Non instrumental method in Forest Mensuration

 Non instrumental method

1.  Single pole Method
2.  Shadow method

1)Single pole Method: The single pole method is a practical technique for estimating the height of a tree using a pole of a known length. Here's a simplified explanation of the method:

Materials Needed -

• A pole (approximately 1.5 meters long)

Steps to Measure Tree Height

1.Positioning the Pole

- Hold the pole vertically at arm's length with one hand.

- Ensure that the length of the pole above your hand (let's call this segment "ab") is equal to

the distance from your eye to the point where you hold the pole ("Eb").

2.Finding the Right Spot

- Move forward or backward until the tip of the pole aligns with the tip of the tree (point A)

when you look straight ahead.

- At the same time, ensure that the point where you hold the pole (point B) aligns with the

base of the tree (point C).

3. Understanding the Geometry

- In this scenario, the following relationships hold:

- The height of the tree (AB) is equal to the distance from your eye to the base of the tree

(EB).

- Since the pole is vertical and the distances are equal, we can set up the equation:

AB = EB

Conclusion

By measuring the distance from your eye to the base of the tree (EB), you can directly determine the height of the tree (AB) using the single pole method. This method is effective because it uses simple geometry and requires minimal equipment.

Figure: Single pole Method

2)Shadow method: The shadow method is a straightforward technique for estimating the height of a tree based on the lengths of shadows cast by both the tree and a pole. Here’s a concise explanation of how to apply this method:

Materials Needed

• A pole of known height (let's call this "ab")
• A sunny day for shadow measurement

Steps to Measure Tree Height

1. Set Up the Pole:

- Fix the pole upright in the ground.

- Measure the height of the pole above ground level (ab).

2. Measure Shadows:

- Measure the length of the shadow cast by the pole (let’s call this "bd").

- Measure the length of the shadow cast by the tree (let’s call this "BD").

3. Setting Up the Proportion:

- Use the principle of similar triangles to relate the heights and shadow lengths.

- Set up the proportion as follows:

AB/BD = ab/bd

  Here:

AB=is the height of the tree.

BD=is the length of the tree's shadow.

ab=is the height of the pole.

bd= is the length of the pole's shadow. 4. Calculate the Height of the Tree:

Rearranging the proportion gives:

AB = BD/ab×bd

- Plug in your measurements to find the height of the tree.

4. Important Considerations

- Timing: This method works best on clear, sunny days, ideally in the early morning or late

afternoon, when shadows are longer and more distinct. Avoid the period between 11 a.m. and 2

p.m. when shadows are shorter.

- Limitations:In dense forests, it may be challenging to obtain a clear shadow of the tree, making

this method less effective.

Conclusion

The shadow method is an effective way to estimate tree height using simple measurements and

proportional reasoning. This technique is especially useful in open areas where the sun casts

clear shadows.