Large fires, fire effects and the fire-regime concept

'Large' fires may be declared so because of their absolute or relative area. Huge fires - with areas of more than 106 ha (10(4) km(2)) have occurred across a wide spectrum of Australian environments and are known on other continents. Such large fires are rare whereas fires with much smaller areas are common. Large fires are initiated by single or multiple ignitions and become large because of some combination of: rapid rates of spread; long 'life'; merging, and failure of initial suppression operations. Fires as ecological 'events' occur within a 'regime' - an historical series. Both events and regimes have effects that may be discerned in terms of water, land, air or organisms. What have been regarded as the components of 'regimes' have differed between observers, the main issue being whether or not spatial variables need to be included; 'area' involvement is briefly addressed. The current trend toward fire-regime control through fuel treatment, including management (prescribed) burning, and fire suppression may be expected to continue. These trends, among others, can be expected to change fire regimes. What is regarded as 'large' among fires may change as the planet becomes increasingly human-dominated.