SoE 2009 > Biodiversity > 7.4 Invasive species

7.4 Invasive species

Invasive species remain one of the greatest threats to biodiversity in New South Wales and one of the most intractable. Over half of all listed key threatening processes relate to invasive species, and pests and weeds have been identified as a threat to over 70% of all threatened species.

The main vertebrate pests found in NSW are now widespread across the state. Predation by foxes and cats is implicated in the decline or extinction of numerous small- to medium-sized animals. Introduced herbivores, particularly rabbits and feral goats, have an impact on native species and ecosystems through overgrazing of native vegetation, land degradation and competition with native herbivores.

To date around 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 arrive and become established. Combining prevention, early detection and rapid eradication is the most cost-effective way to minimise the impacts of these new arrivals.

Complete eradication is seldom feasible once an invasive species becomes widely established, so control must then focus on protecting assets where the environmental benefits of control will be greatest.

There is no effective basis to estimate the full impact of invasive species upon the environment.

NSW indicators

Notes: Terms and symbols used above are defined in About SoE 2009 at the front of the report.

Introduction

Historically, introduced species have contributed significantly to the decline and extinction of native species in NSW, with foxes and cats, in particular, implicated in the extinction of numerous small- to medium-sized ground-dwelling mammals (NPWS 2001). It is also well-established that human disturbance has greatly accelerated the invasion rate of introduced species (Coutts-Smith & Downey 2006; Coutts-Smith et al. 2007).

Statewide monitoring programs have recently been established, so for the first time it is possible to report on the distribution and abundance of new and emerging pests and weeds, and widespread pest species. Many invasive species are broadly established across NSW and most areas now contain a range of weed and pest animal species.

Little is known about the magnitude of the collective impacts of invasive species, either on biodiversity or the whole environment. Some recent advances have been made in our understanding of the impacts of invasive species, specifically on threatened species (Coutts-Smith & Downey 2006; DEC 2006a; Coutts-Smith et al. 2007; NLMG 2009). It is clear, however, that the scale of the task of controlling the impacts of widespread invasive species vastly exceeds the resources available, and that complete eradication of established species is rarely achievable.

Status and trends

Extent of the issue

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 other impacts (McLeod 2004), while the cost of pest animals to the Australian economy is over $1 billion annually (DPI 2008a). Pest animal control alone exceeds $60 million annually in Australia (NLWRA 2008). In NSW weeds account for $600 million per annum in lost production and control costs.

Large numbers of invasive species are widely established and most areas of the state contain a range of weeds and pest animals. Around 3000 introduced weed species have established self-sustaining populations in Australia. Over 1650 of these have naturalised in NSW, and more than 300 have been recognised as significant environmental weeds (Downey et al. 2009, unpublished data).

More than 650 species of land-based animals have also been introduced to Australia since 1788 and, of these, 73 have established wild populations (NLWRA 2008). However, not all of these species are regarded as a threat to biodiversity. Aquatic pest species make up around a quarter of all freshwater fish species in NSW rivers and over 200 species of marine organisms have been introduced into Australian waters (DPI 2008a). It is not presently known how many invertebrate species have been introduced into Australia (Coutts-Smith et al. 2007).

Distribution of pest animals in NSW

For management purposes invasive species are described as widespread, emerging or new, and each of these categories is managed differently. A widespread species is any invasive species that is firmly established within a region. An emerging species is any invasive species that has newly established and is expanding its range. A new species is any invasive species that has not been recorded previously in NSW, but has the potential to invade.

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 of greatest concern are rabbits, feral goats and feral pigs, while in aquatic environments European carp and gambusia are the most significant pests (Table 7.9)

Table 7.9: Main introduced animal species with an impact on listed threatened species

Source: Coutts-Smith et al. 2007

Notes: Introduced species are species found outside their normal range and include both exotic species and translocated natives.
^* Mainland NSW species that have translocated to Lord Howe Island where they are a threat to endemic native species
^** While tench was identified as a threat to a number of threatened species at the time of their listing, it has not been recorded in NSW for over a decade.
^*** Native species that is itself listed as threatened on the mainland but has been translocated to Lord Howe Island where it has a become a threat to endemic species
^**** Native species translocated to other rivers in NSW

Widespread species

The distribution and abundance of seven widespread pest animals – foxes, feral cats, feral goats, rabbits, feral pigs, wild dogs and carp – have been surveyed and Map 7.5 presents the overall results. The map shows that these pest animals are broadly and relatively evenly distributed across the whole state and that no part of NSW is unaffected by the main pest animal species. The heaviest concentrations of pest animal species are in some parts of the north-west of the state.

