SAF Certified Forester (CF) · USA · Society of American Foresters
Original practice questions written to the published syllabus · not past papersPredicting how stands grow and what they will yield: yield tables, stand density, diameter-distribution and individual-tree models, and their use in planning.
In the exams: ICAR AICE-JRF 59 Unit 4 (growth and increment, yield) and Unit 9 (growing stock, site quality); IFoS Forestry Paper II Section A; SAF Certified Forester
SAF Certified Forester
Applied use of growth and yield models, stand density index, relative density thresholds, density management diagrams and the use of projections in harvest scheduling.
How our questions for SAF Certified Forester spread across the units of Growth & Yield Modelling. Difficulty: 5 easy, 12 medium, 3 hard.
| Stand density measures: stand density index, relative spacing, crown competition factor | 4 | |
| Using growth models in harvest scheduling | 3 | |
| Self-thinning rule and density management diagrams | 2 | |
| Whole-stand models | 2 | |
| Diameter-distribution models | 2 | |
| Individual-tree distance-independent and distance-dependent models | 2 | |
| Model fitting, validation and projection | 2 | |
| Growth curves and growth functions | 1 | |
| Normal, empirical and variable-density yield tables | 1 | |
| Process-based and hybrid models | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A managed-stand yield table differs from a normal table because it:
D. Lists main-crop and thinning yields for one stated thinning regime
Managed-stand tables, such as British management tables, follow a defined thinning regime and separate thinnings from the main crop.
A manager wants to keep a plantation fully using the site without competition mortality. Using Long's thresholds, the relative density should be kept roughly between:
B. 35% and 60% of maximum SDI
Above about 35% the site is fully occupied; above about 60% self-thinning mortality begins. Keeping stands between these uses the site while avoiding loss to mortality.
A projection system is path invariant when:
B. Projecting directly from age 10 to 30 equals projecting 10 to 20 then 20 to 30
Path invariance means the result does not depend on the number of steps. It is a desirable property alongside compatibility.
Diameter-distribution models are least suited to which stands?
A. Mixed or recently thinned stands with irregular, multimodal distributions
Simple unimodal distributions cannot represent irregular, multimodal diameter structures without more flexible methods.
Mortality in individual-tree models is usually modelled as:
B. A probability of death, often by logistic regression
Survival or death is binary, so a probability model (often logistic on size, growth, crown ratio and competition) is fitted to remeasured plot data.
A hybrid growth model typically:
C. Adds physiologically based modifiers to an empirical growth model
Hybrids keep empirical accuracy while adding climate or soil sensitivity through process-based terms.
The most common cause of serious error when using a growth model is:
A. Extrapolation beyond the ages, sites or densities in its data
Models are reliable only within the range of their data; extrapolation leads to the largest errors.
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