Lecture 11

Question 1

How do wildfires start? What occurs after a fire?

Answer 1

• wildfire dates to the time when trees first evolved 400 million years ago
• many fires start naturally as a result of lightning or volcanic eruptions
• after a fire, vegetation completes a cycle from early colonizing plants to mature ecosystem
• the ecosystem that evolves adapts to the climate at that location and time

Question 2

How have species adpated to wildfires?

Answer 2

• many species have evolved to withstand fire or promote the life of the species after a fire event
• ex: oak and redwood trees have bark that resists fire damage, some pine trees have seeds that only open after a fire

Question 3

How have wildfires changed through history?

Answer 3

• the geologic record shows an increase in the amount of charcoal in sediment approximately 10 000 years ago
• this suggests high amounts of wildfire activity at the time
• more fire activity because: a warmer and/or drier climate, increased use of fire by humans for clearing land and for heat, cooking, etc.

Question 4

What elements are required for wildfires?

Answer 4

• wildfire requires three elements: fuel, oxygen, and heat
• if any of these are lost, the fire will dissipate
• plants accumulate carbon dioxide and store carbon in their tissues
• during a wildfire, this carbon dioxide is released back into the atmosphere
• there are 3 phases to a wildfire: pre-ignition, combustion, and extinction
• the carbon dioxide that is released from wildfires is not enough to impact global temperatures

Question 5

Describe the pre-ignition phase of wildfires?

Answer 5

• pre-heating: during this phase, vegetation reaches a temperature at which it can ignite
• as vegetation is heated, it often loses water
• the presence of heat radiating from flames of a wildfire can pre-heat nearby vegetation
• the fact that a wildfire can cause pre-heating of a nearby unburned forest is one reason why a wildfire can spread easily and sustain itself for a long time

Question 6

Describe the combustion phase

Answer 6

• pre-heating results in fuel that is prone to ignite
• the combustion phase begins with ignition
• ignition is not a single process; it can occur repeatedly as the fire moves
• not all ignitions will result in a wildfire (the vegetation must be dry)

Question 7

What are types of combustion?

Answer 7

• flaming combustion is the rapid, high temperature conversion of fuel into heat
• it is characterized by flames and large amounts of unburned material
• smouldering combustion occurs in areas with burned material and ash that covers new fuel

Question 8

How is heat transfered in a wildfire?

Answer 8

-as a wildfire moves across the land, three processes control the transfer of heat:

Conduction: transfer of heat by molecule to molecule contact

Radiation: transfer of heat in the form of invisible waves

Convection: transfer of heat by movement of a liquid or a gas

• in wildfires heat transfer is mainly by radiation and convection
• heat from radiation increases the surface temperature of the fuel
• as air is heated, it becomes less dense and rises
• the rising air removes heat from the zone of flaming and is replaced by fresh air
• this fresh air (oxygen) sustains the combustion

Question 9

Describe the extinction phase

Answer 9

• this is the time at which combustion has ceased
• there is no longer sufficient heat or fuel to sustain a fire

Question 10

What are types of fuel?

Answer 10

• types of fuel include leaves, woody debris, decaying organic materials, grasses, shrubs, etc,
• if diseases or storms down large numbers of trees, the decaying material dries and burns easily
• the density of the forest plays a role: in western North America, dense boreal forests contain abundant fuel supplies

Question 11

How does topography affect fuel?

Answer 11

• the amount of fuel can vary by slope orientation
• in the Northern Hemisphere, south-facing slopes are relatively warm and dry
• slopes exposed to prevailing winds are often drier
• wildfires burning on steep slopes preheat fuel upslope from the flames
• this results in the rapid spreading of a fire upslope
• a slope that faces south faces the sun in the afternoon hours
• in NA, the prevailing winds tend to be from the west; therefore, vegetation on a slope that faces west is more likely to become dry

Question 12

How does weather affect wildfires?

Answer 12

• large wildfires are common following droughts
• dry thunderstorms with lightning can produce wildfires but the rain evaporates before reaching the ground
• wind can help preheat unburned materials
• wind carries embers that can ignite spot fires ahead of the fire front
• embers are sparks that fly out of a fire (they are evident in small fires like bonfires)

Question 13

What regions are at risk for wildfires?

Answer 13

• in Canada, the hazard is greatest in BC and in the boreal forests of the Canadian Shield region
• the geographic region most at risk changes annually with the weather and corresponds to areas experiencing drought

Question 14

Describe the Yellowstone National Park Wildfire

Answer 14

• a series of lightning strikes caused 50 fires in the park in 1988
• park officials have a policy that allows naturally caused fires to burn
• this became controversial as hot, dry weather that summer allowed the fires to spread and merge
• officials responded to political pressure and eventually called in nearly 10 000 firefighters
• all national parks have a policy that allows naturally caused fires to burn in order to take advantage of the natural service functions of wildfires
• when people saw through the media that much of Yellowstone Park was on fire, they put pressure on politicians to intervene (most people are not aware of the natural service functions of wildfires)

Question 15

Why did the Yellowstone fires get out of control?

