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SoE 2012 > Biodiversity > 5.4 Invasive species


Biodiversity chapter 5

5.4 Invasive species

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5.4 Invasive species

Invasive species (including pest animals, weeds and diseases) are widespread across New South Wales. They are difficult to manage effectively and remain one of the biggest threats to biodiversity. Many are listed as key threatening processes in NSW legislation, with pest animals and, in particular, weeds identified as a threat to over 70% of all threatened species.

Most pest animals have been well established in NSW for many years, with foxes and cats found across virtually the whole state. The decline or extinction of numerous small- to medium-sized native animals has been attributed to their predation.

Introduced herbivores, particularly rabbits and feral goats, have adverse impacts on native species and ecosystems through overgrazing of native vegetation, land degradation and competition with native herbivores. Deer continue to expand their range with increasing impacts while new sightings of individual cane toads continue to occur intermittently.

To date, over 1650 exotic plant species have become established in NSW and more than 300 of these have been described as significant environmental weeds. New invasive species, particularly weeds, continue to be discovered from time to time at scattered sites in NSW and, when identified, are subject to eradication measures.

Introduced pathogens and diseases have emerged as increasingly significant threats to biodiversity, particularly the plant diseases root-rot fungus (Phytophthora) and myrtle rust, and the amphibian chytrid fungus.

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NSW indicators

Indicator and status


Information availability

Number of new invasive species detected



Spread of emerging invasive species



Impact of widespread invasive species



Notes: Terms and symbols used above are defined in About SoE 2012 at the front of the report.

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Invasive species have been broadly established across NSW for many years and most areas now contain a range of weeds and pest animals. Historically, introduced species have contributed significantly to the decline and extinction of native species in NSW. In particular, foxes and cats have been implicated in the extinction of numerous small- to medium-sized ground-dwelling mammals (OEH 2011d). Human disturbance has greatly accelerated the invasion of introduced species (Coutts-Smith & Downey 2006; Coutts-Smith et al. 2007).

The collective impacts of invasive species are still poorly understood, whether on biodiversity or on the health of the environment as a whole. However, some recent advances have been made in understanding the impacts of invasive species on threatened species (Coutts-Smith & Downey 2006; Coutts-Smith et al. 2007; NLMG 2009). Statewide monitoring programs are also being established, which will enable reporting on the distribution of new and emerging pests and weeds and the extent of widespread pest species.

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Status and trends

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Extent of invasive species

Around 3000 introduced weed species have established self-sustaining populations in Australia since 1788. More than 1650 of these are recorded in NSW, with over 300 recognised as significant environmental weeds (Downey et al. 2010).

More than 650 species of land-based animals have also been introduced to Australia. Of these, 73 have established wild populations (NLWRA 2008), but not all are regarded as a threat to biodiversity. Introduced fish species make up around a quarter of all freshwater fish species in NSW rivers (DPI 2008a).

Australian waters host over 200 species of introduced marine organisms (DPI 2008a). However it is not known how many insects and other invertebrates have been introduced into Australia (Coutts-Smith et al. 2007).

Invasive species place a substantial burden on the Australian economy. Invasive weeds have been estimated to cost about $4 billion per year in lost production, control costs and dealing with the impacts (McLeod 2004; Sinden et al. 2004); in NSW alone, weeds account for $1.2 billion per annum in lost production and control costs (LGSA 2011).

The cost to the Australian economy of dealing with the impacts of pest animals is over $1 billion annually (DPI 2008a), while pest animal control alone exceeds $60 million per year (Bomford & Hart 2002).

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Categories of invasive species

Invasive species are generally categorised as widespread, emerging or new species, depending on their current extent and ability to persist and spread as described below:

Widespread species: any invasive species that has been present for some time and has now established a broad and relatively stable range across a region or the whole state, close to the limits of their likely distribution

Emerging species: any invasive species that has established a self-sustaining population and is actively expanding its range or has the potential to spread further

New species: any invasive species that has not been recorded previously in NSW or has not established self-sustaining populations, but has the potential to invade and spread across broad areas.

Assessment of the threat posed by species that are not yet present is based on their potential to spread and significantly impact on the environment or production.

