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Australia is frequently ravaged by bushfires, more so than any other country in the world. During the severe 2002-2003 season, which lasted from 1 July 2002 to 28 February 2003, there were 5999 bushfires recorded. There has been a long, dramatic history of bushfires on the continent, with fires first sparking around five million years ago when dry grassland began to dominate the landscape. Prior to this period, Australia was predominately composed of lakes, wetlands, rivers and rainforests, conditions far too wet to foster bushfires. Around 40 000 years ago bushfires began to occur more regularly. The early Aboriginal peoples had an intricate understanding of fire and valued its relationship to the land. Today, bushfires wreak havoc across the land, causing significant amounts of damage, destroying buildings and houses, harming livestock, and on occasion, killing humans. See image 1

What is a bushfire?

A bushfire is a wildfire that burns out of control spreading across vegetated regions of bushland. In order for a bushfire to be catastrophic, the right conditions must be present. Most bushfires happen in times when temperatures are high. In addition, conditions must be dry. Areas with dense undergrowth, as can be found in south-eastern Australia, are the most vulnerable to bushfire. Bushfires often start when dry winds blow inland from central Australia. While the winds bring dry weather, they also provide ventilation for the flames. Trees such as eucalypts are especially prone to fire because their leaves have a highly-flammable oil. Dry leaves and bark are especially flammable. See image 2

Due to the size of the continent, and the great diversity of environmental conditions, there is no time of the year when the entire landmass is safe from the potential danger of bushfire. The fire season in different regions of Australia depends primarily on latitude. At the 'top end' of the country, extending north of Tenant Creek in the Northern Territory up to the Gulf of Carpentaria, the main fire season is during winter and spring (the dry season of wet-dry tropics). In contrast to the north, the fire season of the southernmost region occurs during summer and autumn. The most severe bushfires occur south of a parallel line between Adelaide and Sydney.

Once a bushfire has started, it requires fuel and ventilation. Bushfires spread as they seek out more fuel. Wind helps push them onwards and provides fresh oxygen for combustion. Highly flammable eucalypt trees can explode in the high temperatures found within bushfires. This spreads burning material even further. When burning embers are carried into the air by wind, they can be deposited in other areas, creating spot fires ahead of the fire itself. When the canopy of a forest is continuous, sometimes the canopy itself can catch fire, causing a phenomenon called a crown fire. These fires spread quickly as each tree in the canopy catches fire. They are difficult to put out since these fires tend to consume all the oxygen on the forest floor and water must be sprayed high into the canopy to extinguish the fire.

In order to protect people's property and lives, fire-fighters are sent in when bushfire strikes. Fire-fighters use many methods to put out fires, including spraying them with hoses or using special helicopters to water-bomb the fires from the air. See image 3

How do bushfires start?

Bushfire incidents in Australia can be caused in many different ways. The causes of ignition can be split into two groups, 'natural' and 'human influence'. Lightning strikes are the main way bushfires are started naturally. There are, on average, more bushfires initiated due to lightning strikes than any other individual cause, accounting for approximately 26 percent of all bushfires.

The vast majority of bushfires, however, are generated by the actions or influences of humans. On occasions, a campfire can develop into a bushfire, if the campfire is left unattended or not properly extinguished. Some farmers burn vegetation on their properties to rid the land of crop debris, control weeds and remove rubbish. These fires are referred to as agricultural burns and can lead to bushfires when they are not administered carefully. Agricultural burns are responsible for about 15 percent of all bushfires. Machinery or equipment that generates heat or sparks can potentially act as a catalyst for bushfires. Some machines notorious for triggering bushfires include chainsaws, grinders and slashers. The exhaust from vehicles may also cause fires. Cigarettes which have been discarded irresponsibly have the capacity to ignite bushland, although only seven percent of all fires begin in this manner.

Unfortunately, not all bushfires are accidental. Some are deliberately lit by arsonists (people who intentionally start fires). These fires can destroy thousands of square kilometres of land. Remarkably, deliberately-lit fires are the second most common cause of ignition, making up 25 percent of bushfires. See image 4

Effects of Bushfires

Fires rage through the Australian bushland, sometimes creeping into urban areas, damaging the environment, stunting the economy and creating social distress. The intensity of the bushfire dictates the effect on the environment. Severe bushfires may burn all the vegetation in a particular area, while more moderate fires will, generally, cause less damage to the natural surroundings.

The most obvious result of fire is the loss of plant and animal life. When an area is burned out, vegetation is destroyed as it was used by the fire as fuel. In addition, animals are killed in bushfires by high temperatures and suffocation. Due to the frequency of bushfires, some species have developed defence mechanisms to combat the flames. Thick bark and protected shoots and tissue allow plants to regenerate after a fire. Mobile animals, such as birds, kangaroos or wallabies, are able to flee flame-stricken areas. Echidnas and wombats may escape fire by seeking shelter in burrows or logs. Reptiles and amphibians also look to find refuge underground as the fire passes above. Possums and other arboreal mammals (animals that live in trees) scamper up to the crowns of trees to evade peril.

Beneficial uses of fire

The effects of bushfires are not all detrimental to the environment, as fire generates regrowth and new life. In some eucalypt species, for example, fire is an essential part of the life cycle. For these plants, fire splits open seed pods, allowing them to germinate. Without fire, these species are unable to reproduce. Fire also encourages the growth of new grassland plants.

Fire is used to regulate the environment in some cases. Indigenous people have used fire to manage bushland. Fire was used to clear undergrowth and regenerate growth on plants Aboriginal people used for food. The fires used by Aboriginal people for this purpose were low intensity, which means they did not burn as quickly or as hot as an out-of-control bushfire. Since these fires burned back undergrowth, it is possible that they prevented other, more catastrophic fires.

Today, fire fighters use back-burning techniques to clear undergrowth in fire-prone areas.


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