Map 7.5: Distribution and abundance across NSW of widespread pest animals with a high impact

Note: The distribution and abundance index scores were determined by combining the frequency and abundance of each species recorded in each grid cell.

New and emerging species

The distribution and abundance of five new and emerging pest animals of concern – camels, horses, donkeys, deer and cane toads – have been surveyed and Map 7.6 presents the overall results. These animals are scattered across the state with the greatest numbers along the coastal slopes and plains. Deer have the widest distribution of the species surveyed and are thought to be expanding into forested areas that have remained relatively free of pest animals.

Map 7.6: Distribution and abundance across NSW of new and emerging pest animal species

Note: The distribution and abundance index scores were determined by combining the frequency and abundance of each species recorded in each grid cell.

Distribution of environmental weeds in NSW

Invasive weeds may be exotic or translocated native species, but those that have the greatest environmental impact are predominantly introduced species. Weeds threaten biodiversity both directly through competition and indirectly through their impacts on ecosystem structure and function.

Under the Australian Weeds Strategy, 20 introduced plants are identified as Weeds of National Significance because of their invasiveness, potential for spread, and economic and environmental impacts. A number of these are widespread and include alligator weed, bitou bush, blackberry, bridal creeper, Chilean needle grass, lantana, salvinia, serrated tussock and some species of willow. A number have restricted distribution, for example Athel pine, boneseed, cabomba, hymenachne, mesquite and parkinsonia, while occasional parthenium weed incursions from Queensland have been eradicated.

A recent analysis of 1650 weed species in NSW found that more than 300 are likely to have significant impacts on biodiversity (Downey et al. 2009, unpublished data). Table 7.10 contains a list of the 20 most commonly identified environmental weeds in NSW, identified in terms of the number of threatened species that are impacted by them.

A number of weeds have also been identified as collective threats based on functional groupings: these include exotic grasses, vines and scramblers, legumes and aquatic weeds. While they do not figure strongly in the listings of individual weeds, the first two have a significant effect collectively (see Figure 7.7). The significance of aquatic weeds may have been underestimated in this analysis (Coutts-Smith & Downey 2006).

Table 7.10: Most commonly identified weed species posing a threat to biodiversity in NSW

Source: Coutts-Smith & Downey 2006; DECCW data 2009

Widespread species

There are so many widespread weeds in NSW that it is not practical to map their distribution and abundance. A coarse pattern of distribution is available by looking at the number of weeds and the number of threats aggregated by catchment management authority (CMA) region (Table 7.11).

Table 7.11: Number of weeds in each catchment management authority region in NSW

Source: Coutts-Smith & Downey 2006

The Sydney region has the highest number of weeds (758) and the highest number of threatening species (101), while the lowest number of weeds (187) and threatening species (25) is in the Lower Murray–Darling region. Numbers are highest near the coast and in high rainfall areas, and decline from east to west (Coutts-Smith & Downey 2006).

Despite some variation, no part of the state is unaffected by weeds that threaten biodiversity. Weeds now make up more than 20% of the flora of all regions of NSW.

New and emerging species

Map 7.7 shows the spatial distribution of new and emerging invasive weed species.

Map 7.7: Distribution of new and emerging weeds in NSW

Note: The distribution and abundance index scores were determined by combining the frequency and abundance of each species recorded in each grid cell.

The weed abundance index used in Map 7.7 is based on the species listed as noxious weeds (classes 1, 2, 3 and 5), either within a local government area (LGA) or across the whole of NSW. The system of listing weeds as noxious is a mechanism intended specifically to prevent their spread (see Responses) so these listings correspond well with the categories of new and expanding weeds. Broadly, there are greater concentrations of these weeds in eastern coastal regions, around major urban centres and in higher rainfall areas. Most new weed incursions are garden escapes (Groves & Hosking 1998).

