B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 4 — Questions and Answers
Question 1: Which soil amendment is most commonly used to raise soil pH in acidic forest nursery seedbeds?
- Elemental sulfur
- Aluminum sulfate
- Agricultural limestone (calcium carbonate) (Correct answer)
- Ammonium sulfate
Correct answer: Agricultural limestone (calcium carbonate)
Agricultural limestone (CaCO3) neutralizes soil acidity by reacting with hydrogen ions, raising pH, and is the standard amendment for correcting excessively acidic nursery soils.
Question 2: Forest harvesting operations can cause soil compaction, which most directly reduces tree growth by:
- Increasing soil pH above optimal range for nutrient uptake
- Decreasing macropore space, limiting root penetration and gas exchange (Correct answer)
- Raising soil temperature beyond tolerable limits for root growth
- Increasing cation exchange capacity beyond nutrient demand
Correct answer: Decreasing macropore space, limiting root penetration and gas exchange
Compaction destroys large pores needed for root growth, water infiltration, and oxygen diffusion, creating anaerobic conditions and mechanical resistance that inhibit root development.
Question 3: The concept of 'soil organic matter fractions' distinguishes between active, slow, and passive pools primarily based on:
- Their nitrogen content and C:N ratio only
- Their rate of decomposition and mean residence time in soil (Correct answer)
- Their location within the soil profile (O vs. A horizon)
- Their source material (woody debris vs. leaf litter)
Correct answer: Their rate of decomposition and mean residence time in soil
Soil organic matter is partitioned into pools by turnover rate: the active pool turns over in months, the slow pool in decades, and the passive (recalcitrant) pool persists for centuries.
Question 4: In the context of forest health, 'site index' is a measure of:
- Soil nutrient content expressed as kg/ha in the top 30 cm
- Potential forest productivity measured by dominant tree height at a reference age (Correct answer)
- The diversity of soil organisms per gram of soil
- Annual carbon flux between soil and atmosphere
Correct answer: Potential forest productivity measured by dominant tree height at a reference age
Site index is the average height of dominant and codominant trees at a base age (commonly 25 or 50 years), serving as an integrative measure of soil and site productivity.
Question 5: Which of the following nematode feeding groups is considered most beneficial to forest soil health?
- Ectoparasitic plant feeders that attack root hairs
- Fungivorous nematodes that graze on mycorrhizal fungi
- Bacterivorous nematodes that enhance nutrient cycling (Correct answer)
- Endoparasitic nematodes that invade root cortex cells
Correct answer: Bacterivorous nematodes that enhance nutrient cycling
Bacterivorous nematodes consume bacteria and release excess nitrogen as ammonium, mineralizing nutrients and accelerating decomposition and nutrient cycling in forest soils.
Question 6: Prescribed fire in longleaf pine ecosystems is managed partly for soil health because it:
- Increases soil pH by depositing calcium and potassium from ash (Correct answer)
- Eliminates all soil microorganisms, allowing beneficial pioneer species to recolonize
- Prevents soil erosion by increasing vegetative cover year-round
- Oxidizes soil organic carbon, permanently reducing fertility
Correct answer: Increases soil pH by depositing calcium and potassium from ash
Combustion of litter releases base cations (Ca, K, Mg) as ash, temporarily raising soil pH and recycling nutrients that were immobilized in the litter layer.
Question 7: A soil with a platy structure in the surface horizon is most likely associated with:
- High biological activity from earthworm casting
- Historical freeze-thaw cycles or surface compaction by heavy equipment (Correct answer)
- Abundant calcium carbonate cementing soil particles
- Deep roots breaking apart consolidated parent material
Correct answer: Historical freeze-thaw cycles or surface compaction by heavy equipment
Platy structure forms when soil particles are arranged in thin horizontal layers, commonly resulting from freeze-thaw action or mechanical compaction from vehicle traffic.
B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 4
Which soil amendment is most commonly used to raise soil pH in acidic forest nursery seedbeds?