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New South Wales State of the Environment
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SoE 2003 > Biodiversity > 6.4 Introduced terrestrial species

Chapter 6: Biodiversity

6.4 Introduced terrestrial species

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6.4 Introduced terrestrial species

Little progress on dealing with introduced species, although the overall number is reasonably static

Despite substantial efforts to eradicate them, NSW still contains essentially the same group of introduced vertebrate pests that were present in the early 1900s, except for the addition of the cane toad that has entered the north of the State. Approximately 1500 plant species have been introduced since European settlement and the rate appears to be accelerating. Much less is known about the ecological impact of introduced invertebrates and microorganisms, although it is likely to be significant.

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NSW Indicator


Status of Indicator

6.7 Introduced terrestrial species

The number and extent of pests and weeds is not being reduced in most cases.

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Importance of the issue

Some introduced plant and animal species place substantial pressure on society, the economy and the environment in NSW. They have caused extensive damage to native ecosystems and contributed to extinctions and the decline of many native taxa by preying on wildlife and competing with native species. In addition, the presence of introduced species can significantly degrade and reduce habitats, by damaging soil and watercourses, spreading weeds, and carrying diseases. These disturbed environments may become even more vulnerable to invasion by other exotic species. When a species is introduced into a new environment, it is no longer subject to its former natural population constraints, such as predation, competition, parasitism and disease, and this may give it an advantage over local species.

Most areas of NSW have now been colonised by one or more introduced species. The monitoring and management focus is on those organisms known to cause serious problems or pose threats.

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Approximately 1500 plant species have been introduced into NSW since European settlement (RBG 2003). Of these, approximately 3–4% represent a major threat to ecological and economic systems in NSW (Olsen 1998; Benson 1999; NPWS 1999b; NPWS 2001; NPWS 2002c; NSW Agriculture data, as at November 2002). The NSW National Parks and Wildlife Service (NPWS) Weed Management Programs report for 2002 estimates that over 2800 introduced plant species have become naturalised in Australia. Approximately 25% of these are significant or potentially significant environmental weeds (NPWS 2002c).

Most introduced plant species appear to have entered NSW legally for ornamental and domestic horticulture, before escaping into native ecosystems. Despite recognition of the damage caused by introduced weed species, the rate of introduction appears to be increasing.

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Vertebrate pests

Vertebrate pests are widespread throughout Australia and distributed across all bioregions and land tenures in NSW. The main mammal pests in NSW are the rabbit, wild dog, fox, and feral deer, pig, goat and cat. Table 6.5 outlines areas where the main vertebrate pests have been found and highlights their impacts. Some impacts are prolonged and cumulative, such as land degradation caused by rabbits, while others are short-lived, such as those resulting from plagues of house mice. Vertebrate pests are also a major problem within the State's reserve system, with 80% of reserves having at least one species of pest (English & Chapple 2002).

Table 6.5: Main vertebrate pests and their impacts


Main areas found

Main impacts


Extent has contracted in western NSW over recent years (associated with the release of rabbit calicivirus disease), but persistent populations exist across many other regions

Soil erosion and land degradation; negative impacts on agricultural production

Feral pigs

Widespread in the Western Division, but also found in many large areas of the central and northern tablelands and eastern coast of NSW

Soil erosion and land degradation; risk of exotic disease; impact on pasture production


All landscapes of NSW

Predation of wildlife and lambs; risk of exotic disease

Feral goats

Widespread in the Western Division and also found in many moderately sized populations throughout most of eastern NSW

Impacts on native vegetation; competition for pasture; risk of exotic disease

Feral deer

Mainly distributed in eastern NSW in small isolated pockets

Competition for pasture; threat to native vegetation communities; risk of exotic disease

Wild dogs

Abundant along the eastern regions and in far western NSW

Predation of wildlife and livestock

Feral cats

Throughout NSW

Predation of wildlife

Source: NSW Agriculture and NPWS

Cane toads (Bufo marinus) have entered NSW from Queensland. They are now established on the North Coast as far south as the Clarence River near Grafton, but isolated breeding colonies have been confirmed at Angourie near Yamba and around Lake Innes near Port Macquarie (NPWS 2002b).

