Idaho Big Tree Program
Big Tree Nomination Form

Measurement Directions

Minimum size for trees: 3" diameter at 4½' from ground, 13 feet tall.

All wild and cultivated trees in Idaho are eligible to be measured for determination of the largest tree of each species or variety. We issue a list which contains all of the know trees native to Idaho whether or not we have any record for size. We will list dimensions on any cultivated tree which is a valid record.

The Idaho Big Tree Program will follow procedures used by American Forests, the organization which keeps the National Records of Big Trees. Any tree that comes to our attention which may qualify for national record status will be submitted to American Forests under the name of the nominator, as we want to have as many Idaho trees recognized on the national list as possible.

For national records, American Forests requires the tree to either be included in the 1979 USFS Checklist of United States Trees - Native and Naturalized (Agricultural Handbook No. 541) or to have its species approved by a committee for inclusion. For Idaho trees, both native and cultivated, we will accept any verified tree species that meets the minimum criteria of 3" dbh and 13' tall.

 

We require validation of identification of certain wild trees and on all cultivated trees. For many trees positive identification requires fruits, or less commonly flowers, in addition to the usual branches with leaves. Please send pressed, dried specimens to us at the address above.

 

HOW TO MEASURE: Both the Idaho and American Forests programs require three measurements. From these a point total is calculated and the tree with the highest point total holds the record. Record trees within 5 points of each other are declared co-champs. The formula is: circumference (inches) + height (feet) = ¼ average crown diameter (feet) = total points. Measurements must be taken by someone familiar with tree measurement techniques and having the proper instruments. We will refer requests for precise measurements to local foresters. Please write or call for recommendations.

 

1. CIRCUMFERENCE - taken at 4½' above average ground level (Figure A). Use: diameter tape, non-stretching cloth tape, or flexible steel tape. If tree is branched at or below 4½', then take the smallest circumference below 4½' (Figure B).

 

2. HEIGHT - actually the critical feature is length of the stem (bole), but with most trees this equals height for practical purposes. Height is taken to the top of the tree, whether it is dead or alive. Use: clinometer, Abney, Haga altimeter, transit, or similar instrument. The average of several measurements should be taken. Stem length is difficult to measure on severely leaning trees. Some simple trigonometry is needed to calculate the stem length in these instances. If needed, a local forester can make this calculation (Figure C).

 

3. CROWN DIAMETER - on the ground, measure the vertical projection of the widest crown width plus the crown width perpendicular to this measurement; divide by 2 for the average crown width. Use: steel or non-stretching cloth tape and a clinometer or Abney to make sure you are directly below the crown line.

 

DATA RECORDING - use the form on page three. Be sure to complete all of the bold sections marked with an asterisk*.

 

PHOTOS - try to include color slides or prints. Include one or more people or some other familiar object in the picture to add scale. Please identify any people in the pictures.