Regional and landscape-scale pressures: Invasive species

2016

Invasive species represent one of the most potent, persistent and widespread threats to the Australian environment. They have a direct negative impact on species through predation, displacement and competition, and also have enormous detrimental effects on the health, viability and functioning of communities, ecosystems and landscapes. These effects occur through both direct and indirect disruption of ecological services such as soil stabilisation, pollination and seed dispersal, and changed fire regimes (see Box LAN3).

Australia’s biosecurity system is designed to manage the risk of pests and diseases entering, emerging in, establishing in or spreading in Australia, and causing harm to human, animal or plant health, the economy, the environment or the community.

At Australia’s borders, including airports, seaports and international mail centres, the Australian Government coordinates activities that assess and manage potential biosecurity risks before they enter Australia. Onshore and offshore, the Australian Government uses a range of sophisticated technologies and approaches, including research, shared international resources and intelligence, to prevent the introduction and spread of disease, and to manage and contain established pests and diseases.

Invasive species already in Australia are managed through investments and actions at all levels of government, frequently with coordination between the different levels of government. As of December 2015, there were 21 listed key threatening processes under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), 16 of which involve exotic invasive species, and 11 approved threat abatement plans, all of which mention exotic invasive species. Lists of targeted invasive species for various levels of control are also maintained at state and territory level.

The Biosecurity Act 2015 extends the power of the Australian Government to management of invasive pests, consistent with the United Nations Convention on Biological Diversity. The Act is designed to be flexible and responsive to changes in technology and to perceived risks and threats, and provides for improved collaboration across governments and industries. The legislation includes higher penalties for bringing in prohibited goods if they have the potential to cause harm to the environment.

The Australian Weeds Strategy (Australian Weeds Committee 2007) and the Australian Pest Animals Strategy (Vertebrate Pests Committee 2007) provide national guidance on best practice for weed and vertebrate pest animal management. They aim to guide coordination of effort across all jurisdictions and affected stakeholders, and to inform plans and actions by state and territory governments, local governments, regional NRM agencies, industry, landholders and the wider community.

Pathogens and fungi

Australia is free from many of the most damaging agricultural plant pathogens, as a result of concerted biosecurity efforts at all levels of government, but a few significant pathogens are established in Australia or are near our borders. Most of these potentially threaten commercially grown species (e.g. neck rot of onions—Botrytis allii, stem rot of canola—Sclerotinia sclerotiorum, stem rust of wheat—Puccinia graminis, Panama disease tropical race 4—TR4 of banana). Many can also affect native species and may maintain low-intensity reservoirs of potential infection of commercial crops in native vegetation. Most pathogens that significantly affect native forests and plantations of native tree species are native plant pathogens (MPIG & NFISC 2013). Two pathogens are of particular concern at the national scale: Eucalyptus rust or myrtle rust (Puccinia psidiisee Box LAN4) and the rootrot pathogen, Phytophthora cinnamomi.

Phytophthora, which is a member of the kingdom Chromista or Protista rather than being a fungus, has caused extensive damage to whole vegetation communities, particularly in southern and western Australia. In south-western Western Australia, as many as 2300 of the 5710 native plant species are thought to be susceptible to Phytophthora (MPIG & NFISC 2013). Although Phytophthora cinnamomi is the species most usually associated with dieback disease, molecular studies are now identifying other Phytophthora species in native vegetation, some of which are also proving to be pathogenic (Scarlett et al. 2015).

Potentially, the most important fungal pathogen of vertebrates in Australia at present is the amphibian chytrid fungus (Batrachochytrium dendrobatidis), which gained attention in Australia and the Americas in the 1970s by causing rapid declines in native amphibian populations. The disease has been recorded along the east coast, and in south-western Western Australia, Adelaide and Tasmania. A small number of occurrences have been documented from arid habitats (Figure LAN10). Infection rates may be high, and mortality rates attain 100 per cent in some species. Six Australian species have apparently become extinct since the first documented occurrences of chytridiomycosis, and another 7 are at high risk of extinction (Skerratt et al. 2016).