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Distribution of pest animals in NSW

Thirty pest animal species have been identified as posing a threat to at least one endangered or vulnerable species in NSW (Coutts-Smith et al. 2007). Foxes, feral cats and wild dogs are the carnivores with the greatest impact on biodiversity. The herbivores or omnivores of greatest concern are rabbits, feral goats and feral pigs, while in aquatic environments European carp and gambusia are the most significant pests. Table 5.12 lists the state's main pest animals.

Table 5.12: Main introduced animal species in NSW with an impact on listed threatened species





Feral cats

Feral goats


Honey bees

Red foxes


European carp

Grass skinks*

Wild dogs

Feral pigs

Redfin perch

Feral pigeons

Cane toads

Feral deer


Buff banded rail*

Masked owls*

Wild horses


Introduced worms


Black rats 


Black ants*


Brown rats

Rainbow trout



House mice

Brown trout




Banded grunter***


Source: Coutts-Smith et al. 2007

Notes: Introduced species are species found outside their normal range and include both exotic species and translocated native species (those moved from their natural habitat to other locations in NSW).
* Native species translocated from mainland NSW to Lord Howe Island where they are a threat to endemic native species
** Tench was identified as a threat in this study, but has not been recorded in NSW for over a decade and is no longer considered to be a significant threat.
*** Native species translocated to other rivers in NSW

Widespread species

Widespread species have generally been present for a relatively long time, are broadly distributed and are close to the limits of their likely distribution, based on the availability of suitable habitat. The collective distribution and abundance of seven major widespread pest animals – foxes, cats, feral goats, rabbits, feral pigs, wild dogs and carp – was shown in Map 7.5 of SoE 2009 (DECCW 2009a). As is evident from Map 5.5, foxes and cats are considered to be distributed throughout the state while the other five major pests also have wide distributions across NSW, with some limited potential for further expansion.

Map 5.5: Occurrence of foxes and feral cats in NSW in 2009 as reported in surveys of land managers

Map 5.5

One of the greatest threats to biodiversity is predation by foxes and cats. These animals are thought to be responsible for the decline of many small- to medium-sized native animals as well as most of the extinctions that have occurred in mainland NSW. Introduced herbivores, particularly rabbits, feral goats and feral pigs, have an impact on environmental values through land degradation, competition with native species for food and increasing grazing pressure. Agricultural systems also feel their impacts.

New and emerging species

New species are recent arrivals or species with a limited distribution that have not yet established self-sustaining populations. Emerging species are those that have become established and spread but have not yet reached their natural limits of distribution. Some emerging species are already having severe impacts on biodiversity or the environment, including deer and cane toads which are listed as key threatening processes under the Threatened Species Conservation Act 1995.

Monitoring and management of new and emerging species are generally more intensive than that for widespread species as the prospects for achieving control through eradication or containment are better, giving a greater return on the resources expended.

Deer are the main group of pest species that are expanding their range. Map 5.6 shows the distribution of deer species between surveys in 2004–05 and 2009. Deer expanded their range from about 5% of NSW in 2002–03 (41,000 square kilometres) to about 6% in 2004–05 and then to about 8% of the state (64,000 km2) at the time of the 2009 survey. Their spread is continuing. While also found on the coastal slopes and plains, deer appear to be moving into forested areas that have remained relatively free of other pest species. The highly scattered nature of their distribution is unusual, as is that it involves more than one species.

Map 5.6: Change in reported distribution of deer in NSW from 2004–05 to 2009

Map 5.6

Cane toads are also an emerging species of concern. While sporadic sightings of individual toads have been confirmed at various locations along the NSW coast, they have only established viable populations on the far north coast and an isolated population at Taren Point in southern Sydney. A small population established at Port Macquarie but now appears to have been eradicated.

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Distribution of environmental weeds in NSW

Environmental weeds may be either exotic species or translocated native species, but those with the greatest environmental impact are predominantly introduced from overseas. Weeds threaten biodiversity both directly by competing with native species and indirectly through their impacts on ecosystem structure and function.

Under the Australian Weeds Strategy (NRMMC 2006), 20 plants were identified as weeds of national significance because of their invasiveness, potential for spread, and economic and environmental impacts. Those widespread within NSW include alligator weed, bitou bush, blackberry, bridal creeper, Chilean needle grass, lantana, salvinia, serrated tussock and some species of willow. Several others have a restricted distribution, including Athel pine, boneseed, cabomba, hymenachne, mesquite and parkinsonia. Parthenium weed has also made occasional incursions into NSW from Queensland but on each occasion has been eradicated.

