Neil Burrows and Rick Sneeuwjagt
The piece by Byron Lamont and Tianhua He titled “Why prescribed burns don’t stop wildfires” (WAToday 22 January 2020) is complete fiction. It reveals that these authors have no experience or operational understanding of fire behaviour, prescribed burning and bushfire suppression. Their baseless and inhumane opinions, if given any credibility, will give rise to very dangerous fire management policies, a continuation of a cycle of devastating bushfires and further losses of lives and beautiful forests.
The title of their article is a clue to their lack of understanding. Prescribed burning is not designed to stop bushfires. It is designed to make them easier, safer and cheaper to suppress. Experienced land managers, fire fighters, and the bushfire scientists who work closely with them, are in no doubt that the scientific, experiential and historical evidence demonstrates that prescribed burning, done properly, is highly effective at mitigating the bushfire threat, even under severe weather conditions. This is based on the following evidence.
Firstly, fire science. Reducing fuel loads and simplifying fuel structures by regular burning reduces the speed of a bushfire, its intensity (heat energy output), the size of the flames and its ember and spotting potential. All of this makes bushfires less damaging and easier to put out. In mature forests, crown fires cannot be sustained if the surface and near surface fuels are at low levels as a result of regular fuel reduction burning.
Lamont and He make the extraordinary assertion that long unburnt forest fuels are of low flammability and therefore of no significant threat to communities. This is not only demonstrably untrue, it is dangerously wrong. For example, in long unburnt karri forest, much of the live, green understorey dies and becomes dead, dry fuel on the forest floor after about 25-30 years. Bushfires are most likely to occur well before that time.
Dead scrub, together with accumulated dead leaves, twigs and bark, the surface and aerated near-surface fuels can be a meter or more deep with total fuel loads of up to 50 tonnes per hectare. In dryer stringybark forests, the sparser, lower understorey vegetation comprises a small component of the total fuel complex. It is the accumulation of dead fuels (leaves, twigs, branchlets, bark) that drives forest fires. This is because it is at the base of the ‘fuel ladder’, it is dry, and it reaches very high loadings if left unburnt.
Second, real-world experience. We know of hundreds of examples where prescribed burning has ‘saved the day’.
Hot fires ran into areas of low fuel, and the resulting reduced fire behaviour enabled fire fighters to gain the upper hand. Conversely, we can cite numerous recent examples where a lack of prescribed burning has resulted in unstoppable fires and considerable losses. Ask any fire fighter whether they would rather fight a bushfire in 4 year old fuels or in 40 year old fuels? We know what the answer will be. Academics like Lamont and He disdain the experience of bushmen and experienced firefighters, preferring computer models developed on a green, leafy campus. In doing so they reject the experience of real-world Australians and their experience over the last 200 years.
Third, history. There are almost 60 years of historical data from the forests of south west WA, and these data unequivocally show that when the area of prescribed burning trends down, the area burnt by bushfire trends up. There is a simple explanation: bushfires are more difficult to put out in heavy fuels. The area burnt by wildfire escalates rapidly when the area of prescribed burning in a region falls below about 8% per annum. Burning about 8% per annum results in about 40% of the bushland carrying fuels 0-5 years old.
A very powerful factor in the recent bushfire tragedies in NSW is the fact that prescribed burning in NSW has amounted to less than 2% per annum. This means only 10% of the bushland is carrying fuels 0-5 years old and 80% is carrying fuels older than 10 years. This is well below the threshold for effective bushfire mitigation because a high proportion of the region is carrying very old, heavy, flammable fuels. Fires in these fuels rapidly become unstoppable, especially when they have been dried out by years of drought.
Finally, strategic planning. To be effective, prescribed burning must also be strategic – that is, done in the right places to protect communities by intercepting fire runs under the worst fire weather conditions. The fire management cells need to be large enough to ensure a sufficient area for the spread of a bushfire to be slowed and controlled. Burns must be bounded by roads or tracks to enable rapid access by fire fighters. Burning must be done to appropriate standards of fuel removal and fire intensity. Prescribed burns that are too patchy may not slow a bushfire, and in some forests, burns that are too hot can stimulate the regeneration of dense scrub.
Prescribed burning – how and why it works
The purpose of a fuel reduction burning program is not to stop bushfires, but to assist with their safe suppression. The process of bushfire suppression is complex and dynamic. There are a variety of suppression strategies and tactics that can be used in space and time, depending on weather conditions, fuels, topography, fire behaviour, fire shape and fire position in the landscape, and fire intensity around the fire’s perimeter.