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Invertebrate pests

Many introduced invertebrates have become successfully established in NSW, but far less is known about their ecological impacts. Invertebrates often have fundamental roles in ecosystem processes, such as pollination, aeration of the soil and as a source of food for other organisms. Their introduction may therefore have far-reaching consequences for entire ecosystems.

The South American red imported fire ant (Solenopsis invicta) was first reported in Brisbane in 2001. Although it has not been detected in NSW, this very aggressive species poses a serious risk to the State as it is a public, agricultural and environmental nuisance. When disturbed, fire ants aggressively attack intruders, including humans, pets, livestock and other animals. They are also a significant seed harvesting species, which can have an impact on native and introduced grasslands and crops.

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Disease organisms

Little is known about the ecological impacts of displaced native and introduced microorganisms, although they are likely to be significant (Smith et al. 1999). Two of the small number of microorganisms where impacts have been found are cinnamon fungus (Phytophthora cinnamomi), root rot and frog Chytrid fungus. These water-borne pathogens are having significant impacts on many native species, which are being exacerbated by human activities that help to spread them, such as soil and water disturbance and trafficking of infected soil, mud or water by vehicles, walking shoes and camping equipment (Nadolny 1995; NPWS 2002a). Reappraisal of the threat to biodiversity from Phytophthora led to its recent listing as a key threatening process under the Threatened Species Conservation Act 1995 (McDougall & Summerell in press).

Exotic microorganisms that evade quarantine controls present significant risks, especially where they are known to have had an impact on Australian species overseas. For example, eucalypts grown as exotics in South America suffer from the very damaging pathogen guava rust.

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Introduced genes

Introduced species are able to exchange genetic material with local populations through natural processes. This can cause genetic 'pollution' in local populations, which alters natural patterns of genetic variability and potentially causes the loss of native species if hybrids replace them. Although the process occurs naturally, human intervention often speeds it up.

Genetic modification can provide benefits to the agricultural industry by increasing yields, decreasing growing costs, and increasing the quality of the produce. Although genetically modified crops have the potential to reduce some of the environmental impacts of agriculture, there is also the potential for these technologies to have a negative impact on the natural environment. Table 6.6 outlines some of the potential benefits and risks associated with crops developed in this way.

Table 6.6: Potential benefits and risks associated with genetically modified crops

Potential benefits

Potential risks

A reduction of pesticide applications to crops engineered for resistance to insects and pathogens Retention of treated crops contributes to improved soil management, less soil erosion and minimum or no-till cultivation practices Less clearing of native vegetation through the production of crops engineered to grow in less hospitable environments, such as saline soil

Increased herbicide residues in water, soil and food from their wider use on herbicide-resistant crops Escape of genetically modified organisms into the natural environment Transfer of altered genes to non-target organisms through natural gene exchange processes, such as the transfer of herbicide tolerance to weeds Possible changes to the gut flora of wild herbivores

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Response to the issue

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Weed control

The NSW Noxious Weeds Act 1993 provides for the identification, classification and control of weed species considered noxious or a priority problem. To date, Weed Management Plans have been developed for parthenium weed, alligator weed, bitou bush, branched broomrape, hawkweeds, knapweeds, miconia, Mexican feather grass and cabomba. A draft strategy has also been prepared to control salvinia.

Many of the weed control programs run by NPWS focus on 'environmental' rather than 'economic' weeds, which are those of concern to agriculture and other industries. This is because of the need to reduce the adverse impacts of these species on biodiversity. Management measures used by NPWS include the development of Weed Management Plans, reserve rehabilitation plans and monitoring programs. For example, NPWS has coordinated a strategic approach to manage bitou bush in coastal ecosystems and implemented a program to protect species in the Barrington Tops National Park from invasion by Scotch broom.

NSW Agriculture focuses on priority agricultural weeds. The department recently supported the employment and training of weed officers by local councils, resulting in a significant increase in their numbers in the field. Biological control agents have also been used to combat some of the more noxious weeds. Currently, 123 control agents are being developed to control 37 weed species of interest to NSW (NSW Agriculture data, as at June 2002). Of these, 14 have had a significant impact on the target weed population including:

  • Paterson's curse, which is being killed by crown and root weevils in some areas
  • alligator weed, which has been limited to bank infestations in the Georges River by a flea beetle
  • bitou bush, which is under attack from tip moths and seed flies.

