Distribution and abundance of invasive terrestrial plants and animals

Background

• Background
• Invasive plants
• Invasive animals
• Case studies

Invasive plant and animal species are a costly and significant threat to the health of biodiversity and ecosystems in the ACT, as well as a threat to many of the ACT’s endangered species (see Table 1 at the end of the Biodiversity section). In areas where invasive species are dominant, local extinctions of native flora and fauna can occur. They can also prevent the successful reintroduction of native species into otherwise suitable habitat. Exotic pests and diseases such as parasites of fish, dieback fungus (Phytophthora cinnamomi) and myrtle rust are an additional threat to biodiversity, with the potential to affect a wide range of native species. 

In addition to biodiversity and ecosystem health impacts, invasive species have a negative effect on the region’s agriculture through lost production and management costs, loss of social amenity, and human health. 

Invasive plants, sometimes called environmental weeds, are one of the most significant threats to biodiversity in the ACT. Invasive plants are a main cause of biodiversity loss by displacing native species, modifying habitat and ecological functions, and reducing food availability. Invasive plants can also impact soil and aquatic health, alter stream flows and increase flooding. 

Invasive animals threaten biodiversity through predation, competition for food and habitat, and modification of ecosystems and ecological functions. Invasive animals can have significant environmental impacts due to soil disturbance from burrowing, grazing, and the action of hard hooves. These promote erosion and can lead to degradation of aquatic ecosystems. The actions of invasive animals are particularly damaging in sensitive ecosystems such as High Country Bogs and Associated Fens. Invasive animals can also spread disease and parasites.

Pest plants and animals are not restricted to introduced species (those not indigenous to the ACT region); overabundant native animals such as kangaroos can degrade ecosystem health. Some native species, particularly plants, can also become pests if they become established outside their natural range.

Invasive plants and animals require ongoing management to minimise impacts, both on public and private land (see Community leadership in sustainability and science for more information about invasive species management on private land). It is generally not feasible to eradicate widely established invasive species; therefore the goal of management is to reduce numbers to levels where they have no unacceptable impact. This goal is achieved through the monitoring and control of established species, and the detection and eradication of new invasive species before they become established. Prevention and early intervention are often the most cost-effective techniques for managing invasive species.

Climate change is likely to modify and increase the threat of invasive plants and animals in the ACT, through extensions of favourable conditions and the availability of new habitat caused by the loss of native species from increased temperatures, drought and fire.

Condition and trends

It is not possible to monitor the distribution and abundance of all invasive species. Therefore, the monitoring of invasive species concentrates on those known to be causing significant problems or posing significant threats.

Invasive plants

There are a significant number of invasive species present in the ACT – the 2017 Census of the Flora of the Australian Capital Territory found 592 introduced plant species, 53 of which were introduced from elsewhere in Australia.Australian National Herbarium, Centre for Australian National Biodiversity Research, 2017, Census of the Flora of the ACT

Known locations of invasive plants are mapped, along with control activities undertaken.Invasive plant locations and control activities can be found here Data on management activities and outcomes clearly demonstrates the value of invasive plant management to control established populations and to eradicate new outbreaks where possible. Management results also show the risk of invasive plant populations re-establishing themselves in the absence of ongoing control. Most management activity in the ACT focuses on environmental weeds that have high potential for invasiveness and impact.

Over the reporting period (2015–16 to 2018–19), 54,000 hectares of invasive plant control was undertaken in the ACT for over 100 invasive plant species. Figure B25 shows the area treated for the 10 invasive species that were most extensively controlled over the period. Serrated tussock accounted for the largest area treated at nearly 14,000 hectares, followed by St. John’s wort (over 10,000 hectares), blackberry (7,700 hectares) and African lovegrass (6,900 hectares).

Invasive animals

It was not possible to comprehensively determine the distribution and abundance of invasive animals in the ACT for this report. However, records from Canberra Nature Map show the presence of 64 introduced species in the ACT including 17 mammals, 33 birds, 2 lizards, 1 frog and 11 fish (for information on invasive fish see Indicator W1: Aquatic ecosystem health).

