Lesley Head:
This argument depends on accepting evidence for Aboriginal burning that is controversial in its own right, but also problematic in terms of timing. To be a consequence of the build up of uneaten vegetation, it had to have happened after the suggested blitzkrieg. But the claims for Aboriginal burning on which this hypothesis draws are 140,000 years ago from an offshore site northeast of Cairns and about 120,000 years ago from Lake George near Canberra. Further there is no evidence at a continental scale that huge uncontrolled fires changed the whole landscape.
Rod Wells:
I agree with Flannery's hypothesis that if you change the fauna (eg kill off the largest animals because they are the easiest to hunt) then you do change the pattern of flora, the undergrowth does get thicker and fire is more likely, but it is fire frequency not necessarily intensity alone that changes the nature of the vegetation. However the megafauna appear to have died out in the last glacial when there was more desert and grass than anything else, and therefore less thick fuel to sustain intensive fire across the whole environment.
David Bowman:
Aboriginal people entered a continent which had already been on fire for millions of years. They intervened and they changed the habitat balance with their fire management practices and, in doing so conserved some habitats, such as rainforest, that might otherwise have been lost during the extreme aridity that characterised the end of the last ice-age some 10,000 to 20,000 years ago.
John Benson:
Flannery ignores much evidence that points to climate as being the main determinant in megafauna extinction and vegetation change over millions of years - with major changes occurring since the onset of aridity in Miocene but continuing through the last ice age which coincided with the occupation of Australia by aboriginal people. Fires increased in Australia since the Miocene, so many of the country's species were adapted to fire before the Aborigines arrived.
Jim Kohen:
This model has a number of problems. For a start, you need to believe that Aborigines and megafauna were spread across the entire continent and that extinction occurred everywhere at the same time, leading to fires right across the continent. There is evidence of burning at Lake George, ACT, dating back 120,000 years. At Lynch's Crater, on the Atherton Tableland, a similar picture emerges, but the date is 38,000 years ago. The question is whether it was a natural phenomenon or caused by humans. As well, the dates for megafauna extinction range from 19,000 years ago to 6,000 years ago.
Quote:Tim Flannery:
Fire destroys the rainforests and allows fire resistant eucalypts to spread across the continent. A drier climate change occurs as a result of the change in vegetation
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David Bowman:
We are in agreement that fire does destroy rainforests - but I fundamentally disagree with the idea that the rainforests were destroyed by Aboriginal people on a massive scale. Non-rainforest vegetation, including Eucalypt forests, have been on the continent for millions and millions of years. The biodiversity of these systems is too complex, too cleverly arranged to have come about in only 50,000 years (a mere blink in the course of evolution). The idea that changed fire regimes, whether they are attributed to Aboriginal burning or the alleged build-up of fuel following megafaunal extinction, could have triggered the contraction of the rainforest and the expansion and diversification of the eucalypts, is biologically far-fetched. There is simply not enough time for this to have happened. I believe Aboriginal landscape burning conserved biodiversity. It must be remembered that at the end of the last ice-age only 10,000 years ago, rainforest rapidly expanded throughout Australia - in spite of Aboriginal landscape burning. Whereas Flannery believes that all the existing patches of tropical rainforest are remnants from 50,000 years ago, we know that many are in fact of far more recent origin. For example, rainforests in the monsoon tropics are able to colonise recent landforms like flood plain margins and beach ridges.
John Benson:
There is no evidence that rainforest blanketed vast areas of eastern Australia at the time of Aborigines' arrival in Australia. Rainforest apparently declined in the mid Miocene, around 15 million years ago. By 100,000 years ago it probably occurred in patches more or less where it was present at the time of European settlement - confined to rich soils in NSW, in fire protected sites in the inland, protected valleys in Tasmania and Victoria, on the wetter sections of the coastal plain and highland of tropical Queensland and in patches where soils and hydrological factors were favorable in the Northern Territory. During the last ice age (40,000 - 10,000 years ago) rainforest retreated but has recolonised suitable habitats over the last 10,000 years. Most eucalypts were evolved before humans arrived. Their abundance may have varied due to Aboriginal burning.
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