Lecture 10: Wildfires Flashcards
Pre-Ignition Phase
vegetation reaches temp. it can ignite at, loses water
Pyrolysis
Chemical process of breaking large hydrocarbons down into smaller ones
Combustion Phase
ignition of the pre-heated fuel
Flaming Combustion
rapid, high-temperature conversion of fuel into heat
-contains flames and unburned fuel
Smouldering Combustion
-occurs in areas with burned material, ash covering fueled
Conduction
molecule to molecule contact to transfer heat
Radiation
transfer ofheat through invisible waves
Convection
Transfer of heat through movement of liquid or gas
Extinction Phase
combustion ceased due to lack of fuel/heat
Weather conditions for Wildfires
-drought and dry thunderstorms (rain evaporates before hitting the ground, lightning ignites)
Surface Fire
travel close to ground, burn surface fuel
-slow
Crown Fire
move rapidly through canopy with flaming combustion
intermittent: consume some canopy
Continuous: consume all of canopy
Effects of Wildfires
- hydrophobic layer can form on surface of burned soil due to chemicals burning: increases run off and lowers soil permeability, persists for years
- increase particles in the atmosphere, “haze”
Linkages to Climate Change
- increase in drought severity increases wildfire severity
- grasslands replace forests, forests go pole-ward
- insect infestations can make forests more vulnerable to wildfires
Mountain Pine Beetle
80% of mature mountain pines are infested
- threatens Alberta pine forests and Jack pine in Boreal
- warmer temp. makes them last through the winter
Impacts of Wildfires
- fires lead to evacuation of towns, road/airport closure, property loss
- smoke/haze has ocular/respiratory impacts
- ON ANIMALS
- large animals outrun, rodents can hide underground
- opens up grazing grounds
- increase in sedimentation from run off+erosion impacts aquatic ecosystems
Natural Service Functions of Wildfires
- temporarily lower competition for sunlight and water
- surviving/new species can thrive at forest floor
- triggers release and opening of flowers or seeds in some species
- remove parasites from soil
- remove surface litter to allow more moisture infiltration
- removes diseased trees to limit beetle infestation
Pioneer Vegetation
first species to appear after a wildfire
-aspen, lodgepole pine, wire weed
Yellowstone NAtional Park Wildfire
- policy allows natural fires to burn
- fire suppression policies in past allow fuel to build up too much
- lightning caused 50 fire in 1988, all merged
- eventually caused political pressure and 10 000 firemen called in
- eventually revitalized the park
Fire Break
Area with no fuel. steer fire here
- can create artificial break by clearing land with bulldozer
- this causes accumulation of fuel though
Prescribed Burns
- controlled fires purposely ignited to lower fuel in forests
- difficult to predict weather/ fuel amount that’s easy to control