The invasive animal species of most concern in the ACT are feral pigs, deer, foxes, rabbits, horses and wild dogs. Where possible these species are managed with neighbouring land managers to minimise their negative impacts on conservation reserves and surrounding agricultural land.

As with invasive plants, the management of mobile and rapid breeding animals such as rabbits requires continuous control to be effective. Ongoing invasive animal control programs currently account for the majority of vertebrate pest management in the ACT. These include feral pigs in Namadgi National Park, rabbits in areas of Canberra Nature Park and Namadgi, as well as wild dogs at the rural/reserve interface. Rabbit control is the most common management undertaken, occurring in all but one reserve. All priority invasive animal species are controlled in Namadgi National Park; other reserves where management of multiple species takes place include the Tidbinbilla Nature Reserve, Murrumbidgee River Corridor, Googong Foreshores, Goorooyarroo Nature Reserve, and Molonglo River Nature Reserve.

Rabbits

Rabbits are the most widespread and damaging invasive animal in the ACT, impacting on both natural and rural lands. Rabbits pose a particular threat to native vegetation, as they prevent regeneration by removing seedlings. Loss of native vegetation from rabbit grazing threatens the survival of native birds, small mammals and insects that rely on groundcover plants for food and shelter. The presence of rabbits can sustain fox and feral cat populations then these predators in turn place further pressure on native prey species. Rabbits also cause erosion and weed colonisation.

Rabbit numbers have been increasing in the ACT and in all other Australian jurisdictions over the last five years. As with other fast-breeding, mobile invasive species like foxes, effective, sustained management of rabbits relies on coordinated management at the landscape scale to prevent recolonisation from neighbouring, untreated areas. After one or two years of intensive follow-up control, monitoring results show the successful suppression of rabbit populations, but ongoing management is then required to prevent populations from re-establishing themselves. This continuing control has been effective in reducing the densities of rabbits by around 90% in areas of Canberra Nature Park and Namadgi National Park (Figure B26). The rabbit’s propensity to rapidly breed is also shown, with a significant increase in population in 2014, followed by a steep decline in response to effective control programs.

Foxes

Foxes are ubiquitous in the ACT but effective management over large areas is constrained by restrictions on the use of 1080 poison close to residential areas, and by limited resources for 1080 poisoning in non-urban reserves. Predation by foxes has been shown to have a devastating impact on native fauna, causing local extinctions of vulnerable native species. For example, the ACT’s Scientific Committee has advised that foxes were responsible for the loss of Bettongs released in the Lower Cotter Catchment between 2015 and 2017, with most dying shortly after release. The committee has also advised against future wild releases unless fox numbers can be significantly reduced. This shows the successful restoration of some native animals is dependent on the effective control of invasive species.

Horses

Feral horses within Namadgi National Park damage sensitive subalpine wetlands and bogs, which provide habitat for the rare and endangered Northern Corroboree Frog (see Case study: High Country Bogs and Associated Fens). Feral horse management along the south-western border region over the last decade has resulted in the ACT currently being free of resident feral horse populations. The last feral horse was removed in 2011. Management in this region now focuses on surveillance and prevention to detect and control feral horses. Responding promptly has proven successful to prevent feral horses returning to the ACT.

Feral horse management is likely to become more important in the future, particularly for the protection of Namadgi National Park alpine wetlands and water catchment. This is due to the NSW Government’s decision to grant feral horses Heritage status and only allowing non-lethal methods for their removal. This will likely lead to an increase in feral horse populations and result in higher numbers moving into the ACT from NSW. If the feral horse population in Namadgi is permitted to grow and expand its range, there will be increasing damage to sensitive ecosystems, with deleterious consequences for biodiversity.ACT Department of Territory and Municipal Services, 2015, Feral Horse Management, ACT Government, Canberra.

