Underpinnings of fire management for biodiversity conservation in ...

48
What is actually achieved in the field depends on conditions that prevail during the burning operation.
For the improvement of later operations, assessment and evaluation of each burning event in relation
to objectives, field conditions and logistics is necessary. Poor weather may hamper operations and
heterogeneity in fuel moisture may impede fire spread or prevent it in parts of the burn area. Such
factors may lead to a lesser amount being burnt than intended. Mapping of outcomes (Heemstra
2006), in terms of unburnt areas and those burnt with various intensities, would be a useful part of
assessment of the success of the event, let alone for ecological reasons.
Prescribed burning may be used to create linear buffer strips by dropping incendiary capsules from an
aircraft in a line, then relying on the timing and placement of capsules to allow fires to join but then
extinguish at night or when they reach natural and artificial barriers. This process can be particularly
effective in tropical savannas (Crowley et al. 2003, p. 52).
While the protection of economic assets is often a prime objective in prescribed burning, it may be
carried out for ecological reasons too (Fire Ecology Working Group 2004). The trend seems to be for
more control of fire regimes for ecological purposes (Esplin et al. 2003, p. 115).
Assessing the effects of burning on fuel
In the previous section, the detailed objectives for prescribed burning events were given. The purpose
of this section is to look at questions pertaining to the effectiveness of reducing, or otherwise
modifying, fuel as an issue in itself, not in relation to wider questions of, say, threats to biodiversity
conservation or to property.
Fuel modification can be examined in isolation or in a specific context, such as that of the urban
interface (e.g. Bradstock et al. 1998b). Calculation of the risk of unplanned fire and its cost (e.g.
economic, environmental and social), may help the manager decide whether or not the cure (fuel
reduction) and its cost is worse than the disease (high fuel loads). In practice, monitoring the
effectiveness of fuel-modification measures should be undertaken in relation to outcomes (especially
social and environmental), not just in relation to fuel loads or scores.
If the fuels, such as some dominated by grasses, return to a level unacceptable to managers within
one year, then burning or other means of fuel modification are necessary every year; if the effects of
this situation are to be avoided. Frequent burning may reduce the chance of shrubby fuels dominating
the grasses and changing the fuel load and structure in the longer term. In an international review
of prescribed burning emphasising forests, Fernandes and Botelho (2003) concluded that ‘Fuel
accumulation rate frequently limits prescribed burning effectiveness to a short post-treatment period
(2–4 years)’. However, what happens in particular areas depends on local fire weather, growing
conditions, species present and suppression capacity, for example.
The most recent work on fires in Australian forests, by Gould et al. (2007, p. 79), emphasised both
loads and structure in assessing the effects of fuel reduction by prescribed burning on fire behaviour.
These authors suggested that in the Jarrah forests of Western Australia the effects of prescribed
burning on future fire behaviour may last for 10–15 years. However, because only the bark on the
lower parts of the tree bole are affected by low intensity fires (p. 114), bark characteristics on upper
boles will continue to change in a way that favours the development of fire brands and spot fires.
Consequently, they argue, ‘There may be a good case for alternating mild spring burns with hotter
autumn burns’ (p. 79).
In grasslands, thresholds for fire control are unknown, although the discussion of fuel-break width
provides some leads (Chapter 2). If a threshold fuel load can be identified, then some indices of
effectiveness, or lack of it, are:
• The time (years) the fuel load is above the threshold as a proportion of the interval between fires
• The cumulative sum of the weight of fuel each year it is above threshold loads
• Potential maximum fire intensity.
Fire and adaptive management Underpinnings of fire management for biodiversity conservation in reserves