Chapter 1 - Introduction
Non-native species are referred to by many names: exotic, alien,
non-indigenous, or introduced. When they spread aggressively, they're called
This chapter provides an overview of the current
invasive species situation in Australia
and describes their economic, environmental and social impacts.
While invasive species are generally argued to be the
second biggest threat to Australia's biodiversity after land clearing and other
forms of habitat destruction, Dr Barry Traill, President of the Invasive
Species Council, went so far as to say:
with land clearing hopefully now sorted out as a destructive
problem, with controls in Queensland
and New South Wales, invasive
species are probably now the No. 1 threat to nature in Australia.
The economic impact of invasive species is also high.
The economic impact of weeds and 11 key vertebrate pest animals has been
calculated at $4 billion and $720 million per annum respectively. These figures
primarily represent production losses and control costs, as the cost of weeds
to the environment and biodiversity is largely incalculable. This compares to
an estimated combined annual cost of salinity, sodicity and soil acidity of
$2.4 billion. A 1997 Australian Bureau
of Statistics survey showed 47% of farmers reported weeds as a major problem,
compared with about 15% for dryland salinity. However:
despite estimates that weeds are costing the economy 10-20 times
as much as salinity, planned government programs on invasive plants amount to less
than 10% of the resources dedicated to the salinity issue..
demonstrated through the funding of $1.4 billion for the recent National Action
Plan for Salinity and Water. More
contemporary data on the cost of invasive species is given below.
The threat to Australia's
biodiversity and economy is from weeds, vertebrate and invertebrate pests, and
plant and animal diseases, and it is contended that the threat is increasing:
Addressing the problem of these invasive alien species is urgent
because the threat is growing daily and the economic and environmental impacts
The physical isolation of Australia
has favoured the evolution of unique species and ecosystems that occur nowhere
else in the world. At the species level about:
45 percent of terrestrial birds;
85 percent of flowering plants;
89 percent of reptiles; and
93 percent of frogs are endemic to Australia.
The evolutionary processes associated with being
isolated has meant that:
[Native] [s]pecies are especially vulnerable to predators,
pathogens, and parasites.
has had an unfortunate history of incursions by plants and animals since
colonisation. Mammals, birds, fish and
plants have been imported, mainly for commercial reasons, but often simply for
the purpose of making early settlers feel more 'at home'. We now know that many
of these early species which were imported for seemingly innocent or harmless
reasons have gone on to have significant adverse environmental impacts.
The rate of incursions has increased dramatically in
more recent years, with the growth of international trade and travel leading to
importation of thousands of invasive weeds, pest animals and diseases. The
problem of invasive species has also been exacerbated by the ability of people
to trade over the Internet.
Until recently many plants and animals were brought
without being subject to rigorous pre-import risk assessment. Most of the
plants and animals that have become invasive were brought in deliberately.
Plants were brought in for pasture, horticulture and as ornamentals. Animals
were brought in for sport shooting, as food sources or as pack animals. The
Bureau of Rural Sciences noted in its submission that based on the history of
current vertebrate pests and weeds in Australia:
introduction of new vertebrate species and plants is likely to
be deliberate, legal or illegal introduction rather than by accidental
human-assisted dispersal. Hence for exotic plants and vertebrates it is highly
desirable to have robust, scientifically-based risk assessment processes to
distinguish species that pose a high threat of becoming future pests or weeds
from those that pose a low threat, and a sound process to ensure that species
identified as posing a high threat are not allowed to enter Australia.
Unfortunately, the Committee heard evidence that
current import risk assessment methods for plant and animal importation are
neither robust nor highly effective in preventing the entry of future pest
species. Loopholes in plant import legislation and the import risk assessment
system for animals are detailed in Chapter 5.
CSIRO put the scale of the invasive species problem in
context. It told the Committee that the ratio of species that become invasive
is roughly 1 in 1000. Of one thousand species entering Australia, 10 may become
naturalised and 1 of that 10 naturalised species will become a pest species.
Obviously, prior identification of the 1 in 1000 that is likely to become an
invasive species is a significant challenge for authorities charged with the
protection of Australia's
environment and agricultural sector.
