Background: Biodiversity

Biodiversity is the variety of life. This can include the diversity of genes within a species, the diversity of species within a landscape and the diversity of ecosystems across landscapes. It can also include the diversity of ecological processes that underpin the functioning of ecosystems such as seed dispersal, pollination and nutrient cycling.

Healthy biodiversity is essential to the natural world and fundamental to human life. The complex and dynamic interactions between plants, animals, microorganisms, soil, water and air underpin the health of ecosystems. Whilst biodiversity is dependent on good ecosystem health, biodiversity itself plays a pivotal role in maintaining ecosystems. Biodiversity loss or decline can have significant consequences for natural processes, decrease the availability of habitat, and impact on predator–prey relationships. In severe cases, biodiversity loss can lead to significant changes in ecosystems and the functions they provide.

Biodiversity may also make ecosystems more resilient to pressures such as climate change and fire. A diversity of species and ecological processes can help ecosystems to maintain their core functions in the face of environmental change.

Because terrestrial ecosystems are intimately connected to aquatic ecosystems, their degradation has consequences for the condition of the ACT’s rivers, lakes, and wetlands (see Water).

Healthy ecosystems, biodiversity and land also provide a range of benefits to human wellbeing, including climate regulation, clean air and water, nutrient cycling, pollination, control of pests, carbon sequestration, and the supply of foods and fibres. Biodiverse environments, including in urban green spaces, have also been associated with increased mental wellbeing. It is important to maintain and, where necessary, improve the health of ecosystems to ensure the continued availability of the services they provide.

Pressures on biodiversity

The main pressures on biodiversity in the ACT are climate change, invasive plants and animals, vegetation loss, habitat fragmentation and changes to the frequency and intensity of fire, and land use change (particularly greenfield development). The use of chemicals such as pesticides can also have significant impacts on biodiversity, especially insects.

Climate change is predicted to compound existing pressures on biodiversity. Projections of significant shifts in local climates and increases in drought, bushfires and storms will have an impact on biodiversity and natural ecosystems. Climate change is likely to impact species with limited capacity to migrate, such as those restricted to particular habitats and fragmented landscapes, or those that tolerate only narrow ranges of temperature and rainfall. Species dependent on wetland and mountainous ecosystems have been identified as being at greatest risk. Climate change will exacerbate current environmental pressures; therefore the capacity of natural ecosystems to adapt to climate change will improve if existing threats are addressed.

Background to indicators

Indicator B1: Threatened species and ecological communities

It is not possible to accurately measure the distribution and abundance of all species in the ACT. This is because not all species occurring in the ACT are known, let alone counted, and not all areas of the ACT can be surveyed and monitored. Consequently, assessment of biodiversity is mainly focused on the monitoring and management of threatened species.

It is important to note that some species found in the ACT are temporary residents. Migratory and highly mobile species such as birds may only be present for breeding, or in response to food and water availability. For such species, changes in their annual abundance and distributions in the ACT may result from external influences including changes to food availability, loss of habitat or increase in invasive species. Consequently, populations can increase or decrease regardless of the condition of the ACT environment.

Listing of threatened species and ecological communities in the ACT

The Nature Conservation Act 2014 establishes a formal process for the identification and protection of threatened species and ecological communities, as well the identification of ecologically significant threatening processes. The ACT Scientific Committee is responsible for providing advice on listings under the Act.

The listing of threatened species reflects the International Union for the Conservation of Nature categories and criteria to improve alignment with the Commonwealth’s listing categories. The different categories provide a guide as to the level of management which a species may require. A species may be assessed at the national scale and listed in a national category as extinct, extinct in the wild, critically endangered, endangered, vulnerable, or conservation dependent. A native species occurring in the ACT may be listed in a regional category if it does not meet national criteria.

Limitations of threatened species and community lists

The extent and abundance of threatened flora and fauna species and associated changes in threatened status may provide a measure of the condition of biodiversity and highlight those species at risk. For example, if a species moves from vulnerable to endangered it may indicate potential biodiversity loss. However, the number of threatened species needs to be interpreted with caution as listings are influenced by factors such as effort and attention given to different species, improved knowledge rather than actual changes in status, changes in the methodology used to assign status, and the number of taxa reviewed regularly. It is also important to note that conservation status for a species is assessed for all of the ACT; it does not reflect local variations in population status, nor the status of species in other parts of Australia.

The status of threatened species may also be of limited value in determining changes in environmental condition. This is because a species may be affected by a combination of pressures, or by subtle drivers that do not impact on the wider ecosystem. Despite these factors, the listing of threatened species and ecological communities, as well as changes to threat status over time, can be useful for assessing the effectiveness of management actions.

Threatened ecological communities

An ecological community is defined as a naturally occurring group of native plants, animals and other organisms that are interacting in a unique habitat. The community’s structure, composition and distribution are determined by environmental factors such as soil type, position in the landscape, altitude, climate, and water availability. The native plants and animals within an ecological community have different roles and relationships that, together, contribute to the healthy functioning of the environment and to the provision of ecosystem services.

