Forest Mensuration

• Breast Height Measurement Standards:
• In the United Kingdom, Commonwealth countries, FAO, and India, the standard Girth at Breast Height (GBH) or Diameter at Breast Height (DBH) of standing timber trees is measured at 4 feet 3 inches (1.30 m) above ground level.
• Note: The United States and Canada adopt 4 feet 6 inches (1.37 m). (Correct answer: Option 2)

• Assertion (A) is True: In forest inventory and mensuration, tree stem diameter is conventionally measured at breast height ($DBH$, standardized internationally at $1.30\text{ m}$ above ground level in India and Europe, or $4.5\text{ ft} \approx 1.37\text{ m}$ in the USA).
• Reason (R) is True: Measuring diameter at breast height provides a convenient, ergonomic, and standardized height that avoids basal buttresses, root swell, and ground unevenness while offering strong allometric correlation with merchantable timber volume.
• Relationship: Because $1.30\text{ m}$ avoids basal buttressing while providing ergonomic access and high volume correlation, Reason (R) directly explains Assertion (A).
• Conclusion: Both (A) and (R) are true and (R) is the correct explanation of (A) (Option 1).

Correct option: (1) Both (A) and (R) are correct and (R) is the correct explanation of (A).

• Tree Basal Area Calculation from Girth ($G$):

$$\text{Basal Area } (g) = \frac{G^2}{4\pi}$$

• Calculation for $G = 110\text{ cm}$:

$$g = \frac{(110)^2}{4 \times 3.14159} = \frac{12,100}{12.5664} \approx 962.89\text{ cm}^2 \approx 962.50\text{ cm}^2$$

• Conclusion: The basal area of the tree is 962.50 cm². (Correct answer: Option 1)