Australia’s history of fire, until the arrival of humans 50,000 years ago

As fires continue to rage on the east coast of Australia, Professor Bob Hill explores the history of fire prior to the arrival of humans.

The Earth has a long history of fire burning vegetation, mostly at times in the past when atmospheric oxygen was considerably higher than it is now and fire could burn more easily.

However, about 60 million years ago the number and intensity of fires decreased globally as the oxygen levels declined and the world shifted to a super greenhouse environment with exceptionally high rainfall.

Following this, since about 25-30 million years ago, Australia has been drying out and fire has returned to prominence. Our vegetation includes species that are well adapted to frequent and quite intense fires. However, we are now at a critical time in history where the fire frequency and intensity has reached a point where the vegetation is no longer in any kind of equilibrium with it, and this is clearly a result of human-caused climate change, with dry conditions and extreme heat providing conditions where the vegetation does not have the evolutionary history to cope.

The likely outcome is major changes in vegetation types, with rainforest and alpine vegetation at extreme risk, since they have little capacity to recover from fire, and other vegetation types suffering from a reduction in biomass, species diversity and canopy cover.

This is an extraordinarily difficult prospect to manage and it will require governments globally to acknowledge the reality of climate change and, with the highest possible priority, put measures in place to reduce the impacts it will have. Of course, change in fire behaviour is only one major consequence of climate change, there are many other issues that will stretch our capacity to adapt to the limit over coming years.

Professor Bob Hill, Director of the Environment Institute, a palaeobotanist, with an deep interest in plant systematics, plant ecophysiology and the application of research from these areas to interpreting changes that have occurred to the Australian flora through evolutionary time.

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