Bushfire

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One of the blazes of the 2006 Central Coast bushfires on New Years Day, 2006. Photo taken at Umina Beach.

A bushfire is a wildfire that occurs in the bush (collective term for forest, scrub, woodland or grassland of Australia, New Zealand, New Caledonia). In southeast Australia, bushfires tend to be most common and most severe during summer and autumn, in drought years, and particularly in El Niño years. In the north of Australia, bushfires usually occur during winter (the dry season)^[1], and fire severity tends to be more associated with seasonal growth patterns. In the southwest, similarly, bushfires occur in the summer dry season and severity is usually related to seasonal growth. Fire frequency in the north is difficult to assess, as the vast majority of fires are deliberately started by humans.

Plants have evolved a variety of strategies to survive fires, (possessing reserve shoots that sprout after a fire, or developing fire-resistant or fire-triggered seeds) or even encourage fire (eucalypts contain flammable oils in the leaves) as a way to eliminate competition from less fire-tolerant species. It is also a method of reproduction for eucalypts and grevilleas as their seed pods explode in the intense heat. Many native animals are also adept at surviving bushfires.

The natural fire regime was altered by the arrival of humans in Australia about 50,000 years ago. Fires became more frequent, and fire-loving species — notably eucalypts — greatly expanded their range. It is assumed that a good deal of this change came about as the result of deliberate action by early humans, setting fires to clear undergrowth or drive game.

Most rural areas have bush fire services, largely staffed by volunteers, to help control bushfires. As well as the water-spraying trucks commonly used in urban firefighting, bushfire services often own or lease aircraft, particularly helicopters, that can douse areas inaccessible to ground crews. However, large fires are often of such a size that no conceivable firefighting service could attempt to douse the whole fire directly, and so alternative techniques are used.

Typically, this involves controlling the area that the fire can spread to, clearing control lines which are areas which contain no combustible material. These control lines can be produced by bulldozing, or by backburning — setting a small, low-intensity fire to burn the flammable material in a controlled way. These may then be extinguished by firefighters, or, ideally, directed in such away so that they meet the main fire front, at which point both fires will run out of flammable material and be extinguished.

Regrowth two years after the Bogong bushfire, 2003.

Unfortunately, such methods can fail in the face of wind shifts causing fires to miss control lines, or because fires jump straight over them (for instance, because a burning tree falls across a line, or burning embers are carried by the wind over the line).

The actual goals of firefighters vary. Protection of life (both the firefighters and civilians) is given top priority, then private property according to economic and social value. In very severe fires, this is sometimes the only possible action. Protecting houses is regarded as more important than, say, machinery sheds, though firefighters, if possible, will try to keep fires off farmland to protect stock and fences (steel fences are destroyed by the passage of fire, as the wire is irreversibly stretched and weakened by it). Preventing the burning of publicly owned forested areas is generally of least priority, and, indeed, it is quite common (in Australia, at least) for firefighters to simply observe a fire burn towards control lines through forest rather than attempt to put it out more quickly — it is, after all, a natural process.

Smoke from bushfires can cover a large area, as seen here in eastern Victoria.

The city of Melbourne swathed in smoke during the 2006-2007 bushfire season.

The risk of major bushfires can be reduced by reducing the amount of fuel present. In forests, this is usually accomplished by conducting controlled burns — deliberately setting areas ablaze during favourable weather conditions in spring or autumn. Controlled burns can be controversial, both because they can be regarded as tampering with the forest ecosystem, and because serious fires can be started if a control burn gets out of hand. The Australian Aborigines used controlled burning to encourage new growth of plants.

Contrary to urban understanding of bushfire, rural farming communities are comparatively rarely threatened directly by them. They are usually located in the middle of large areas of cleared, usually grazed, land, and in the drought conditions present in bushfire years there is often very little grass left. However, urban fringes often spread into forested areas, and communities have literally built themselves in the middle of highly flammable forests.

On occasions, bushfires have caused wide-scale damage to private property, particularly when they have reached such urban-fringe communities, destroying many homes and causing deaths.

In fire-prone areas, people living in them typically take a variety of precautions. These include building their home out of flame-resistant materials, reducing the amount of fuel near to the home or property, constructing firebreaks, and investing in firefighting equipment.