Deer

Deer have the potential to cause significant environmental damage, as well as affecting agricultural productivity and social amenity. They can be particularly destructive to sensitive alpine bogs and fens (see Case study: High Country Bogs and Associated Fens). Deer are an emerging invasive species in the ACT and are common across eastern NSW and other parts of Australia. Three species of feral deer, Fallow (Dama dama), Red (Cervus elaphus) and Sambar (Rusa unicolor) are widespread in the ACT. Although these species have been present in low numbers in the territory for a considerable period, there has been an increase to the known range and distribution of all three species in recent years. 

Deer management poses a challenge to public and private land managers due to the animals’ cryptic and wary behaviour. To assess the effectiveness and feasibility of managing high priority emerging deer populations, the ACT Government has implemented several pilot management programs including: 

• ground shooting of Fallow Deer at Googong Foreshores, and areas of the Murrumbidgee River Corridor 
• ground shooting Sambar Deer in the Upper Cotter Region of Namadgi National Park, and 
• the first aerial shooting program targeting fallow deer in the ACT took place in the Molonglo and Murrumbidgee river corridors in June 2019.

Feral pigs

Feral pigs are widely distributed throughout non-urban parks and reserves in the ACT, and are occasionally found in areas of the Canberra Nature Park. Ground rooting by pigs creates bare ground, contributing to erosion and weed invasion, and impacting on visual amenity for park visitors. Pigs have a varied diet including small mammals, reptiles, amphibians, birds’ eggs, soil invertebrates and roots and tubers of native plants. On rural land they dig up pasture, kill lambs, damage fencing and are a potential vector for several serious endemic and exotic livestock diseases such as foot and mouth disease.

Annual baiting and trapping programs are conducted in Namadgi National Park and the Murrumbidgee River Corridor. In recent years, cooperative control programs have been conducted with neighbouring landholders. The deleterious impact of feral pigs in Namadgi National Park has been assessed annually since the mid–1980s and the data shows a dramatic decline in damage as a result of sustained control activities.

Wild dogs

Populations of wild dogs (dingoes and dingo-like dogs which are dingoes with a small proportion of domestic dog genes) are found in Namadgi National Park, areas of the Murrumbidgee River Corridor, Rob Roy Nature Reserve and adjacent areas of timbered land in the ACT. 

Wild dogs are controlled in these areas to minimise attacks on sheep on neighbouring rural properties. Management involves a range of methods including 1080 poison baiting, trapping and opportunistic shooting. This integrated approach also achieves effective fox management in dog control areas. In contrast, wild dogs are protected in core reserve areas including the Gudgenby Valley, Cotter Catchment and the Tidbinbilla Nature Reserve where they are the top-order predator in the ecosystem.

In addition to controlling wild dogs on ACT rural lands to protect livestock, the ACT Government is also a signatory to three cooperative Wild Dog Management Plans with New South Wales authorities and landholders. These are aimed at protecting livestock from wild dogs originating from Namadgi National Park.

Cats

Despite the significant impacts on native wildlife, the ACT has no formal programs to manage stray or feral cats. Both domestic and feral cats prey on native animals including birds, reptiles and small mammals. Domestic cats are controlled in many new urban areas through cat containment legislation.

Indian Myna

Indian Mynas were introduced to the Canberra region in 1968. They have shown a distinct liking for woodland nature reserves and are strong competitors with native wildlife for food and nesting hollows. They are now well established across the ACT. Indian Mynas are very aggressive and intelligent, and are known to evict native birds (including parrots, kookaburras and peewees) from their nests, dumping out their eggs and chasing them from their roosting areas.

In 2006, the Canberra Indian Myna Action Group was formed to reduce the impact of this exotic invader on native birds and other animals. The group’s concentrated trapping and removal efforts has been shown to reduce the population of Indian Mynas across Canberra (see Community leadership in sustainability and science).

Kangaroos

Overabundant native animals such as kangaroos can have an impact on ecosystem health. Eastern Grey Kangaroos are managed in the urban reserves of Canberra Nature Park to protect conservation values from overgrazing. Information on kangaroo management in the ACT can found in the Kangaroos and grassy ecosystem management case study.

Case studies

• The importance of invasive plant management in the ACT
• Kangaroos and grassy ecosystem management