Underpinnings of fire management for biodiversity conservation in ...

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The first proposition examined considers that access to all points (corners and intersections of lines)
in the study area (Figure 2.4) is necessary for effective fire control – a reliance on aggressively and
quickly getting on top of the fire and putting it out. Later, suggestions will be made about aggression
being directed to the fire rather than the land – minimum impact suppression tactics or M.I.S.T. (Mohr
1989) – including the perceived use of aerial instead of ground suppression. In this example, access
to all points at minimum cost is desired; the usual expectation and the one to which attention is first
directed. The example quickly shows the inadequacy of considering minimum length alone, and the
importance of other variables.
In Figure 2.5, a sample square cell from the study area (Figure 2.4) is used to illustrate ways in which
access to all points could be reached. Which has the minimum length and, by implication, minimum
cost? A unit of track length is set as the length of one side of an individual cell.
a b
c d
Figure 2.5 Four options for tracks reaching all corners of a sample cell of dimensions L by L units within a square-grid study
site: (a) perimeter track has length 4L; (b) all points are reached with a track length of 3L; (c) tracks totalling 2.83L cut across
the cell – 94% the length of the track in (b); (d) sketch of the minimum length of tracks reaching all points (Stewart 1997, pp.
287ff), 2.73L – 91% of the length of track in (b).
Notice the savings in length as one goes from Figure 2.5 (a) to (b) – perimeter tracks – to (c) and
(d) – a spanning tree and Steiner tree, respectively (Stewart 1997, pp. 287ff). The minimum length is
(d), the Steiner tree, where the angle made by the intersecting arms of the tracks is 120 o (Brazil et al.
1997; Stewart 1997, p. 287ff). While example (d) shows a saving of only 9% over (b), the value of
this saving increases as the number of cells increases.
Fire and adaptive management Underpinnings of fire management for biodiversity conservation in reserves