wildfires

self-sustaining fires that start and spread out of control; often move into populated or agricultural areas

number 1 natural cause → lightning

arson

campfires, smoking, playing

transport

elec power

machinery

debris burning

unknown

other anthropogenic causes

90% forest firest in US caused by human activity

humans

ecosystem

numb of fires each yr in Canada n total burned

there is no correlation between the total area and the num of fires, as a few individual large fires account for most of the area

there r many small fires

less big ones

when gases react w/ oxygen to produce heat and light

superheated gases (carbon dioxide, carbon monoxide, nitrogen, oxygen, water vapour and organic chemicals)

breakdown of cellulose, fats, oils and sugar in plant walls and cells produces gases which fuel the fire

cellulose and hemicellulose

burn at higher temperature than cellulose

tree species high in lignin (e.g., oak) will not burn as readily

flame suddenly when exposed to heat

contribute to the violence of wildfire in many conifer forest

ex. resins, fats, oils

unpredictable

oxygen

heat

fuel

known as the fire triangle

heat source raises a fuel’s temperature; water evaporates

molecs in fuel decompose to produce gases that rise in the air

gases ignite and react with oxygen → produce fire

dominates early fire

produces large flames and little smoke

initiated by ignition of volatile gases at 260ºC -450ºC

temperatures can rise to 1,500ºC; high enough to melt metal and glass

produces the most smoke

lack flames - associated w/ conditions where oxygen is lim

within roots and buried organic matter

creep along under ground surface

little flaming, more smoldering; limited oxygen

burn low-lying vegetation (undergrowth and forest litter ex. grasses and dead leaves)

burn slowly with smoldering, limited flaming

undergrowth and medium-sized trees (below the forest crown)

flaming is carried via tree canopies

driven by strong winds and steep slopes

can jump from crown to crown without burning undergrowth

percent biomass that burns during a fire

measure of energy released during burning

distance from the base to the end of the flame

more intense fire = longer flame length

transfer of heart directly from molec to molec

transfer of heat by the movement of heated air

hot gases are less dense and rise; pulls in fresh air to sustain combustion

radiant energy heats fuel within 10-35m of a wildfire

sparks and embers can land on fresh fuel beyond the wildlife; start new fires

start most often when a small heat source (spark from campfire, cigarette) comes into contact with dry grasses, leaves, small sticks

heat from this small fire pre-heats surrounding fuel

fuel

weather (wind)

terrain

less intense wildfires

seasonal changes dictate moisture lvls in fuel

oxygen consumption

also tilts flames causing preheating and spreading firebrands

convection

allows for fires migrate faster up slopes than down slopes

trees like cork oak have adapted to fire

• their sponge bark does not burn

Jack pine are well adapted to fire, as the heat of the fire opens their cones liberating the seeds

injury and death

property, agricultural, and forest losses

health effects from smoke inhalation

increased soil erosion

destabilizes slopes - can lead to landslides

longer impact

known as the “black summer”

5,900 buildings destroyed

34 deaths

affected ~3 billion animals

some endangered species believed to have been driven to extinction

air quality hazardous in all southern and eastern states of Australia

estimated to cost upwards of $100B

Australia costliest natural disaster to date

biggest concern was wildlife

• millions animals killed

no ele, water, phone service in some areas

not much govern help

strong winds

firebreak construction

plane dropping retardant

create break + start new fire

total fire suppression (1940’s-1980s) results in large fuel accumulations and larger fires

increased knowledge in forest ecology demonstrated the importance of fire for forest renewal

policy has shifted toward prescribed burns in some areas to reduce large fuel accumulations

natural lightning-caused fires were allowed to burn unless they posed threats to people, commercial timber lands or scenic attractions

interface communities

homes should be constructed from flame resistant material

area around homes should be clear of brush

a clear emergency plan and response should be in place