NR 307 Dicus Final exam with complete
solutions
1. What are some factors (biological and physical) that affect the depth and
degree of soil heating during a fire event?
Soil heating depends on amount of fuel loading and distribution, soil texture, and
soil moisture.
Larger fuels burn longer, lead to greater amount of heat in soil.
Soils that are more airy are better conductors of heat.
Takes more heat to heat up moisturer soils.
2. In regard to soil heating, why is the length of time of burning more important
than the temperature of a fire?
Residence time is more important than peak temperature because soil is a good
insulator against heat, and the longer soil is exposed to heat the more it is able to
heat up.
3. During a fire event, do soil temperatures increase much?
No, in fact they decrease with depth as:
-There is little effect on temperature after 3 cm of depth
-Even most severe fires have no effect after 10 cm
4. During a fire event, explain why moist soils do not get as hot as dry soils.
more heat intensity is needed because the moisture/water acts as a heat sink but
the heat can be dissipated more downward.
5. During a fire event, explain why moist soils experience increases in soil
temperature at a greater depth than dry soils.
water is a better conductor of heat than dry soil therefore more heat is dissipated
downward. This reduces surface heating and organic matter is retained.
6. Why is litter and duff moisture important to soil heating during a fire event?
, more important than moisture in a mineral soil because it has a better chance of
combustion: fuel
7. In the months following a fire event, soil temperatures are usually raised
significantly, often to a greater extent than during the fire event itself and at
depths that were totally unaffected during the fire. a. Why? b. What are some
factors that influence the degree of soil heating?
Post fire temperatures are elevated due to more radiation exposure from the sun,
and darker soils. In the long term, can increase 10 degrees C at 10 cm. This
affects recolonization of site.
8. Why is some ash white, while other ash is black?
White ash: Fire burned for a really long time
Black ash: Fire burned at high intensity for a short time
9. Why is soil moisture usually INCREASED in the other soil horizons following a
wildfire?
- Less vegetation, greater evapotranspiration on surface soils
- water table rises
- Long dry streams commonly flow after stand replacement fires.
10. Why is soil moisture usually DECREASED in the upper soil horizons following
a wildfire?
Due to greater evaporation because of greater organic matter and decreasing
post fire temperatures. Additionally, less percolation due to ash and char
plugging up holes. Impacts recolonization.
11. What is a "nurse crop"? a. Give an example of a nurse crop following a fire.
A species that arrives after an event and modifies an environment allowing more
species to come back to and area and survive. For example, lodgepole pine
(modified quickly, but slow growth), quaking aspen (modified slower, but grew
fast)
12. What is hydrophobicity? a. How are hydrophobic soils formed? b. What are
some factors that lead to increased levels of hydrophobicity? c. Does
hydrophobicity increase or decrease erosion?
Hydrophobicity: Water repellant soils
- hydrophobic compounds in litter, fire moves the compunds downward creating
water repellant layer below to soil surface.
-common factors: thick littler, severe fire, coarse textured soils
-importance: less availbale water for plants, increased water flow increases
erosion, may limit erosion due to water only eroding hydrophobic layer.
13. Why is wind and water erosion so significant on burned sites? a. What are
some factors that influence the amount of erosion on a burned site? b. What are
some steps to mitigate erosion on a burned site?
As erosion increases, infiltration rates decreases due to decrease in porosity,
less worms, and increased rainfall because of lack of canopy. Amount of erosion
solutions
1. What are some factors (biological and physical) that affect the depth and
degree of soil heating during a fire event?
Soil heating depends on amount of fuel loading and distribution, soil texture, and
soil moisture.
Larger fuels burn longer, lead to greater amount of heat in soil.
Soils that are more airy are better conductors of heat.
Takes more heat to heat up moisturer soils.
2. In regard to soil heating, why is the length of time of burning more important
than the temperature of a fire?
Residence time is more important than peak temperature because soil is a good
insulator against heat, and the longer soil is exposed to heat the more it is able to
heat up.
3. During a fire event, do soil temperatures increase much?
No, in fact they decrease with depth as:
-There is little effect on temperature after 3 cm of depth
-Even most severe fires have no effect after 10 cm
4. During a fire event, explain why moist soils do not get as hot as dry soils.
more heat intensity is needed because the moisture/water acts as a heat sink but
the heat can be dissipated more downward.
5. During a fire event, explain why moist soils experience increases in soil
temperature at a greater depth than dry soils.
water is a better conductor of heat than dry soil therefore more heat is dissipated
downward. This reduces surface heating and organic matter is retained.
6. Why is litter and duff moisture important to soil heating during a fire event?
, more important than moisture in a mineral soil because it has a better chance of
combustion: fuel
7. In the months following a fire event, soil temperatures are usually raised
significantly, often to a greater extent than during the fire event itself and at
depths that were totally unaffected during the fire. a. Why? b. What are some
factors that influence the degree of soil heating?
Post fire temperatures are elevated due to more radiation exposure from the sun,
and darker soils. In the long term, can increase 10 degrees C at 10 cm. This
affects recolonization of site.
8. Why is some ash white, while other ash is black?
White ash: Fire burned for a really long time
Black ash: Fire burned at high intensity for a short time
9. Why is soil moisture usually INCREASED in the other soil horizons following a
wildfire?
- Less vegetation, greater evapotranspiration on surface soils
- water table rises
- Long dry streams commonly flow after stand replacement fires.
10. Why is soil moisture usually DECREASED in the upper soil horizons following
a wildfire?
Due to greater evaporation because of greater organic matter and decreasing
post fire temperatures. Additionally, less percolation due to ash and char
plugging up holes. Impacts recolonization.
11. What is a "nurse crop"? a. Give an example of a nurse crop following a fire.
A species that arrives after an event and modifies an environment allowing more
species to come back to and area and survive. For example, lodgepole pine
(modified quickly, but slow growth), quaking aspen (modified slower, but grew
fast)
12. What is hydrophobicity? a. How are hydrophobic soils formed? b. What are
some factors that lead to increased levels of hydrophobicity? c. Does
hydrophobicity increase or decrease erosion?
Hydrophobicity: Water repellant soils
- hydrophobic compounds in litter, fire moves the compunds downward creating
water repellant layer below to soil surface.
-common factors: thick littler, severe fire, coarse textured soils
-importance: less availbale water for plants, increased water flow increases
erosion, may limit erosion due to water only eroding hydrophobic layer.
13. Why is wind and water erosion so significant on burned sites? a. What are
some factors that influence the amount of erosion on a burned site? b. What are
some steps to mitigate erosion on a burned site?
As erosion increases, infiltration rates decreases due to decrease in porosity,
less worms, and increased rainfall because of lack of canopy. Amount of erosion