Additional weeds of national significance were announced in 2012. Species found in NSW include African boxthorn, asparagus weeds (six species in addition to bridal creeper), brooms (three species), cat's claw creeper, fireweed, Madeira vine, Opuntoid cacti (several species), Sagittaria, silver leaf nightshade and water hyacinth.

Over 1650 species of weeds have become established in NSW and more than 340 have significant impacts on biodiversity (DPI & OEH 2011). Table 5.13 lists the top 20 weeds based on their potential impact on NSW biodiversity (Downey et al. 2010).

Table 5.13: The 20 weed species posing the greatest threat to biodiversity in NSW

Common name

Scientific name

Common name

Scientific name

Madeira vine

Anredera cordifolia

Cat's claw creeper

Macfadyena unguis-cati


Lantana camara


Salvinia molesta

Bitou bush

Chrysanthemoides monilifera subsp. rotundata


Ulex europaeus

Ground asparagus

Asparagus aethiopicus


Chrysanthemoides monilifera subsp. monilifera


Rubus fruticosus agg.

Serrated tussock

Nassella trichotoma

Scotch broom

Cytisus scoparius

Cape ivy

Delairea odorata

Japanese honeysuckle

Lonicera japonica

Blue morning glory

Ipomoea indica

Large-leaved privet

Ligustrum lucidum

Balloon vine

Cardiospermum grandiflorum

Small-leaved privet

Ligustrum sinense


Phyla canescens

Alligator weed

Alternanthera philoxeroides

Bridal creeper

Asparagus asparagoides

Source: Downey et al. 2010

Widespread species

There are too many widespread weeds in NSW to map their distribution and abundance. A broad pattern of distribution is available by looking at the total number of weeds and the number identified as having an impact on threatened species, aggregated by catchment management authority (CMA) region (Table 5.14).

Table 5.14: Number of weeds in each CMA region in NSW

CMA region

Number of weed species present

Total number of flora species

Contribution of weeds to total flora (%)

Number of weed species with an impact on threatened species

Sydney Metropolitan










Northern Rivers





Hunter/Central Rivers





Southern Rivers










Central West




















Border Rivers–Gwydir










Lower Murray–Darling





NSW total





Source: Coutts-Smith & Downey 2006

The widespread weeds with the greatest impact on NSW biodiversity and the biodiversity values most at risk have been determined and documented in Biodiversity Priorities for Widespread Weeds (DPI & OEH 2011). Priorities for each CMA region are listed in individual reports.

All parts of NSW are affected by weeds that threaten biodiversity. Weeds now make up 21% of the state's total flora. The numbers of weed species are highest near the coast, particularly around major towns and cities, and in regions with high rainfall, and tend to decline from east to west (Coutts-Smith & Downey 2006).

New and emerging species

Map 7.7 of SoE 2009 (DECCW 2009a) showed the spatial distribution of new and emerging invasive weed species, based on their listing as noxious weeds Classes 1, 2, 3 or 5. The map displayed patterns of spread similar to those described for widespread species above.

The listing of noxious weeds is a means of preventing their further spread and these listings correspond well with the categories of new and emerging weeds. Noxious weeds have the potential to cause significant environmental or economic impacts, but can still be controlled through reasonable means. Most importantly, they are likely to spread further within an area or to other areas. Most listings apply regionally to local government areas, although some apply to the whole state.

Table 5.15 describes the five classes of noxious weed listed in NSW and the number of species currently listed in each class.

