SAF Field Survey & Data Collection 2 — Questions and Answers
Question 1: When using a prism or angle gauge in variable-plot sampling, a tree is counted in the plot when the tree's DBH appears:
- Smaller than the prism gap
- Larger than the prism gap (Correct answer)
- Equal in size to the prism gap
- Any size relative to the gap
Correct answer: Larger than the prism gap
A tree is tallied when its DBH appears larger than the prism gap, indicating the tree falls within the variable radius plot.
Question 2: What is the primary purpose of using a clinometer in forest inventory?
- Measuring horizontal distance
- Measuring tree height by recording vertical angles (Correct answer)
- Determining compass bearing
- Estimating crown width
Correct answer: Measuring tree height by recording vertical angles
A clinometer measures vertical angles to calculate tree height using trigonometric relationships with a known horizontal distance.
Question 3: In forest mensuration, 'merchantable height' refers to the height of a tree from the stump to:
- The very tip of the crown
- The first live branch
- The point where the stem reaches a specified minimum top diameter (Correct answer)
- Breast height (4.5 feet)
Correct answer: The point where the stem reaches a specified minimum top diameter
Merchantable height extends from the stump to the point where the stem diameter falls below a specified minimum usable diameter.
Question 4: A forester establishes 20 fixed-area plots, each 1/10 acre, and tallies 400 trees total. What is the estimated trees per acre?
- 20 trees/acre
- 200 trees/acre (Correct answer)
- 400 trees/acre
- 40 trees/acre
Correct answer: 200 trees/acre
With 400 trees on 20 plots × 1/10 acre each (= 2 acres total), trees per acre = 400 ÷ 2 = 200 trees/acre.
Question 5: Which sampling method is most appropriate when rare or clustered species need targeted detection across a large landscape?
- Simple random sampling
- Systematic sampling
- Adaptive cluster sampling (Correct answer)
- Two-stage sampling
Correct answer: Adaptive cluster sampling
Adaptive cluster sampling adds additional plots around any initial plot where the rare feature is detected, improving detection efficiency.
Question 6: When recording tree species in a mixed stand, a forester uses a tally sheet with a 'miscellaneous' category. Best practice recommends this category should contain no more than:
- 50% of tallied trees
- 25% of tallied trees
- 10% of tallied trees (Correct answer)
- 5% of tallied trees
Correct answer: 10% of tallied trees
Best practice limits miscellaneous tallies to roughly 10% or less so the data remains meaningful for stand analysis and management decisions.
Question 7: The 'limiting distance' concept in variable-plot sampling means that for a given BAF, larger-diameter trees are tallied from:
- A shorter distance than smaller trees
- The same distance regardless of DBH
- A greater distance than smaller trees (Correct answer)
- Only within a fixed 1/10-acre radius
Correct answer: A greater distance than smaller trees
Larger-diameter trees subtend the critical angle from farther away, so they are included (tallied) from greater distances than smaller trees.
SAF Field Survey & Data Collection 2
When using a prism or angle gauge in variable-plot sampling, a tree is counted in the plot when the tree's DBH appears: