INDUSTRY & RESEARCH
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litter, but you may actually promote more
flammable, short-lived plants.
So you may actually perversely increase
the fuel. But the fuel is a different type.
It’s living material, but under extreme fire
weather conditions that fuel becomes
available. And we’re still trying to discover at
what point a living plant becomes fuel, and
at what point it becomes a barrier to fire.
And that then leads to the next problem.
So does fuel reduction work or not?
There’s a debate about that, and you’d
say, “Well, how’s it possible that it could
be ambiguous? One study could show it
works, but another study could show it
doesn’t work. Why would that be?”
The explanation for that is the
contingency of weather conditions.
Because under extreme weather
conditions, there are phenomenally high
temperatures, strong winds and antecedent
drought. What ends up happening is pretty
well everything is burning, everything is
becoming available to burn.
That’s why it can race across heavily
grazed paddocks, because the organic
matter on the surface layer of the soil can
burn. The fire is being driven by literally
billions of embers, which are just exploring
the landscape to find carbon-based fuels
to burn.
In those conditions, the benefit of fuel
reduction seems to evaporate because you
don’t get a perfect reduction of fuel – it’s a
reduction, not an elimination. Imagine an
atomic bomb on vegetation that vaporises
everything and fuses the soil into glass.
That would probably be an example of the
complete and utter removal of all fuel.
Some of the very high severity fires are
pretty well atomic bombs, but they’re
very localised, and that’s where that
habitat complexity comes in. One of the
misnomers that has occurred with this fire
season is that people have looked at the
jaw-dropping perimeters and extrapolated
in their mind that the entire area inside that
fire is like being hit by an atomic bomb.
And even, say, in the south coast of NSW,
where there were these truly mind-bending
fires, there are actually large areas of the
landscape that were more moderately
or lightly burned. So it’s way more
complicated.
With fuel reduction burning, there’s
always going to be a residual amount of
fuel that, under extreme conditions, can
burn. And even fires of the most extreme
sort, which we’ve seen in southeastern
Australia, the pyrocumulonimbus, which
coupled to the stratosphere and are really
honorary atomic bombs, but they are
actually localised elements in larger fires.
So the bad news is that even those
firegrounds have been burned by wildfire,
which is way more intense than a fuel
reduction burn, they will become available
for burning again quite soon.
So that explains the reason why there’s a
debate about prescribed burning, because
it’s contingent on the sort of fire conditions
and on the fire weather conditions. In other
words, a moderate prescribed burn, which
is controllable, will leave a fair bit of fuel
behind. Under moderate fire conditions,
that will result in a moderate fire, but under
catastrophic fire conditions that could
sustain a catastrophic fire.
And the problem is that you may be
creating more fuel types by frequent hazard
reduction burning. So it’s a very complex
and nuanced topic. And a lot of people just
don’t understand that. They’re seeing it in a
very simplistic view, that fire managers turn
fuel on and off.
Can you explain the idea of there being
a trade-off with controlled fire burning and
the carbon emissions that can be released
from that, versus the emissions from
a wildfire?
It’s a hugely complicated, mind-boggling
question. And I just want to jump back
to that point about firebreaks. Because
in certain systems which are burnt very
frequently, namely tropical savannas, you
can see the effect of prescribed burning,
changing fire behaviour by creating
firebreaks, because you’re burning early in
the season to deny a fire late in the season.
That’s how it works.
So the idea is you apply fire early and
create burnt areas. You’ve burnt up the fuel,
which is grass, and that creates a barrier for
a fire later in the year. So that’s where most
of the carbon abatement programs have
been focused. And the idea there is that
the fires in the early part of the dry season
are less intense. They are less efficient at
burning, particularly the woody fuels. So
they’re emitting less greenhouse gases.
So the idea is – and I would argue that
it’s not a completely perfect or proven
idea – that if you can do this sort of fire
management, you could end up with this
benefit or reduction of emissions.
With the eucalypt forests in southern
Australia, it’s much more complicated. The
objective is not to create firebreaks like you
can do in the tropical savannas, but it’s
actually to reduce fuel loads.
If you do a lot of prescribed burning,
you’re getting lots of packets of low smoke
emissions, low greenhouse gas emissions.
But lots of them versus not many but very
extreme wildfires that put out a gigantic
pulse of smoke and a gigantic pulse of
greenhouse gas emissions.
And the question is, can you see the
benefit from those two strategies? And as
far as I know, nobody’s really certain of
this because the trade-offs are not really
well understood. But if you say, oh well,
you do lots and lots of prescribed burning,
you’re going to reduce a damaging wildfire;
therefore, you’re going to have less carbon
emissions. But you go, hang on – you’ve
got to add up all of the emissions from
your prescribed burning. Does that actually
end up being about equal to the amount
of smoke and the amount of greenhouse
gas emissions you’re going to get from
a wildfire?
The other complexity with this is
that, again, one of the intellectual traps
of thinking about that trade-off is that
you’re representing the wildfire as the
most extreme element tile of a wildfire
fireground. And in fact, as it turns out, if you
look at the fire severity maps, absolutely
huge areas got burnt in NSW particularly.
But the thing is, a lot of them were really
just gigantic prescribed burns. That’s all.
They were quite low intensity, but much of
the time they were just very big.
You can’t just represent a wildfire as the
maximum amount of greenhouse gas
emissions and the maximum amount of
smoke, because there’s a lot of variability.
There are days where they’re emitting, say,
10 times more than a prescribed burn per
unit area. But there are many, many days
in the life of a wildfire which are actually
identical to prescribed fires. They’re doing
exactly what a prescribed fire is doing.
So how do you work out that trade-off
and add up over the course of 10 or 20
years the balance between the greenhouse
gas emissions?
You’ve also got to factor in tree mortality
and tree recovery. And nobody knows the
answer to this.
It’s a really interesting research problem.
I think Dr Owen Price of the University of
Wollongong was saying that when you
actually look at it overall, it basically comes
out to be about the same. n
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