Under the Nature Conservation Act 2014 a community may be listed as collapsed, critically endangered, endangered, vulnerable or provisional.

Key threatening processes

A process is defined as threatening if it has the potential to threaten the survival of a species or ecological community in the ACT. These processes include effects of past clearing, fragmentation and modification of habitat, the impacts of invasive plants and animals, the alteration of hydrological regimes and the increasing threat of climate change.

Under the Nature Conservation Act 2014, a process may be listed as a key threatening process. This listing is a formal recognition of a conservation threat and requires an Action Plan to be prepared to address the threatening process.

Indicator B2: Extent and condition of conservation areas

The ACT’s conservation areas are critical for the protection of natural ecosystems and the biodiversity and services they support. Parks and reserves provide habitat for many threatened species and ecological communities. They represent the ACT’s most extensive and least disturbed environments, as well as remnant ecosystems within urban and agricultural lands.

Conservation areas provide a range of benefits for the ACT community including ecosystem services such as clean air and water. Conservation areas also play an important role in nature-based recreation and tourism, which provides significant health and education benefits and contributes to the ACT economy.

Whilst conservation areas exclude damaging land uses and activities, the ecosystems and biodiversity they protect are still at risk from a range of pressures. Invasive species, inappropriate fire regimes, pathogens and diseases present a serious threat to the ACT’s ecosystems and biodiversity and require ongoing intervention to minimise impacts. Climate change will also threaten conservation areas, especially where changes to temperature and rainfall, and the occurrence of fire, exceed the tolerances of ecosystems.

Environmental Offsets

Environmental offsets are land added to environmental reserves to address potential development pressures. In the ACT, offsets provide environmental compensation for a development that is likely to have adverse environmental impact on a protected matter. In the ACT, offsets are categorised as those that are:

• required under the Environment Protection and Biodiversity Conservation Act 1999 to compensate for the residual adverse impacts of an action on Commonwealth-listed threatened species and communities classed as Matters of National Environmental Significance.
• required under the ACT’s Planning and Development Act 2007 to provide environmental compensation for the likely impact on a declared protected matter.

Almost all environmental offsets within the ACT are delivered via direct land offsets which protect, conserve and restore areas land with specific ecological values. Indirect offsetting is generally a last resort or an additional requirement such as the proposal of development funding research into a protected matter.

Indicator B3: Representation of threatened species and ecological communities in conservation areas

ACT’s conservation areas contribute to the National Reserve System – Australia’s network of protected areas, designed to conserve Australia’s remaining biodiversity. To ensure that the ACT’s reserve system meets the standards for comprehensiveness, adequacy and representativeness, it is essential that conservation areas protect the range of ecosystem types and biodiversity present in the region. This includes both threatened and common species and ecological communities.

Indicator B4: Extent and condition of native vegetation

Native vegetation is integral to ecosystem services such as the protection of biodiversity, protection of water quality and soil health, and sequestration of carbon. Declines in the extent and quality of native vegetation have profound implications for the health of the ecosystem.

The loss of vegetation is considered to be the main threat to biodiversity in Australia.

Historic land clearing for agriculture and urban development has produced a legacy of fragmented native vegetation in some areas of the ACT. The diversity and resilience of ecological communities relate directly to their spatial configuration, patch size, contiguity, condition and connectivity. Fragmented landscapes prevent the movement of species, limiting opportunities for mating and dispersal, and potentially creating genetic isolation. Research suggests that most animals of southern Australian woodlands and forests will not usually cross a canopy gap of more than 100 metres, and will not travel more than 1.1 kilometres from a patch of at least 10 hectares of suitable living habitat.^[1]

Although large-scale clearing is not an issue in the ACT, native vegetation remains under continuing pressure from urban expansion. Native vegetation in conservation areas has not been extensively cleared and is more intact than native vegetation on private land and those lands separated by urban developments. In these largely intact landscapes, vegetation communities are more likely to be resilient to natural disturbances such as fire and drought. In fragmented landscapes, native vegetation remnants are more vulnerable to natural disturbance as well as pressures arising from agriculture and residential activities. This results in the decline of vegetation, or being at risk of decline, in extent, quality and regenerative capacity. Fragmentation can also exacerbate the impacts of land use change and climate change by restricting opportunities for fauna to migrate or adapt.

Historic land clearing in the ACT

Most of the ACT’s vegetation loss has been from historic clearing and ecosystem modification for agriculture and urban development. Although there has not been a comprehensive assessment of the native vegetation extent in the ACT before European settlement, there are some examples of significant losses. For example, before European settlement, Natural Temperate Grasslands were thought to cover over 25,000 hectares or 11% of the ACT area, but today they only cover around 1,100 hectares, less than 1% of the ACT (Figure 1).^[2]

For Lowland Box Gum Woodlands, the pre-European settlement distribution was thought to be over 47,000 hectares or 20% of the ACT area, but these woodlands now only cover some 11,500 hectares, around 5% of the ACT (Figure 2).^[3] Most of the native vegetation changes are thought to be on lowlands due to the abundance of grass and absence of dense trees for agriculture, and later for urban development. It is estimated that there has been little change in the distribution of upland vegetation types.