Table 5.15: Numbers and classes of noxious weeds listed in NSW

Control class


Objectives of management

Number listed 2008

Number listed at 30 Sept 2011

Class 1: State prohibited weeds

Plants that pose a potentially serious threat to primary production or the environment, and are not currently in the state, or are present only to a limited extent

Prevent introduction and establishment



Class 2: Regionally prohibited weeds

Plants that pose a potentially serious threat to primary production or the environment of a region, and are not currently in the region, or are present only to a limited extent

Prevent introduction and establishment



Class 3: Regionally controlled weeds

Plants that pose a serious threat to primary production or the environment of an area, are not widely distributed in the area and are likely to spread in the area or to another area

Reduce extent and impact



Class 4: Locally controlled weeds

Plants that pose a threat to primary production, the environment or human health, are widely distributed in an area and are likely to spread in the area or to another area

Minimise negative impact on community, economy or environment



Class 5: Restricted plants

Plants that are likely, by their sale or the sale of their seeds or movement within the state or an area of the state, to spread in the state or outside the state

Prevent introduction into NSW, spread within NSW or spread from NSW to another jurisdiction



Source: DPI data 2011

Notes: Apart from Class 1 which is statewide, weeds are counted in a class if they are listed in that class in any region or local area in the state. Some species will appear in more than one class as they may be listed under different classes in different regions.
The numbers given reflect the minimum value as sometimes an entire genus containing a number of unspecified species is listed.

When a weed becomes so widespread that eradication or containment is no longer feasible, its declaration as a noxious weed may be repealed on the basis that it no longer meets the criteria for listing. Some widespread weeds are not listed in regions where they are abundant, but may be listed in neighbouring areas where their distribution is limited, they can still be controlled, and there is the potential for further spread.

Table 5.16 summarises outbreaks of new and newly emerging weed species that have occurred in NSW from 2008 to 2012. Predominantly, these are weeds that are listed as noxious weeds Class 1 or 2, but several are yet to be considered for listing. Eradication of these weeds to prevent their establishment and further spread has the highest priority in regional weed control strategies.

Table 5.16: Outbreaks of new and newly emerging weeds in NSW, 2008–09 to 2011–12


Noxious weed class

Number of new infestations

Number of repeat infestations

Aleman grass




Alligator weed




Asparagus falcatus

Not listed







Cape broom




Cecropia peltata

Not listed



Chinese violet
























Mahonia (Berberis) lomariifolia

Not listed







Mexican feather grass












Orange hawkweed




Orbea variegata

Not listed







Parthenium weed








Senegal tea plant




Tropical soda apple




Water hyacinth




Water lettuce




Source: DPI and OEH data 2012

Orange hawkweed (Hieracium aurantiacum) is an example of a weed in the early stages of establishment. It is one of 28 weeds on the National Environmental Alert List for environmental weeds because it is a major weed overseas and is considered to be a serious threat to biodiversity in south-eastern Australia. It also has the potential to cause serious losses to the grazing industry, which in 2002 were predicted to be around $48 million per year.

In NSW, orange hawkweed is currently only recorded in Kosciuszko National Park, where it was first detected in 2003. During 2010–11, the weed was discovered at 63 new locations in the park, bringing the total area detected since 2003 to 7.43 hectares. All known infestations have been managed, but ongoing surveillance is required to monitor known locations and search for new populations across a large remote and rugged area.

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Introduced aquatic species

Data on introduced freshwater fish species was collected from 669 sampling sites in NSW rivers in the three years up to the end of 2011. Across NSW, only 31% of the sites sampled – mostly coastal rivers – were free of introduced fish while 6.7% of sites contained only introduced fish. Averaged across all sites, 33% of the fish species at each site were introduced taxa, making up 34% of total fish abundance and 45% of total fish biomass.

The inland rivers of the Murray–Darling Basin were most heavily affected, with introduced fish present at 90% of all sites sampled. Introduced species made up 40% of all fish species, representing 44% of total fish abundance and 68% of total fish biomass.

Coastal rivers were less affected by exotic fish species. Introduced fish were present at 39% of sites, making up 10% or less of species collected, total fish abundance and total fish biomass.

Table 5.17 provides information on the abundance of individual introduced fish species. Since 2009, the pearl cichlid (Geophagus brasiliensis), a fish species native to Central America, is the only newly established species with a population detected in the Tweed catchment.

Table 5.17: Introduced fish at sampling sites

Fish species

% of sites where present: 2008

% of sites where present: 2011

European carp









Rainbow trout



Redfin perch



Brown trout



Eel-tailed catfish (translocated native species)



Oriental weatherloach



Climbing galaxias (translocated native species)






Silver perch (translocated native species)



Macquarie perch (translocated native species)






Pearl cichlid



Golden perch (translocated native species)



Murray cod (translocated native species)



Trout cod (translocated native species)



Rainbow fish (translocated native species)



Source: DPI data 2012

Notes: * Species present in very low numbers.