As will be discussed, addressing the invasive species
problem is not simply a border control issue, but also includes managing those
species that are already here: in gardens, aquariums, farms, aviaries and the
like, and that would pose a threat if they escape.
The Committee was also alerted to the challenge of
'sleeper' species which have the potential to become the next generation pest
problem. Invasive species were identified as a major threat to Australia's
biodiversity in both the 1996 and 2001 State of the Environment reports. The
2001 report noted that:
'sleeper' weeds (species that have established, but are yet to
become a widespread problem) are now recognised to be of major concern, as are
exotic organisms that might find their way in through Australia's
quarantine barriers as a result of trade and other human activities.
As a result of the introduction of pest species to Australia,
ecosystems have become more homogenous and biodiversity has been affected. It
is widely recognised that vast areas of the Australian landscape have been
seriously altered and degraded by invasive plants and animals. Human
intervention has also seen native plants transferred within Australia,
often with equally dramatic adverse effect on native ecosystems elsewhere.
On a global level, Jeffrey
This inadvertent ending of millions of years of biological
isolation has created major ongoing environmental problems that affect
developed and developing countries, with profound economic and ecological
Climate change, degradation caused by habitat
destruction, fragmentation of native vegetation, disruption to conditions for
the breeding of native animals and birds, and changes to the nutrient status of
soil, have all enabled invasive plants and animals to spread.
The current situation in Australia
Evidence provided by the CRC for Australian Weed
Management (generally referred to as the Weeds CRC) states that in the last 200
years over 28,000 foreign plants have been introduced to Australia. Most of the
species that have become invasive were from deliberate introductions. The Weeds
CRC advised that:
Between 1947 and 1985 460 pasture grasses and
legume species were trialled in northern Australia. Sixty became weeds, 13 of
which are now serious crop weeds. Only 4 proved useful without also causing
Between 1971 and 1995 two-thirds of the 300
plants that became established as weeds in the wild were introduced as
Over 2500 species of introduced plants have
established in the wild, and many threaten the integrity of valued places, such
as Kakadu National Park.
Many of the species that have become established in the
wild may be sleeper weeds, as was Mimosa
pigra (Mimosa). Mimosa was introduced to Darwin
in the late 1800s. The plant was not considered a problem until 1952, when it
was discovered growing outside Darwin.
Following the wet year of 1974 it spread further and by 1981 much of the Adelaide
River floodplain in the Northern
territory was covered with Mimosa, some areas with
monospecific stands. Currently, half
a million dollars a year is spent to keep it out of Kakadu.
The Vertebrate Pests Committee (VPC) has created a list
of all exotic vertebrates (except fish) present in captivity or in the wild in Australia.
The list includes:
12 amphibian exotic species.
In its submission the Bureau of Rural Sciences stated
that over 80 species of exotic vertebrates (excluding marine species) have
established wild populations in Australia.
These species include:
23 freshwater fish on mainland Australia;
plus 1 mammal, 7 birds and 2 reptiles on
The Bureau of Rural Sciences acknowledges that species
that are already in Australia
have passed through quarantine barriers, legitimately or otherwise, and
relatively few of the listed species have had a risk assessment conducted to
determine the threat they pose should they escape and establish wild
populations. In its submission it stated that:
The cost and responsibility for conducting risk assessments of
pest potential for exotic vertebrates already present in Australia
but not yet established in the wild is an issue to be resolved.
As will be discussed in Chapter 6, evidence indicated that
there are weaknesses in Australia's
biosecurity policy that should be addressed.
The major vectors for the introduction of marine pests
in Australian waters is through ballast water and hull fouling, although they
have also spread as a consequence of aquaculture and the aquarium trade.
the majority of research into marine pest species is conducted by CSIRO Marine
Research. Dr Nicholas
Research Scientist, CSIRO Marine Research told the Committee that 1593 invasive
marine species have been identified worldwide. Of which:
between 135 and 308 have invaded Australia;
of those that have invaded, 53 to 73 are
classified as having had economic and/or environmental consequences; and
36 more have been identified as on their way to
Australia. They have been identified as causing damage overseas and have been
identified as being in the ports of Australia's trading partners.
has 22,000 ship visits per year; half of which are from international sources.
