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, Secretary, South East Timber Association (SETA), 24 October 2022
Following the critique of a research paper by Zylstra, Bradshaw and Lindenmayer “Self-thinning forest understoreys reduce wildfire risk, even in a warming climate,” by Jack Bradshaw, readers might be interested in some broader analysis of Mr Zylstra’s fire research work.
Mr Zylstra’s 435 page, 2011 PhD thesis, Forest Flammability – Modelling and Managing a Complex System, is a key plank in his journey, which seems to be directed to rewriting Australian pre-European fire history. His research appears to be the base to advocate for what might be described as a wilderness approach to fire management across the broad Australian landscape.
In his PhD thesis, Mr Zylstra stated: “As discussed in section 1.1, the lack of scientific understanding cannot be compensated for with traditional knowledge, as the European-Australian understanding of Aboriginal fire has been irreconcilably altered from the original understanding. Collectively, these facts suggest that the current state of Australian fire knowledge is not sufficient for underpinning effective fire and fuel management.
It is intended that by developing a model which explicitly provides a physical understanding of the role of various fuels in a fire, this thesis will make significant advances toward addressing these shortfalls.”
In 2016, two CSIRO scientists issued an eight page critique of the most recent version of Mr Zylstra’s flammability model, which in part concluded: “The FFM is described by its author (Zylstra et al. 2016) as a ‘biophysical mechanistic model’ that incorporates heat transfer processes to describe fire behaviour through complex interactions between fuels, weather and the fire itself. Although the heuristics underlying the FFM in regard to the importance of fuel structure in determining fire behaviour are essentially valid (and described by others previously, see for example Kessell et al. (1978), Kessell (1979) and Malanson and Butler (1985), the physical basis of the FFM and its sub-models is flawed and incorrect.
In part, this is because much of the sub-modelling is based on small-scale table-top experiments that fundamentally do not incorporate key mechanisms of fire dynamics but also because many of the assumptions in the geometric construct linking a flame vector with a fuel location totally disregard fundamental concepts of heat transfer and fluid dynamics. As a result, these flaws invalidate the model and thus its results will be erroneous.”
A number of “other concerning issues” with the paper were also detailed in the CSIRO memo.
It is not clear from Mr Zylstra’s March 2021 peer-reviewed paper “Linking fire behaviour and its ecological effects to plant traits, using FRaME in R,” if the flaws in his model, identified in the CSIRO critique, have been addressed.
On 19 October 2022, the Australian National University held a Disaster Solutions Update titled, From Fires to Floods. Mr Zylstra was a panel member in the fire panel session, which was described as “An integrated approach to protecting Australia from catastrophic bushfire”. If the aim of the project is to protect Australia from catastrophic bushfire, many of his comments would be of deep concern to experienced fire managers.
Mr Zylstra’s opinions contributed to the disaster solutions update included: “We need to understand what drives fire, what makes forest flammable. My work on this has been to develop what is still the only peer-reviewed fire behaviour model for most forest across Australia. It takes quite a different approach to what we are used to hearing about. You have probably heard a lot of language about fuel load as a simple catchall concept that was adopted from the US in the 1960s.”
“Over time, a forest actually changes. It passes through a period of very high flammability and passes on into a stage where it is less flammable.”
Mr Zylstra seems to ignore the fact that forest ground, fine fuel loads (less than 6mm in diameter), which are typically in the order of 20 to 50 tonnes per hectare, in long unburnt forest, along with larger coarse woody debris, contribute significantly to the risk of crown scorch or crown fires.
He explained, “You notice in the background here in this forest, the trees are not on fire. Yet those trees are actually influencing that fire behaviour. They are actually slowing that fire down. They are not silent bystanders.” (See the schematic below)
“Vegetation that isn’t burning is not fuel, it is overstorey shelter. Plants can either accelerate a fire or slow it down.
“Over time, a forest actually changes. It passes through a period of very high flammability and passes on into a stage where it is less flammable. (See the schematic below). Looking at an example of that, this is an area of red tingle forest we have been studying in Western Australia and from the left to the right we are looking at a time sequence that is from straight after fire where you can see some epicormic growth on the trees. A period of very dense understorey regrowth, which then self thins. On the right hand side, we have a much more open understorey. (See the schematic below).