It is estimated that over 400 exotic species have been introduced into Australia's marine environment, but most of these are not considered pests. Relatively few of the exotic marine species found in NSW, including several species of toxic dinoflagellates and several species of invertebrates, are considered to be a serious threat to biodiversity.

The European shore crab (Carcinus maenas) has been recorded in 22 estuaries and coastal lakes from Burrill Lake south to Nadgee Lake (DPI 2008b). Its distribution has not changed greatly since the last SoE report or indeed since the 1980s, despite many more estuaries and lakes being searched in recent years. Monitoring is in place to detect any future changes in its distribution. As yet, there is no evidence that the European shore crab causes severe environmental impacts, but some oyster farmers consider it a nuisance as it can eat juvenile oysters.

The marine weed caulerpa (Caulerpa taxifolia) is possibly the most significant threat to the marine environment of NSW as it spreads easily from small fragments and can quickly colonise large areas of subtidal soft sediment, including seagrass beds. Introduced initially as an aquarium plant, caulerpa's impact is mainly on soft-sediment invertebrates and sediment chemistry with no direct impacts on seagrasses, although investigatory work is ongoing.

Caulerpa was first recorded in NSW coastal waters in April 2000. It initially spread to 14 estuaries and coastal lakes, ranging from Lake Macquarie to Wallagoot Lake. After considerable control work, caulerpa has not been found in Lake Macquarie since 2006 or in Wallagoot Lake and St Georges Basin since 2009. It was not detected in underwater surveys in Narawallee Inlet and Durras Lake in late 2011, nor in Burrill Lake or Lake Conjola in surveys during 2012. It is believed that increased salinity due to drought conditions and closed entrances has caused the decline in caulerpa in some lakes, whereas greatly reduced salinity due to more recent flooding killed much (or possibly all) of the caulpera in Burrill Lake and Lake Conjola.

The European fanworm and New Zealand screw shell are both still restricted to Twofold Bay on the NSW far south coast (DPI 2008b).

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Pathogens and diseases

Pathogens and diseases are an emerging threat to biodiversity and are becoming more prevalent, both internationally and in Australia. The impacts of exotic and translocated native microorganisms on biodiversity are still poorly understood. However, four diseases are listed as key threatening processes (KTPs) under the Threatened Species Conservation Act 1995 (TSC Act), with all four having potentially serious consequences for the health of the environment. The KTPs are:

  • infection by psittacine circoviral (beak and feather) disease affecting endangered psittacine species and populations
  • infection of native plants by Phytophthora cinnamomi
  • infection of frogs by the amphibian chytrid fungus causing the disease chytridiomycosis
  • introduction and establishment of exotic rust fungi of the order Pucciniales pathogenic on plants of the family Myrtaceae.

Psittacine beak and feather disease appears to have been present naturally in the environment and affects a number of species of parrots. Phytophthora root rot fungus is thought to have been introduced with European settlement. It is a soil-borne fungus that infects, and causes dieback in, a large range of mainly woody perennial plant species and some crops, particularly in higher rainfall areas.

The remaining diseases appear to have been introduced relatively recently. Chytrid fungus causes skin infections and death in native amphibians and is responsible for rapid declines in the populations of many native frog species.

Myrtle rust (Uredo rangelii) is a fungus which is a serious plant pathogen infecting species of the Myrtaceae family. This family includes many Australian native species such as eucalypts, paperbarks, teatrees and a range of understorey shrubs. Myrtle rust was first detected in April 2010 on the central coast of NSW and despite containment efforts it has now spread widely in NSW, Queensland and Victoria. There is serious concern about the threat it poses to the survival of many native plants in bushland areas, particularly those which are either highly susceptible to the fungus or are naturally rare or threatened (OEH 2011b).

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Environmental impacts of invasive species

Impacts on threatened species

Collectively, weeds and pest animals have been identified as a threat to approximately 70% of the threatened species listed under the TSC Act and Fisheries Management Act 1994 (FM Act). Invasion by exotic species has an impact on the second highest number of threatened species, after land clearing (Coutts-Smith & Downey 2006).