The Committee has heard that most new introductions will have no large-scale
impact on the environment or marine industries, however, a small number will
become significant marine pests with associated impacts and an unknown fraction
will be sleepers.
A web accessible database, the National Introduced
Marine Pest Information System (NIMPIS), has been developed by the CSIRO to
meet national needs for a central repository of information on known and
potential introduced marine species. The project was jointly supported by the
Department of the Environment and Heritage, with funding from the National
Heritage Trust (NHT) Introduced Marine Pests Program, CSIRO and a consortium of
State agencies. The database contains detailed information on over 80 known
introduced species in Australia,
and limited information concerning 35 species not currently known to be in Australia
but that pose a potential threat. Users who are aware of introductions of
marine or brackish water species not currently included in the database are
requested to submit a report of their sighting.
The NIMPIS database is one of a number of key
initiatives aimed at providing tools to prevent further introductions of exotic
marine species, facilitate rapid responses to new incursions, and assist in the
management of existing introduced species in Australian waters. Reported
sightings are automatically referred onto the Centre for Research on Introduced
Marine Pests at CSIRO Marine Research.
Marine pests are discussed in detail in Chapter 6.
Invasive species represent a major cost to the
Australian economy. As the management of invasive species is a shared
responsibility of government, industry and the community each sector bears the
costs of responding to the threat or managing the consequences of it. However,
the primary responsibility for managing invasive species primarily rests with
land holders and consequently management costs are largely borne by private
citizens, particularly farmers, not government (except when government is also
the landholder, such as reserves and parks). These costs take the form of
direct management costs and also the increased cost of foods, loss of land
value and reduced economic welfare.
The CRC for Australian Weed Management (Weeds CRC) and
the Pest Animal Control CRC (Pest Animal CRC) have sought to quantify the cost
of invasive species in recent reports entitled, respectively, The economic impact of weeds in Australia
and Counting the Cost: Impact of Invasive
Animals in Australia, 2004. These are discussed in the next sections.
The cost of weeds
The Weeds CRC report released in 2003 assessed the
economic impact of weeds on agricultural land, national parks, other public
land and indigenous land. The report assessed costs for the 2001-02 financial
year. It estimated that the economic impact of weeds, across Australia,
was approximately $4 billion per annum and it acknowledged the fact that weeds
have monetary and non-monetary costs and benefits:
If there were no weeds, incomes to agricultural producers and
benefits to consumers of food would rise by $3.927m in the mean case and $112m
of government expenditure would be released for productive investment
The report identified that the impact of weeds could be
measured as the:
direct financial costs to control the weeds
changes in net money revenue; and
and changes in welfare.
The estimated cost of $4 billion per annum is, in fact,
conservative as it does not include the financial impacts on:
labour costs of volunteers; and
other asset and industry costs that could not be
Some estimated costs of weeds to primary production are
set out in the table below.
Table 1.1 - Estimated costs of weeds to primary production
National cost of weeds in
annual winter grain regions
Annual cost of wild oats
in grain crops in 1987-88
Annual cost of serrated
tussock in NSW pastures
Annual cost of serrated
tussock in Victorian pastures
$5.1 million (1997), estimate
increasing to $15 million by 2007
Cost of weeds to farmers
in the southern cropping zone
$70/ha per year (average);
Cost of attempts to
eradicate Kochia scoparia in WA,
where it was introduced for use with salinised soils
While several submitters argued that weed management
programs should be based on the 'public good', the CRC report notes that the
allocation of monies to such programs is based on comparing costs and benefits
and allocating to the project with the greatest rate of economic return. A
downside of this approach is that a funding application based predominately on
environmental grounds may not receive the same level of support as one that has
impacts on agriculture. The Committee was told that non-economic factors, such
as social and environmental impacts, warrant consideration in comparing costs
Total expenditure by Commonwealth and state agencies
(other than the National Parks and Wildlife Services), other government
authorities, local government and other public land managers in 2001-02 was
estimated as being at least $80.775 million, with $8.252 million spent by the
Commonwealth on weed management and research.
