Weeds spraying graphic

Weeds cost the NSW economy

$1.8 billion

each year in lost agricultural production and management costs

Pest fish and weed graphic

Pest animals and weeds threaten over


of threatened species and endangered ecological communities in NSW

Carp fish graphic

Introduced fish in NSW


dominates most freshwater communities

Fox head graphic

Pest animal impacts

$170 million

annual cost to the NSW economy

The NSW environment and community face significant challenges from invasive pests and weeds, and introduced pathogens. Invasive species are widespread across land, freshwater and marine environments in NSW. Ongoing resources will need to be available to manage new outbreaks and biosecurity risks.

Many invasive species have been in NSW for a long time and most parts of NSW are affected by weeds that harm native species, ecosystems and agriculture. Once established, they are difficult to control effectively and remain a significant environmental and economic issue.

Pest animals and weeds are identified as a threat to over 70% of threatened species under the Biodiversity Conservation Act 2016. In NSW, weeds account for $1.8 billion a year in lost production and control costs while the estimated annual economic loss to the NSW economy from the impact of pest animals in NSW is estimated to be more than $170 million including the cost of management actions.

Many native animals have become threatened or extinct from being preyed on or out-competed by introduced animals such as cats and foxes. Grazing and browsing by introduced herbivores such as rabbits, goats and deer has led to habitat degradation and a decline in native vegetation diversity and productivity. Pest fish threaten native fish species and aquatic ecosystems, with carp present across most of the Murray–Darling Basin.

New and emerging invasive species pose an additional threat and burden to the environment and the wellbeing of our communities. Invasive pathogens are an emerging threat to both biodiversity and agriculture.

The NSW Invasive Species Plan 2018–2021 (DPI 2018a) sets goals, strategies and guidelines to exclude, eradicate or manage invasive species. These will be monitored and reported on in a new NSW State of Biosecurity Reporting framework.

Related topics: Threatened Species | Native Fauna | Native Vegetation | River Health

NSW indicators

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Indicator and status Environmental 
Number of new invasive species detected
Stable  ✔✔ 
Spread of emerging invasive species
Stable  ✔✔  
Impact of widespread invasive species
Stabilising  ✔✔ 


Terms and symbols used above are defined in How to use this report.


Invasive species have been implicated in the decline or extinction of many native plants and animals in land-based and water-based ecosystems. See the Threatened Species, Native Fauna and Native Vegetation topics for more information.

Australian native plants and animals have co-evolved over millions of years. When invasive species are introduced, they can have major negative impacts because native species have not evolved ways to deal with them. Invasive species harm native species and the natural environment in NSW by:

  • eating or infecting them
  • competing with them for resources
  • modifying and degrading habitats
  • transmitting disease
  • reducing native biodiversity
  • disrupting ecosystem processes.

Introduced marine species can threaten marine environments and animals and the industries and communities they support. Fresh water fish, such as carp and tilapia, out-compete native species, disrupt ecosystems and reduce water quality and native biodiversity.

In NSW, many invasive pest animals and weeds were introduced intentionally before people realised how damaging they were to native species and livelihood. Examples include:

  • pigs and goats, and various crops, for agricultural production
  • pets such as cats, and garden plants
  • foxes introduced for fox-hunting
  • plants used for erosion control such as bitou bush used for sand dune stabilisation.
  • nuisance insect control, such as Eastern Gambusia introduced for mosquito control in the early 20th century.

New invasive species in NSW have been introduced inadvertently in vehicles, equipment, packing material, soil or garden refuse; or through ocean shipping. Emerging threats include:

  • pest birds such as Indian mynas
  • introduced turtles such as red-eared slider turtles
  • insects such as fire ants and yellow crazy ants.

In this report, estimated costs to the economy do not include environmental and social impacts but do include the costs of control in environmental areas.

Definitions of invasive species

Pest animal: an animal (usually non-native) having, or with potential to have, an adverse environmental, economic, or social impact on native plants and animals

Weed: a non-native plant or native plant removed from its natural habitat that has the risk of negative environmental, economic, or social impacts

Invasive species: A general term to include pest animals, weeds or other organisms such as pathogens that are introduced to places outside their native ranges, where they negatively affect local ecosystems and species (IUCN 2014).

Indicators for future reporting

This report adopts similar indicators to previous State of the Environment reports. Development of new indicators to more effectively identify the impacts of invasive species and the effectiveness of management practices were published in the NSW State of Biosecurity Report (DPI 2018b). Following the first publication, a report will be published every four years. Future reports will:

  • check progress
  • refine the indicators
  • report on changes in distribution and population size of invasive species in NSW
  • report on the effectiveness of stakeholder and government programs.