Distribution of aquatic pests

The NSW Government is collecting baseline data on new, emerging and widespread introduced freshwater fish species from 470 sampling sites. This will deliver improved information for the next SoE report. So far, 411 sites have been sampled, with 40% of all fish recorded at these sites introduced fish species. Table 7.12 provides some detail about the abundance of individual introduced fish species recorded.

Table 7.12: Introduced fish at sampling sites

Source: DPI data 2008

Since 2006, the platy (Xipophorus maculates), a fish species native to Mexico, was the only newly introduced fish species recorded in NSW rivers.

More than 200 exotic species have been introduced into Australia's marine environment. Of those found in NSW, very few are listed on the schedule of marine pests to be targeted in Australia. Most of these have limited distributions and are not considered a serious threat to biodiversity in NSW. These include several species of toxic dinoflagellates and several species of invertebrates. The European shore crab has been recorded in 12 estuaries or coastal lakes, from Batemans Bay south to the Wonboyn River, while the European fanworm and New Zealand screw shell are both restricted to Twofold Bay (DPI 2008b).

The aquarium weed caulerpa (Caulerpa taxifolia) is the most significant threat to the marine environment as it spreads easily from small fragments and can quickly colonise seagrass beds. An invasive strain of caulerpa was first recorded in NSW coastal waters in April 2000. It has since spread to 14 estuaries, with new infestations in Batemans Bay, Durras Lake, the Hawkesbury River and Lake Wallangoot since SoE 2006 (DEC 2006b), while its elimination from Lake Macquarie has recently been confirmed.

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 Threatened Species Conservation Act 1995 (TSC Act) and the 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). The level of impact of selected key pest and weed threats to threatened species is illustrated in Figure 7.7.

Figure 7.7: Numbers of NSW species, populations and ecological communities threatened by selected terrestrial invasive species

Source: Modified form Coutts-Smith & Downey 2006

Notes: The threatened species, populations and ecological communities are those listed under the TSC Act.
The invasive species selected are generally those listed as key threatening processes.
Data was compiled by aggregating the threats affecting each threatened species, identified at the time of listing, across all threatened species.

Individually, widespread pest animals, such as feral cats and foxes, have a greater impact than individual weed species. However, collectively, 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 directly threaten 40% of them (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 a relatively large number of invasive species as key threatening processes (KTPs) under both state and federal legislation. Eighteen of the 33 listed KTPs in NSW deal with the impacts of weed and pest animal species. Pest animals listed as KTPs include rabbits, foxes, feral cats, ship rats, feral pigs, feral goats, 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 and Scotch broom, while vines and scramblers are listed collectively, as are exotic perennial grasses.

Broader environmental impacts

The total impact of introduced species on biodiversity or the environment as a whole is difficult to quantify. Most of the information available on the impacts of invasive species on biodiversity concerns impacts specifically on threatened species, not on all flora and fauna (Coutts-Smith & Downey 2006). Even this is descriptive only of the extent of impacts and is not in any way indicative of their magnitude.

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

Pressures

Invasive species, which are the subject of this issue, are themselves a pressure on the environment. Therefore the discussion that follows relates specifically to risk factors that exacerbate the impacts of invasive species.

Habitat disturbance

Disturbed and nutrient-enriched ecosystems are at greatest risk of incursion by invasive species. This applies to both physical disturbances and imbalances in the natural biota (Lake & Leishman 2004). Invasive species are generally unaffected by the constraints that operate in intact natural systems and are able to rapidly exploit disturbed areas, where natural systems are under stress.

Greater mobility and trade

Greater mobility and the globalisation of international trade have significantly increased the movement of people and goods across Australia's borders in recent years. This increases the risk of accidental introductions, particularly of diseases and insect and other invertebrate pests. The ballast water and hull fouling of cargo ships are well-known pathways for the incursion of many pests into the marine environment.

The nursery trade is responsible for introducing many new plant species into Australia and many have escaped from gardens to become weeds. Sixty-five per cent of the weed species in NSW that pose a risk to threatened species were introduced as ornamental plants (Coutts-Smith & Downey 2006) and some are still available for sale in NSW. The aquarium industry is 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.

Changes in distribution

Many invasive species are yet to reach their distribution limits. For example, weed species such as orange hawkweed, boneseed, olives, cabomba and some exotic vines occupy only a small part of their potential range. Even widespread species, such as lantana, bitou bush, blackberry and Coolatai grass, have the potential to spread further. Pest animal species such as cane toads are continuing to spread southwards and westwards from the far north coast, while a national program is under way to eradicate red fire ants before they spread into NSW.