The CRC report's findings of the high per hectare
benefits, benefits to the agricultural sector and benefits relative to other
environmental problems that could be achieved from improved weed management
adds support to claims that weed programs should be a major recipient of
research, management and control funds.
The cost of pest animals
Pest animals have a triple
bottom line effect. Dr Peacock,
CEO, Pest Animal Control CRC, told the Committee that:
They affect our environment, our economy and our society. Often
it is very difficult to quantify that cost. How do you value a threatened
species or cost in another factor that makes life in the bush even harder than
it should be? How do you measure the frustration of recreational anglers who
cannot catch anything but carp? It is hard to measure but it is a big cost
A report released by the Pest Animal CRC in mid 2004
estimated that the economic, environmental and social impact of 11 major introduced
vertebrate pests of Australian agricultural industries and the environment was
$719.7 million per annum. The report
assessed those species that are included in the CRC's research priorities,
impacts were assessed Australia-wide and a triple bottom line assessment was
Economic impacts were able to be calculated for all 11
vertebrate pest animals:
Table 1.2 - Economic impact of vertebrate pests
Total Cost ($m)
Rabbits, foxes, feral pigs and feral cats were
identified as inflicting the greatest cost impact on the Australian economy,
with a total impact of $553.1 million. The major component of the impact from
rabbits and pigs was reduced agricultural production, principally for sheep and
cattle industries. To address this issue, the Pest Animal CRC report noted
Given the heavy impact these pests impose on these industries,
collaborative research projects should be sought with sheep and cattle
producers, as they would be the major beneficiaries of such research.
The environmental impact of the pest animals could only
be quantified for foxes, feral cats and carp. Their impact was assessed as
being $190.0m, $144.0m and $11.8m respectively. Feral cats and foxes were
identified as inflicting the greatest cost impact on native fauna, primarily as
a consequence of bird deaths.
The major control costs were identified as including
baiting, fencing, shooting and research associated with improving management of
the invasive species. Production losses for sheep, cattle and cropping
industries were predominately identified as being the result of invasive
species predation on young stock, crop damage and competition for feed. The
report identified that:
Feral pigs, rabbits, kangaroos and feral cats were estimated to
account for 83% of losses and agricultural productivity loss accounts for about
half of total costs estimated.
In calculating the economic cost of the invasive
species, expenditure on public sector research and management costs were
assessed. The report noted that the social impacts of the pest animals were not
able to be quantified.
Other species which were identified as having
significant impacts, but for which costs were not calculated, were:
noted that impact assessments on these species need to be conducted if the
complete cost of vertebrate pests in Australia
is to be determined.
The cost of marine invasives
While there is a lack of specific information on the
economic impact of marine pests, the Bureau of Rural Sciences advised that:
the economic threat of marine pests is also substantial to the
Australian mariculture industry which is worth in excess of $600 million per
The Bureau of Rural Sciences noted that Tasmanian
oyster and mussel growers are already experiencing heavy stock predation by the
Northern Pacific Seastar. The
Committee heard evidence that Port Phillip Bay recorded
a 40 per cent reduction in fish stock numbers over the past three years as a
consequence of invasion by the Northern Pacific Seastar.
Outbreaks of toxic dinoflagellate or other invasive
microbial agents also pose a threat to aquaculture stock (mussels, oysters,
scallops). If there is an outbreak it could lead to the closure of fisheries
for human health reasons, such an event has the potential to be economically
costly. The potential loss of Australia's
'clean' reputation could have a significant impact on mariculture if export
markets are lost.
The extent of the economic impact of marine invasives
is demonstrated through the campaign to eradicate the Black-striped Mussel that
entered the marina in Darwin
in 1999. The eradication campaign cost over $2 million in materials alone.
However, if left unchecked, it had posed a major threat to the local $40
million per annum pearl industry. In assessing its response to the outbreak, Australia
was able to learn from America's
experience with the closely related zebra mussel that cost the United
States $100 million per annum to control in
the Great Lakes alone.