Future NSW State of the Environment reports may adopt similar NSW State of Biosecurity indicators.


Habitat disturbance

Factors stressing the natural environment including the addition of nutrients, altered hydrological regimes, and the frequency and severity of altered fire regimes promote the invasion of introduced species. This, in turn, puts more pressure on native plants, animals and ecosystems (Lake & Leishman 2004).

Introducing weeds through trade

Greater mobility and the globalisation of international trade are significantly increasing the movement of people and goods across borders. This increases the risk of accidentally introducing pathogens, insects and other invertebrate pests.

Greater Sydney currently receives more than 38.5 million international visitors, over 500,000 tonnes of air freight and one million shipping containers every year (DPI 2018b).

Many new plant species have already been introduced to NSW via the nursery trade, with many escaping from gardens to become weeds (Groves & Hosking 1998). Of the weed species that threaten endangered species in NSW, 65% were introduced as ornamental plants (Coutts-Smith & Downey 2006).

Other industries that have introduced pests and weeds into NSW:

  • the black-market pet trade introduces exotic animals, especially reptiles
  • the aquarium industry introduces exotic fish such as goldfish and tilapia, and aquatic plant species that have been released into the wild and flourish
  • the ballast water of cargo ships and hull biofouling help spread pests into the marine environment.

Expansions of range

Many invasive species have not yet reached the potential limits of their distribution. For example, weed species such as orange and mouse-ear hawkweed, boneseed, African olive, cabomba and some exotic vines occupy only a small part of their potential range.

Already widespread weeds such as lantana, bitou bush, blackberry and Coolatai grass can spread further without control.

Emerging pest animal species such as deer and cane toads have not yet reached their potential range. While deer are continuing to expand, the spread of cane toads has been contained.

Climate change

The impact of climate change on weed invasion is becoming clearer in Australia. As climate regimes continue to change, it is likely that new invasive plants will emerge (Duursma et al 2013).

The extent of suitable habitat for invasive species has been modelled and predicted under current and future climate change scenarios.

  • The alpine eco-region in NSW may be particularly vulnerable to future incursions by weeds (Duursma et al 2013).
  • Changing climate regimes may create more favourable conditions for weeds in southern NSW.
  • Many native species and ecological communities affected by climate change will become more vulnerable to the threat of pest animals and weeds (NSW Government, 2011).

As a result, climate change scenarios and species distribution models will be useful in predicting future breakouts and spread of invasive plants and to devise suitable management strategies.

The New South Wales State of Biosecurity report 2017 (DPI 2018b) notes other pressures that are likely to affect biosecurity in NSW, including:

  • the need to maintain the willingness of government, industry and the community to share responsibility for controlling invasive pests and weeds
  • population growth combined with urbanisation and land clearing for development is providing an increasing biosecurity risk, but also opportunities to engage people in surveillance, detection and control
  • the need to embrace new technology and strategies to tackle the changing risk profile of biosecurity in NSW.


The NSW Government determines priorities for control of, and resources to manage, invasive species. The highest priority species for protection are threatened species and other entities listed under the Biodiversity Conservation Act. For cross-tenure impacts, the community can participate through the regional planning process.

All land managers have a duty to prevent, eliminate or minimise the risk of invasive species under the Biosecurity Act 2015, including participating in coordinated regional strategies.

NSW Invasive Species Plan

The NSW Invasive Species Plan 2018–2021 (NSW Government 2018) focuses on the four goals to:

  • exclude – prevent the establishment of new invasive species
  • eradicate or contain – eliminate, or prevent the spread of new invasive species
  • effectively manage – reduce the impacts of widespread invasive species
  • capacity building – ensure the NSW Government and community can manage invasive species.

These four goals align with the invasion process from pre-arrival of new invasive species to widespread establishment (as illustrated in Figure 15.2). Prevention is the most cost-effective way to minimise the impacts of invasive species. Once an invasive species has appeared, it can colonise areas rapidly. Successful control requires a rapid effective response. Once widespread, the eradication of invasive species over wide areas of different land tenure is rarely practical. Priorities for the control of these species may include focused efforts in areas where the benefits of control will be greatest for environmental, primary production or community benefit. 