“Now to take that from a conceptual thing to one of ecological cooperation, we need to see how that translates into fire behaviour. That is where I bring in FRAME, which will give us very concrete fire behaviour predictions such as the percentage of the time you can use aggressive fire fighting techniques, rather than having to fall back to backburning.
“There are two periods of that. There is either a very short period straight after fire or there is a very long period and this allows us to plan our landscape planning around this.
“This is the problem with trying to manage large landscapes, as if we have that much power. So, I suppose what we need to do is to take the bits we are directly going to intervene with and pull back to the areas that we can manage. Around urban fringes, around places where there is a strategic spot where you will actually put fire fighters right where you can really make use of that very recently burnt country and leave the rest of the area to age.”
Mr Zylstra’s approach appears to effectively abandon all biodiversity and any livestock, human lives and property in the path of any high intensity bushfires. As fire authorities and government land managers do less and less broad area fuel reduction or ecological burning, as advocated in the Zylstra wilderness approach, bigger and bigger ecological, social and economic disasters will result from mega fires in drought years.
He said “It is a totally different way of thinking about this. It is not about burning country burnt to change it. It is about having areas that we have strategically modified where that is valuable. Then leaving the broad landscape to operate with its’ own ecological controls.” The proposal to leave the broad landscape to operate with its’ own ecological controls is not supported by the historical record.
More importantly, research by Professor Simon Haberle from the ANU and Dr Michael-Shawn Fletcher from Melbourne University show that Aboriginal burning was not, as Mr Zylstra stated: “Traditional fire management is very much about only taking the bit you need. So, you have intensive fire management along certain travel lines or in places that you have designated.”
Dr Fletcher believes the loss of cool, mosaic burning since European settlement has left us, as a nation, dangerously fire prone.
“It has created a situation where we have connected incredibly flammable overstocked forests that go for hundreds, if not thousands, of kilometres across the south-east Australian seaboard,” he said.
“It is important, to unpack the history of landscape change from Aboriginal management through to the modern day, not only for how we manage this country but understanding how it operates,” Dr Fletcher said.
Dr Fletcher’s findings are profoundly important for understanding the past. Crucially, they point to how we approach the future.
“We see a shift from an open-forest system to a closed-forest system in all the examples that we’ve analysed,” he said.
“Universally, across landscapes that are not now farms, we see open forests turning into closed forests.
“In terms of fire, that’s a ramping up of fuel levels.
The study of pollens and other organic matter from earth samples also indicates a loss of plant biodiversity.
Many less flammable species have disappeared, replaced by highly combustible eucalypts.
Paleoecologist Professor Simon Haberle visited Bega Swamp, near Bemboka, NSW to try and better understand the relationships between Indigenous Australians, the environment and fire.
The sediment, sampled at a very fine resolution, paints a picture of the landscape in freeze frames of every 20 years, stretching back over 15,000 years.
“The results show that the number of samples including charcoal has increased since European settlement, confirming other studies that big fires have occurred more frequently than during the time of Aboriginal land tenure in the Australian high country,” Professor Haberle said.
“It also shows that in the past mega fires only occurred very rarely, once every 4000 years, and that the current situation of big and intense fires is unusual in the long-term history of the region.”
“You see big changes in fire management, because you can look at the charcoal and see what burning regime took place,” he said.
“It was a regular regime, Aboriginal people knew how to keep fuel loads lower.”
According to Professor Haberle’s research from Tasmania to the Kimberley, big fire events are becoming more common, fires are starting sooner and problematic trends are forming.
“Big disastrous fires used to be rare, but are more common now,” he said.
“The difference now is the regular burning doesn’t occur anymore, so we don’t know what will happen in the future.”
The above findings and the experience of a broad range of professional fire and land managers make it clear that Mr Zylstra’s revisionist opinions on Aboriginal fire management are taking us on a very dangerous revisionist fire management path, from environmental, social and economic perspectives.
It is to be hoped that the Director of the ANU/Optus Bushfire Centre of Research Excellence understands the role of the Centre is to reduce the risk of future bushfire disasters, not lock in wilderness ideology driven regimes that create even bigger disasters in future.
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 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.
Philip Zylstra responded to this article: Philip Zylstra’s response #3 – self-thinning forest understoreys and wildfire risk debate and Peter Rutherford responded further: Peter Rutherford to Philip Zylstra #2 – self-thinning forest understoreys and wildfire debate.