A case study on the Black-striped Mussel eradication campaign is provided in
The cost of invasive marine species is not limited to
mariculture industries. It also impacts upon shipping and ports, coastal
amenity, human health, species and ecosystem health and diversity. Hassall and
Associates has suggested that:
Marine pests have the potential to reduce this public amenity by
reducing the chances of catching a fish, reducing the attractiveness of a
diving trip, leading to beach closures or increasing the time spent by a boat
owner in maintaining their vessel.
The impacts listed in the Hassall report have flow-on
economic impacts, such as:
loss of revenue for dive operators and bait
shops in tourist areas;
increased costs associated with maintaining
costs associated with having to close marinas
and waterways for treatment.
A key area that could be affected is tourism. If
outbreaks occur in waters near tourist areas such as the Great
Barrier Reef, and limit recreational use of the water, they have
the potential to cause significant losses. This is demonstrated through the
The existence and option value of the Great Barrier
Reef, at risk from human activities, has been estimated to be in
the order of $AUS45 million per annum.
The Commonwealth Government has recognised the
potential threat to tourism in the Great Barrier Reef
that is posed by the Crown of Thorns Starfish. In the 2004-05 budget it
provided $0.9 million over three years to assist tourism operators to implement
a control program.
The cost of plant diseases
Invasive plant diseases include pathogens and
invertebrate pests, such as viruses, fungi and various insects. Plant pests
pose a major threat to the Australian economy through their potential to impact
on primary production. A comprehensive study of the cost of plant diseases to
the Australian economy has not been prepared, however, information is available
on the economic impact of individual plant diseases. In its submission CSIRO
noted that annually approximately 12% of losses to global crop production are
caused by diseases. 
As with weeds and pest animals, plant pathogens have
the potential to seriously reduce the productivity of crops once they become
established in Australia.
A known case is sorghum ergot, which costs industry $4 million per annum to
control. One crop in Australia
for which comprehensive data is available is wheat. In the 1980s annual crop
losses of 14.5% of total production were attributed to wheat diseases; this
amounted to $300 million per annum.
This supports claims that the economic impact of plant diseases is significant.
In its submission Plant Health Australia (PHA) listed
citrus canker (xanthomonas axonopodis
pathovar citri), a highly contagious bacterial disease of citrus, as having
a potential negative impact on the industry if it were to become established in
Citrus canker is spread by wind-borne rain, lawnmowers and landscaping
equipment, animals, birds, movement of plants and fruit. PHA advised that
citrus canker could also have an adverse impact on the six native species of Citrus, potentially resulting in the
loss of biodiversity of the native species if it were to enter Australia. Outbreaks can result in dieback,
defoliation, blemished fruit, premature fruit drop and although not harmful to
humans the crop cannot be sold.
Outbreaks have occurred in Australia
in 1912, 1991, 1993 and most recently in July 2004 in Emerald, Queensland.
The most recent outbreak resulted in the Shires of Emerald, Peak Downs and
Bauhinia being gazetted by Queensland
as pest quarantine areas to further restrict the movement of citrus products.
The cost of surveillance and eradication for the first six weeks of the
outbreak was $1.6 million. This activity will be followed by a further two
years of surveillance which will cost significantly more. Though these costs
are high they do not compare to the potential losses to the Queensland
citrus industry, which is worth $120 million per annum and the Australia-wide
industry which is worth $420 million.
The disease was eradicated from the infected property through removing and
destroying host plants in the wider vicinity of the area.
Apart from their economic impact, invasive species are
a major threat to Australia's
In some cases, as with mimosa in the NT, it takes only one type
of invader to cause total landscape change. Scientists refer to these invaders
as 'transformer species' because they have the ability to transform entire
ecosystems. Their legacy is a degraded, foreign environment, stripped of native
plants and animals. Future generations may never realise what was lost.
Habitat disturbance and destruction, and changed fire
and water regimes, are often linked to the presence of invasive species. Grazing,
predation and competition by introduced vertebrates are also recognised as impacts
of invasive species.
