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

Campbell (1977, quoted by Gardener 1998) observed that Nassella trichotoma first appears in an area as widely sccattered
tussocks, seven to twelve years later as patches, with scattered plants between them, and four to six years later as complete
infestations. It appears that the development of N. neesiana infestations may show a similar pattern.
Weed status
Nassella species appear to become a problem wherever they naturalise. Verloove (2005, p. 112) that the complex of exotic
stipoids including Jarava and Nassella spp. naturalised in Europe were“a serious threat for native vegetation” and “worldwide
among the most troublesome weeds” the control and eradication of which was “very time consuming and expensive”.
In New Zealand N. neesiana has been rated as extremely undesirabable (Bourdôt and Ryde 1986). It was declared a Class B
noxious plant under the Noxious Plants Act 1978 by the Marlborough District Noxious Plants Authority in 1979 (Bourdôt and
Hurrell 1987a) and later Class B in the whole country(Bourdôt 1988). However some have questioned its potential for major
impact. Jacobs et al. (1989 p. 569) considered it “a localised troublesome weed of pastures”, Connor et al. (1993 p. 301) thought
it has achieved only ‘modest success’, and that there were “no serious grounds” for predicting it would become a widespread
problem, while Edgar and Connor (2000) considered to be only. “locally troublesome”. As of 2002 it was classed under the
Biosecurity Act 1993 as requiring “Progressive Control” in the Marlborough region , and “Total Control” with the aim of
eventual eradication in Hawkes Bay region (Slay 2002a).
Although native to Chile, it was classified as a weed there because of the effects of the seeds on livestock and livestock produce
(Gardener et al. 1996b - see their citation).
N. neesiana was listed as one of 20 Weeds of National Significance (WONS) in Australia in 1999 (Iaconis 2003). The process of
determining WONS was “the first attempt to prioritise weeds over a range of land uses at the national level” and was “not a
purely scientific process” (Thorp and Lynch 2000 p. v). Of 71 weeds nominated by States and Territories N. neesiana was
ranked 12th, based on evaluation by technical experts on six invasiveness questions, seven impact questions, potential for spread,
and documentation of socioeconomic and environmental impacts (Thorp and Lynch 2000, McLaren et al. 2002a). The
environmental impact assessment was rudimentary and “could be achieved only by taking a few pertinent environmental
indicators and combining them into a ranking” (Thorp and Lynch 2000 p. 6). These were: 1. presence in a biogeographical
region (each region being assigned equal value); 2. monoculture potential (ability to form pure stands giving a high score); 3.
biodiversity indicator - based on the number of threatened species and special conservation areas (Thorp and Lynch 2000). N.
neesiana was rated medium impact in respect of impact on threatened species, low impact in terms of threatened communities,
“minimal national relevance” based on presence in less than 25% of biogeographic regions and low monoculture potential
(Thorp and Lynch 2000 pp.15-16). Despite this, the species given a national listing. Recognition as a WONS resulted in a
National Strategic Plan (ARMCANZ et al. 2001), increased mapping and recording, codes of practice to prevent spread and the
development of better management methods (McLaren et al. 2002a).
Groves et al. (2003b) developed a weed rating system for invasive plants in Australia and came up with the following
ratings for N. neesiana:
Australia
5S
New South Wales
5nceS
Victoria 5S,
Tasmania
OXS
South Australia
OXS
Queensland, Western Australia, Northern Territory no rating
where:
5 = naturalised and known to be a major problem at 4 or more locations within a State or Territory
0 = naturalised but only known naturalised population now removed or thought to be removed
S = potential to spread further
n = naturalised in part of a State
c = under active control in part of a State
e = eradication being attempted in part of a State
X = potentially a greater agricultural problem than the rating shown
The weed risk assessment process in Victoria, known as the the Victorian Pest Plant Prioritisation Process (Weiss et al. 1999,
Weiss and McLaren 2002) enables the relative importance and potential impact of a species to be determined by scoring weeds
on their invasiveness characteristics, current and potential distribution, and impact criteria. On a scale of 0-1, an invasiveness
score of 0.72 was determined for N. neesiana, slightly less than that for N. trichotoma and much higher than Eragrostis curvula
(0.50) (McLaren, Weiss and Faithfull 2004).
There is little dissent from the view that N. neesiana is a serious pasture and environmental weed in south-eastern Australia
(McLaren et al. 1998), however Grice (2004b) did not rate it as a threat in terms of non-pastoral agriculture, forestry, fire or
amenity. Carr et al. (1992 pp. 41, 51) considered it to be a “very serious threat to one or more vegetation formations in Victoria”.
McLaren et al. (1998) considered it to be potentially the worst environmental weed of indigenous grassland in Victoria, while
McLaren, Stajsic and Iaconis (2004) considered it to be rapidly degrading critically endangered native grassland remnants in
Victoria. It was listed as a perennial grass ‘weed of concern’ for South Australia (Virtue et al. 2004). Groves et al. (2003b)
determined that it was having a direct impact on rare or threatened native plant species. In Victoria it has been portrayed as a
strong resource competitor, “even choking out Nassella trichotoma ... in indigenous grasslands” (Iaconis 2003 p. 6).
McLaren et al. (2002b) undertook a survey of land owners and managers in Victoria, the ACT and NSW and found that 5% of
respondents, all from NSW, considered it a beneficial plant, while 86% did not. Even in the Angahook-Otway region of Victoria,
an area largely occupied by forest, heathy woodland or heathland it has been rated by expert opinion as a weed of importance
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