Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Measuring tree diameter at breast height (DBH) is standard practice in forest inventories.
Reason (R) : DBH provides consistent reference point for all trees, allowing for rough calculation of basal area and volume.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explation of (A)
• B. Both (A) and (R) are correct but (R) is NOT the correct explation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Standard DBH Height: - India, UK, USA = $1.37\text{ m}$ ($4\text{ ft } 6\text{ in}$). - Continental Europe & FAO = $1.30\text{ m}$. Formula: $\text{Basal Area } (g) = \frac{\pi D^2}{4}$.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to validate the standard mensuration practice of measuring Diameter at Breast Height (DBH) in forestry inventory.

Step 2: Alysis of Assertion (A):

• In forest mensuration, tree diameter is universally measured at a standard height above ground level termed 'Breast Height' ($1.37\text{ m}$ in India/USA, $1.30\text{ m}$ in European conventions).
• Thus, Assertion (A) is correct.

Step 3: Alysis of Reason (R):

• Measuring at ground level is problematic due to base buttresses, root swells, and ground irregularities.
• DBH provides a convenient height for forest inventory workers and establishes a standardized reference point across all trees.
• Tree basal area ($g$) is calculated directly from DBH ($d$) as: \[ g = \frac{\pi d^2}{4} \]
• Basal area combined with tree height ($h$) and form factor ($f$) yields tree timber volume ($V = g \times h \times f$).
• Thus, Reason (R) is correct and provides the direct explation for why DBH is the universal standard in forest inventories.

Step 4: Fil Answer:
Both (A) and (R) are correct, and (R) is the correct explation of (A). Therefore, option (A) is correct.