Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
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Floristic composition, vegetation structure and ecology<br />
“Unfortunately, there exists no really satisfactory description <strong>of</strong> the vegetation when the grazier first began to exploit the<br />
country” (Wadham and Wood 1950 p. 87). Eighty years after exploitation commenced, Schimper (1903 p. 503) noted that there<br />
were “no available descriptions <strong>of</strong> the extensive savannahs and steppes <strong>of</strong> the interior <strong>of</strong> New South Wales and Victoria”. Some<br />
decades later, McTaggart (1936), as part <strong>of</strong> an <strong>Australia</strong>-wide ‘survey’ <strong>of</strong> pastures, provided a description <strong>of</strong> the open <strong>grass</strong>lands<br />
(in which he included “savannah”, now <strong>grass</strong>y woodland) <strong>of</strong> south-eastern <strong>Australia</strong>, but it is evident from his text and the listed<br />
information sources that no detailed compositional and structural knowledge then existed for most areas.<br />
The earliest detailed studies <strong>of</strong> <strong>Australia</strong>n <strong>grass</strong>land vegetation, made in the decades preceding 1950, provide “no guide to the<br />
proportions <strong>of</strong> the various species, or the composition <strong>of</strong> the vegetation from the standpoint <strong>of</strong> grazing value” <strong>of</strong> the areas before<br />
grazing commenced, but it is known that “pr<strong>of</strong>ound” changes had occurred, particularly where rainfall was low or highly<br />
variable (Wadham and Wood 1950 p. 87). By 1875, for example, the <strong>grass</strong>lands <strong>of</strong> South <strong>Australia</strong> had “mostly disappeared” by<br />
conversion to cereal growing (Schimper 1903 quoting Schomburgk 1875). The “lack <strong>of</strong> adequate description before alteration<br />
occurred” (Jones 1999b p. 29) is an ongoing problem. Lunt (1990a p. 47) thought that an accurate representation was “almost<br />
impossible”, while Lunt et al. (1998) considered “any reconstruction <strong>of</strong> the original vegetation must be somewhat speculative,<br />
particularly at a detailed level”. The pre-European composition is still considered to be “poorly understood” (McIntyre and<br />
Lavorel 2007) but pre-European <strong>grass</strong>land was probably more diverse than current reference areas, and many species have<br />
presumably been eliminated or greatly depleted in most areas (Sharp 1997).<br />
A similar situation exists with the temperate <strong>grass</strong>lands <strong>of</strong> South America. One <strong>of</strong> the first floristic surveys <strong>of</strong> pampas vegetation<br />
was made by L.R. Parodi in 1930 by which time so-called “virgin <strong>grass</strong>lands” were rare (Soriano et al. 1992 p. 381) and after<br />
which agricultural development greatly intensified.<br />
Early historical descriptions<br />
One <strong>of</strong> the earliest <strong>Australia</strong>n descriptions is Schomburgk’s (1875, quoted by Schimper 1903 pp. 504-505) portrait <strong>of</strong> South<br />
<strong>Australia</strong>n <strong>grass</strong>lands, in which the <strong>grass</strong>es mentioned are already a mixture <strong>of</strong> native and introduced species, although the forbs<br />
appear to be entirely native: “The plains near the coast ... the soil mostly fertile, extending <strong>of</strong>ten to the sea ... The <strong>grass</strong>es consist<br />
<strong>of</strong> more nourishing kinds ... Poa, Panicum, Festuca, Agrostis, Aira, Andropogon, Cynodon, Stipa, Pennisetum, Bromus,<br />
Eriachne, Anthistiria [Themeda], Hordeum ... The banks <strong>of</strong> the rivers and creeks, which mostly cease running druing the<br />
summer, are lined with majestic gum-trees ... the shrubs extending more or less on the plains, according to the nature <strong>of</strong> the soil<br />
... the appearance ... has during the dry season, the ... sunburnt yellow character ... destitute <strong>of</strong> all green herbage ... In the month<br />
<strong>of</strong> May the rainy season generally commences ... a few showers change the aspect ...into a green and beautiful carpet ... in a few<br />
days the plains appear clothed with luxiarant verdure ... With the <strong>grass</strong>es are also recalled to new life Ranunculus ... Oxalis ...<br />
Hypoxis glabella ... Drosera ...Wahlenbergia gracilis ... Anguillaria [Wurmbea]... Stackhousia ... Every week adds new colours<br />
to the beautiful carpet ... Kennedya [sic] prostrata...Swainsona procumbens ... and S. lessertiaefolia [sic] ... Thysanotus ...<br />
