B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 5 — Questions and Answers
Question 1: Which soil water potential component represents the attraction of water molecules to soil particle surfaces and organic matter?
- Gravitational potential
- Matric potential (Correct answer)
- Osmotic potential
- Pressure potential
Correct answer: Matric potential
Matric potential (always negative or zero) results from capillary and adsorptive forces that bind water to soil surfaces, controlling water availability to plants.
Question 2: The 'permanence' of soil organic matter is now understood to be primarily controlled by:
- The chemical recalcitrance of lignin and wax compounds
- Physical protection within soil aggregates and organo-mineral associations (Correct answer)
- Annual freeze-thaw cycles that stabilize organic compounds
- The presence of specific decomposer-inhibiting compounds in conifer litter
Correct answer: Physical protection within soil aggregates and organo-mineral associations
Current research shows that physical occlusion within aggregates and bonding to mineral surfaces (especially iron and aluminum oxides) is more important than molecular recalcitrance in stabilizing soil organic matter.
Question 3: Verticillium wilt, a soilborne fungal disease affecting hardwood trees, persists in forest soils primarily as:
- Ectomycorrhizal resting spores attached to feeder roots
- Microsclerotia that survive for many years in the absence of a host (Correct answer)
- Motile zoospores during wet spring periods
- Mycelium colonizing the bark of infected stumps
Correct answer: Microsclerotia that survive for many years in the absence of a host
Verticillium species produce microsclerotia—compact hyphal aggregates—that remain viable in soil for years without a host, making this pathogen very difficult to eradicate.
Question 4: Which of the following best explains why nitrogen mineralization rates are generally slower in boreal conifer forests than in temperate deciduous forests?
- Conifers take up nitrogen more efficiently, leaving less in the soil
- Cool temperatures and acidic, high C:N ratio litter slow microbial decomposition in boreal forests (Correct answer)
- Boreal soils have lower clay content and therefore lower CEC
- Deciduous forests receive more atmospheric nitrogen deposition annually
Correct answer: Cool temperatures and acidic, high C:N ratio litter slow microbial decomposition in boreal forests
Boreal conifer litter has high C:N ratios and contains recalcitrant compounds like resin and tannins; combined with cold temperatures, these factors greatly slow decomposer activity and N release.
Question 5: When evaluating a reforestation site for planting success, a forester finds a restrictive claypan at 18 inches depth. The most appropriate management response would be to:
- Apply heavy lime applications to dissolve the clay layer
- Use deep ripping or subsoiling to fracture the restrictive layer before planting (Correct answer)
- Select only shallow-rooted grass species instead of trees
- Increase planting density to compensate for reduced individual tree growth
Correct answer: Use deep ripping or subsoiling to fracture the restrictive layer before planting
Mechanical subsoiling or deep ripping breaks up the restrictive claypan, improving root penetration depth, drainage, and water-holding capacity in the root zone.
Question 6: The process by which fine clay particles migrate downward through the soil profile to accumulate in a lower horizon is called:
- Illuviation of clay (lessivage) (Correct answer)
- Cheluviation
- Ferrallitization
- Gleization
Correct answer: Illuviation of clay (lessivage)
Lessivage (clay illuviation) is the mechanical translocation of clay particles in suspension downward through soil pores to accumulate in the B horizon, forming an argillic horizon.
Question 7: In forest pathology, 'damping-off' of conifer seedlings in nurseries is most commonly caused by which group of soilborne pathogens?
- Armillaria and Heterobasidion species
- Pythium and Fusarium species (Correct answer)
- Cronartium and Melampsora rust fungi
- Cylindrocladium and Dothistroma species
Correct answer: Pythium and Fusarium species
Pythium (an oomycete) and Fusarium (a true fungus) are the primary causes of damping-off, attacking seedling stems at the soil line either before or after emergence.
B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 5
Which soil water potential component represents the attraction of water molecules to soil particle surfaces and organic matter?