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

pyramidata (Benth.) P.G. Wilson and M. sedifolia (F. Muell.) P.G. Wilson that were originally dominant over most of the area,
and resulted in their replacement by low-growing, spiny, unpalatable Sclerolaena spp., or by “degraded grassland vegetation ...
of annual, and to a lesser extent perennial, grasses and herbs”. Kirkpatrick et al. (1995) thought that the original vegetation
before livestock grazing might best be characterised as chenopod shrubland with a grassy ground layer, and suggested that
drought, fire or rabbit grazing may have destroyed the original shrubland, rather than livestock grazing which merely prevented
regeneration of woody species. According to Moore et al. (1973 p. 236) no stands of the original vegetation then existed, but
observations suggested that the trees had been up to 9 m high, the shrub layer was well-developed but discontinuous, that
Atriplex predominated on grey and brown clay soils and the Acacia was dominant on red-brown earths. The other main shrubs
were the chenopods Rhagodia spinescens R.Br., Enchylaena tomentosa R.Br. and M. aphylla. The grassy ground layer varied in
composition according to soil texture. Chloris truncata and Austrostipa “variabilis” (= A. scabra/A.nodosa) were then common
on light-textured soils. Austrodanthonia caespitosa and C. truncata were the main species on clays, although Austrostipa
artistiglumis was probably once more common or dominant. Leigh and Mulham (1965) considered the latter species to be found
on most soil types and to often occur in dense, localised stands. Other common and widespread native grasses included Chloris
ramosus B.K. Simon, Eragrostis spp., Eriochloa pseudoarcrotricha (Stapf ex Thell.) J.M. Black, Panicum spp., Sporobolus
caroli Mez, (Leigh and Mulham 1965). Other common native species included Bulbine bulbosa (R.Br.) Haw., Lomandra effusa
(Lindl.) Ewart, Hypoxis glabella R.Br., other Atriplex spp., Chenopodium spp., Disphyma crassifolium (L.) L.Bolus, Swainsona
spp., Sida spp., Haloragis spp., Plantago varia R.Br., Asperula conferta Hook. f., Wahlehbergia spp., herbaceous Goodenia spp.
and a large suite of small daisies (Leigh and Mulham 1965).
Leigh and Mulham (1965) provided an illustrated compendium of the important pastoral plants of the Riverina grasslands.
Grassland fauna
The fauna of temperate Australian native grasslands is very poorly known. Much of the vertebrate fauna, particularly the
mammals, was eliminated during the early years of European occupation, and the invertebrate fauna has received limited
attention, apart from a few agricultural pests and iconic native species, some exploratory inventory studies in Victoria and the
ACT, and several detailed studies in the ACT. Australian grasslands have been said to have relatively few specialist animal
species and “a modest but distinctive array of animals that feed on on the foliage or the seeds of grass” (Keith 2004 p. 104).
Grasslands are characteristed by high rates of herbivory compared to many other terrestrial ecosystems, with consumption
efficiencies generally c. 25% compared to c. 5% in forests (Tscharntke and Greiler 1995). High root: shoot ratios in temperate
grasslands means there is a large subterranean plant biomass to support soil fauna, and the subterranean standing crop consumed
by insects is 2-10 times higher than the above-ground crop (Tscharntke and Greiler 1995). Thus an underground life stage is
typical in grassland insect genera (McQuillan 1999).
The seral stage of T. triandra grassland affects its suitability for animals. Biomass of the grass determines the floral composition
of the grassland, presence of food plants, amount of shade and the structure of habitat. Watson (1995 cited by Lunt and Morgan
2002) “found substantial seed predation beneath a dense grass cover, but little in burnt open areas”.
In this review, the vertebrates are first examined, with a particular emphasis on the extinct mammalian fauna, then invertebrates,
with a particular emphasis on insects, including an examination of several rare and threatened taxa, and a detailed review of
what is known about the fauna of grasses.
Vertebrates
Many of the mammals and birds that forage in grasslands require structural habitat features for shelter, nesting, etc. that
grasslands do not provide (Keith 2004), this being the case for example with insectivorous bats. But today, and in geologically
recent times, the often complex vegetation mosaics around or within south-eastern Australian grasslands have meant that
vertebrates dependent on woodland and shrubland for shelter etc. have been widely able to use grasslands to meet some of their
requirements.
Vertebrate species can be detrimentally or beneficially impacted by the floristic and structural vegetation changes caused by
weeds, including alterations to food supply and foraging potential, nest sites, cover, predator protection, etc. (Brown et al.
1991). Conversely, the activities of vertebrates may hinder or facilitate weed populations by bioturbation, defecation and
urination, feeding and other activities.
Mammals
Grassland mammal assemblages are characterised by the lack of arboreal species and of browsers, and restricted diversity of
grazers (Webb 1977). Australian grasslands were once occupied by a marsupial megafauna, which disappeared, like similar
faunas in North and South America, during the Miocene and the end of the Pleistocene (Webb 1978). The major extinction phase
in Australia occurred in the late Pleistocene, possibly mostly c. 26 kbp and continuing to c. 18-15 kbp, and has been associated
with general continental drying (Kershaw et al. 2000). The marsupial megafauna occurred in 250-750 mm rainfall zones, and one
of three groups was specifically adapted to southern grasslands (Kershaw et al. 2000). Aboriginal Australians may have played
little part in their disappearance, since fossil evidence suggests coexistence for at least 20,000 years, although recent redating
appears to have markedly reduced this overlap period (Kershaw et al. 2000) and consensus now favors hunting as the major
cause of extinctions (Flannery 1994, Johnson 2009). Subsequent to the extinction of the megafauna, another set of medium sized
animals largely disappeared from south-eastern Australian grasslands, mainly during early historical times (Table 15).
According to Lunt et al. (1998), 8 of 26 mammal species (excluding bats), mostly rodents and small to medium sized marsupials,
once found in the grassy plains of south-eastern Australia are now no longer present. In the South East of South Australia the
mammals that have disappeared since European occupation have been those that “lived mainly in woodlands and grasslands”
(Aitken 1983 p. 127). Numerous species have been lost in Victoria including Potoroidae (Bettongs Bettongia spp., Rufous
Bettong Aepyprymnus rufescens Gray), Macropodidae (e.g. Eastern Hare-wallaby Lagorchestes leporides (Gould), Bridled
Nailtail Wallaby Onychogalea fraenata (Gould), Toolache Wallaby Macropus greyi Waterhouse, Tasmanian Pademelon
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