Did you know that Illinois currently has six national champion Big Trees? Any tree that comes to our attention that may qualify for the National Register of Big Trees will be forwarded to American Forests® under the name of the nominator. Only trees recognized as native or naturalized are eligible for the National Register. Please visit American Forests® for more information on the National Big Tree Program.

Illinois Big Tree Measurements

Figure 1

Figure 1


Circumference is measured at 4.5 feet above ground level (Figure 1). Unfortunately, for measuring purposes, not all trees have a single, straight, branch-free main stem. Therefore, in order to properly measure tree circumference, it must be determined whether the tree has a single stem that can be measured at 4.5 feet; a single stem with a growth, defect, or fork directly at 4.5 feet; or two or more stems growing very close to one another.

Figure 2

Figure 2

Figure 3

Figure 3

If the tree has a growth, defect, or forks directly at 4.5 feet, simply measure the smallest circumference below 4.5 feet (Figure 2). If the tree is growing on a slope, take the circumference measurement at 4.5 feet above the mid-point of the base of the tree (Figure 3).

Figure 4

Figure 4

Stems that have clear separation at or “near” the ground should be considered separate trees and measured accordingly (Figure 4). Likewise, if the circumference measurement below the lowest fork places the measurement at ground level, then it should also be considered separate trees. Please note, it is up to the nominator and the inspector to determine if the tree is, and always was, one tree or if it is actually the result of two or more stems that began as separate sprouts and fused together. Quite often on multi-stemmed trees, there is a “seam” indicated where the two stems fused together (adapted from National Register of Big Trees). Useful tools to measure circumference include a forester’s diameter tape or any flexible tape-measuring device.

Vertical Height

Figure 5

Figure 5

Vertical Height is the measurement of the vertical distance between the base of the tree and the topmost branch (figure 5). Quite often, the topmost branch will not be directly over the base of the tree, so adjust accordingly. To improve accuracy, please take several height measurements and average the results. Useful tools for measuring tree height include stick method, telescoping pole, drop-line, transit, Abney level, clinometer, laser hypsometer, Haga altimeter, yardstick, etc.

Average Crown Spread

Figure 6

Figure 6

Average Crown Spread is determined by taking the widest horizontal distance (spread) of the crown and averaging it with a crown spread measurement taken at right angles to the widest measurement (figure 6). Useful tools for determining average crown spread include wooden stakes or wire flags and a 100’ tape measure.

  1. Observe and identify the widest crown spread, from crown edge to crown edge. Identify these two points with markers or wire flagging. Using a tape measure, record the horizontal distance between these two points (A to B).
  2. Observe and identify the crown spread at right angles to the two measurement points identified in Step 1. Again, using a tape measure, record the horizontal distance between these two points (C to D).
  3. Add the crown spread measurements from Step 1 and Step 2, and divide by two. This number is the average crown spread.

Helpful Resources

Mohlenbrock, Robert H. 2006. Forest Trees of Illinois. 9th Ed. Illinois Department of Natural Resources. 332pp.

Mohlenbrock, Robert H. 2002. Vascular Flora of Illinois. 3rd Ed. Southern Illinois University Press. 490pp.

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