New evidence points to bushfires 60 million years ago
NEW RESEARCH INTO the evolution of banksias provides some of the latest evidence that fire ravaged parts of the Australian landscape 40 million years earlier than traditionally thought.
Until recently, most scientists agreed that bushfires have only been commonplace in Australia for 20 million years. This timeframe coincides with a global shift to a warmer, drier climate. It also corresponds with the receding of rainforests that had previously dominated Australia.
However, a new study of the evolution of fire-adapted traits in banksias by researchers at Curtin University, in Perth, suggests these plants were reacting to fire as far back as 61 million years ago, shortly after the dinosaurs disappeared. The findings add to evidence from another recent study which suggested that gum trees have been fire resistant for 62 million years.
Banksia is a genus of wildflower found across Australia, predominantly in the south west. A distinctive feature of the plant is its fruiting ‘cone’, in which seeds are stored for regeneration, usually following a bushfire. The new study, led by Professor Byron Lamont, suggests that banksias have had the ability to protect seeds in this way ever since the species originated, and that this is a fire-adapted trait.
“We already knew that banksias had been around for at least 60 million years,” says Byron. “The interesting part of our findings is that they’ve probably been subjected to fire since that time as well.”
In the face of some criticism from other scientists, Byron and his team argue that while Australia’s landscape was dominated by rainforest during this period, there were drier, more fire-prone areas, to the extent that species elicited evolutionary responses to fire. “If there were fires that early, they have probably had a profound effect on the evolution of animals as well as plants,” says Byron.
Kingsley Dixon, professor of plant biology at the University of Western Australia, says that fire-resistant traits in one or two species is not sufficient evidence that bushfires were commonplace in the Australian landscape.
“One plant might show a strong link to a particular evolutionary signal,” says Kingsley. “But to say all plants therefore must have had the same signal, is just flying in the face of good science and sound reason.”
Two studies, one result?
Kingsley says it is unlikely that fires would have been pervasive enough to cause an evolutionary response so early in Australia’s natural history. He urges that the findings should be received with great caution.
David Bowman, a professor of forest ecology at the University of Tasmania, was a co-author on the earlier study on eucalypts. While David appreciates scientific scepticism of this new proposal of bushfire history, he believes that two separate studies adding up to the same conclusions is too much of a coincidence to ignore.
“The two studies present a striking coincidence and warrant serious thought,” he told Australian Geographic. “Scholars are now beginning to think that the relationship between fire and plants has probably been underestimated.”
David admits that much more research is required. However, he argues the two independent studies have pushed the evolutionary relationship between fire and plants to centre stage, and the timing of the birth of bushfires as a dominant force in the Australian landscape needs to be reconsidered.
The research was published in the July 2011 edition of the journal New Phytologist.