Indicator assessment
CONDITION
TREND
DATA QUALITY
Invasive plants and animals continue to have a significant impact on native species and ecosystem health. Invasive species also represent a significant management burden. In areas where invasive species are controlled, outcomes clearly demonstrate the value of well-resourced and ongoing invasive species management to reduce established populations and to eradicate new outbreaks where possible.
CONDITION
Environmental condition is healthy across the ACT, OR pressure likely to have negligible impact on environmental condition/human health.
Environmental condition is neither positive or negative and may be variable across the ACT, OR pressure likely to have limited impact on environmental condition/human health.
Environmental condition is under significant stress, OR pressure likely to have significant impact on environmental condition/ human health.
Data is insufficient to make an assessment of status and trends.
TREND
DATA QUALITY
Adequate high-quality evidence and high level of consensus.
Limited evidence or limited consensus.
Evidence and consensus too low to make an assessment.
Assessments of status, trends and data quality are not appropriate for the indicator.
Introduction
For information on this indicator see Background: Biodiversity.
It is not currently possible to monitor the distribution and abundance of all invasive species. Therefore, the knowledge of invasive species in the ACT is limited to those known to be causing significant problems or posing potential significant threats. In addition, most available information is on management activities rather than long-term changes in invasive species populations. Consequently, it is difficult to assess the status and trends in invasive species in the ACT.
Invasive plants
There are a significant number of invasive species present in the ACT — the 2019 Census of the Flora of the Australian Capital Territory found 700 introduced plant species, 79 of which were introduced from elsewhere in Australia.[8] In the absence of control, invasive plants can significantly expand their distribution and abundance over a short period of time, impacting on native species and ecosystems.
The ACT reports on the locations of invasive plants as well as the control activities undertaken. These can be found on the Environment, Planning and Sustainable Development Directorate Invasive Weeds website.
Dozens of invasive plant species are managed in the ACT, with the top five widespread species accounting for around 60% of the total area treated. The highest priority for weed management is to eradicate, contain or slow the spread of transformer species — invasive plants that have the capacity to severely degrade native ecosystems. Examples of transformers include blackberry, African Lovegrass, and Serrated Tussock. Early intervention is vital for the successful management of these species.
Over the reporting period (2019–20 to 2022–23), nearly 35,000 hectares of invasive plant control was undertaken in the ACT for the ten most extensively managed invasive plant species (Figure 17). African Lovegrass accounted for the largest area treated at over 7,000 hectares, followed by Serrated Tussock (over 6,500 hectares) and St. John’s Wort (5,800 hectares). Pine wildlings, blackberry and woody weeds were also subject to widespread control. It is important to note that the control of all invasive plant species is critical regardless of their distribution extent. For example, eradicating a small area of an invasive plant species may be vital to prevent wider establishment, especially for those plants classed as transformers.
Figure 17: Top ten controlled invasive plants in the ACT by area treated, 2019–20 to 2022–23.
Data sourced from: Environment, Planning and Sustainable Development Directorate.
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.
In addition to the control of established invasive plants, it is important to detect and control new invasive species. In 2022–23, there were 28 new and emerging invasive plants identified as posing a threat to native ecosystems including Fireweed, Coolatai Grass, African Feather Grass, Alligator Weed, Rambling Dock, Codlins and Cream, Bridal Creeper, Whisky Grass, Rose Campion, Oregon Grape, Spanish Heath, Tree-of-heaven, Spanish Lavender, Ox-eye Daisy and Feathertop. The ACT community provides vital information on new and emerging species with sightings reported on Canberra Nature Mapr.
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 Mapr show the presence of 64 introduced vertebrate species in the ACT including 17 mammals, 33 birds, two lizards, one frog and 11 fish.
The invasive animal species of most concern for the protection of the ACT’s native ecosystems and biodiversity are feral pigs, deer, foxes, rabbits and feral horses. 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 and deer 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.
General trends for selected invasive animal species are shown below.
Rabbits
Rabbit numbers have been increasing in the ACT and in all other Australian jurisdictions over the last five years. This ongoing control has been effective in reducing the densities of rabbits by around 90% in areas of Canberra Nature Park and Namadgi National Park.
Over the reporting period (2019–20 to 2022–23), rabbit densities were found to be increasing above acceptable levels due to the favourable conditions provided by wetter conditions from 2020. To control the growing rabbit population, the ACT introduced thermal assisted shooting to complement other control methods. Rabbit control has been successful at Mount Ainslie, Mount Majura, Mount Pleasant and Percival Hill with significantly reduced populations. For example, the number of rabbits populations at Mount Pleasant was reduced from more than 20 rabbits per square kilometre to less than four.