Climate change

Limited data is available on the potential impacts of climate change on invasive species in the future (DPI 2008a). It is likely that the impact of invasive species will increase as a result of climate change. Invasive species are generally well adapted as colonisers of disturbed ecosystems and will probably cope better with changes in environmental conditions, such as increased temperatures and changes in rainfall and fire regimes that are likely to result from climate change. Species movements and contractions of both native and exotic species due to climate change are likely to differentially favour invasive species. The Weeds and Climate Change program is a collaborative research program to understand the interaction between climate change and invasive species, with preliminary results of this research now becoming available.

Lack of information

Information on the distribution and abundance of invasive species is patchy and largely subjective in nature. A framework has been established through the New South Wales Invasive Species Plan 2008–2015 (DPI 2008a) and the Natural Resource Management Monitoring, Evaluation and Reporting (MER) Strategy. In many cases there is a lack of standardised procedures and databases to collect and maintain consistent information at the statewide level.

Other than the impacts on threatened species, there is no basis to record or estimate the impacts of invasive species on the environment. This lack of information limits the ability to identify priorities and manage the impacts of invasive species on biodiversity and reduce the threats they pose to the environment as a whole. The lack of information about the impacts of invasive species upon systems and processes at the landscape level is a significant risk in effectively managing adaptation to climate change.

Responses

Target 4 under Priority E4 of State Plan 2006: A new direction for NSW (NSW Government 2006) is: 'By 2015 there is a reduction in the impact of invasive species'. The MER Strategy is being implemented to monitor progress towards all E4 targets. A review of State Plan 2006 commenced in August 2009 and this may adjust some of the plan's priorities and targets.

Legislation

A variety of laws, policies and programs are administered by a range of government agencies to manage invasive species in NSW. The most important legislation relating to invasive species management are the Noxious Weeds Act 1993, Rural Lands Protection Act 1998, Threatened Species Conservation Act 1995 (TSC Act), Fisheries Management Act 1994 (FM Act), Game and Feral Animal Control Act 2002 and the Commonwealth Quarantine Act 1908.

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 a range of strategies to control or reduce the impacts of invasive species that are most effective at different stages in the cycle of incursion and establishment of an invasive species (Figure 7.8).

Figure 7.8: Strategy for managing new, emerging and widespread weeds in NSW

Source: DPI 2009a

The four main strategies identified are:

• prevention, precautionary measures with the objective of preventing the arrival of any new species that are likely to become invasive and have a significant impact
• eradication, the detection and permanent removal of any newly arrived invasive species that is likely to have a significant impact before it can establish a self-sustaining population
• containment, restricting the spread of recently established or emerging invasive species for which there is no longer any realistic prospect of eradication
• protection, targeting control at the most severe impacts of widespread invasive species to areas of high conservation value (asset protection).

Management of invasive species

Management of new invasive species: prevention and eradication

Prevention of initial incursions and the early detection and rapid eradication of new incursions are the most cost-effective ways of managing invasive species, as eradication is seldom feasible once an invasive species has become established. This is the primary focus of the Australian Biosecurity System for Primary Production and the Environment (AusBIOSEC). The system is being enhanced through a whole-of-government project, which was established in October 2005. The aim is to bring together, under an overarching national framework, biosecurity activities being undertaken by federal, state and territory governments, industry, landholders and other key stakeholders in primary production and the environment.

The NSW New Weed Incursion Plan 2009–2015 (DPI 2009b) has recently been developed to address the first two objectives of the NSW Invasive Species Plan 2008–2015 (DPI 2008a) as it relates to weeds. This plan will help coordinate the surveillance and identification of weeds and weed pathways, risk assessment of species and implementation of effective barriers to prevent their establishment. The plan will also outline how responses to weed incursions will be coordinated, implemented, monitored and reported.

There are few management programs targeting invertebrates, 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 to limiting its spread. Containment zones have been established for several Weeds of National Significance including bitou bush (on the south coast and far north coast) and lantana (south coast). The objective of weed management in these zones is complete eradication of the weed species.

