Underpinnings of fire management for biodiversity conservation in ...

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Environmental effects of grazing
The environmental effects of grazing are readily observed. Differences in vegetation across fence
lines are sometimes marked in terms of biomass, structure, composition and colour (due to curing,
flowering, growth stage or composition). While the causes of these changes can be confounded with
other treatments, such as fertilising, sowing, harrowing and herbiciding, enough evidence can be
seen close to the fence to indicate when changes are largely due to grazing.
This is not an attempt to comprehensively review the literature on the effects of grazing; rather the
purposes are to provide examples of grazing effects and to elicit principles. Recent overviews of the
impacts of grazing by domestic animals on biodiversity in Australia include those by Dorrough et al.
(2004), Lunt (2005) and Lunt et al. (2007). Caution is required because, as Dorrough et al. (2004)
points out, ‘We still have only a very basic understanding of the effects of different grazing strategies
and pasture management on biodiversity’.
Information on the effects of grazing
The main sources of information about grazing effects are:
• Historical observations – ‘A striking effect of the wool industry on Australian vegetation has
been the virtual elimination of T. [hemeda] australis’ (Moore 1962). Moore also noted, ‘The trend
under grazing [by exotic animals] is towards communities of short-lived alien species’. Woinarski
and Fisher (2003) quote Finlayson (1945) as saying, ‘It is not so much, however, that species are
exterminated by the introduction of stock, though this has happened often enough, but the
complex equilibrium which governs long established floras and faunas is drastically disturbed or
even demolished altogether’. Lunney (2001) attributed the extinction of 24 medium-sized mammal
species in western New South Wales during the first 60 years of settlement – ‘the greatest period
of mammal extinction in Australia in modern times’ – to the presence of ‘sheep, and the way that
the land was managed for the export wool industry’.
• Historical legacies – quantitative studies of the effects of grazing practices (including burning) have
been carried out in north-eastern New South Wales by Henderson and Keith (2002) and Tasker
and Bradstock (2006); quantitative comparisons across different land tenures that have historically
experienced different, unknown grazing regimes, such as paddocks, roadsides and reserves (e.g.
Prober and Thiele 1995).
• Observations made across fence lines (Noble 1997) or at camping spots, sheltering spots, dung
heaps (for certain species), watering points and yards compared with areas outside them. Moore
(1962) noted that in sheep ‘camps’ there was an increase in the exotic genera Marrubium
(Horehound), Urtica (Stinging Nettle) and Onopordon (Scotch Thistle). The effects of different
historical grazing regimes have manifested in spring in Canberra, ACT, where massive blue
flowerings of the exotic Patterson’s Curse (Echium plantagineum) can occur in paddocks grazed by
domestic animals. In contrast, across the fence and along the adjacent roadside, numerous yellow
flowers of the native Bulbine bulbosa and the absence of Echium have been seen (Plate 4.2). In
farm surveys Reseigh et al. (2003) found that ‘the never grazed and infrequently grazed sites had
significantly higher native species richness than grazed sites’. Driessen et al. (1990, pp. 75–76)
showed that the greater the intensity of grazing by stock, the fewer the number of indigenous
Tasmanian Bettongs (Bettongia gaimardi) found (as indicated by their diggings).
• Direct observation of diet – bite rates for sheep and goats in a Mediterranean shrubland were
directly observed by Papachristou (1997).
• Measurements made at different distances from water sources (Landsberg et al. 1997) or from
intensively grazed areas, such as near rabbit burrows (Leigh et al. 1989).
• Experiments – ‘Rabbits reduced the cover and biomass of 39 species of forb, in some cases to zero’
(Leigh et al. 1987; Plate 4.3). In the studies analysed by Kemp et al. (2003), ‘where the herbage
mass was maintained between 2 and 4 t DM/ha [dry matter per hectare] then species were
maintained and productivity [for sheep] was optimised’.
Fire and adaptive management Underpinnings of fire management for biodiversity conservation in reserves