L3 Flashcards
What are the 3 conditions needed for wildfires?
Dry weather
Fuel load (dry plant biomass)
Ignition
Dry weather is due to:
Dry season
Dry years
Fuel load (dry plant biomass) is due to:
Productivity
Fire suppression
Ignition is due to:
Lightning
Humans
Fire in ecosystems:
- Dry weather in a particular location causes fire
- Typically fire prone ecosystem occur in locations with a dry season
- Fuel load increases in places where human management suppress fires
- Fires have been in ecosystems a long time (most are human lit today)
What are the three types of fire?
Crown fires
Surface fires (Savannas)
Ground fires (Moorland)
Crown fires
- Climb up into tree canopies, everything burns
- Hot
- Many mature trees die (lethal)
Surface fires (savannas)
- Burn fuel on ground surface (grass or litter)
- Cool
- Many mature trees survive, doesn’t get up into tree canopy
- Immature trees have to start again as they are not at escape height
Ground fires (moorland)
- Organic matter smoulders underground
- Often occur in peatland
- Burn slowly over a long period
- Produces high particulate
- Tough to identify if one is occurring
Global importance of fire
- Satellite data
- Heat satellites, surface reflectance
- We can look at different characteristics of fire
- Large shifts in biomass, particularly in forests. In drier areas there is less biomass change
- The frequency and burned area of fires is greatest in surface fires eg savanna and grassland
- Consume less fuel
- Tropical forest fires are very infrequent
There is less biomass change after a fire in dry or wet areas?
Less in drier areas
Frequency and burned area of fires is greatest in…?
Surface fires eg savanna and grassland
Global ‘pyromes’ analogous to biomes
- Fires that have different characteristics can classify vegetation according to fire regime
- Mapping biomes according to fire characteristics - frequency, intensity, size
Plant regeneration strategies
- Kills competitors (more sunlight)
-Burns plants (releases nutrients)
What are the two strategies for plant establishment?
Seeder strategy
- Seed release or germination triggered by fire
Sprouter strategy
- Resprouting of surviving plants after fire
What are the two seeder strategies?
Refractory seeds
Serotiny
Refractory seeds
- When seeds are heated they germinate
- Heat cue
- Chemicals in smoke that can be detected in soil can trigger germination
- Acacia (Australia)
- Adenostoma fasciculatum (California)
Serotiny
- Fruiting bodies that hold onto seeds
- After fire fruiting bodies open up and release seeds
- Leucospermum conocarpodendron
- Banksia
- Pinus halepensis - cones open up after fire
Three methods of sprouter strategy?
- Sprouting from belowground stores
- Lignotubers
- Sprouting from the crown: Epicormic buds
Sprouting from belowground stores
- Chamaerops humilis
- Quercus coccifera
Lignotubers
- Woody structures that grow close to surface and store starch (energy)
- Used to start regrowing a tree after a fire
- Adenostoma can resprout and seed
Sprouting from the crown: Epicormic buds
- If the crown is scorched but not killed
- Protected underneath the tree bark
- Resprout and reconstruct the canopy
Quercus suber
Eucalyptus pulchella (Aus)
FIre in ecosystems
- Factors necessary for wildfires, and different types of wildfires
- Plant adaptations - regeneration strategies
Plant flammability strategies
- Flammable vs inflammable
- Of the flammable plants: Hot vs cool (fast) flammable
Non- flammable plants
- Mature trees
- Protective bark
- Thick insulating layer around trunk
- Eg Cork and Coastal redwood
- Growing cells in wood are between wood and bark (tree tries to protect these cells and epicormic buds)
How does thick bark protect the vascular cambium?
- As bark thickness increases cambium temperature decreases
- Time to kill the cambium increases with bark thickness
- Flameproof bark works against surface fires but not crown fires (high mortality)
- Protects trunk of tree at surface level
Fast flammable grass example
Savanna grasses
Fast flammable strategy
- Plant ignites easy
- Plant burns fast low heat release
- Minimises damage to meristems
- Sprouting regeneration
Savanna grasses post fire
- Sprout rapidly post fire
- Burned plants recover in a few months
- Resources below ground so can capture these and resprout
What promotes frequent fires that burn fast in Savanna?
- Rate at which they burn depends on biomass accumulation
- Fire grasses tend to be large with high biomass
Hot flammable strategy
Eg crown fires
- Fine, dense biomass burns slowly (trees and leaves) - High heat release - Fires typically lethal - Seeding regeneration
Mature plants are killed
Plant flammability strategies
- Must be linked to particular regeneration strategies
- Eg hot flammable must be coupled with re-seeding
- Adaptive under particular fire regimes
How are savanna ecosystems structured by fires?
- Open woody plant cover, C4 grass- dominated ground layer
- Fast flammable grasses and non-flammable trees
- Sprouting strategy in response to fire and herbivory
- Both trees and grasses tend to resprout after fire
- Savanna existence relies largely upon fires
What would happen if there was no fire in savanna ecosystems?
- C4 savanna is replaced by forest
Agriculture in savannas
- Expansion and intensification of agriculture in savannas leads to fewer and smaller fires
- No allowance for fuel accumulation
Mediterranean type ecosystems
- Cool wet-winters and hot- dry summers
- Crown fires most frequent and diversity of strategies eg:
- Hot flammable/seeders and non-flammable/ sprouters
- Refractory seeds/serotiny or thick bark/ epicormic buds
Temperate forest ecosystems
- Often have fires and are fire adapted
- Surface fires, thick litter fuel - thick bark and serotinous cones
- Dry summer leaf litter can be susceptible to fire
- Cones drop and open during fire
Mismanagement of fire prone ecosystems
- Fire suppression causes fuel accumulation, stops trees establishing
- Mismanagement caused a thick layer of leaf litter fuel
- Stopped seedlings accumulating as there was too much leaf material
Western US redwood fire regimes
- Climate change and fire suppression have altered western US redwood fire regimes- greater risk of crown rather than surface fires
- More fire weather
- Fires can climb into canopy instead of burning on the ground
- Greater risk of crown fires than surface fires
- Mature trees have fireproof trunks but not fireproof canopies
Can plant traits influence the fire regime?
Yes
- Boreal forest (North) - Different trees species on different continents have different plant flammability strategies - Despite them all being boreal species
North America boreal forest
- Hot flammable trees “fire embracers”
- Branches close to ground
- Flammable needles
- Thin bark (tree dies)
- Serotinous cones (allow for reproduction)
Eg black spruce, jack pine
- Tend to be crown fires
Eurasia boreal forest
- Non-flammable trees “fire resisters”
- Self-pruning branches
- Moister needles
- Thick bark
Eg Siberian larch, scots pine
- Tend to be surface fires
Satellite fire regime data
- North America has hotter fires (crown)
- Change in surface albedo after fires
- North American fires increase surface albedo due to hotter fire burning more trees so there is more snow cover
- Eurasia results in tree covering snow
- Interconnection to feedback on climate
- High albedo = higher reflectance back to space (this is good for climate)
