Australian plant species vary markedly in their fire responses, and the evolutionary histories of the diverse range of traits that lead to fire tolerance and fire dependence almost certainly involves both exaptation and traits that evolved directly in response to fire. The hypothesis that very long-term nutrient poverty in Australian soils led to intense fires explains many of the unusual responses to fire by Australian species, as does near global distribution of evidence for fire during the Cretaceous, possibly driven by high atmospheric oxygen concentration. Recent descriptions of leaf fragments from a Late Cretaceous locality in central Australia have provided the first fossil evidence for ancient and possibly ancestral fire ecology in modern fire-dependent Australian clades, as suggested by some phylogenetic studies. The drying of the Australian climate in the Neogene allowed the rise to dominance of taxa that had their origin in the Late Cretaceous, but had not been prominent in the rainforest-dominated Paleogene. The Neogene climatic evolution meant that fire became an important feature of that environment and fire frequency and intensity began to grow to high levels, and many fire adaptations evolved. However, many plant species were already in place to take advantage of this new fire regime, and even though the original drivers for fire may have changed (possibly from high atmospheric oxygen concentrations, to long, hot, dry periods at different times in different parts of the continent), the adaptations that these species had for fire tolerance meant they could become prominent over much of the Australian continent by the time human colonisation began.
The Natural History of Oxygen
