Measuring a tree without having felled it yet is at first sight a difficult task. However, there are various techniques that can be used to quickly and easily determine the height and circumference of a tree.
Height of a tree
Let’s first look at the forestry square technique, an interesting alternative to measuring the tree by guesswork. It is a 45° square allowing the aiming. The positioning is done with a plumb bob. Be careful, the plumb line must be parallel to the edge of the square!
Then, you just have to move backwards until the line of sight passes by the top of the tree. The height to be measured is simply the distance from the base of the tree, plus the height of your eye.
Circumference of a tree
The circumference of a tree is measured on the bark at 4 ft. above the ground using a forestry compass or a forestry tape. A reduction is then made to account for metric decay based on species averages. Remember: the larger the tree, the greater the reduction.
How to measure a tree ?
There are 2 methods to easily measure a tree:
Measuring the height of a tree with the logger’s cross is the most used because the technique is simple and simply requires the use of 2 sticks of the same length. By aiming the cross at the foot and the top of the tree, the distance between you and the tree gives you its height.
The second method is based on measuring the shadows of the tree and a person whose height you know.
These two methods are derived from the application of Thales’ theorem. There are simpler graduated sights to use for measuring small or curtained plants.
Note that the dimensions of a deciduous tree in nurseries are based on the circumference of the trunk at 1.30 m height and not on its height. The size of the trunk (diameter or circumference) gives a more accurate idea of the age of the tree.
Here are 2 methods to measure a tree.
Method 1: Make a logger’s cross
Take 2 wooden sticks of the same length (l), 8 or 12 inches long, and hold them perpendicularly in front of your eye to form a cross.
Move away from the tree so that the base of the vertical stick coincides with the base of the tree and the end of the stick with the top of the tree.
The distance to the tree (L) is the height of the tree (H).
Count the number of steps (1 m long) from the tree or use a tape measure to make a more accurate measurement.
Method 2: Measure the tree’s shadows to determine its size
The shadows should be long enough to facilitate measurement. Avoid the middle of the day.
Stand with your back to the tree and align the shadow of the top of your head with the top of the tree. This point is called O.
The distance OB from the tree to point O, by counting the number of 1 m steps or using a decameter.
The height of your shadow OA.
Then do the following calculation: height of the tree = t × OB/OA, where t is your height in meters.
How to determine the age of a tree?
Accurate or crude, dating a tree can be done in several ways. How to determine the age of a tree?
The coring method
The scientific method consists of coring the tree with a tool called the Pressler auger. The core sample (piece of wood extracted from the trunk) is analyzed in the laboratory for dating thanks to the measurement (width) of the rings represented graphically. This work is done by computer and is called dendrochronology.
Beyond the age, this method allows to measure the average annual growth and the growth speed which corresponds to the time necessary for the radius of the tree to increase by 1 inch.
It should be noted that a tree grows in height by an average of 10 inches per year with periods of rest, especially in winter, when the sap does not flow or only a little. This change is visualized by a darker coloration of the wood visible on the rings present in the trunk. It is these rings that allow us to roughly identify the years when the tree is cut.
The calculation method
- A less invasive method allows dating by means of the tree’s circumference. However, the precise variety of the tree must be known, as it determines the multiplication factor by :
- 1.5 for silver maple, elm, poplar ;
- 2 for birch, white pine, red pine, Austrian pine, ash, red maple, oak and larch; by 2.5 for balsam fir, beech and ash;
- 3 for very slow growing trees such as red oak and walnut.
Measure the circumference of the tree at a height of about 1.40 m from the ground, then determine the diameter of the trunk by dividing the circumference by Pie (3.1416). Finally, multiply the trunk diameter by the multiplication factor corresponding to your type of tree and you will have an approximate age of the tree.