Pest animals

Although a large number of introduced animal species have naturalised in Australia, a relatively small number are currently the focus of major management programs. Significant investments have recently been made in the control of feral cats and camels, partly in response to a much greater realisation of the impacts of these species, particularly in the arid zone. For example, predation by feral cats is regarded as one of the primary factors in the decline and extinction of a number of native mammal species in Australia, and feral cats are recognised as a potential threat to 74 mammal species and subspecies, 40 bird species, 21 reptile species and 4 amphibian species (Woinarski et al. 2014a). Citizen surveillance for monitoring has also been brought to bear through the FeralScan website developed by the Invasive Animals Cooperative Research Centre (CRC) and partners, which is collating data on 16 feral animal species and hosts more than 50,000 community records.

Currently, the 2007 Australian Pest Animal Strategy (Vertebrate Pests Committee 2007) is being revised following a review completed in 2013 (Community Solutions 2013).

The European rabbit (Oryctolagus cuniculus) is Australia’s most costly vertebrate pest animal, estimated to cause damage of more than $200 million to agriculture every year. Rabbits are also linked to more than 300 threatened native species. The impact of rabbits is predominantly through soil erosion, modification of soil structure and loss of vegetation. A biocontrol program has operated through the Invasive Animals CRC since 2005, achieving nearly $6 billion of savings associated with reduced rabbit populations and reduced impacts on agriculture. Despite this, rabbit numbers are now increasing as a result of increasing resistance to the biocontrol agent rabbit haemorrhagic disease virus (RHDV1 v351). Release of a new strain of the virus (RHDV1 K5) is currently under consideration by the Australian Government Department of the Environment and Energy, subject to review and public consultation.

A national survey conducted in 2014–15 showed that average stock losses and control costs for wild dogs ranged from $22,900 per year for a small property to $1,940,000 per year for large (pastoral) properties (WoolProducers Australia 2014). In response, the Australian and Western Australian governments, supported by livestock producers, their representative organisations and government agencies, have launched the National Wild Dog Action Plan (WoolProducers Australia 2014) to guide the implementation of a nationally agreed framework for a strategic and risk-based approach to wild dog management. Most other states and territories also have wild dog or pest animal management plans in place.

More controversially, control of wild horses in the Snowy Mountains has been associated with extensive public consultation by the New South Wales Office of Environment and Heritage, following a thorough review of the 2008 Kosciuszko National Park Horse Management Plan and development of a new Kosciuszko National Park Draft Wild Horse Management Plan (NSW OEH 2016). The consultation explored the deeply polarised views held by major stakeholder groups about whether, and how, wild horses should be managed.

Feral goats, pigs and buffalo also exert considerable damage on soil and vegetation through trampling, browsing and erosion. Introduced invertebrates also pose threats to biodiversity, agriculture, infrastructure and people (see Box LAN5).

Box LAN5 Pest ant species in Australia

Twenty-three exotic ant species have established in Australia. An additional 3 species are subject to eradication programs that aim to remove them completely from Australia and prevent their establishment. Another 5 are the focus of more localised eradication efforts. Because of their severe impacts, 2 ant species are listed as key threatening processes under the Environment Protection and Biodiversity Conservation Act 1999, and a third is categorised as a key threatening process by novel biota.

The red imported fire ant (Solenopsis invicta) has been undergoing eradication measures since 2001 at a cost to date of more than $400 million. Without an eradication program, fire ants would eventually infest all states of Australia, and their impacts could potentially surpass the combined effects of many of Australia’s current worst invasive pests (rabbits, cane toads, foxes, camels, wild dogs and feral cats—which cost Australia an estimated $964 million each year). Despite the increased biosecurity focus on the red imported fire ant, 7 incursions have been detected to date in Australia, 4 of which were within the past 2 years.

No ant species has ever been entirely eradicated from Australia, but all known populations of 2 species (electric ant—Wasmannia auropunctata, and browsing ant—Lepisiota frauenfeldi) are likely to be fully eradicated in the next few years. Australia is the world leader in dealing with exotic ants, having achieved 78 per cent (113) of localised eradications in the world.

