The Truth About Fuel Reduction Burning

In the aftermath of the disastrous 2019/2020 fire season in the Eastern States there have been many examples in the media of personnel associated with State fire suppression agencies, as well as academics, putting forward their theories concerning the role of fuel reduction burning (aka prescribed burning). Their theme has been “fuel reduction burning did not stop the bushfires, so it is of no use in fire management”.

These comments have been made by people with apparently little no understanding or operational experience of bushfire behaviour, prescribed burning and bushfire suppression. These critics include academics who dabble in fire management from their ivory towers. Very few of them know anything at all about the realities of bush fire management. Their baseless opinions, if given credibility, will give rise to very dangerous bushfire management policies, a continuation of an increasing cycle of devastating bushfires and further losses of lives, properties and beautiful forests.

Prescribed burning is not designed to stop wildfires. 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.

What they claim is garbage. And here is the proof. The graph below is the result, not of junk science modelling, but of real data gathered from almost 60 years of historical data from the forests of south west WA. These data unequivocally show that when the area of prescribed burning trends down, the area of uncontrolled bushfires (wildfires) trends up. There is a simple explanation: bushfires are more difficult to put out in long-unburnt, heavy fuels. The area annually burnt by bushfire escalates exponentially when the area of prescribed burning in a region falls below 8 percent per annum. Burning about 8% per annum results in about 40 % of bushland carrying fuels 0 to 5 years old.

The graph below shows how effective the prescribed burning is in preventing large damaging bushfires.

 

Proportion of the SW forest region (2.5 M ha) burnt by prescribed fire (mean of 4 yrs) with proportion burnt by wildfire (mean of succeeding 4 years) (Source: Sneeuwjagt 2008 + updates to 2016/17).

A very powerful factor in the 2019-2020 bushfire tragedies in NSW and Victoria is the fact that prescribed burning in these states has on average amounted to less than 1.5% per annum. This means only about 8% of the bushland is carrying fuels 0-5 years old. Therefore, outside of bushfire affected areas, about 85% 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.

To be effective, prescribed burning needs to be done across the landscape, over all land tenures – national parks, nature reserves, state forests and private property. The key to successful fire management is active management across the whole landscape.

It must also be :

  • Strategically planned to protect forests, communities and other high value assets by intercepting fire runs under the most severe weather conditions. Burns must be bounded by roads or tracks to enable rapid access by ground forces.
  • Done in sufficiently large cells, at least several thousand hectares, to be effective in retarding and controlling large bushfires.
  • Cover at least 8% of the bushland in a region every year with the aim of ensuring that at least 40% of the bushland in a region carries fuels less than 6 years old
  • Done to appropriate standards of fuel removal and fire intensity/ burns that are too patchy (less than 60% burnt) may not slow an intense bushfire

In mixed forest types multiple ignitions may be required to achieve a satisfactory burn coverage in each cell of greater than 60 percent.

It is crucial that fuel reduction burning is not confined, as some suggest, to a fringe buffer around developed areas. To do so would consign the bulk of Australia’s forests to a never-ending cycle of disastrous bushfires. A large, fast moving bushfire can send burning embers to start spot fires at least 10 km ahead of the fire front, and so such a buffer zone would be ineffective.

Critics of prescribed burning argue that no amount of fuel reduction burning would have restricted the 2019-2020 high intensity bushfires burning under extreme fire weather conditions. This may be true where fuel reduction burns are too narrow, small and patchy and therefore easily overwhelmed by large conflagrations.
Severe 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 wildfire control. 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. gale force winds) 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.

We know of dozens 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.

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 can be costly and comes with an element of risk, but the alternative, a cycle of massive bushfires, is far more costly to communities and the environment.

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