Individual widespread animal pests such as feral cats and foxes have a far greater impact than individual weeds. However, the number of weeds is much greater and their combined impact is broader than the impact of pest animals. Weeds have a negative impact on 45% of threatened species, populations and ecological communities in NSW, while pest animals threaten 40% (Coutts-Smith & Downey 2006; Coutts-Smith et al. 2007).

Listings of invasive species as key threatening processes

The magnitude of the impacts of pest and weed species is reflected in the listing of many invasive species as KTPs in both state and federal legislation. Twenty-three of the 45 KTPs listed in NSW under the TSC Act or FM Act relate to the impacts of weeds and pest animal species and a further four to pathogens. Pest animals listed as KTPs include foxes, feral cats, rabbits, feral pigs, feral goats, black rats, deer, cane toads, gambusia and four invertebrates (feral honey bees, fire ants, yellow crazy ants and large earth bumblebees). Weed species listed as KTPs include lantana, bitou bush, Scotch broom and African olive, while vines and scramblers are listed collectively, as are exotic perennial grasses.

Broader environmental impacts

It is difficult to quantify the total impact of introduced species on biodiversity and the environment as a whole. Most of the information available is specifically about impacts on threatened species, not on all native flora and fauna (Coutts-Smith & Downey 2006) and generally only describes the extent of these impacts, not their intensity or magnitude.

The broader impacts of invasive species on the environment and ecosystem health are substantial, but largely unassessed. These broader impacts include soil degradation, landscape and habitat disturbance, structural change and decline in vegetation condition, and changes to watercourses and water quality.

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Invasive species are not present in naturally functioning ecosystems and are recognised as a threat to them. Therefore the discussion of pressures in this section relates specifically to risk factors that exacerbate the impacts of invasive species or that facilitate their spread.

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Habitat disturbance

Systems that are suffering from disturbance are at the greatest risk of incursion by invasive species as the balance in the dynamic processes that maintain natural systems in equilibrium has been upset. The disturbance may be physical or caused by an imbalance in the natural biota (Lake & Leishman 2004; DPI 2008a). Invasive species are generally less affected by the constraints and balances that operate in natural systems, so they can rapidly exploit suitable habitat where natural systems are disturbed or under stress and tend to have a lower impact on healthy ecosystems.

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Greater mobility and trade

Greater mobility and the globalisation of international trade are significantly increasing the movement of people and goods across Australia's borders. The risk of accidental introductions, particularly of diseases, insects and other invertebrate pests, has therefore increased.

The nursery trade is responsible for introducing many new plant species into Australia with a significant number escaping from gardens to become weeds (Groves & Hosking 1998). Sixty-five per cent of the weed species that pose a risk to threatened species in NSW were introduced as ornamental plants (Coutts-Smith & Downey 2006) and some are still available for sale in NSW. The nursery trade may also have played a role in introducing new diseases, such as myrtle rust, as most early detections of this disease were found in nurseries.

The aquarium industry is also responsible for introducing a number of fish and aquatic plant species that have been released into the wild and flourished. Illegal international trade in a variety of exotic species is a further pathway for unplanned introductions. The ballast water of cargo ships and hull biofouling are well-known pathways for the incursion and spread of pests into the marine environment.

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Expansions of range

Many invasive species are yet to reach the limits of their potential distribution. For example, weed species, such as orange hawkweed, boneseed, olive, cabomba and some exotic vines, occupy only a small part of their potential range. Even some widespread species, such as lantana, bitou bush, blackberry and Coolatai grass, have the potential to spread further. Emerging pest animal species, such as deer and cane toads, are also continuing to spread.

A national program is under way to eradicate red fire ants before they spread into NSW.

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Climate change

Limited information is available on how climate change might affect invasive species, but it is likely that the impact of invasive species will increase (DPI 2008a). Invasive species are generally well-adapted as colonisers of disturbed ecosystems and are likely to cope better than native species with expected changes in environmental conditions, such as increased temperatures and changes in rainfall and fire regimes. Expansions and contractions in the range of both native and invasive species due to climate change are likely to differentially favour invasive species.