Many of the exotic ant species present in Australia are considered to be among the worst invasive species in the world because of their significant effects on biodiversity, agriculture, infrastructure and people. Two recent vertebrate extinctions on Christmas Island are believed to be partly attributable to the exotic yellow crazy ant (Anoplolepis gracilipes). This species is also present on mainland Australia, including in Queensland’s Wet Tropics World Heritage Area, where an infestation was identified in 2012. In 2013, the Wet Tropics Management Authority received more than $2 million over 5 years under the Caring for our Country program to eradicate a large infestation within the Wet Tropics World Heritage Area; another $8.8 million has just been earmarked by the Australian Government for the next 3 years.

Yellow crazy ant (Anoplolepis gracilipes), and aerial baiting on Christmas Island to control yellow crazy ants.

Yellow crazy ant (Anoplolepis gracilipes), and aerial baiting on Christmas Island to control yellow crazy ants.

Yellow crazy ant (Anoplolepis gracilipes)

Photo by Phil Lester, Victoria University of Wellington, New Zealand 

SoE2016_Aerial baiting on Christmas Island to control yellow crazy ants.jpg

Yellow crazy ant (Anoplolepis gracilipes), and aerial baiting on Christmas Island to control yellow crazy ants.

Aerial baiting on Christmas Island to control yellow crazy ants

Photo by Ben Hoffman, CSIRO

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Source: Ben Hoffmann, CSIRO

Weeds

Weeds continue to have a negative impact on:

  • the productivity of Australian agriculture and forestry
  • the natural environment, through impacts on biodiversity, ecosystem function and environmental health, and promotion of bushfires
  • access to sites of significant Indigenous cultural heritage
  • public health, through toxicity, allergic reactions and respiratory diseases.

An independent review of the 2007 Australian Weeds Strategy concluded that the strategy was effective in prioritising weeds and weed management problems, and implementing solutions for priority weeds and weed problems (Community Solutions 2013). It was less successful in achieving direct on-ground weed management, particularly in failing to implement action against emerging weed threats, to communicate to stakeholders the importance of their engagement in addressing national weed problems, and to establish nationally consistent legislation to address weed problems. The Invasive Plants and Animals Committee is revising and updating the strategy, whose release is imminent.

The list of Weeds of National Significance (WoNS) was updated in 2012 from 20 to 32 WoNS (see Table LAN1), which includes more than 40 species within the 32 weed groups. Strategic plans for WoNS (2012–17) have been published, and management manuals have been released for the new WoNS species. An additional 28 non-native weeds that have established naturalised populations in the wild have been added to the National Environmental Alert List. These are species that are in the early stages of establishment and have the potential to become a significant threat to biodiversity if they are not managed.

Although understanding of the pressures exerted by weeds on the landscape is increasing, there is no evidence that the rate of naturalisation of alien species is increasing—the number of naturalised species increased linearly between 1880 and 2000 (Dodd et al. 2015). This generalisation is reinforced in an assessment of the naturalisation patterns of one group of weeds—tropical invasive grasses. Again, there is no evidence for increased naturalisation rates over time, or with increased trade, for 155 grass species naturalised between 1788 and 1980 (van Klinken et al. 2015).

An emerging issue in all cropping areas of Australia is herbicide-resistant weed populations. In June 2014, at least 39 weed species in Australia were resistant to 1 or more herbicides, and the number of identified resistant species is growing. A herbicide resistance problem can develop through selection of naturally occurring resistant weeds, or through importation of already resistant weeds through flood, animals, or practices such as the purchase of contaminated grain or use of contaminated machinery (Michael et al. 2010). Herbicide-resistant weeds pose a potential threat to both native vegetation communities and agricultural crops. They also threaten the viability of some no-till farming systems that are designed to limit soil disturbance, and thus loss of soil and nutrients through erosion (GRDC 2016).

Weed management is one of the biggest influences on the management of cropping systems. Herbicide resistance is estimated to cost approximately $187 million in additional herbicide treatments in the grains industry, part of the estimated $2573 million per year spent on weed management in this industry. Despite this investment, grain yield loss as a result of weeds is still estimated to be about $745 million per year (Llewellyn et al. 2016).