Answer 15

• the fires were beyond the control of the crews and burned for several months
• it is believed that the fires became uncontrollable because many years of fire-suppression policies in the past had allowed fuel amounts in the park to reach dangerous levels
• the fire-suppression policies of the past were a mistake
• when fires are frequently suppressed, it allows a dangerous amount of fuel to build up
• the fires of 1988 revitalized ecosystems in the park
• officials remain committed to the natural-burn policy today; this is a common policy in national parks

Question 16

What are types of wildfires?

Answer 16

• classified according to the layer of fuel that is allowing the fire to spread; surface or crown
• surface fires travel close to the ground and burn shrubs, leaves, twigs, grass, etc.
• they vary in intensity but most move relatively slowly
• crown fires move rapidly through the forest canopy by flaming combustion
• they can be fed by surface fires that move up limbs or tree trunks, or they may spread independently of surface fires
• they are driven by strong winds and are common in boreal forests
• intermittent crown fires consume the tops of some trees in an area
• continuous crown fires consume the tops of all trees
• the wind may cause embers to blow a far distance thus creating spot fires far from the main fire therefore causing an intermittent crown fire

Question 17

What are the effects of wildfires?

Answer 17

• fires that burn soil may leave behind a hydrophobic layer at the surface
• this layer is caused by accumulation of chemicals from burning vegetation
• this layer increases surface runoff and erosion
• it may persist for several years following a fire
• wildfires increase the amount of particulates in the atmosphere and these can persist for weeks
• increases of airborne particles and haze can be observed thousands of km downwind of large fires

Question 18

How are wildfires linked to climate change?

Answer 18

• climate change may increase the intensity of wildfires
• climate change affects both temperature and precipitation and can lead to severe droughts
• in some parts of the world, grasslands will replace forests
• current areas of forest will expand poleward
• insect infestations can cause disease throughout a forest making it more vulnerable to wildfire

Question 19

Describe the Fort McMurray Wildfire

Answer 19

• the disaster in May 2016 caused $10B in damage making it the costliest disaster in Canadian history
• there were no deaths or injuries caused by the fire due to the evacuation of the entire community
• residents were displaced for 4 weeks and over 2000 people lost their homes in the wildfire
• the cause of the fire has not been determined
• a prolonged drought occurred in the area during the winter before the fire and record high temperatures occurred in the days prior

Question 20

What is the Mountain Pine Beetle?

Answer 20

• the beetle has destroyed forests throughout western Canda
• currently, 80% of mature mountain pines are impacted
• the consequences will be felt for decades in BC
• the beetle is posing a threat to Alberta’s pine forests and the Jackpine stands of Canada’s boreal forest lands
• consequences refers to economic consequences (forestry)
• with warmer temperatures, the beetle has been able to survive through the winter in BC
• the beetle used to be killed by the cold but it has now adapted to the warming temperatures
• it bores into the trunk of the tree and sucks nutrients out

Question 21

What are impacts of wildfires?

Answer 21

• fires can lead to evacuations of entire towns, road and airport closures, and severe property loss
• in NA, organized evacuations have minimized the amount of deaths
• exposure to smoke and haze can affect the ocular and respiratory systems

Question 22

What are the impacts of wildfires on animals?

Answer 22

• most animals can escape fires unharmed
• rodents can take refuge underground and larger animals can outrun the fire
• fires can produce open areas suited for grazing mammals thus acting as a natural service function
• aquatic species may be impacted by increased sedimentation from runoff and erosion

Question 23

What are natural service functions of wildfires?

Answer 23

• wildfire temporarily reduces competition for sunlight and moisture in a forest
• it allows both surviving and new species to thrive by allowing sunlight to reach the forest floor
• in some species, it triggers the release of seeds or stimulates flowering
• lodgepole pine, aspen, and fireweed are examples of pioneer vegetation that grow quickly after a fire
• pioneer vegetation: the first plant species to appear after a wildfire
• fires can remove micro-organisms in the soil, some of which are parasites
• fires remove surface litter and excess fuel (leaves, etc.)
• fires remove weak or diseased trees and can limit the spread of beetle infestations
• of all hazards, wildfires have the most natural service functions

Question 24

How are fires managed?

Answer 24

• the objective is to control wildfires for the benefit of ecosystems while preventing them from harming people and destroying property
• in Canada, the fire season is from April to October and is managed by provincial/territorial governments
• good management requires research of the fire regime of an area
• satellite imagery is providing insights on fire potential in remote areas
• fire regime: the potential for wildfires in an area

Question 25

What is fire suppression?

Answer 25

• a strategy in fire suppression is to steer the fire toward an area with no fuel
• examples of fire breaks include rivers, lakes, roads, etc.
• if a natural fire break does not exist an artificial break can be created from bulldozers clearing land
• reliance on fire suppression has led to a build-up of fuel in forests and potential for intense fires

Question 26

What are prescribed burns?

Answer 26

• one way to counter the build up of fuel is by prescribed burns
• these are controlled fires that are purposely ignited to reduce the amount of fuel
• difficulties relate to predicting the fuel and weather conditions under which the fire can be safely controlled

Question 27

What is the perception of the wildfire hazard?

Answer 27

• population growth in areas that are prone to wildfires has increased the risk to public safety
• since 2000, over 50 000 people have moved to locations in California considered high-risk areas due to wildfires

Question 28

In Canada, slopes facing in which direction are most susceptible to wildfires?

Answer 28

• slope facing west (prevailing winds in NA)
• south facing slopes are relatively warm and dry in northern hemisphere