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

populations have been found in the City of Toowoomba, probably spread by an energy utility company (Queensland
representative on the National Chilean Needle Grass Taskforce 28 February 2007).
The Queensland infestations most likely are the result of seed movement via vehicles or livestock from the Northern Tablelands
of New South Wales. A plan with the long term objective of eradication from the State is being implemented (Snell et al. 2007).
Tasmania
An infestation at Hobart is mentioned by Mallett and Orchard (2002) and Hocking (2005b). This infestation, at the University of
Hobart, was mapped in 2005 and was the only one then known in Tasmania. The outbreak was sprayed with herbicide in autumn
2005, with a follow-up spray, mulching and planting of trees in winter. Other potential invasion sites were surveyed in 2006,
including open space and grasslands at Montague Bay, Rose Bay, Rosny and Mornington (Iaconis 2006b). New infestations
were discovered in 2005 that prompted further surveying (Iaconis 2006a). However according to the Tasmanian Department of
Primary Industries and Water (DPIW)(2007 p. 2) N. neesiana had been recorded from only a single site, in Hobart, “from which
it has ... been eradicated”.
Hocking (pers. comm. 2006) noted that the recent reports were in central and southern Tasmania. As of July 2009 the core
infestations were all located in urban settings on the eastern shore of the Derwent estuary in Hobart in the suburbs of Montague
Bay, Rosny and Bellerive (National Chilean Needle Grass Task Force Agenda, July 2009). The main infestations were along
walking tracks, road easements and the grounds of a primary school. It was also found west of the Derwent River, in small areas
of The Domain and near the Technopark (Karen Stewart, DPIW Tasmania, pers. comm. July 2009). DPIW mapped and treated
all known infestations during 2007-08. Hocking (pers. comm. 2006) noted that bioclimatic modelling indicated that
establishment was highly likely in areas around Devonport and Launceston where ferries from mainland Australia regularly
deposit large numbers of motor vehicles. Bioclimatic modelling indicated that much of eastern Tasmania was suitable for its
establishment (ARMCANZ et al. 2001), although Hobart was outside the predicted area (Hocking 2005b). DPIW (2007)
prescribed hygiene and quarantine procedures to prevent breaches of the Tasmanian importation prohibition.
This basic data for the whole of Australia suggests at least four very widely separated areas of introduction, excluding the
deliberate importations to Western Australia: on the northern outskirts of Melbourne, the New England tablelands of NSW,
southern NSW or the ACT, and South Australia, however dispersal from the earliest known area of infestation north of
Melbourne to the other major foci cannot be ruled out.
It is apparent that the known extent of infestations during the course of the N. neesiana invasion has been closely related to the
ability to identify the plant and the effort devoted to detecting it. As Grice and Ainsworth (2003) pointed out, the confounding
‘awareness factor’ means that very little can be concluded about the actual rates of population increase and dispersal. Ongoing
control activity further confounds any attempts to determine whether N. neesiana might be reaching the limits of its potential
range and population size. Nevertheless, understanding of the invasion would be improved through retrospective mapping of the
extent of infestations at appropriate historical intervals and would assist in theoretical discussions of lag phases and the time
courses of plant invasions, and potentially contribute to improving prediction abilities for weeds in general (Grice and Ainsworth
2003).
Potential distribution in Australia
Various predictions of the potential Australian distribution of N. neesiana based on climate parameters have been made. These
all suffer from a poor understanding of the range of the grass, both in South America and in countries where N. neesiana has
been introduced, resulting from misidentifications or uncertainty about the true classifications of material, and inadequate floral
studies, and in the introduced ranges, of continued colonisation of new areas.
Gardener (1998) estimated a potential range in Australia of nearly 40 million ha, from Western Australia to south-east
Queensland, using the climate modelling program CLIMATE, which analysed 16 parameters for each data point, based on
temperature and rainfall. He made two separate analyses, using firstly the 224 then known locations of infestations in Australia,
and secondly a sample of locations in the rest of the world, based on herbarium specimens and literature records.
McLaren et al. (1998 p. 63) used distribution and altitude data from a “representative sample” of known infestations in Australia,
analysed the data with the BIOCLIM program and used CLIMATE to predict areas with a similar climatic profile. Their map
showed a potential distribution range covering much of south-east Queensland, most of the eastern half of New South Wales,
most of Victoria, southern parts of South Australia and Western Australia and parts of north-east Tasmania, covering a total of
41 million ha. A map provided by D. McLaren in Liebert (1996) derived using BIOCLIM based on the climatic parameters of all
Victorian infestations then known, showed the potential distribution in Victoria was approximately 3.86 million ha. These
climate-based predictions ignore other potentially important factors affecting distribution such as land use, tree cover and soil
type (Liebert 1996). They also rely on geographical proximity of weather stations to assign climate parameters to a record, a
problem likely to lead to major distortions when records are a long distance from weather stations, at a different altitude, etc.
Under the State of Victoria’s weed risk assessment process (Weiss 2002, Morfe et al. 2003), the maximum potential distribution
of N. neesiana was estimated based on world distribution data, climate modelling (rainfall and temperature data) and
geographical information system layers of susceptible land uses, vegetation classes and soil properties. A map was produced
showing the likely and unlikely distributions (Morfe et al. 2003p. 879). An additional estimate was made that N. neesiana would
take about 75 years to occupy its entire potential range in Victoria, or 50 years if the rate of spread was “very high”. Any future
expansion of range and area occupied was acknowledged to be critically dependent on the extent and effectiveness of
management activity directed against the weed. In the absence of government-coordinated mangement, the level of infestation in
Victoria was predicted to expand from less than 1000 ha to c. 1.5 million ha in 30 years (Morfe et al. 2003).
Thorp and Lynch (2000) provided a grid map generated by Agriculture Western Australia based on the known world distribution
of N. neesiana, using the CLIMATE system with ‘core’ and ‘high’ predicted densities (± 20% of the average climate required).
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