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

This indicated that a small part of south eastern NSW, parts of Tasmania, much of Victoria, south-eastern South Australia and
parts of the southern coast of Western Australia had high climatic suitability, but ‘core’ areas were restricted to near-coastal
Victoria and South Australia.
According to Gardener et al. (1999 p. 8) N. neesiana “appears to have the ability to colonise most grasslands and grassy
woodlands in temperate areas of Australia with more than 500 mm of rainfall”. The expansion of range of an invasive plant at a
regional level is generally faster from many, small infestations than from a single large one of similar area (Mack and Londale
2001). The presence of many small populations is certainly a feature of the Australian invasion, so continued rapid spread can be
expected. Increases in the frequency and density in landscapes already invaded can be expected if inadequate management is
undertaken. Lunt and Morgan (1998, 2000) documented an increase in frequency at Derrimut Grassland Reserve from 16% of
quadrats in 1986 to 42% in 1996, largely driven by senescence of the dominant native grass T. triandra.
Habitat and climatic and biotic tolerances
N. neesiana is an “extremely hardy” (Benson and McDougall 2005) grass, adapted to a wide range of conditions (Muyt 2001). It
reportedly “has the capacity to switch from being stress tolerant to being vigorous” (Bedggood and Moerkerk 2002). In South
America it is the most widely distributed Nassella species with a distribution from the Pacific coast across the Andes, through
the Pampean and Paranaense biogeographical provinces to the Atlantic, a range similar to the overall distribution of Stipa sens.
lat. in that continent, and occupying a variety of habitats (Longhi-Wagner and Zanin 1998), “primarily” steppe (Barkworth
2006).
N. neesiana is a particularly prominent species in the 750,000 km 2 Rio de La Plata grasslands, consisting of the Argentine
pampas and the Uruguayan and southern Brazilian campos (Soriano et al. 1992). Campos and pampas are similar formations and
the Rio de la Plata is often considered the boundary between them (Overbeck and Pfadenhauer et al. 2007). The “typical”
landscape of the Pampas south of Buenos Aires in 1960 was described by Durrell (1964) as “flat golden grassland in which the
cattle grazed knee-deep ... a lush, prosperous and well-fed-looking landscape that only just escaped being monotonous”. Lorentz
(1876 quoted by Schimper 1903 p. 503) described the pampas grasslands as consisting of “scattered dense tufts of stiff grasses,
chiefly species of Stipa and Meliea, which rise like islets above the yellowish-brown loam ... between these isolated tufts of grass
bare loam, which is frequently washed out and carried away by the rain, so that the separate tufts of grass rest on actual mounds;
but also frequently, especially during the favourable season of the year, it is covered by all kinds of more delicate grasses and
herbaceous perennials, few in species ... Viewed from a distance, these grasses seem to form a close grassy covering, and the
pampa presents the appearance of extensive grassy tracts whose colouring varies with the seasons: coal-black in spring, when the
old grass has been burned; bright bluish-green when the young leaves sprout; later on brownish green, the colour of the mature
grass; finally – at the flowering time – when the silvery white spikes overtop the grass, over wide tracts its seems like a rolling,
waving seas of liquid silver ... After the Gramineae ... the greatest number of individuals is that of Compositae; usually twiggy
under-shrubs with inconspicuous flowers ...Verbena, species of Portulaca, of Malva and a few Papilionaceae are chiefly
responsible for the meagre floral beauty ...”. A similar picture is presented by Soriano et al. (1992): Poaceae is the predominant
family, with Stipa sens lat. the best represented genus (25 spp.), followed by Piptochaetium and Poa (each with 8 spp.) and
Aristida and Melica (each with 6 spp.); Asteraceae are next most abundant, including species of Baccharis, Eupatorium,
Hypochoeris and Veronia; native Fabaceae, sensitive to cultivation, poorly represented, with Cyperaceae, Solanaceae,
Brassicaceae, etc, in order of abundance. In the Brazilian Campos region Asteraceaeare is the most diverse family (c. 600 spp.),
followed by Poaceae (c. 400-500 spp.), Leguminosae (c. 250 spp.) and Cyperaceae (c. 200 spp.) (Overbeck et al. 2007).
N. neesiana was a dominant species in a climax grassland community that once covered the majority of the formation known as
Rolling Pampa, extending south and west of the Río Paraná and the Rio de La Plata and encompassing the Río Salado basin.
Rolling Pampa covered a gently undulating, well drained plain, commonly with very deep soils, and regular drought and
flooding. In the very fertile soils common in Rolling Pampa, such as in La Plata district of Buenos Aires Province, N. neesiana
was dominant along with the shortly rhizomed summer-autumn growing Bothriochloa laguroides (DC.) Herter and three smaller,
tufted grasses Piptochaetium montevidense (Spreng.) Parodi, Aristida murina Cav. and Jarava plumosa (Spreng.) S.W.L. Jacobs
and J. Everett (Cabrera 1949, Soriano et al. 1992). This type of grassland is called “flechillar”, in reference to the dominance of
grasses with piercing seeds (Soriano et al. 1992). Shrubs are generally a minor component but include Baccharis spp.
(Asteraceae), and the inter-tussock spaces are occupied by many species of small herbs and sedges (Soriano et al. 1992), with the
“original” plant diversity in well-drained soils being c. 222 species (Aguiar 2005). The weed flora has many species in common
with the more mesic grasslands of south-eastern Australia. In other areas of Rolling Pampa Nassella charruana and Amelichloa
brachychaeta were the dominant grasses, the former in parts of the eastern zone and the latter in the north west (Sante Fe
province) (Soriano et al. 1992). Distribution of N. neesiana in Rolling Pampa has probably been radically altered by
development. Six million ha of the formation had been cultivated by c. 1900 but by 1984 this had increased to 26 m ha (Aguiar
2005).
N. neesiana was a dominant species in thhe natural vegetation of the Southern Pampa, covering much of southern Buenos Aires
province, along with N. clarazii (Ball) Barkworth, N. trichotoma, N. tenuis (Phil.) Barkworth, Piptochaetium napostaense
(Spegazzini) Hackel, P. leiopodum (Spegazzini) Henrard and Poa ligularis Nees ex Steud. with many other grasses also
abundant and very similar non-grass components to Rolling Pampa (Soriano et al. 1992). Some of the stipoid species in Southern
Pampa “often ... form pure stands in areas that have never been cultivated” (Soriano et al. 1992 p. 385). The stipoids are largely
displaced by shrubby vegetation on hills, rocky sites and wet areas in this region.
N. neesiana is one of the most abundant species in mixed flechilla-Paspalum quadrifarium Lam. grassland in the Tandilia Range
system of the southern Pampas of Argentina, where the stipoid dominants include Piptochaetium spp. and Nassella trichotoma
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