Fire fighters rarely make a direct attack on the head fire – it’s usually too ‘hot’. Instead, they implement other strategies including a variety of direct, indirect and parallel attacks – the options, and likelihood of early success, are greater if the fire is burning slower and at a lower intensity because it’s burning in young, light fuels. Appliances such as water bombers will be more effective on slower moving, lower intensity fires. Fire intensity varies around the fire’s perimeter, affording suppression opportunities – there will almost always be a place on the fire’s perimeter that can be attacked – even under severe fire weather conditions – and if fuel loads are low, this opportunity widens significantly.
The most trying bushfire situation occurs when there is wind shift and the long flank of the fire becomes a wide head fire. Therefore, containment work on the ‘pressure flank’ is critical and is more likely to succeed in young, low fuel situations when flank fire intensity is relatively low, even under severe weather conditions.
If part of the fire is burning in very light fuels as a result of prescribed burning, then if resources are stretched, it can be ignored and resources deployed to higher priority areas around the fire perimeter, or to defending properties, or dispatched to other fires in a multiple fire situation.
Prescribed burning provides ‘anchor points’ and ‘tie in’ points for fire fighters. These low fuel areas are very important for indirect suppression strategies including back burning. Attempting to back burn in old, heavy fuels against old, heavy fuels is a slow, resources demanding, dangerous and risky process. Back burning in young, light fuels surrounded by young, light fuels is much safer, more likely to be successful and requires less resources. Low fuel areas are also very important for ‘tying in’ containment lines, enabling faster, more efficient suppression. The speed of construction of containment lines is crucial in the battle against a growing fire. Fire suppression is a race in terms of rate of fireline construction and containment verses rate of perimeter growth of the bushfire. Fires burn slower in younger, lighter fuels, not only improving the likelihood of early detection and suppression, but increasing the odds of fire fighters getting the upper hand.
Severe fire weather fire weather conditions don’t last very long in the life cycle of a bushfire – when diurnal fire weather conditions ease (and they always do at some point), and if the fire is burning in young, light fuels, there is a larger window of opportunity for safe suppression, than if it’s burning in old, heavy fuels.
There are two other critical ways in which fuel reduction programs assist with bushcontrol:
The first is that it allows fires to be suppressed in the lead-up days to extreme conditions. Firefighters are nearly always overwhelmed when ‘catastrophic’ conditions (i.e.hot, dry, windy weather) strike fires that are already burning in the landscape. The presence of low fuel areas makes it more likely that these fires can be controlled before the catastrophic conditions occur.
The second is that when there are multiple fires on the same day, as occurred during the Cyclone Alby crisis in WA in 1978, fire controllers can set up a “triage” response. Fires burning in 1 or 2 year old fuel can be temporarily ignored, while all the focus is placed on the most threatening fires. This allows the best use to be made of resources.
Regardless of fire weather conditions, to firefighters, fuel load matters. It directly affects fire intensity (heat energy output) around the fire’s perimeter, and the size of the suppression windows in space and time. Also, containment line break outs such as hop overs and spot fires, are much easier to control in light fuels than in heavy fuels.
The fuel load burning behind the flame zone, which is greater in older fuels, is critical for suppression difficulty because total heat output acts in a number of ways. It is an input to convection which increases wind speeds in the flame zone, boosting spotting and fire behaviour. It increases the likelihood of high energy release rates and deep flaming, conditions that can trigger a transition to a dangerous and unpredictable plume-driven fire.
It increases the likelihood of re-ignition and breaching of the containment line by burning across it or by blown embers or by hop-overs. Radiation from glowing combustion adds to the heat load on firefighters and increases the time that the burnt ground can be used for safe refuge. It substantially decreases the effectiveness of water and other suppressants /retardants applied from the ground or from the air. Heavy fuel also hinders fire line construction and in some fuels, make it impractical.
Of the elements that make up the bushfire triangle – fuel, weather and topography – only fuel can be managed. But this must be done the right way – underpinned by good science, well planned and well executed by trained, experienced people who are well resourced. Prescribed burning is costly and comes with an element of risk, but the alternative, a cycle of bushfires, is far more costly to communities and the environment.
Conclusion: The article by Lamont and He in WAToday is not only factually incorrect, it is dangerous and inhumane. If the authorities were to take any notice of their assertions, and curtail the fuel reduction program, the result in WA would be identical to that currently occurring in NSW: death, destruction, heartbreak. Our advice to Lamont and He is to get some actual fire experience in the bush, get on the back of a fire truck, and then let’s see what they think about the value of fuel reduction in assisting with bushfire control.