Underpinnings of fire management for biodiversity conservation in ...

Underpinnings of fire management for biodiversity conservation in reserves
on rate of spread and/or suppression difficulty in eucalypt forests. The Overall Fuel Hazard1 (OFH)
Guide (McCarthy et al. 1999a) provides an overall rating system for the fuel array based on Wilson’s
concepts.
Following the trend for fuel rating, described above, Gould et al. (2007, in Table 3.2) have depicted
forest-fuel arrays in south-western Western Australia and given ratings a numerical score. In doing
this, their aim was to develop a better understanding of the way in which fuels in different parts
of the array affected fire behaviour in the dry eucalypt forests of their study. They described their
fuels in relation to five layers within the forest: surface, near surface, elevated, intermediate and
overstorey (pp. 17–20). Bark was the predominant fuel of the intermediate and overstorey layers. A
‘combustibility score calculated from the sum of the products of hazard score and cover in each of the
five fuel layers’ was correlated with rates of spread of their experimental fires (p. 73). However, their
final rate of spread model used the variables wind speed, ‘fine-fuel moisture function’, ‘surface fuel
hazard score’, ‘near surface fuel hazard score’, ‘near surface fuel height’ and slope (p. 91).
From the above consideration of forest fuels, the value of the structural approach is apparent. There
may be further issues to resolve in terms of thresholds and contingencies – as in Wilson (1993) where
4 t ha-1 was a precondition for overall fuel rating – and the weightings given to each of the layers
of a forest (Gould et al. 2007, p. 30). What is apparent is that there is considerable overlap in the
attributes that are important to habitat (for certain animals) and fire behaviour (for determining rate
of spread or degree of suppression difficulty), and vegetation classification also. Managers seeking
to keep track of both habitat and fuels may choose to rate or measure attributes at the same sites in
order to minimise the effort needed to monitor them. Table 3.1 compares attributes of the HCS, OFH
and the vegetation classification scheme of Specht (1970).
The use of profile diagrams to depict fuel arrays, habitat and vegetation change may be worth
exploring. For example, the initiatives for depicting fuels described above could be supplemented
using the profile diagrams, such as those of Walker and Penridge (1987). In this way, the vertical
profile of fuels could be depicted in terms of the variation of cover and fuel load and type with
height, in particular. Profile diagrams could provide a visual image of changes with time. Their use
would facilitate the recording of fire occurrence and severity at monitoring stations (taking severity
to be a measure of post-fire scorch (fire-browned leaves), fire defoliation (black canopy), intact green
canopy and bark char; thereby forecasting scorched-leaf fall, bark shed in smooth-barked eucalypts
and branch contribution to post-fire fuels and nutrient cycling.
Table 3.1 A comparison of the component variables of the Habitat Complexity Score (Newsome and Catling 1979), Overall Fuel
Hazard (McCarthy et al. 1999a), vegetation classification (Specht 1970) and a potential vegetation-profile method (after Walker
and Penridge 1987) for Australian forests. Attributes used for each purpose are marked with a ‘+’.
Attribute
Vegetation
classification
Habitat
complexity
Score
Overall fuel
hazard
Fuel-profile
diagrams
Bark type and condition – – + +
Ground herbage cover or near-surface fuels + + + +
Litter depth/cover/loading – – +
Logs, rocks, debris etc – + –
Moisture in the soil – + –
Shrub canopy cover + + + +
Shrub canopy height + – + +
Tree canopy cover + + – +
Tree canopy top height + – – +
1 Fuel hazard may be considered a misnomer as fuel per se is not a hazard until it supports a fire that threatens specified assets (Esplin et al.
2003 p. 76).
Fire and adaptive management 45