This article relates to the ongoing debate on Australian Rural & Regional News into Bushfires, Logging, Burns & Forest Management, in particular, into a debate into self-thinning forest understoreys and wildfire risk. The series of articles relating to this particular debate are all extracted on the general debate page.

Peter Rutherford, 6 November 2022

After reading Philip Zylstra’s reply, he has generated more questions of his understanding of fire in a complex ecological system, than I had after his presentation to the ANU Disaster Solutions webinar.

He continues to doggedly defend a view of fire management which has already shown widescale tragic consequences for humans and biodiversity living in and around forest environments in southern Australia. He seemed to have only read those parts of Roger Underwood‘s and my responses that fitted with his opinions.

The research of Dr Fletcher and Professor Haberle is the scientific analysis of cores from swamps. These cores provide a foundation for understanding fire management by Aboriginal people for tens of thousands of years.

Both researchers I referenced show regular low intensity burning, as practised by Aboriginal people across the landscape, has been lost and Dr Fletcher believes the loss of cool, mosaic burning since European settlement has left us, as a nation, dangerously fire prone. Mr Zylstra seems to have missed this critical point.

If this issue was not so serious, we could laugh off Mr Zylstra’s view, “but it is also true that they did not account for the well-proven fact that so many understoreys thin by themselves if they are allowed to age,” if it didn’t have such disastrous consequences for biodiversity and human lives and assets.

The leave the forests to self-thin approach is perhaps best summed up in the words of Darryl Kerrigan; “tell him he’s dreaming.” If the burning of 79 per cent of the Greater Blue Mountains World Heritage area, 855,310 hectares and 143.1 million birds, mammals and reptiles does not give Mr Zylstra cause to rethink the self-thin mental model, then we do have a problem.

I think the recently released paper, “The Fiery Curse of Conservation” provides excellent background to the apparent conundrum we find ourselves in, when it comes to sensible and effective fire management in Australia.

The self-thin, long term fire exclusion option has a number of consequences aside from repeated high intensity bushfires breaking into Mr Zylstra’s thought bubble.

For example, the issue of chronic decline in tree health across the landscape seems to be ignored by those that support Mr Zylstra’s view of managing fire by leaving forests to self-thin and just manage fuels close to houses. Long-term exclusion of fire results in changes in soil chemistry (slowly declining pH). More acid soils have a higher availability of aluminium, manganese and other toxic trace elements. This impacts tree root and then crown health.

Farmers well understand this issue, otherwise we would starve. Most forest land managers and academics seem to be unaware of this issue. The general decline in forest health and the impacts of high intensity bushfires is either decreasing or eliminating eucalypt flowering for a decade or more across millions of hectares of native forest. What will be the ecological consequences of lost flowering? See To Burn or not to Burn.

Those involved in preparing the Threatened Species Scientific Committee advice to the federal Environment Minister on “Fire as a threatening process,” failed to address this issue in their advice.

Dr Fletcher has also stated that “The study of pollens and other organic matter from earth samples also indicates a loss of plant biodiversity.” I will use one example of potentially a thousand or more species being driven towards extinction, by benign neglect and exclusion of low intensity bushfires.

I have only seen mass flowering of the type of terrestrial orchid in the photo (R) on two occasions. These observations occurred in the early 1980s, after two low intensity FRB/ecological burns. The orchid in the photo is the first small terrestrial orchid I have seen in forty years. Just a single plant, not hundreds or thousands that would germinate after low intensity burns, if the ground fuels were managed effectively.

While talking to a NSW National Parks & Wildlife Service ranger after the 2019-20 fires, I asked about these orchids, as the area, where they had grown, has been permanently protected in the South East Forest National Park for 25 years. The concerning response was “I didn’t know we had any.”

The tragedy is, after 20 plus years of the tubers being smothered with bark and leaves, many of the tubers may not have survived. Given these orchids have a single flower stem and a leaf like a small blade of grass, less than 15cm tall, the tuber is likely to be less resilient than larger orchids. If there were any surviving tubers, they would likely have been killed by the high intensity bushfires of 4 January 2020. So much for permanent protection and the environmental benefits of fire exclusion.

Those involved in preparing the Threatened Species Scientific Committee advice to the federal Environment Minister on “Fire as a threatening process,” seemed to either default to a fire exclusion approach or else a burn return time that results in hot burns, that do not deliver the cool mosaic burning that many species need. Given the complexity of the advice to the Minister, this rule book will favour the fire exclusion approach to forest fuel and bushfire management, helping to lock-in negative environmental, social and economic outcomes in future drought years, as more and more forest is decimated by high intensity bushfires.

There are other examples of the positive foraging response of critical weight range mammals I could provide, but time and space is limited.

See also by Peter Rutherford: To burn or not to burn? Is that the question? : SETA; Forest fire management – hard won lessons almost forgotten.

Related stories:

The Zylstra theory: a final comment: Roger Underwood;
Philip Zylstra’s response #4 – self-thinning forest understoreys and wildfire debate;
Jack Bradshaw to Philip Zylstra #2 – self-thinning forest understoreys and wildfire debate;
Philip Zylstra’s response #3 – self-thinning forest understoreys and wildfire risk debate;
Self-thinning forest understoreys and wildfire risk debate – Roger Underwood responds;
Philip Zylstra’s fire research: Adding value or creating risk? : Peter Rutherford;
Philip Zylstra continues the debate – self-thinning forest understoreys and wildfire risk;
Self-thinning forest understoreys and wildfire risk debate – Jack Bradshaw responds to Philip Zylstra;
‘Self thinning forest understoreys reduce wildfire risk, even in a warming climate’: Philip Zylstra responds to Jack Bradshaw;
Comment on ‘Self-thinning forest understoreys reduce wildfire risk, even in a warming climate’: Jack Bradshaw.