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Lack of information

Information on the distribution and abundance of invasive species is patchy and largely subjective. A management framework has been established through the NSW Invasive Species Plan 2008–2105 (DPI 2008a) and a monitoring program has been set up following the mid-term review of the Natural Resources Monitoring, Evaluation and Reporting Strategy 2010–2015 (DECCW 2010d) to provide high level information. A pest and weed information system has been established for NSW parks, but there are few standardised procedures and databases for collecting and maintaining consistent information on invasive species statewide.

As most of the information available concerns threatened species, further work is needed to estimate the impacts of invasive species on the environment as a whole. This information would assist in identifying priorities for control, and managing both the impacts of invasive species on biodiversity and the adaptation of invasive species to the effects of climate change.

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Established responses

NSW 2021

NSW 2021: A plan to make NSW number one (NSW Government 2011) is the Government's 10-year plan for NSW. Under Goal 22 – 'Protect our natural environment', the plan contains the following target: 'Manage weeds and pests'. One of the strategies for achieving this target is to 'Reduce the impact of invasive species at priority sites on National Parks and Wildlife Service (NPWS) parks and reserves, leading to a positive response of native biodiversity at 50% of these sites by October 2015'.

The priority actions associated with this target are to:

  • '... use the knowledge and experience of local communities to target our resources to protect and restore natural ecosystems'
  • 'address core pest control in national parks through the delivery of NPWS regional pest management strategies …'


The most important legislation relating to invasive species management is the Noxious Weeds Act 1993, Rural Lands Protection Act 1998, TSC Act, FM Act, Game and Feral Animal Control Act 2002 and Quarantine Act 1908 (Cwlth).

Invasive Species Plan

The response of the NSW Government to invasive species impacts is set out in the NSW Invasive Species Plan 2008–2015 (DPI 2008a). The plan describes the control strategies that are most effective at different stages in the cycle of incursion and establishment of invasive species (Figure 5.7).

Figure 5.7: Strategies for managing new, emerging and widespread pests and weeds in NSW

Figure 5.7

Source: DPI 2009a

The four main strategies for managing invasive species in NSW (shown in Figure 5.7) are:

  • prevention – precautionary measures which prevent the arrival of any new species that is likely to become invasive and have a significant impact on native species and ecosystems or agricultural production
  • eradication – the detection and permanent removal of any newly arrived invasive species that is likely to have a significant impact on native species and ecosystems before it can establish self-sustaining populations
  • containment – restricting the spread of recently established or emerging invasive species which cannot realistically be eradicated
  • asset protection – targeting control at the most severe impacts of widespread invasive species in areas of high conservation value and where the prospects for successful control are greatest.

Programs that aim to prevent, eradicate or contain weeds or pests during the earlier stages of incursion are considered to be 'weed-led' or 'pest-led'. The focus of such programs is on individual weed or pest species and priorities are determined by the characteristics of each species and its potential impacts (Figure 5.7).

When invasive species are well established, programs for their control are considered to be 'site-led'. Rather than managing a specific weed or pest affecting the site, the focus is on protecting the native species or ecosystems (assets) that are most affected by the invasive species. Strategies target sites where the benefits of protection or control will be greatest.

Management of new invasive species: prevention and eradication

The most cost-effective means of managing invasive species are to:

  • prevent their incursion, or
  • if they occur, to rapidly detect and eradicate them.

Eradication is seldom feasible once an invasive species becomes established.

Preventing incursions is the primary focus of the Australian Biosecurity System for Primary Production and the Environment. This whole-of-government initiative brings together biosecurity activities undertaken by federal, state and territory governments, together with industry, landholders and key stakeholders in the fields of primary production and the environment within a national framework.

The NSW New Weed Incursion Plan 2009–2015 (DPI 2009b) was developed to address the prevention and eradication objectives of the NSW Invasive Species Plan 2008–2015 (DPI 2008a) for weeds. The incursion plan:

  • coordinates surveillance in NSW
  • identifies new weeds and weed incursions
  • provides for risk assessments of species
  • facilitates the implementation of effective barriers to prevent the establishment of weeds
  • specifies ways in which responses to weed incursions are coordinated, implemented, monitored and reported.

Few management programs target invertebrates (including insects), apart from those which deal with regular outbreaks of plague locusts. However, one of the most successful programs has been the apparent eradication of an incursion of yellow crazy ants detected in 2004 at Goodwood Island, near the mouth of the Clarence River. Following a collaborative campaign of regular treatment and surveillance of the infested area during 2004 and 2005, no yellow crazy ants have been observed on the island since 2005.

