1. Ocular estimate

In estimating height of trees by eye, a height scale has to be fixed in mind. This is easily done by measuring the heights of a few trees with some instruments before the start of the work and that of a few trees again in the middle of the work. With this standard in mind, the estimator judges the heights of trees to be measured and records them. To make it more reliable, a pole of 3 m length may be placed against the tree and then the treeis imagined to be divided in 3 m sections and the height is calculated. If estimator has no practice in dividing the tree in imagination, he can make use of a pencil and divided into sections.

2. Non-Instrumental Methods

All non-instrumental and instrumental methods are based on the assumption that the tree is vertical. So, the calculated height does not give the actual height of height because all trees lean on one side or the other some of non-instrumental methods are given below:

• Shadow Method: In this method, a pole of convenient length is fixed upright in the ground and its height above the ground is measured.

Let, AB is the tree, ab is the pole, BD is length of shadow of tree, bd is the shadow of ab. The height of the tree can then be calculated by simple proportion as follows:

It can be applied on clear sunny days. It gives accurate results in the early mornings or late evening (avoiding 11:00 am to 2:00 pm), when tree cast long shadow. It is difficult to apply in well-stocked forests.

• Single Pole Method: Let AB be the tree and ac be a pole about 1.5 m long, held at b vertically so that distance from observer’s eye E to b is equal to ab.

Eb= ab, then

(Since, ab = Eb, AB = EB)

3. Instrumental

Hypsometers, altimeters and clinometers are used to measure height.

• Hypsometers: Used for determining the height of standing tree from observations taken at some distance from the tree.
• Altimeters: Generally altitude measuring instruments, which can be devised to determine heights of tree.
• Clinometers: It measures angle of slope. Any instrument which measures angles of slope can be used for height of tree by trigonometrical methods.

Some clinometers designed for this purpose called hypsometers are based on geometrical principles of similar triangles or based on relations between the sides of right angled triangles.