Tree Measurement : National Register of Big Trees

Tree Measurement


Champion Status and Verification

When a tree has a Point score that falls within 5% of the Champion, it becomes a Co-Champion.

The underlying determination of a Champion is that it is a Champion until challenged. This challenge can only be upheld by means of a simple verification process. Trees grow, so a Champion is constantly under challenge.

All nominations, tree species and measurements are taken on trust.

All trees must have a single stem, or in other words, a single pith. The pith is the soft, spongy part located in the centre of the stem. It is encircled by a ring of xylem , and outside that, a ring of phloem.

If you need help with identifying and measuring trees, you may consider contacting a local arborist. See:

Base Point

To have a standard system of height and circumference measurement, the point at which the tree germinated must be estimated. It is this base point from which height is measured, and also the base point from which the 1.4m trunk height is established for the measurement of circumference. Many of the bigger trees have large accumulations of bark, twigs and/or leaves around the base. Taking the 1.4m measuring height from the top of this litter will give an incorrect measurement of both height and girth.

Trunk Circumference

Circumference is measured at 1.4m above ground level.

If the tree forks, record the smallest circumference between 1.4m and the ground below the lowest fork excluding dead branches and epicormic sprouts; also record the height above the ground level where the measurement was taken.

Many big trees grow on sloping ground, and some are difficult to measure. Take the measurement where the centre line of the trunk meets the ground i.e. mid-slope.

Trees with large buttresses present challenges when measuring circumference. Most species of figs fall in this category. The buttresses result in a lot of 'air points' that are not reflective of the trunk mass and distort the objectivity of the Points system. Varying issues arise when dealing with branches that grow out almost horizontally - predominantly with figs. The current, and subjective, adjustment to the circumference of the tree is to use 60% of this measurement.

Certain species of figs, and trees with large buttresses, present challenges when measuring circumference. In the case of heavily leaning trees, circumference is measured perpendicular to the axis of the tree.

If you are unsure about how to deal with these unusual trunks, please consult with the Register Coordinator to obtain help, and the current measuring guidelines.

Tree Height

The measurement of height is the one where we have the greatest inaccuracy. Whilst there are clinometers and height meters available, which will accurately measure tree height to within about 1/2 metre, these are moderately expensive and are inaccessible to most members of the general public. If you do not have access to a height meter or clinometer, we suggest two methods for obtaining the height of a tree.

Determine the highest point of the canopy from a distance as it is often difficult to determine the highest point when you are close to the tree.

Method 1.

Person 1 stands near the trunk of the tree. Person 2 stands at a distance where the base and the top of the tree are visible. Person 2 holds a classroom ruler upright at arms' length and walks forwards or backwards until the entire length of their ruler covers the tree from base to top.

Still holding the ruler at arms' length, Person 2 turns their wrist right or left so that the ruler is now horizontal, with one end on the base of the tree.

Person 1 now moves away from the trunk in the direction the ruler is pointed (at a 90 degree angle) until Person 1 standing where the end of the ruler points.

Person 1 is now standing the same distance from the trunk as the tree is high.

Use a tape measure to record this distance.

[You can also use a metre rod as it makes it easier to read off a centimetre height and then spin the rod horizontally and re-grip it in a more comfortable position. The zero end of the rod is the top of the tree, and the height is the reading on the rod that lines up with the base of the tree to where Person 1 is standing.]

Method 2.

Hold the stick at its base vertically, making certain that:

The length of the stick above your hand equals the distance from your hand to your eye.

Staying on the same level [on the same contour] as the base of the tree, move away from the tree while sighting the trunk base above your hand. Stop when the top of the stick is level with the top of the tree. You should be looking over your hand at the base of the tree and, moving only your eyes, looking over the top of your stick at the top of your tree. Measure how far you are from the tree and that measurement is the tree's height.

Average Crown Spread

Two measurements of the crown spread are taken and recorded (in feet), at right angles to one another. The first is the widest crown spread, which is the greatest distance between any two points along the drip line of the tree. (The drip line is the outline on the ground of the outermost leaves of the crown.) Once the widest spread has been found, turn the axis of measurement 90 degrees and find the second crown spread. The crown spread used in the formula is the average of the two measurements taken.


If you wish to have more information about tree measurement techniques, please read this link to: American Forests Champion Trees MEASURING GUIDELINES HANDBOOK.

The Register is meant to be about fun and enjoyment, and all the issues dealt with above should in no way detract from the process or status of the nominated trees.