Underpinnings of fire management for biodiversity conservation in ...

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Indirect effects of grazing
There are less direct effects of grazing. Grazing can affect biodiversity by reducing soil productivity
(Friedel and James 1995). Excessive grazing can remove vegetative cover, thereby allowing wind
erosion, loss of productivity, loss of soil seed and loss of safe sites for seed lodgement (see Noble
and Grice 2002). Carr (1962) noted that shrubs in the high country of Victoria were not affected
by grazing per se, but by trampling. Eldridge and Rath (2002) found that kangaroos in semi-arid
woodland in western New South Wales affected soil properties by creating frequent shallow hollows
– hip holes – thereby considered ‘important elements in the maintenance of heterogeneity’. Hobbs
(2001), in reviewing practices in south-western Australia, found evidence for substantial effects
of trampling by livestock, as determined by increased soil density and decreased infiltration. The
presence of cattle in the high country of south-eastern Australia, through the alteration of drainage
patterns in bogs and wetlands, may have altered the habitat of indigenous plants and animals
(Ashton and Williams 1989). The effects of naturalised Water Buffalo (Bubalis bubalis) in the Northern
Territory included ‘accelerated soil erosion, channelling of floodwaters, saltwater intrusion … and
reduction in the diversity and abundance of wetland flora and fauna …’ (Corbett 2004).
Seed transport is another less direct aspect of grazing. Jolaosho et al. (2006) contrasted the seed
carriage of cattle, sheep and goats in a field experiment on native pastures in Nigeria – in terms of
numbers of seeds per gram dry weight of faeces, germination rates of voided seeds and numbers
of species of voided seeds. Cattle had the highest number of seeds per gram dry weight of faeces
(1.8), and sheep the least (0.4). However, germination rates were least for cattle (5%) and similar for
sheep and goats (32 and 28% respectively). Cattle excreted the highest richness of seeds (13 spp.),
while sheep and goats voided nine and five species, respectively. Thus effects of grazing can be more
substantial and subtle than the effects of herbivory.
Effects of grazing on vegetation types
For various Australian vegetation types, the negative effects of grazing by livestock or feral vertebrates
have been described as follows:
• Mallee vegetation – Parsons (1981) stated, ‘It is clear … that the most serious single threat to
the future regeneration and conservation of mallee vegetation is the destruction of seedlings by
grazing [feral] rabbits. Unless controlled, rabbits will certainly lead to the eventual disappearance of
numerous species and communities’.
• Desert communities – degradation is attributed to ‘over-use … by domestic livestock as well as
by uncontrolled grazing of feral animals, such as rabbits, horses, donkeys, camels and goats’
(Cunningham 1981).
• Alpine/subalpine vegetation – ‘the practice of summer grazing of sheep, cattle and occasionally
horses for a period of more than 50 years, combined with the associated practice of burning off’
had consequences such that ‘Plant cover was reduced, soil erosion promoted and some plant
species … became rare and disappeared locally’ (Costin 1981).
• Natural grasslands – Groves and Williams (1981) suggested that ‘Substantial differences in stocking
rates (sheep and cattle per unit area per year) cause some differences in botanical composition but
usage has to be severe and prolonged for permanent changes in vegetation to occur’.
• South-western Australian woodlands – Hobbs (2001), in reviewing the effects of livestock grazing,
pointed out that the ‘most obvious changes were in understorey composition, with a reduction
or removal of the native shrubs and herbaceous perennials’ and increases in cover of non-native
plants.
• South-eastern Australian grassy woodlands – Prober and Thiele (1995) concluded that, ‘For the
maintenance of native plant diversity and composition in little-grazed remnants, it is critical that
livestock grazing continues to be excluded’.
• Eucalypt-dominated dry forests and woodlands in Victoria – regular livestock grazing reduced the
probability of finding eucalypt regeneration (Dorrough and Moxham 2005).
Fire and adaptive management Underpinnings of fire management for biodiversity conservation in reserves