Noxious weeds are listed in the schedules of the Noxious Weeds Act 1993. Weeds that are declared noxious have the potential to cause significant environmental or economic impacts, can be controlled by reasonable means and, most importantly, still have the potential to spread within an area, or to other areas. Most listings apply regionally to LGAs, although some species are listed for the whole state.

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

Table 7.13 describes the five classes of noxious weeds listed in NSW, either statewide or regionally, and the number of species currently listed in each class, anywhere in the state.

Table 7.13: Numbers and types of noxious weeds listed in NSW

Source: DPI data 2008

Note: Apart from Class 1 which is statewide only, weeds are counted in a class if they are listed in that class anywhere in the state, either regionally or statewide. 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 is listed which contains a number of unspecified species.

Management of widespread invasive species: asset protection

While prevention and eradication of new threats and the containment of emerging threats are more cost-effective control strategies, many invasive species are already widely established in NSW and are responsible for the majority of environmental impacts. No matter what resources are deployed, it is virtually impossible to eradicate, or achieve long-term and lasting landscape-level control, of any invasive species that has become widespread. The rare exception is where a suitable biological control has been identified (as for prickly pear, water hyacinth and, to a lesser extent, rabbits).

The control of widespread species must therefore be strategically targeted to reduce their impact on priority assets (native species, populations, regional ecosystems and ecological communities). This requires the prioritisation of both the entities most at risk and the most effective sites for control, to identify where the benefits are expected to be greatest based on the likelihood of recovery of biodiversity.

Threat abatement plans (TAPs) for invasive species are based on the principles described above and are covered in greater detail in Biodiversity 7.2. TAPs have been implemented for foxes, gambusia and bitou bush, and are being developed for lantana and feral goats. An important component of all TAPs for invasive species is monitoring programs to measure the response of priority threatened species in order to demonstrate the effectiveness of controls. Results from the fox TAP have demonstrated positive outcomes for some species, such as the improved breeding success of little terns.

However, with more than 300 weed species considered to have an impact on biodiversity, it is not practical to develop single-species TAPs for each species. Therefore, an asset-protection approach is now being developed to apply to all widespread weeds at a regional scale.

Management of aquatic pests

The FM Act lists species that are restricted for import (live) into NSW without a permit. The species listed have been identified as posing a significant threat to wildlife, ecosystems, human health or the aquaculture industry. The list is divided into two classes: noxious fish that pose such a significant threat to the environment or production that destruction orders are in place (eight species and one genus), and other noxious species that may only be imported into NSW with a permit (19 species, 14 genera and nine families). Noxious species are not permitted to be kept privately and must be destroyed.

Future directions

With the growth in global travel and trade, it is inevitable that new and potentially invasive species will continue to be introduced into NSW, either deliberately or accidentally. A key challenge is to prevent new incursions or contain and eradicate emerging species quickly to avoid further additions to the current array of widespread invasive species.

Measures to more effectively identify species that are potentially invasive and prevent their introduction by the agricultural, horticultural and aquarium industries and the wider community, reinforced by a greater awareness of environmental impacts among these sectors, would assist in reducing future incursions.

The prevention and eradication of new threats must be complemented by an increasing focus on managing widespread invasive species to protect assets (native species, populations, regional ecosystems and ecological communities) at locations where the benefits of control will be greatest. The TAPs for foxes and bitou bush are good models of how this prioritisation process is working.

To demonstrate the effectiveness of control programs, it is important to monitor the response of both the invasive species and the native species affected by them, to confirm that invasive species are a limiting factor in the success of conservation and recovery programs.

In order to provide broadscale control of widespread invasive species that is both effective and affordable, further research is essential, particularly on biological controls.

Measures that afford some control over the introduction of marine species from overseas via ballast water are now in place, but hull fouling is less well controlled.

Climate change will produce shifts in the distribution of both introduced and native species. A better understanding of the interactions between climate change, natural systems and invasive species will assist in managing the adaptation of biodiversity to changes in climate. Future priorities for invasive species management will need to be sufficiently flexible to mitigate the effects that climate change may have on invasive species incursions, spread and impacts.

Better information on the distribution and spread of invasive species, and better systems for collecting and maintaining data that is available statewide in a consistent and standardised way would significantly improve knowledge and management of invasive species. This will assist all facets of management including improving detection, identifying priorities, directing controls, monitoring effectiveness and reporting outcomes, as well as promoting better understanding of the issues.