Thanks, pdq; I don't have to do the conversion all that often these days and the old cortex was a bit crowded.

A couple of days back goatfell asked in the northern terrortyevery day the burn off scrub so that house and land wouldn't catch fire so why doesn't the rest of Australia do that

Further to Joybell's response I'd like to add the following.

Over much of the Top End of the Northern Territory, the climate is tropical (with seriously wet Wet Seasons and seriously dry Dry Seasons and the dominant vegetation is Savannah Woodland or Savannah Grassland. The trees are rarely much more than 30' high and their canopies rarely have a density of more than 30%; there isn't much of an understory. For most of the last 40,000 years they have been "managed" by a pattern of patchwork-burning.

In the SE highlands of Australia and certainly around Kinglake the dominant vegetation is Dry Sclerophyll Forest and here the canopies are at least 30 metres high and with a density of 30-70%; routinely they are 50m tall and emergents may be taller. The Wet Sclerophyll Forest around Marysville has much the same parameters but is routinely 70m high with emergents frequently exceeding 80m; there is a fairly dense understory in both types.

The Top End Savannahs might, in any one hectare, have experienced a fire of mild intensity (a few kilowatts per metre of flame front) only every three to five years or so; there's not enough fuel to sustain frequent fires of high intensity. The DSFs have a pre-contact fire history of once in every 150 years or so and the WSFs have a pre-contact fire history of once in every 250 years or so. In both cases, a higher frequency changes the vegetation so that more frequent fires are likely to occur. Low intensity fires (of the sort used as fuel reduction burns elsewhere actually kill the standing timber but leave it in place so that regeneration is impaired.

There is no reliable evidence that Aborigines routinely practised burning in Dry Sclerophyll Forests of SE Oz and a fair amount of evidence that they never practised it in WSFs. Frequent controlled burning is just as destructive to these forests as these wildfires

On the occasions that these forests dry out enough and are exposed to high or extreme fire danger, their structure is such that a ground fire can get up through the understory and into the canopy to cause a high intensity crown fire. Intensities of multi megawatts and gigawatts per linear metre of flame front are produced and spotting (bits of branch, bark etc up to a metre long and burning) can carry the conflagration many kilometres ahead of the flame front. Such spotting leapt into Jannali (a suburb of Sydney) 7km across the harbour in the '94 fires and 10km across Lake Jindabyne in the 2003 fires of the Australian Alps.

Perhaps I've said enough.

Cheers, Rowan