Underpinnings of fire management for biodiversity conservation in ...

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Researching the effectiveness of aircraft, across a range of fire behaviours, can only be done with
great difficulty, because of the immediacy of operational circumstances and the need to instantly be
available in the right place at the right time during the bushfire season. However, as an alternative
to this, McCarthy and Tolhurst (1998) studied the effectiveness of aircraft in putting forest fires out
early in their development (initial attack) by looking at the influence of fire behavioural circumstances
indirectly – through a knowledge of fuel arrays and weather conditions at the time of fire outbreak.
Their results, expressed in the form of a statistical model, indicated that the probability of successful
suppression was very low to nil when fuels were abundant (i.e. ‘extreme’) and the McArthur forest
fire danger index (FFDI; McArthur 1967) was above 50 (i.e. ‘extreme’). A decrease of overall forestfuel
levels of just one category, however, caused the chances of successful initial suppression to rise
to a maximum of 70% and a minimum of 10% for the same FFDI range. Where fuels were in low to
moderate categories, the success rate under any weather conditions, even the ‘worst possible’, was
modelled as greater than 90%.
The above considerations have not been explicit as to the type or number of aircraft used in any
suppression operation. Loane and Gould (1986) concluded that ‘a combination of helicopters and
agricultural aircraft’ – perhaps supplemented by a large fixed-wing aircraft in ‘very severe fire seasons’
– would be better than the use of ‘any single aircraft type alone’. There will likely be optimum mixes
of aircraft types and capacities for fire suppression operations depending on assets threatened,
budgets, travel distances, water sources, weather, fire circumstances, terrain, and fuel arrays.
In steep terrain the use of machines on the ground is limited, but aircraft may still operate – perhaps
with some support from ground crews with hand tools. It is possible that aircraft could be the
only means available for initial suppression in remote and steep terrain. Helicopters may have an
advantage over fixed-wing aircraft for pinpoint suppression operations of recently ignited fires in
steep country, and the possible follow-up using helicopters to deliver specialist fire crews.
Environmental impact of aerial suppression operations
While there could be an assumption that the use of aircraft in suppression would have no
environmental impact at all, this cannot be sustained. There could be the effects of:
(i) Helipad establishment and operation (Mohr 1994), including service tracks
(ii) Artificial water storage development and maintenance
(iii) Water contaminated with seeds and spores of unwanted species from external sources
(iv) Retardant chemicals and suppressant foams used to aid suppression (Adams and Simmons
1999) – discussed in further detail, below
(v) Spills of chemicals (see Adams and Simmons 1999), fuel and oil
(vi) Depletion of scarce water resources from farm dams.
The first two of these effects are likely to occur in particular sites in the landscape. These sites
could potentially be prime sites for biodiversity. These ‘prime sites’ are not necessarily ‘hot spots’ of
exceptionally high diversity, but may have rare or threatened species present. Given an awareness of
the possibility, sites can be chosen with biodiversity implications in mind. All except the first of these
effects apply to ground-based suppression operations also.
The effects of chemicals added to water to enhance the effectiveness of suppression operations needs
to be quantified (Adams and Simmons 1999). There are two basic types of chemical additives. The
first are the plant fertilisers based on nitrogen, sulphur and phosphorus, like ammonium phosphates,
which retard flaming combustion. Their delivery may be accompanied by thickeners, colouring
material and corrosion inhibitors. Adams and Simmons (1999) describe a variety of types of retardants
and their composition.
Fire and adaptive management Underpinnings of fire management for biodiversity conservation in reserves