5.6: Fires in Nature Flashcards
The nature of a fire depends on…
- type of plant involved
- strength of winds
- topography of the area
- behaviour of fire itself
What conditions of the largest fires occur in?
Dry, windy weather with low humidity.
For a natural fire to occur, what are the two things needed?
An ignition source and fuel.
Outline ignition sources as a cause for fires.
Lightening (affected by climate).
Around human settlements (such as by falling power lines, discarded cigarettes, campfires, agricultural fires, children playing with matchsticks).
Outline fuel as a cause of fire.
The fuel has to be of sufficient quantity and dry enough to burn.
How can climate affect the fuel and therefore affect fires?
Climate affects the frequency and duration of droughts during which the vegetation and litter has an opportunity to accumulate and dry out.
Climate also agents the type of vegetation that will grow in an area and the rate at which litter can be produced.
As for the distribution, which areas are most likely to ave wildfires?
Areas with a dry season, as those regions with a semi-arid climate and are susceptible to drought. Includes:
- parts of Aus
- USA and Canada
How do fires affect natural ecosystems?
Fries can clear vegetation,
aid new seed germination,
stimulate the growth of certain plants,
rid an area of insects and some parasites
What kind of plants are less affected by fires? Why?
Pyrophytic vegetation.
These can withstand fire, with methods of survival including thick bark, underground storage structures and tissue with a high water content.
Why does fire nor usually affect the tropical rainforest?
Due to the humid climate
Why has fire more recently affected tropical rainforests?
Because recent burning for forest clearance has gotten out of hand, resulting in widespread fires that burn out of control for long periods. Eg in the Amazon basin.
Why is the LA area susceptible to wildfires?
Due to a dry wind called Santa Ana, that descends from local mountains and increases the dryness of vegetation to the point where a spark, lightening or discarded cigarette can cause a major fire.
Wind also allows for the easy spread of fire.
What are the primary effects of wildfire?
- loss of crops, timber, livestock: takes many years to replace fibre. In the USA, $10m per day is spent fighting such fires.
- loss of properties: especially due to urban expansion, the fringes are more susceptible, eg Sydney and LA. Large numbers of people left homeless.
- release of toxic gases and particulates: the SE Asia ‘haze’ is fire related large scale pollution caused by the illegal slash-and-burn practices in Indonesia. The resulting pollution covers many countries in the region including Singapore, Malaysia. Introduces political dimension.
- damage to soil structure and nutrient content: with the intense heat generated at ground level, wildfires can destroy many soil nutrients and lead to alteration in the soil structure.
- loss of life: although much of the time people can get out the way, some fires move so fast that people are trapped. Eg in Victoria (Aus), 173 people died.
What are some secondary effects of wildfires?
- increase flood risk: due to lack of trees and vegetation, causing depletion of nutrient stores and increased leaching.
- evacuation: people forced to flee the area, some not allowed back for a long period. Emergency accommodation provided.
- replacement of farm infrastructure.
- review laws re use of countryside for leisure.
How can wildfires affect global systems?
- local ecosystems affected, eg habitats destroyed, animals kills, soil nutrient stores deleted.
- toxic ash washes into water courses, adversely affecting aquatic ecosystems.
- loss of vegetation affecting water cycle; reducing humidity (less evapotranspiration) and altering the relative significance of transfer processes eg surface runoff, infiltration.
- burning will release carbon stored in trees, plants and peat. This will increase the amount of CO2 in the atmosphere, enhancing greenhouse effect and creating +ve feedback loop (as increased temp increase the likelihood of wildfires).