Horses
The threat of feral horse impacts in the ACT has been significantly increased due to the lack of effective feral horse control in NSW which has allowed populations to grow in Kosciuszko National Park. This may lead to an increase in feral horse numbers in Namadgi National Park, causing damage to sensitive ecosystems, with deleterious consequences for biodiversity.[9]
The ACT Government’s zero-tolerance policy on feral horses is critical to successfully protecting the natural and cultural values of Namadgi National Park. Only two feral horses have been removed from Namadgi since 2019. Management in this region now focuses on surveillance and prevention to detect and control feral horses.
Deer
Although deer are widely distributed in the ACT, ongoing control has kept populations at low numbers in most areas, Sambar deer occupy much of Namadgi National Park and surrounds, and Fallow deer occupy river corridors and the Googong Foreshores.
Thermal assisted aerial control was first introduced in Namadgi to help control feral deer and pigs and has been expanded since 2021 to include most conservation areas in the ACT. This technique is now a critical component of the feral animal control program.
Between 2019 and 2022, thermally assisted ground and aerial control programs were successful in removing 229 feral animals from the ACT’s alpine sphagnum bog ecosystems and surrounds, including 116 Sambar Deer. This is a significant reduction in the proportion of animals able to make an impact on this fragile ecosystem.
Pigs
Annual thermal assisted aerial shooting and annual baiting and trapping programs are conducted for feral pigs in the 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.
In 2021 and 2022, a thermally assisted aerial shooting program was completed in the Upper Cotter Catchment in conjunction with Namadgi National Park Sambar Deer management. Control activities removed 409 feral pigs, the highest number since 2007. In 2023, 302 feral pigs were removed 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 managed in many new urban areas through cat containment legislation.
Indian Mynas
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.
Canberra Indian Myna Action Group
The Canberra Indian Myna Action Group (CIMAG) includes retired scientists and community members working to raise awareness and reduce the impact of this exotic avian invader on native birds and animals.
CIMAG undertakes community education, collaboration with other like-minded groups, physical bird trapping and humane disposal methods, as well as monitoring and evaluation. While the work of its members had seen Indian Myna numbers drastically reduce from being the third most common bird in Canberra in 2006 to the 24th most common bird in 2020, in recent times there has been a resurgence in Indian Myna numbers as a consequence of CIMAG’s inability to maintain the supply of traps during the COVID-19 period. However, without this community-led action, populations would have been considerably greater and exceeded manageable numbers – as is the case throughout much of eastern Australia.
Since CIMAG’s inception in 2006 to March 2023, there have been 2,834 volunteers involved in CIMAG control activities, removing over 79,000 Indian Mynas from the Canberra environment. Post COVID-19, CIMAG are keen to rekindle and expand on this work.
The declaration of Indian Mynas as pest animals by the Minister for Environment in 2021 presents the opportunity and the obligation for the ACT Government to broaden Indian Myna control activities from backyards to the wider urban and peri-urban landscape. This would further reduce the risk that these birds pose to local wildlife, especially to some rare, endangered and threatened local species.
Kangaroos
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 (see Background: Biodiversity).
Between 2009 and 2022, over 24,000 Eastern Grey Kangaroos were culled to protect grassy ecosystems within Canberra Nature Park (Figure 18 and Figure 19). The largest annual cull was 4,035 kangaroos in 2019. In recent years, culling numbers have reduced across many sites. This is because of the effectiveness of previous kangaroo management in reducing densities; and also in response to higher sustainable kangaroo densities due to increased rainfall since 2020. At other sites where kangaroo management has not been undertaken and the population remains well above the desired target density, grass height has remained below optimal threshold despite the increased rainfall.
Figure 18: Annual number of Eastern Grey Kangaroos culled and number of program sites (right axis), 2009 to 2022.
Source: Environment, Planning and Sustainable Development Directorate.
Figure 19: Kangaroo management areas, 2023.
Data sourced from: Environment, Planning and Sustainable Development Directorate.
Notes: Not all Kangaroo Management Units (KMU) are actively managed each year. Once a KMU is added to the program it is assessed each year and culling is only recommended if herbage mass monitoring and kangaroo population surveys indicate the population is above the target density. The ACT Government only undertakes culling in the conservation land within each KMU. Kangaroo management on other land tenures is the responsibility of the individual land managers.
Following many years of small-scale research trials, the use of fertility control was incorporated into the kangaroo management program for the first time in 2022 with the aim of limiting population growth and reducing the need for future culling. The treatment of female kangaroos with a contraceptive vaccine commenced at Mulligans Flat Woodland Sanctuary and Farrer Ridge Nature Reserve where the population had previously been managed by culling. Further treatments will be administered at these sites to achieve the level of infertility required to reduce population growth. It is intended to add additional sites to the program in the future.
Data gaps
- Data on the distribution and abundance of invasive animals in the ACT needs to be improved.
- There are few reliable, quantitative measurements for the environmental damage inflicted by invasive species.