climbing up the dry <strong>grass</strong> stalks ... Compositae are seen blooming over the plains in all colours ... But by the middle <strong>of</strong><br />
November the number <strong>of</strong> flowering plants already lessens considerably, the annual <strong>grass</strong>es and other herbaceous plants begin to<br />
dry up, droop and disappear, and in January the <strong>grass</strong> land resembles a ripe thinly-sown cornfield, and we find only ... a few<br />
plants <strong>of</strong> Convolvulus erubescens, Lobelia gibbosa ... and Mesembryanthemum australe [?Disphyma crassifolium] ... The seeds<br />
<strong>of</strong> the annual plants have been scattered, perennial herbage returned to its dormant state ... and the plains have during the summer<br />
months a dismal, dried-up appearance”.<br />
The earliest study <strong>of</strong> note for Victoria is Sutton’s (1916-1917) “Sketch <strong>of</strong> the Keilor Plains flora” at the drier, eastern end <strong>of</strong> the<br />
Victorian volcanic plains. He provided a valuable census <strong>of</strong> the vascular flora that included species from neighbouring<br />
vegetation associations, but deliberately excluded all <strong>of</strong> the exotic species. Patton (1935) provided a list <strong>of</strong> vascular plants for<br />
Victorian basalt plains <strong>grass</strong>lands, discussed their structure, composition and seasonal dynamics and the climate and soils.<br />
Contemporary studies<br />
A much greater range <strong>of</strong> more detailed studies have taken place in the last fifty years, commencing with investigations such as<br />
those <strong>of</strong> Willis (1964) and Groves (1965). These describe <strong>grass</strong>land generally dominated by perennial tussock <strong>grass</strong>es including<br />
T. triandra, Poa, Austrodanthonia and Austrostipa species, with the latter two genera being more dominant in drier areas (NSW<br />
Riverina, Northern Plains <strong>of</strong> Victoria and Northern L<strong>of</strong>ty region <strong>of</strong> South <strong>Australia</strong>) (Kirkpatrick et al. 1995, Sharp 1997, Lunt<br />
and Morgan 2002). Bothriochloa, Enteropogon and Chloris may also be dominant <strong>grass</strong>es, while Lomandra is the major<br />
dominant in some South <strong>Australia</strong>n formations (Carter et al. 2003).<br />
Based on readings <strong>of</strong> historical records T. triandra is thought to have been the dominant species across much <strong>of</strong> the plains before<br />
European occupation, although this is based on the assumption that the vernacular term “kangaroo <strong>grass</strong>” was applied only to T.<br />
triandra (Lunt et al. 1998). T. triandra was almost certainly the most widespread and dominant <strong>grass</strong> (Groves 1965, Mack 1989,<br />
Moore 1993, Kirkpatrick et al. 1995) and is considered the major dominant in Victoria, but is replaced by Poa spp.,usually Poa<br />
labillardieri Steud. on wet sites and in higher rainfall areas (Willis 1964, Moore 1993, Entwisle et al. 1994). Austrodanthonia<br />
and Austrostipa species were the dominant <strong>grass</strong>es in drier areas including the Murray River plains <strong>grass</strong>lands and in parts <strong>of</strong><br />
South <strong>Australia</strong> (Kirkpatrick et al. 1995). Moore (1993) considered Austrostipa bigeniculata was the principal T. triandra<br />
associate in drier sites. Sutton (1916-1917) found Austrodanthonia penicillata (Labill.) H.P. Linder to <strong>of</strong>ten be the dominant in<br />
drier areas <strong>of</strong> the Keilor Plains with Poa, Austrostipa setacea (R.Br.) Jacobs and Everett, A. semibarbata (R.Br.) Jacobs and<br />
Everett and Dichelachne crinita (L.f.) Hook. f. more prominent in moister areas along with “Panicum” spp. Willis (1964) found<br />
that Austrodanthonia spp. became less prevalent in wetter areas. A large proportion <strong>of</strong> these <strong>grass</strong>lands have been modified by<br />
grazing and became dominated by shorter <strong>grass</strong>es such as Austrodanthonia auriculata (J.M. Black) H.P. Linder, A. carphoides<br />
(Benth.) H.P. Linder and Austrostipa scabra (Lindl.) S.W.L. Jacobs and J. Everett (Moore 1993). Shrubs are rare and<br />
substantially absent (Entwisle et al. 1994, Lunt et al. 1998). Except for T. triandra, the dominant <strong>grass</strong>es have the C 3<br />
photosynthetic pathway and grow mostly in spring and autumn (Groves and Whalley 2002). Most have seeds with an ‘after<br />
ripening’ period (Groves and Whalley 2002) which presumably acts to prevent germination in the dry season (summer) and<br />
delay it until adequate soil moisture is more likely to be available for seedling establishment. Annual native <strong>grass</strong>es are rare.<br />
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