Table LAN1 Weeds of National Significance

Common name(s)

Scientific name

Alligator weed

Alternanthera philoxeroides

Gamba grass

Andropogon gayanus

Pond apple, pond-apple tree, alligator apple, bullock’s heart, cherimoya, monkey apple, bobwood, corkwood

Annona glabra

Madeira vine, jalap, lamb’s-tail, mignonette vine, anredera, gulf madeiravine, heartleaf madeiravine, potato vine

Anredera cordifolia

Asparagus fern, ground asparagus, basket fern, Sprengi’s fern, bushy asparagus, emerald asparagus

Asparagus aethiopicus

Climbing asparagus, climbing asparagus fern

Asparagus africanus

Bridal creeper, bridal veil creeper, smilax, florist’s smilax, smilax asparagus

Asparagus asparagoides

Bridal veil, bridal veil creeper, pale berry asparagus fern, asparagus fern, South African creeper

Asparagus declinatus

Climbing asparagus fern

Asparagus plumosus

Asparagus fern, climbing asparagus fern

Asparagus scandens

Prickly pear

Austrocylindropuntia spp.

Cabomba, fanwort, Carolina watershield, fish grass, Washington grass, watershield, Carolina fanwort, common cabomba

Cabomba caroliniana

Boneseed

Chrysanthemoides monilifera subsp. monilifera

Bitou bush

Chrysanthemoides monilifera subsp. rotundata

Rubber vine, rubbervine, India rubber vine, India rubbervine, Palay rubbervine, purple allamanda

Cryptostegia grandiflora

Prickly pear

Cylindropuntia spp.

Broom, English broom, Scotch broom, common broom, Scottish broom, Spanish broom

Cytisus scoparius

Cat’s claw vine, yellow trumpet vine, cat’s claw creeper, funnel creeper

Dolichandra unguis-cati

Water hyacinth, water orchid, Nile lily

Eichhornia crassipes

Flax-leaved broom, Mediterranean broom, flax broom

Genista linifolia

Montpellier broom, cape broom, canary broom, common broom, French broom, soft broom

Genista monspessulana

Hymenachne, olive hymenachne, water stargrass, West Indian grass, West Indian marsh grass

Hymenachne amplexicaulis

Cotton-leaved physic-nut, bellyache bush, cotton-leaf physic nut, cotton-leaf jatropha, black physic nut

Jatropha gossypifolia

Lantana, common lantana, kamara lantana, large-leaf lantana, pink-flowered lantana, red-flowered lantana, red-flowered sage, white sage, wild sage

Lantana camara

African boxthorn, boxthorn

Lycium ferocissimum

Mimosa, giant mimosa, giant sensitive plant, thorny sensitive plant, black mimosa, catclaw mimosa, bashful plant

Mimosa pigra

Chilean needle grass

Nassella neesiana

Serrated tussock, Yass River tussock, Yass tussock, nassella tussock (New Zealand)

Nassella trichotoma

Prickly pear

Opuntia spp.

Parkinsonia, Jerusalem thorn, jelly bean tree, horse bean

Parkinsonia aculeata

Parthenium weed, bitter weed, carrot grass, false ragweed

Parthenium hysterophorus

Mesquite, algaroba

Prosopis spp.

Blackberry, European blackberry

Rubus fruticosus aggregate

Delta arrowhead, arrowhead, slender arrowhead

Sagittaria platyphylla

Willows, except weeping willow, pussy willow and sterile pussy willow

Salix spp. except S. babylonica, S. × calodendron and S. × reichardtii

Salvinia, giant salvinia, aquarium watermoss, kariba weed

Salvinia molesta

Fireweed, Madagascar ragwort, Madagascar groundsel

Senecio madagascariensis

Silver nightshade, silver-leaved nightshade, white horse nettle, silver-leaf nightshade, tomato weed, white nightshade, bull-nettle, prairie-berry, satansbos, silver-leaf bitter-apple, silverleaf-nettle, trompillo

Solanum elaeagnifolium

Athel pine, athel tree, tamarisk, athel tamarisk, athel tamarix, desert tamarisk, flowering cypress, salt cedar

Tamarix aphylla

Gorse, furze

Ulex europaeus

Prickly acacia, blackthorn, prickly mimosa, black piquant, babul

Vachellia nilotica

Metcalfe D, Bui E (2016). Land: Regional and landscape-scale pressures: Invasive species. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/land/topic/2016/regional-and-landscape-scale-pressures-invasive-species, DOI 10.4226/94/58b6585f94911