fires in the earth system (terrestrial lecture 11)

Question 1

What are the conditions for wildfires?

Answer 1

Dry weather:

• dry seasons
• dry years

Fuel load:

• productivity
• fire prevention

Ignition:

• lightning
• humans

Question 2

What are crown fires?

Answer 2

• climb into canopies, everything burns
• v hot
• many mature trees die
• high fuel consumption

Question 3

What are surface fires?

Answer 3

• burn fuel on ground: litter/grass
• cool
• many mature trees survive
• more frequent, greater burned area

Question 4

What are ground fires?

Answer 4

• organic matter smoulders underground

- burns slowly for long period

Question 5

What are global “pyromes”? Fire prone biomes

Answer 5

Savannahs:
- frequent, intense, large
or
- frequent, cool, small

Boreal forest:
- rare, intense large
or
- rare, cool, small

Agriculture/deforestation:
- intermediate, cool, small

Question 6

Plant regeneration strategies:

How does fire provide opportunity for plant establishment?

Seeders & sprouters?

Answer 6

fire provides opportunity for plant establishment

• kills plants, more sunlight
• burns plants, more nutrients

Seeders:
- seed release (seritony)/germination triggered by fire (refractory)

Sprouters:

• resprouting of surviving plants
• below ground stores
• lignotubers
• sprouting from the crown: epicormic buds

Question 7

What are plant flammability strategies?

Answer 7

Non-flammable

• e.g. cork oak (Quercus suber)
• thick insulative bark

Fast-flammable

• plants ignite easily
• burn fast, low energy release
• minimise meristem damage
• sprouting regeneration
• e.g. savannah

Hot-flammable

• fine, dense biomass burns slowly
• high heat release
• fire typically lethal
• seeding regeneration

Question 8

Which biomes are structured around fire?

Answer 8

Savannah, medditeranean type, boreal and temperate forests

Question 9

How are savannah ecosystems structured by fire? Effect of agriculture?

Answer 9

• open woody plant cover, primarily C4 grasses on ground
• fast-flammable grasses, non-flammable trees
• sprouting strategy maintained by fire and herbivory
• expansion and intensification of agriculture leads to smaller and fewer fires

Question 10

How are medditeranean-type ecosystems structured by fire?

Answer 10

e.g. Mediterranean, SW Australia, South Africa

• crown fires and diversity of strategies
• hot flammable/seeders and non-flammable/sprouters
• refractory seeds/serotiny or thick bark/epicormic buds

Question 11

How are temperate forest ecosystems structured by fire?

Answer 11

e.g. Eastern US redwood forests

• surface fires, lighter fuel – thick bark and serotinous cones
• fire suppression causes fuel accumulation, stops trees establishing

Question 12

How do plant traits influence fire regime in boreal forest ecosystems?

North America v Eurasia

Answer 12

North America: Hot flammable trees - fire embracers

• branches close to ground
• flammable needles
• thin bark
• seritonous cones
  e. g. black spruce, jack pine
• intense crown fires

Eurasia: Non flammable trees - fire resisters

• self pruning branches
• more moist needles
• thick bark
• trees survive
  e. g. siberian larch, scots pine
• low intensity surface fires