The situation is not helped if ecosystems are already
A sick ecosystem is likely to allow new pests to establish
themselves more easily and extensively and heighten their collective impact.
as serrated tussock and Chilean needle grass (Nasella neeisana) easily invade pasture lands through dispersal by
wind, birds or human assistance.
The environmental impact of invasive species is part of
a suite of impacts that can threaten the survival of native species. Impacts
from invasive species include:
reduced floral diversity by competing with
native species for water and nutrients;
shading out lower vegetation strata;
reducing the productivity of pastoral land; and
Invasive plants have the capacity to spread across
significant areas. Examples include:
Table 1.3 - Coverage of invasive plants
8 million ha nationally
6.6 million ha in Qld in 2002
(potentially 50m ha nationally)
4 million ha nationally
700,000 ha, and now found
acress 20% of Qld
80,000 ha in the Top End of NT
McNeely summed up the impact of invasive
species when he wrote:
invasives may cause changes in ecological services by disturbing
the operation of the hydrological cycle, including flood control and water
supply, waste assimilation, recycling of nutrients, conservation and
regeneration of soils, pollination of crops, and seed dispersal.
It is very difficult to attribute a cost to such
factors. The Hassall and Associates report noted that:
A significant factor limiting the capacity of researchers to
determine the impact of these pests has been the absence of base-line
environmental data and the consequential difficulty in determining the
pre-existing environmental valuation of the resources. In many cases impacts
are simply reported in a subjective manner as being "real and
alarming"...Similarly, the impact on the environment is often noted as
significant, relative to that on another sector, without real valuation.
The invasion of native ecosystems by invasive species
regarded as a major threat to biological diversity worldwide.
Traits common amongst invasive species include:
broad environmental tolerances (salinity,
temperature, water quality);
lack of specific dietary requirements;
capacity to exploit an available niche; and
capacity for broad dispersal.
Hybridisation of native and introduced species poses a
threat to the survival of native species. The Committee heard from Mr
Vice President, AgForce Cattle, AgForce Queensland,
with domestic dogs mating with dingoes we now have a much larger
population of wild dogs than we have of pure dingoes. In fact pure dingoes tend
to be dying out.
Additional evidence of the hybridisation of native and
introduced species was provided by Dr Black,
Committee Member, Nature Conservation Society of South Australia. He told the
the mallard has eliminated the pure New
Zealand grey duck, and it is progressively
invading genetically the black duck in Australia.
advised that foxes predate on small animals in the range from 300 grams - mouse
size - to 5 kilograms - small wallaby size. In discussing the decimation of
small animals by foxes Dr Peacock
As Tim Flannery said, half a century ago no-one even knew about these small
mammals and in half a century from now it will be too late to do anything about
The Committee received evidence that invasive species
often flourish when introduced to new environments as generally they do not
have natural predators to control their spread. An example of this is cane
toads which have flourished since their introduction to Queensland
in the 1930s. One reason that they have flourished is that they are poisonous
in all stages of their life-cycle. Current estimates show cane toads are
spreading in the tropics at about 27 kilometres a year. The Pest Animal CRC
report noted that:
Populations of Northern Quoll, D.
haaucatus, have seriously declined in Queensland
following colonisation by cane toads (Burnett 1997). These
quoll populations have not recovered in the past 10 years, therefore cane toad
impact on quolls is likely to be a long-term phenomena (Burnett 1997, in
Recent research undertaken in Kakadu
National Park indicates that cane
toads cause substantial declines in northern quoll populations. The Department
of the Environment and Heritage acknowledged the threat that cane toads pose to
native species survival. In its submission it stated that:
There is a significant risk that quoll species across northern Australia
may become locally extinct in areas invaded by cane toads. As a precautionary
measure, a representative sample of northern quolls have been moved to cane
toad-free islands off Arnhem Land to safeguard the
Evidence indicated that limited research is being
conducted into the impacts of cane toads and possible control methods. Funding
had been cut to a research program that had sought, through tracking the impact
of cane toads on northern quolls and goannas in Kakadu
National Park, to verify stories
from indigenous communities in Cape York that cane toads
led to the disappearance of the native animals. The research project had been
commissioned by Parks Australia North and had been operating since 2001. The
Committee expresses its regret that support for the project was withdrawn, at
such a late stage, when:
To finish the radio-tracking, the project needed another four to
five months and about $16,000-$20,000, roughly a tenth of what has already been
Cane toads have cut a swathe through native animals.
