Underpinnings of fire management for biodiversity conservation in ...

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of grazing needs to be determined with respect to species which contribute the bulk of the fuel (‘fuel
species’; Gill 1999a), and at larger scales than for relatively rare species. In simple terms, when the
palatable species have been consumed, animals turn their attention to less and less palatable species,
‘when these minor species had been consumed, sheep were forced to eat the dominant grasses’
(Leigh and Holgate 1978). The intensity or grazing varies with palatability and may be seen to apply at
a point scale. In Leigh and Holgate’s example, at first the grazing intensity was relatively high for the
minor species, but very low for the dominant species.
Interval between grazing events
At the paddock scale, the interval between grazing events can be measured by the timing of
livestock additions and removals each year. The interval may be rated as short term or seasonal,
measured in days or months. As with Tscharke (2001) – noted by Lunt (2005) – long-term outcomes
are unavailable as yet. The interval for an individual resprouting plant – considered to be at a point
– may be measured in days, weeks, months or years. As with intensity, interval may be determined
differently according to the purpose of the measurement.
If the dominant species, a fuel species, of a natural sward is the most palatable to domestic stock,
while the lesser ranked species are less palatable, then the periodic removal or reduction of the
shoots of the dominant may be beneficial for conservation and fuel minimisation. This may have been
the case with Themeda pastures in Victoria where periodic, high-frequency (short-interval) burning
favours the expression of a variety of herb species, while not eliminating the dominant (Lunt and
Morgan 2002). However, the palatability of Themeda to domestic stock, probably under continuous
grazing, may have led to its demise over wide areas, as surmised by Moore (1962) and supported by
subsequent studies, including those of Fensham (1998) and Allcock and Hik (2004).
The effects on palatable and non-palatable (fuel) species at point, patch or paddock scales merge
when large numbers of animals are imposed on the vegetation for short periods. In this case, the
shoots of the more palatable plants are quickly removed. The animals then concentrate on the
less palatable materials and may remove them before the shoots of the palatable plants recover
sufficiently to again be available for grazing. It has been argued that this sort of treatment would
have the minimum adverse conservation effect and maximum fuel-reduction effect, but the resilience
and relative palatabilities of the species present in any local area would need to be taken into account.
Furthermore, other potential adverse effects associated with the presence of the animals would need
to be considered, including the creation of areas of nutrient concentration (‘camps’), exposure of the
soil to erosion, ringbarking of trees by rubbing, trampling effects, fouling of water bodies and the
promotion of unpalatable or highly resilient exotic species.
Seasonality of grazing
‘Poa annua [an exotic grass] was positively affected by past grazing in spring, and negatively affected
by past grazing in summer’ (Kirkpatrick et al. 2005).
‘Seasonal effects’ may be seen as an interaction between herbivores of various type and the feed
on offer. Different plant species have different palatabilities and accessibilities at different stages
of the year and at different times in the life cycle. Young succulent shoots of grasses have a higher
palatability to many animals than coarse dead stalks. Flower heads or seeds that appear seasonally
can be preferentially selected (as by rabbits in subalpine vegetation of New South Wales, see Leigh et
al. 1987), a circumstance that may have consequences to plant reproduction in the short- and longterm.
Thus if animals are introduced to an area for short lengths of time at different times of the year,
the results could be different for different plant species.
Whalley and Lodge (1986) set out to manipulate pasture species’ composition through livestock
grazing in order to favour a ‘desirable’ native grass in a grazing system – Danthonia linkii. They
succeeded by using heavy summer and early autumn grazing and then light winter and spring
grazing. Sheep were more effective than cattle. The idea was to manipulate the grazing regime to
minimise adverse effects on the desirable Danthonia and maximise adverse effects on an undesirable
native grass, Aristida ramosa.
Fire and adaptive management Underpinnings of fire management for biodiversity conservation in reserves