The plan:

  • dedicates resources to manage invasive species
  • identifies key responsibilities of the key parties involved in invasive species management in NSW
  • supplies critical actions to be undertaken up to 2021.
Figure 15.2: Actions appropriate to each stage of invasive species incursion
Invasive species management - four approaches are aligned with the invasion process from arrival to widespread establishment


NSW DPI, cited as Biosecurity Victoria, DPI, Victoria

NSW Biosecurity Strategy 2013–2021 and NSW Biosecurity Act 2015

The NSW Government launched the NSW Biosecurity Strategy 2013–2021 in May 2013. The strategy:

  • explains the principles for sharing responsibility for effective biosecurity management
  • increases awareness of biosecurity issues in NSW
  • outlines ways in which the NSW Government will partner with other government agencies, industry and the community to identify and manage biosecurity risks.

A key component of the strategy is the NSW Biosecurity Act 2015 and Biosecurity Regulation 2017. The Act and Regulation will provide for the prevention, elimination, minimisation and management of biosecurity risks.

One of the key components of this legislation is the introduction of a General Biosecurity Duty. This duty requires any person dealing with biosecurity matter (such as pest animals or weeds) or a carrier, and who knows or ought to know of the biosecurity risks posed by that matter, to take measures to prevent, minimise or eliminate the risk as far as is reasonably practicable. The occupier of lands (both private and public) is required to take all practical measures to minimise the risk of any negative impacts of pest animals or weeds on their land. The occupier could discharge their duty by complying with control actions outlined in the LLS regional strategic weed plans and regional pest animal management plans.

NSW Authorised Officers undertake regular audits and inspections to ensure implementation of biosecurity practices to enable ongoing market access for trade. In 2016–17, 6,650 compliance and enforcement activities were conducted to protect NSW biosecurity (DPI 2018b). Local Land Services and Local Control Authorities also support local land holders to meet their responsibilities.

Land Management (Native Vegetation) Code 2018

The Land Management (Native Vegetation) Code 2018 is created under section 60T of the Local Land Services Act 2013. The Code commenced on 25 August 2017 and facilitates native vegetation management on rural land, enabling landowners to productively manage their land while supporting biodiversity and managing environmental risks. The Code allows the removal of invasive native plant species on private land that have reached unnatural densities and dominate an area. Management of invasive native species promotes the regeneration and regrowth of native vegetation that is not invasive, contributing to positive environmental outcomes.

Containment lines

To effectively manage new and emerging invasive species, the best method is to eradicate or contain them before they can cause significant environmental impacts.

Establishing strategic containment lines can be an effective method of control. Containment lines are mapped lines, often delineated along a natural feature such as a river or along local government or other management boundaries.

A containment line is placed around the core distribution of the weed or pest, which is eradicated. Any population outside the containment line, and any isolated populations well away from the core distribution area are then fragmented or depleted and can be easily eradicated. 

Regional weed and pest committees

The NSW Government has established regional weed committees and regional pest animal committees in each Local Land Services region. The committees coordinate regional pest animal and weed management activities on both public and private land. These committees have developed 11 Regional Weed Plans and 11 Regional Pest Animal Management Plans, which identify actions that can help land managers to manage weeds and pest animals on their land under the NSW Biosecurity Act 2015.

Saving our Species program

Biosecurity control measures provide a general level of protection for species and ecosystems. Saving our Species sets specific priorities for ensuring threatened species are secured in the wild. Many of the actions to recover species under Saving Our Species focus on controlling pest animals and weeds, which affect over 70% of listed threatened species, populations and ecological communities.

For more information on threatened species protection and Saving Our Species, see the Threatened Species topic.

National Carp Control Plan and NSW action

The National Carp Control Plan includes all Australian jurisdictions working in partnership to identify safe, effective and integrated measures to control carp populations in Australia, focusing on biocontrol methods.

NSW is a collaborative partner in research being undertaken as part of the National Carp Control Plan and participates in the Science Advisory Group, Policy Advisory Group, Operations Working Group, and Communications Working Group.

Between 2008 and 2017, the NSW Government spent $107 million on significant biosecurity plant and animal disease and pest incident responses in NSW. It has also made a significant contribution to sharing costs to control incidents in other states and territories. Future opportunities include:

  • Continual improvements to surveillance and biosecurity measures can help prevent new and potentially invasive species from threatening natural ecosystems and the productivity of farming systems.
  • Development of biological control solutions and other new techniques will help provide opportunities to effectively and affordably manage widespread invasive species.
  • Pathogens of native plants and animals continue to emerge as an increasing threat to natural systems and are likely to present challenges for effective management and control.


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