14 - Summary

Summary

Rainforests in Australia occur as scattered islands within vast tracts of the quintessential Australian vegetation dominated by Eucalyptus and Acacia. Rainforest ‘islands’ are found from Tasmania in the temperate zone to the monsoon tropics in the north across wide gradients of rainfall, altitude and temperature. In this book, I argue that their patchy distribution is the consequence of tens of millions of years of fires started by lightning and other natural causes. Fire became a feature of the Australian landscape as the continent became progressively drier. This occurred because of the dominance of the subtropical high pressure system beginning in the mid Tertiary when the continent drifted into the mid latitudes, the thermal gradient between the equator and the South Pole intensified, and the Antarctic ice sheet formed. An increase in the frequency of wildfires triggered a major diversification of the fire-tolerant biota. In plants, there was selection for new traits such as serotiny, and the refinement of pre-existing traits such as the lignotuber. Some fire-tolerant vegetation became fire-adapted and ultimately fire-promoting, sealing the fate of most rainforest vegetation. This evolutionary divergence is responsible for the fundamental and often sharp ecological and floristic dichotomy of the current Australian biota into rainforest and non-rainforest types. Thus the evolution of the current Australian flora was forged in a fiery environment in which the ancestral rainforests become scattered and burnt.