There is a national research program on the biological control of bitou bush while collaborative research is under way in NSW on the biological control of lantana.

As pests and weeds do not respect human boundaries, management on private lands can be undermined by a lack of management on public lands or vice versa. Thus several NPWS weed control programs target agricultural weeds as well. To facilitate such programs, a regional/catchment approach to both weed and pest animal management is used, involving a range of stakeholders (NPWS 2002c).

In addition, a large number of community groups are involved in the removal of exotic weeds from remnant areas of native vegetation and sensitive environments. Bush regeneration groups formed and funded by councils, private residents, private industry, the National Trust of Australia and groups supported by government, such as Landcare, Coastcare, Rivercare and Dunecare, make significant contributions to the control of weeds. Not only do they supply resources, especially labour, for this work, but they also help to educate others in their communities about responsible disposal of garden waste and preventing the spread of weeds.

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Pest animal control

The main responses to managing pest animals in NSW include:

The NPWS aims to manage populations of pest animals to minimise their adverse impacts on natural and cultural heritage and on neighbouring lands. It directs resources to those species or localities where the benefits of control are likely to be greatest (NPWS 2002b; NPWS 2002c). In 2000–01, the NPWS conducted more than 900 pest animal control programs of which more than 70% were run in collaboration with neighbouring landholders and other stakeholders. NSW Agriculture conducts research and develops programs to reduce the environmental and agricultural impacts of vertebrate pests, such as rabbits, foxes, feral goats and wild dogs.

In 2001 a threat abatement plan was approved for the red fox (Vulpes vulpes). The plan identifies species most at risk from fox predation and the localities where the benefits of fox control will be greatest.

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Preventing the introduction and movement of species

Prevention of the introduction of new species is handled primarily at the national level, although NSW contributes to national programs, such as intergovernmental efforts to eradicate the South American red imported fire ant from Australia. In 2001–02, new and upgraded regulations were introduced to control the movement of soil and other materials out of fire ant-infested areas to stop the pest spreading to NSW. Approximately $137 million of state and federal funds will be spent over the next five years to combat this pest.

Nationally, the Australian Quarantine and Inspection Service facilitates the import of animals, plants, and animal and plant products, which are free of exotic diseases and pests. Quarantine polices aim to protect Australia's environment and human health, as well as the sustainability of the nation's agricultural industries.

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Management of genetically modified organisms

The Gene Technology Act 2000 (Cwlth) has set up a national scheme to regulate the use of gene technology on the basis of its likely impact on human health and the environment. This is complemented by a national regulatory regime for food safety, which specifically addresses genetically modified foods.

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Effectiveness of responses

Well-tested, robust and accepted management approaches and control techniques are available to reduce the damage pests cause. However, pest numbers continue to rise in NSW despite more than a century of concerted effort under a wide range of control programs (English & Chapple 2002). Pest animals continue to cause significant damage to the environment and agriculture.

Despite the stream of cane toad introductions to the State, the animals have not yet established breeding colonies south of Taree. With the exception of colonies at Angourie and Lake Innes, all cane toads reported south of Grafton were individual animals only.

Some introduced species have been successfully controlled or reduced using biological elements, including prickly pear, salvinia and rabbits.

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Future directions

Prevention will be the key to avoiding potential problems with introduced species in the future.

Agricultural industry and householders can use measures to eliminate the spread of domesticated plants and animals into native ecosystems, such as maintaining buffer areas and carefully disposing of unwanted biological material. Government and industry can work to transform current planting preferences to substitute plant varieties that are based on native species in agriculture, urban development and other activities.

Government can also ensure that Catchment Blueprints adequately address the issues associated with pests.

Individuals can move towards the use of local native species for gardens in environmentally sensitive areas. They can also act to stop the spread of weeds from their properties, control and desex pets, and not dump unwanted animals and plants in the bush.

The community can also continue the valuable involvement in bushland restoration projects and activities to identify the spread of feral animals.

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Linked issues

2.1 Population and settlement patterns

4.1 Land-use changes

6.1 Terrestrial ecosystems

6.2 Native vegetation clearing

6.3 Terrestrial species diversity

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