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

McLaren, Weiss and Faithfull 2004), a common native species with a very wide distribution across southern Australia (Vickery
et al. 1986).
Lack of recognition is widely acknowledged: N. neesiana “does not stand out in the landscape” (Frederick 2002) and is “difficult
to identify” (Auckland Regional Council 2002). Gardener et al. (1996a) state that its spread “went unnoticed” until about 1981,
while Virtue et al. (2004 p. 85) refer to the “relatively unnoticed spread” of Nassella species. Duncan (1993) noted that plants in
the vegetative state “can be mistaken for many other winter green species, chiefly Danthonia and Fescue”. Even with intensive
public education and awareness raising, public reporting rates have been very low, with most new reporting by people with
botanical interests or previous familiarity with the plant (Frederick 2002). The date of arrival in a particular area or site is rarely
known, so the rates at which invasion is occurring can generally only be approximately calculated.
Origin
The geographical origin of N. neesiana populations in Australia and the means by which propagules first entered the country
remain mysterious. The means of introduction has been said to be “unknown” (Grice 2004b), and a common assumption has
been that the species is an accidental introduction. No published records of quarantine interceptions appear to exist. Carr (1993 p.
291) listed both South and North America as possible origins of Victorian populations and was non-committal on the possibility
of deliberate introduction. Kirkpatrick et al. (1995) suggested that New Zealand was “perhaps” the source. Slay (2002a) stated
that N. neesiana was accidentally introduced into Australia in the late 1920s, but that is just speculation: the possibility of
deliberate introduction has not been ruled out and the dates at which the species was first recorded are not necessarily a good
guide to the actual dates of introduction. Caley et al. (2008) found in an analysis of herbaceous perennials naturalised in South
Australia that the time between introduction and recorded naturalisation could extend up to 140 years, although the majority of
species that naturalised did so within 40 years. A further complication in the Australian history of N. neesiana is the lack of
certainty that the first herbarium specimens were from truly naturalised populations – current populations may have arisen from
later introductions rather than being progeny of the earliest specimens.
Deliberate introductions of the plant to Australia for evaluation as a pasture grass have been made (see below), but some records
of wild individuals existed before all of the known deliberate importations.
Agricultural contaminant
Gardener et al. (2003a), influenced by numerous European records of alien stipoids associated with commerce, including
Hayward and Druce (1919), suggested the possibility of introduction in wool, on sheep or in fodder. Hayward (Hayward and
Druce 1919) had found the species downstream of the woollen mills at Galashiels, Scotland, where the adventive flora, totalling
348 alien species, clearly reflected the naturalisation of species from seeds imported on wool from many parts of the world,
including Argentina, Chile, Peru and Bolivia (Vines 2006).
Reflecting the diverse range of possible introduction methods, Muyt (2001) suggested that N. neesiana arrrived “probably as an
agricultural impurity”, while Benson and McDougall (2005 p. 159) considered it an accidental introduction “probably as an
agricultural contaminant”. In a newspaper article, quoting no source, Dalton (2000) stated that it was “believed to have
hitchhiked to Australia on a haybale”. Slay (2001) stated that seeds were distributed to Australia on exported pelts and wool, a
presumption apparently based on the 19th century European experience. Australia however has long been a major exporter of
wool and sheep skins: wool exports were initiated in 1807, grew enormously from 1870 onwards and approximately quintupled
in the following 70 years (Australian Wool Bureau 1963). Australia also appears to have been largely self sufficient in hide
production for leather over the period when introduction may have occurred, except for a few specialised leather types, and had
substantial exports of cattle, horse and sheep hides in 1938-39. However New Zealand was the chief source of hides and skins
imported into Australia in the early 1960s (Anderson 1963).
Evidence of establishment of exotic (Australian) stipoids in New Zealand indicates that the late 19th century was “a prime time”
for dispersal (Connor et al. 1993 pp. 303-304), however N. neesiana was probably first collected in that country in the late 1920s
(Connor et al. 1993). Establishment of Austrostipa spp. and other Australian grasses in the Canterbury area of New Zealand has
been correlated with the importation of Australian sheep in the 1840s and 1850s (Connor et al. 1993). Slay (2002a p. 4) thought
it “possible” that New Zealand populations of N. neesiana may have resulted from importation of contaminated heavy machinery
from Europe for the construction of bridges and railways, but stated (p. 11) that there was anecdotal evidence that the
infestations in Marlborough had most likely arisen from pasture seed imported from South America.
Introduction to Australia in pelts or wool, or on sheep or cattle from South America or New Zealand seem unlikely given
Australia’s long history as a significant exporter of these products, and its general low levels of trade with South America. Wild
animal furs are a possible source of introduction: as recently as 1980 Argentina exported over 4 million Nutria (Myocastor
coypus (Molina)) pelts to the USA and Europe (Soriano et al. 1992). Importation of fodder from these countries would seem to
be similarly improbable, unless accompanying livestock. Introduction as an external contaminant of livestock is a possibility, the
trade in racing horses perhaps being the most likely means. The possibility of importation as a seed contaminant deserves better
evaluation, while further investigation of deliberate importation of potential pasture species may prove enlightening.
Coincidentally, another major pest species native to South America, the Argentine Ant Linepithema humile (Mayr), established
in Melbourne for the first time in Australia at about the same time as N. neesiana was first detected. The ant first came to official
attention in 1939, but was originally noticed in Balwyn about 1931 (Clark 1941). Surveys from late 1939 to March 1940 found a
second major infestation at Yarraville and Footscray, and small infestations in Williamstown, Brunswick and Caulfield (Hogan
1940). The possibility that the same commercial vectors brought both species to Melbourne is perhaps worthy of further
investigation.
Deliberate introduction
An alternative hypothesis is that of deliberate introduction, however the deliberate importations identified to date by weed
researchers all post-date the first collection of N. neesiana in Australia. Cultivation of N. neesiana, leading to naturalisation
would appear to be not unlikely, since “there are few modern examples of accidental first introductions of a weedy species to a
new range” (Mack and Lonsdale 2001 p. 96) and a high proportion of invasive grasses are deliberately introduced (e.g. Lonsdale
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