While the loss of native vegetation remains of concern for urban development, it is unlikely to be the largest source of native vegetation change in the ACT. Chronic degradation of habitat condition, mainly in fragmented landscapes is a significant problem in the ACT. This degradation is compounded by climate change impacts such as decreasing rainfall and higher temperatures. Such degradation has led to an increased occurrence of dieback in the ACT.

Impacts of fire on native vegetation

Bushfire is an important occurrence for many native vegetation communities in the ACT. Although fire can cause a temporary loss of vegetation, fire is necessary for the regeneration and regrowth of many plant species. The appropriate fire regime to promote native biodiversity (intensity, frequency, season, extent and type of fire) varies between native vegetation communities. Changes to ecologically appropriate natural fire regimes can have significant impacts on the composition of vegetation communities and the ecosystems they support.

The ACT’s fire regimes have changed over time due to increased human sources of ignition, the suppression of natural fire to protect human life and assets, and prescribed burning practices for the management of fuel loads (see Fire). In addition, periods of prolonged drought and higher temperatures increase the risk of more frequent and severe fires. Climate change is expected to further influence the occurrence of bushfires in the ACT.

Tolerable fire intervals

Tolerable fire intervals (TFI) assess the likely ecological response of native vegetation communities to subsequent fire and are based on the requirements for sensitive plant species and key habitat elements. Assessments of TFI are based on:

• Minimum TFI: the minimum period of time between fires to avoid a loss of plant biodiversity. This period is based on the time it takes fire-sensitive plant species to grow to reproductive maturity and produce adequate viable seed banks. Frequent burning below minimum TFI can lead to localised loss of these fire-sensitive species, and can also prevent the development of key habitat features required by some fauna such as mature overstorey, tree hollows, and the accumulation of leaf litter and logs.
• Maximum TFI: the maximum period of time between fires to avoid a loss of plant biodiversity. Native vegetation communities not exposed to fire for extended periods can have reduced viability of shorter lived plant species which require fire to germinate seeds. Lack of fire may also result in a decline of key habitat features required by some fauna species such as dense mid-storey vegetation.

Minimum and maximum TFI are ecosystem-specific and are typically longer for vegetation communities that have evolved with less frequent fire, for example those occurring in cooler and moister environments where fires are naturally less frequent and where the growth rates of plants is slower.

It should be noted that the TFI status is only a potential issue should a large, high-severity fire occur in areas that are below minimum TFI. There is no requirement that ecosystems be within a specific TFI, only that fire outside of these thresholds be limited. To promote maximum biodiversity, a range of TFI status is required to provide different habitat resources.

Growth stage

Post-fire growth stages represent the recovery of native vegetation communities after fire and the progression from early response (re-sprouting and seed germination) to the maturation of plant species and animal populations, and eventually senescence and species turnover at longer times subsequent to fire. Each growth stage is characterised by a different structural arrangement of vegetation and may be dominated by different component species. Similarly, the faunal community supported by an area will vary as the vegetation progresses through growth stages. Biodiversity values are most likely enhanced at a landscape scale by achieving a range of growth stages within each vegetation community and across the landscape.

Indicator B5: Distribution and abundance of terrestrial invasive plants and animals

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. 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.^[4] 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. 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.

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.

Some of the main invasive animals are discussed below.

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.

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.

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 devasting 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 horse management is likely to become more important in the future, particularly for the protection of Namadgi National Park’s alpine wetlands and water catchment. Feral horses damage sensitive subalpine wetlands and bogs, which provide habitat for the rare and endangered Northern Corroboree Frog. 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.

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. 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.

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.

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.

Kangaroos

Eastern Grey Kangaroos are managed in the urban reserves of Canberra Nature Park to protect conservation values from overgrazing. Conservation culling is undertaken, in accordance with the Eastern Grey Kangaroo: Controlled Native Species Management Plan 2017. Kangaroos are managed within a kangaroo management unit, which are typically comprised of one or more nature reserves and any adjacent habitat available to an isolated kangaroo population. These adjacent land tenures include rural lease, Commonwealth land, parklands, and government horse paddocks.

Eastern Grey Kangaroo conservation culling program has been undertaken annually since 2009. Managing kangaroos at any given site usually involves larger initial reductions in kangaroo population density over 1 to 3 years, followed by smaller annual maintenance programs to maintain an equilibrium between kangaroo grazing pressure and grassy habitat.

The number of kangaroos to remain in each individual kangaroo management unit is calculated annually in accordance with the Conservation Culling Calculator Determination. This calculator formulates target densities based on ecological models of how much kangaroos eat coupled with how quickly pasture grows according to historical weather information. In an average grassland, this model indicates that approximately one kangaroo per hectare is consistent with maintaining appropriate grassy layer structure to maintain biodiversity values.

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.