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.
Jack Bradshaw, 6 November 2022
In his 24 October response on this issue, Zylstra states that in their study seven times more area of recently burnt forest was burnt than long unburnt forest. That is not in dispute. But was this because there were seven times the number of ignitions in these areas to start with because of chance or differences in area or because of some flammability factor? We simply do not know because this basic statistical requirement was not considered in the study. Is the conclusion biased, by how much, and in what direction? Who knows?
In a similar way no account was taken of any suppression activity that may have affected the result. Zylstra agrees that this was not considered but says that that is OK by presenting a whole suite of assumptions he makes about the way the fires might have been managed. I have no intention of arguing about hypothetical suppression tactics. That is not scientific method. The fact is that no objective measurement of the impact was attempted. Is the conclusion biased, by how much, and in what direction? Who knows?
I am well aware that fire rate of spread is not directly related to fuel load but it is related to severity, damage and difficulty of control. It is also true that litter decays over time but it is also added to by leaf fall each year, finally reaching an equilibrium – about 50 tonnes/hectare in the case of karri forest.
Zylstra regards my explanation of the relationship between fire and regeneration and the physical evidence of pre 1850 fire as nothing more than ‘educated guesses’. With 50 years working in the fields of forest inventory, resource management and silviculture (with a bit of fire control tossed in) it is certainly educated but a guess it is not. If Zylstra cannot accept the extensive mapping and documented measurements and is unable to recognise the existence of different aged fire-induced cohorts in the forest then there is nothing more I can do to assist his understanding of the forest dynamics involved.
The assertion that the natural karri forest fire interval could be anything up to 1,000 years and the subsequent statement that forests prior to 1850 did not experience fire despite indisputable evidence to the contrary is just too silly to be taken seriously. Crossing your fingers, no matter how hard, for 1,000 years is hardly a viable fire management strategy.
Zylstra et al have presented empirical data on areas burnt in different post disturbance stages. However, because of major omissions in the study it has rendered invalid the conclusions they have drawn from it and provides no support or otherwise for their theories on flammability. I have made no comment on the theory itself which has already been dealt with by others more qualified than I.
Zylstra continues to claim that no flaws have been found in the study, despite agreeing that two key factors, probability of ignition and fire suppression impact, were ignored. The fact that these and other errors or omissions were not picked up by the reviewers of the pay-to-publish journal, rather than being the imprimatur of sound science, simply confirms that the peer review process was inadequate.
Related stories:
The Zylstra theory: a final comment: Roger Underwood;
Philip Zylstra’s response $4 – 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;
Peter Rutherford to Philip Zylstra #2 – self-thinning forest understoreys and wildfire debate;
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.
