SAF Field Survey & Data Collection 3 — Questions and Answers
Question 1: When measuring slope distance to convert to horizontal distance, a forester records a slope of 30% over 100 feet of slope distance. The horizontal distance is approximately:
- 95.4 feet (Correct answer)
- 100 feet
- 97.1 feet
- 90.0 feet
Correct answer: 95.4 feet
For a 30% slope (angle ≈ 16.7°), horizontal distance = slope distance × cos(16.7°) ≈ 100 × 0.954 = 95.4 feet.
Question 2: What is the standard diameter at breast height (DBH) measurement point in the United States?
- 3.5 feet above ground
- 4.5 feet above ground (Correct answer)
- 5.0 feet above ground
- 1.3 meters above ground
Correct answer: 4.5 feet above ground
In the US, DBH is measured at 4.5 feet (1.37 m) above the ground on the uphill side of the tree.
Question 3: In a two-phase (double) sampling design for forest inventory, Phase 1 typically involves:
- Full ground measurement of all trees
- Rapid, inexpensive measurements on a large sample to stratify the population (Correct answer)
- Remote sensing classification only
- Installing permanent monitoring plots
Correct answer: Rapid, inexpensive measurements on a large sample to stratify the population
Phase 1 collects inexpensive auxiliary data (e.g., aerial photo interpretation) on many points used to stratify before the smaller, costlier Phase 2 ground sample.
Question 4: Which instrument is specifically designed to measure the diameter of standing trees at heights above ground without climbing?
- Biltmore stick
- Diameter tape
- Optical dendrometer (Correct answer)
- Relaskop
Correct answer: Optical dendrometer
An optical dendrometer (such as the Wheeler pentaprism or Barr & Stroud) allows measurement of stem diameter at any height without climbing.
Question 5: A forester uses a Biltmore stick to estimate tree diameter. The stick works by holding it at a fixed arm's length distance and reading the scale. This method relies on the principle of:
- Trigonometry of vertical angles
- Similar triangles using the eye as the apex (Correct answer)
- Basal area factor projection
- Ocular estimation calibrated by species
Correct answer: Similar triangles using the eye as the apex
The Biltmore stick uses similar triangles: the stick at arm's length, the eye, and the tree diameter form proportional triangles, allowing diameter estimation.
Question 6: When measuring crown closure (canopy cover) with a spherical densiometer, readings are taken in how many directions?
- 2 (north and south)
- 3 (north, east, west)
- 4 (north, south, east, west) (Correct answer)
- 8 cardinal and intercardinal directions
Correct answer: 4 (north, south, east, west)
Standard spherical densiometer protocol calls for four readings—north, south, east, and west—which are then averaged to estimate canopy cover.
Question 7: In forest inventory, 'cruise control' or 'quality control' checks are best performed by:
- Having the same cruiser re-measure selected plots
- An independent checker re-measuring a random subset of plots (Correct answer)
- Comparing results to adjacent county averages
- Running a regression against LiDAR data
Correct answer: An independent checker re-measuring a random subset of plots
An independent checker measuring a random subset of plots detects both systematic bias and random error without the original cruiser's influence.
SAF Field Survey & Data Collection 3
When measuring slope distance to convert to horizontal distance, a forester records a slope of 30% over 100 feet of slope distance.
The horizontal distance is approximately: