FM FM Forest Measurements & Inventory 1 — Questions and Answers
Question 1: Diameter at Breast Height (DBH) is the standard measurement of tree diameter taken at:
- Ground level at the base of the tree
- 4.5 feet (1.37 meters) above ground on the uphill side of the tree (Correct answer)
- The base of the live crown
- The midpoint of the merchantable stem
Correct answer: 4.5 feet (1.37 meters) above ground on the uphill side of the tree
DBH is universally measured at 4.5 feet (1.37 m) above ground on the uphill side of sloped terrain, providing a standardized reference point for comparing tree sizes.
Question 2: What instrument is most commonly used to measure tree DBH in forest inventory?
- Clinometer
- Diameter tape or calipers (Correct answer)
- Hypsometer
- Prism or wedge
Correct answer: Diameter tape or calipers
Diameter tapes (which convert circumference to diameter) and calipers are the standard field instruments for measuring tree diameter at breast height in forest inventory work.
Question 3: In a prism or wedge cruising system, a tree is counted in the plot when:
- It is larger than a minimum DBH threshold
- Its image in the prism appears to overlap with the actual tree trunk (Correct answer)
- It falls within a fixed radius from the plot center
- It is taller than the cruiser's eye level
Correct answer: Its image in the prism appears to overlap with the actual tree trunk
In variable-radius (angle gauge) cruising, a tree is tallied when the displaced image seen through the prism overlaps the stem, selecting trees with a probability proportional to their basal area.
Question 4: The term 'basal area' in forest mensuration refers to:
- The total surface area of tree bark per acre
- The cross-sectional area of a tree stem or all stems per unit area, typically expressed in square feet per acre (Correct answer)
- The area of soil disturbed at a tree's base
- The total leaf area of a forest canopy
Correct answer: The cross-sectional area of a tree stem or all stems per unit area, typically expressed in square feet per acre
Basal area is the cross-sectional area of a tree at DBH (or the sum for all trees per acre), serving as a key measure of stand density and growing stock used extensively in forest management.
Question 5: A 'site index' in forest management is used to:
- Rank forest land by property tax value
- Measure forest site productivity based on the height of dominant trees at a base age (Correct answer)
- Estimate the number of trees per acre
- Calculate the slope percentage of a harvest area
Correct answer: Measure forest site productivity based on the height of dominant trees at a base age
Site index is a numerical measure of forest site quality based on the average height of dominant and co-dominant trees at a specified base age (commonly 25 or 50 years), predicting potential timber productivity.
Question 6: Which of the following sampling methods uses plots of fixed size and shape to estimate forest conditions?
- Variable-radius plot sampling
- Fixed-area plot sampling (Correct answer)
- Point sampling
- Line-intercept sampling
Correct answer: Fixed-area plot sampling
Fixed-area plot sampling uses circular, square, or rectangular plots of predetermined size (e.g., 1/10 acre), tallying all trees within the plot to estimate per-acre conditions.
FM FM Forest Measurements & Inventory 1
Diameter at Breast Height (DBH) is the standard measurement of tree diameter taken at: