Literature review: Impact of Chilean needle grass ... - Weeds Australia

1995d p. 280). Rabbit grazing preferences reportedly result in increases of less palatable grasses and weeds (Frith 1973). In the
Riverina the combined effects of rabbit and sheep grazing “practically eliminated” T. triandra (Lunt et al. 1998). Annual grasses,
such as Hordeum spp. often proliferate where rabbit damage has been severe (Bloomfield and McPhee 2006).
Rabbit grazing is a recognised threat to a range of endangered vascular plants in temperate grasslands. These include Senecio
macrocarpus (Hills and Boekel 1996 2003) and Comesperma polygaloides (McIntyre et al. 2004). Grazing by rabbits or
European hares Lepus capensis L. is a threat to remnant populations of Swainsona spp. in the Wimmera and Northern Plains of
Victoria (Earl et al. 2003). Thesium australe, once common in grasslands, is also threatened by rabbits (Archer 1984).
Rabbit grazing, like that of bovid livestock, can also be beneficial by reducing cover of grasses. Lunt (1990d) thought it may
have contributed to the high richness of vascular plants in herb-rich woodlands he surveyed in western Victoria.
Rabbits and the rabbit industry had a severe impact on grassland animals. Large number of bandicoots were killed in rabbit traps,
by poisoning, and the fumigation and ripping of burrows and the spread of rabbits probably assisted the proliferation of foxes,
which after the introduction of myxomatasis in the early 1950s, had to switch their prey preferences to include a larger
proportion of native animals (Brown 1987). Paradoxically, for a time, the availability of rabbit burrows for shelter may have
aided the survival of the Eastern Barred Bandicoot Perameles gunnii Gray after destruction of tussock grass cover (Brown 1987).
Rabbits “not only till the soil they fertilize it as well” (Bloomfield and McPhee 2006 p. 150): rabbits displace large quantitites of
soil by digging, create bare areas around their warrens and deposit large quantitites of dung at discrete latrine sites, which
become nutrient enriched. These areas seasonally support dense patches of weeds and can function as establishment foci for new
weeds (Hobbs 1989, Bloomfield and McPhee 2006).
Rabbit plagues accompanied by livestock grazing have severely affected grasslands in the Victorian Wimmera and Murray
Mallee (DNRE 1997) and overgrazing by rabbits is still a problem in native grasslands west of Melbourne (Brereton and
Backhouse 2003) and elsewhere.
Hares select higher quality food than rabbits, consume much more food per unit body weight and produce much more faecal
material, but have relatively smaller stomachs and caeca and retain a significantly smaller proportion of poorly digestible
material (Stott 2007). They forage much further from cover than rabbits (Stott 2007). European hares were introduced into
Victoria in the 1870s and spread through much of south-eastern Australia “particularly in the better-grassed areas” (Frith 1973 p.
81). In the Glen Innes area of the Northern Tablelands the first sightings occured in 1889, numbers increased steadily through the
1890s with a bounty first offerred for scalps in 1893, but populations declined and ceased to be problematic by 1920 (Cameron
1975). A bounty was offerred in the Armidale district by 1902 and scalp returns peaked in the middle of that decade, decling to
c. 30,000 by 1914 when the bounty was removed due to budgetary problems (Johnson and Jarman 1975). The grazing habits of
hares in Australia have not been studied (Frith 1973, McDougall and Walsh 2007).
Marsupials
South-eastern Australian grasslands were once occupied by a diverse array of marsupial herbivores (see section below on the
mammalian fauna of grasslands) of which nearly all are now absent. Little is known about the intensity or nature of marsupial
grazing (Ellis 1975, Morgan 1994). Moore (1993 p. 351) stated that southern Australian T. triandra grasslands “evolved under
light and intermittent grazing by native marsupials”, but this statement conceals a pronounced level of ignorance and is probably
a misleading generalisation. Marsupials would have consumed significant quantities of plant material and maintained a much
more rapid and patchy cycling of nutrients than occurs today in ungrazed grasslands (Flannery 1994). Kangaroos would have
been very numerous, particularly in areas with adjacent tree cover (Willis 1964, quoting George Russell, an early settler). Early
historical records in Tasmania describe ‘marsupial lawns’ created by heavy marsupial grazing, and such closely grazed areas
exist today in areas where large numbers of Macropus spp., Thylogale billardierii (Desmarest) and Vombatus ursinus (Shaw)
occur, as well as in areas grazed both by sheep and marsupials (Kirkpatrick 2007).
Little information appears to be available about the ecological functioning of marsupial grazers in native grasslands and their
impact on exotic grasses. Ellis (1975) mentioned studies in north-eastern NSW that found that nine sympatric species grazed
both native and introduced plants and maintained niche segregation by differences in habitat utilisation. Cameron (1975 p. 20)
reported that kangaroos in the Glen Innes area of the Northern Tablelands “seemed to prefer the green shoots on the kangaroo
grass in the late spring and summer”, but there were “signs that [they like] the imported grasses and ... numbers will increase” (p.
24). Robertson (1985) investigated the interactions between the most important and widespread of the extant marsupial
herbivores, the Eastern Grey Kangaroos Macropus giganteus in open grassy woodlands at Gellibrand Hill, Victoria. The diet of
M. giganteus was found to consist almost entirely of monocots, mainly grasses. Green shoots and new growth were selectively
eaten and the species selected tended to be those with the highest nutritional value at a particular time. From late spring to
autumn T. triandra was by far the most important dietary constituent, but other warm season grasses were also eaten. Cool
season grasses were the main forage during other periods, with Austrodanthonia spp., Microlaena stipoides and a range of exotic
species being the most important. Grass inflorescences were readily consumed, particularly those of the exotics Lolium rigidum
and Briza maxima L., but species with long awned and sharp seeds such as Austrostipa spp. and T. triandra were usually
avoided. Poa sieberiana Spreng. and Austrodanthonia spp. , both large grasses with relatively fine leaves, were largely avoided
once they developed large amounts of attached dead litter, but T. trianda plants with high standing litter were not. Burning
provided more palatible and accessible fodder. McIntyre (1995) noted that grassland sites in National Parks on the Northern
Tablelands of NSW were rich in native vascular plant species, because they had marsupial grazing, an effect resulting from
release from competition with the dominant grasses (Morgan 1994). Lunt (1990d) thought kangaroo grazing may have
contributed to the herb richness of woodland vegetation in the Grampians and Langi Ghiran in a similar way. Murphy and
Bowman (2007) referred to a study in semi-arid western NSW which found that 16 months post-fire, areas burnt but ungrazed by
kangaroos had four times the abundance of Austrostipa variabilis (Hughes) S.W.L. Jacobs and J. Everett than areas that were
kangaroo-grazed, suggesting a feedback loop between fire, kangaroos and the dominant grass.
The toes of macropods are padded and soft in comparison with the feet of bovid livestock, and extant large macropods have
masses much less than cattle (large male Macropus giganteus 80 kg: Hume et al. 1989) and more comparable with sheep. They
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