Underpinnings of fire management for biodiversity conservation in ...

Underpinnings of fire management for biodiversity conservation in reserves
diet selection and spatial variation to be expressed through probability measures. When the concern is
with hundreds of plant species within an area, rather than a general effect of feed on the growth of
animals, or fuel for fires, a point approach seems appropriate.
Type of animal
Differences in diet have been identified between introduced animals, such as Alpacas (Lama pacos)
and sheep (McGregor 2002); native and introduced species, such as the native Bettong (Bettongia
lesueur) and the introduced Rabbit (Oryctolagus cuniculus) (Robley et al. 2001); and native species,
such as Wallabies (Nailtail Wallaby, Onychogalea fraenata, and Black-striped Wallaby Macropis
dorsalis) (Evans and Jarman 1999). ‘Cattle, goats, kangaroos and rabbits have a different pattern of
selectivity [and] have different impacts on the vegetation …’ (Wilson and Harrington 1984).
Similarities, or partial similarities, in diet may lead to competition for food. A significant conservation
example is that of the endangered Golden-shouldered Parrot (Psephotus chrysopterygius) on Cape
York Peninsular in Queensland: Cockatoo Grass (Schizachyrium spp.), an important seed source for
this parrot, is selectively targeted by feral pigs and is also subject to overgrazing by cattle, thereby
depleting seed production (Crowley et al. 2003, p. 41–42).
While there may be an assumption that only vertebrates need to be considered in terms of removal
of grassy fuels, invertebrates (e.g. termites) can also be important consumers with a similar aggregate
body weight to cattle in the arid zone (Watson et al. 1973). Grasshoppers can be significant
herbivores at times also.
Allcock and Hik (2004) studied the effects of sheep and cattle (exotic), rabbits (exotic) and kangaroos
(native) on the survival and growth of transplanted seedlings of two species of tree and one of
grass, over a period of almost three years. They summed up their results, and perhaps the topic
generally, as, ‘While our study was limited in its ability to tease apart the individual effects of each
herbivore species, it provided substantial evidence that herbivore identity is important in determining
the outcomes of herbivory in multi-species communities, and that these effects vary with habitat
characteristics associated with grassland and woodland communities’.
Intensity of grazing
The intensity of grazing at paddock scale may be controlled by adding or removing domestic animals;
culling feral herbivores, such as rabbits, deer, pigs, goats, sheep, horses, buffalo, cattle, donkeys and
camels; and culling native species, such as kangaroos. A land-use combination of farms and reserves
may increase numbers of [native] kangaroos in reserves, a circumstance that has the potential to increase
grazing intensity in the reserve. Such increased intensity may occur due to the permanent availability of
water in paddocks or the extra feed there. Native animals, such as kangaroos, can potentially overgraze
native-plant communities like those in some of the Mallee region of Victoria, but the situation can also
be confounded due to the presence of rabbits and goats (Sendell 1995).
Kemp et al. (2003) assessed the results of ten livestock grazing experiments in southern Australia,
with up to seven treatments examined over three to four years. Numbers of ‘native [plant] species
increased by 1 or 2 ... where the grasslands were less intensively used … but decreased in more
heavily grazed treatments’. In the high country of south-eastern Australia, Leigh et al. (1987) found
that ‘Rabbits reduced the cover and biomass of 39 species of forb, in some cases to zero’.
The effects of removal of grazing are also pertinent to the understanding of the effects of grazing
intensity. Noble (1997, p. 61) documents the ‘substantial increase in species richness, especially in
terms of perennial grass species … achieved by excluding all vertebrate grazing animals [sheep and
kangaroos presumably] for the last twenty years confirming the overwhelming effects of past grazing
history’ at a site in western New South Wales. Lunt (2005, p. 42) provides examples of a number of
such studies, and points out that palatable weed species may also increase when grazing pressure is
removed.
When indigenous species conservation is the aim of management and diets are selective, the intensity
of grazing needs to be determined in relation to the species of concern. In relation to fuel, intensity
Fire and adaptive management 65