Management of emerging invasive species: containment

Containment is the main focus of strategies for managing emerging invasive species. Once an invasive species becomes established and starts to expand in range, the main objective shifts from eradication to limiting its spread (see Figure 5.7). Containment zones have been established for several weeds of national significance including bitou bush on the south and far north coasts of NSW and lantana on the south coast. The objective is to completely eradicate the weeds from these zones.

As discussed earlier in this section, the listing of noxious weeds in the schedules of the Noxious Weeds Act 1993 aims to prevent the establishment of significant new weeds and restrict the spread or limit the impact of existing significant weeds (see 'Distribution of environmental weeds in NSW').

Management of widespread invasive species: asset protection

Many invasive species are already widely established in NSW and these have the greatest impact of all invasive species on the environment. It is usually impossible to eradicate an invasive species that has become widespread or to achieve lasting control, regardless of the resources deployed. The rare exception is where a suitable biological control is identified and remains effective as is the case for prickly pear and water hyacinth, and was for rabbits for a time.

The control of widespread species must therefore be strategically targeted to reduce their impact on native species and populations, regional ecosystems and ecological communities. This targeting requires prioritising the natural values most at risk and identifying the sites where these values are greatest and controls are expected to be most effective, based on the likelihood of recovery or maintenance of biodiversity.

Biodiversity Priorities for Widespread Weeds (DPI & OEH 2011) and 13 regional documents produced by the CMAs have been developed to guide regional decision-making in:

  • identifying weed priorities, asset importance and high value sites
  • developing programs to control widespread weeds and manage assets and natural values.

Threat abatement plans (TAPs) have been developed to manage a number of invasive species identified as key threatening processes, including foxes (OEH 2011c), Gambusia holbrooki (NPWS 2003) and bitou bush (DEC 2006). All TAPs incorporate a monitoring program to measure their effectiveness and the response of the main threatened species affected.

As over 300 weed species are considered to have an impact on biodiversity, it is not practical to develop single-species TAPs for every weed species. Therefore, regional weed strategies which have a focus on protecting native species and ecosystems (DPI & OEH 2011) have been developed to apply to all widespread weeds.

Strategic priorities for weed management

Due to the number of invasive weed species that have become established in NSW, most CMAs have developed regional weed strategies, based on a strategic framework (DPI & OEH 2011) and a commonly accepted process for managing weeds (Randall 2000). These strategies take account of the weeds' impact, invasiveness, distribution and rate of spread. Highest priority is generally given to weeds that have a limited distribution and the lowest to those that are already widespread.

Controls for most pest animals and invertebrates are usually conducted individually, depending on the characteristics of the invasive species, even where the focus of the program is on protecting natural values.

Pest management strategies in national parks

Management of invasive species across NSW national parks and reserves is conducted in accordance with a statewide management framework (OEH 2011d) and 14 Regional Pest Management Strategies. These are consistent with the principles set out in the NSW Invasive Species Plan 2008–2015 (DPI 2008a). The state strategy sets the high level goals, objectives and the prioritisation methods under which regional pest and weed programs operate.

Management of aquatic pests

The FM Act lists noxious fish species and marine weeds. The species listed pose a significant threat to wildlife, ecosystems, human health or the aquaculture industry. The list is divided into three classes representing the level of threat the species poses to the aquatic environment. Most noxious fish are listed in Class 1 which prohibits their live possession and sale and applies to 108 species, 25 genera, one subfamily and one family. There is also one Class 1 noxious species of marine vegetation: caulerpa. Fisheries officers have the power to seize and destroy any live fish or plants listed as a Class 1 or 2 noxious species.

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Future opportunities

With the growth in global travel and trade, new and potentially invasive species will continue to be introduced into NSW, either deliberately or accidentally. Improvements to surveillance and biosecurity measures may be needed to prevent new incursions from threatening natural ecosystems and the productivity of farming systems.

Biological controls will continue to provide the best opportunities for effective and affordable management of widespread invasive species and further opportunities should continue to be explored.

Pathogens and diseases are emerging as an increasing threat to natural systems and are likely to present new challenges for effective management and control.

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Contents SoE 2012 View printable page Last modified: December 2012