Australian native fauna that has been killed by cane toads
include Goannas, Freshwater Crocodiles, Tiger Snakes, Red-bellied Black Snakes,
Death Adders, Dingoes, and Northern Quolls.
Evidence indicated that preference for funding is given
to invasive species that cause significant economic impact over those that have
non-economic impacts, such as environmental or cultural impacts. The
preservation of biodiversity and the flow-on cultural impacts need to be
accorded a commensurate level of recognition. The Indigenous Land Corporation
weed management on a pastoral lease where the invasion is
clearly affecting the economic capacity of that land is far more likely to be
funded than where weed invasion is affecting Indigenous peoples capacity to
hunt, gather food, undertake management of site and management [of the] country
in accordance with cultural traditions. There needs to be a greater focus on
invasive species that do not necessarily have a negative commercial impact.
...Indigenous landholders are responsible for a significant part
of the country, but are not major economic players commensurate with the extent
of title held. 
The Bureau of Rural Sciences noted that weed species
can reduce biodiversity and contribute to local extinctions of native plants
and animals through competition. An example cited was blue trumpet vine (Thunbergia grandiflora) which spreads
rapidly, smothering rainforest in the tropical lowlands of coastal north Queensland.
It can invade about 0.6 of a hectare of rainforest per year, and can climb
trees up to 40 metres tall.
When pasture biomass is low, competition for food and
water can occur between stock and invasive vertebrates. Invasive vertebrates
can cause significant land degradation as they do not cease grazing if farmers
de-stock pastures. Changes in the composition and cover of the vegetation
caused by grazing vertebrate pests can influence populations of ants, termites
and topsoil micro-arthropods. Changes in the vegetation may have long-term
effects on the soil structure by increasing soil disturbance. This can have a
flow on effect of reducing land values.
Invasive pest animals can have a variety of biodiversity
Camels may deplete shelter and refuge for desert
animals. Camel grazing can impact on native vegetation.
Rabbits and goats overgraze, resulting in
increased soil erosion.
Wild horses can increase soil erosion, destroy
native plants along frequently used routes, foul water holes, collapse wildlife
burrows, spread weeds through their hair and dung, and compete with native
wildlife for food and shelter.
Foxes predate on mammals and birds. It has been
estimated that they are responsible for the 9.5 million kilograms per year of
live bird predation. Based on an average bird weight of 50g this accounts for
190 million fatalities per year.
Feral pigs threaten native species through feed
competition. Native vegetation is also affected by damage from trampling, the
spread of rootrot fungus (Phytophthora
cinnamomi) and dieback disease.
Carp increase water turbidity which releases
sediment nutrients and destroys aquatic plants. They result in a reduction in
the abundance of invertebrates and aquatic plants, which form the basis of
native fish diets.
The impact of wild dogs on biodiversity was highlighted
by Mr John
Stewart, Vice President, AgForce Cattle,
AgForce Queensland, who explained
There is a significant impact on the survival of remnant populations
of endangered fauna such as small macropods, and we have bilbies, bandicoots
and smaller wallabies within the target range for wild dog food. In Central
Queensland the last remaining population of northern hairy-nosed
wombats has had to be fenced to protect it from the predations of wild dogs.
The Invasive Species Council
noted in its submission that despite the identified negative impacts:
there is virtually no momentum to address
the invasive species threat to biodiversity. Currently, institutions, policies
and funding are overwhelmingly concerned with protecting agricultural
production values, and there is little public or private investment in
It went on to advise that:
every year of neglect is a year when the
long term costs blow out, usually with irreversible consequences on indigenous
Naturalisation of invasive species
The already daunting task of managing invasive species
is augmented by the fact that many people accept some introduced species as a
normal part of the landscape, despite the harm they cause. This was
demonstrated to the Committee during its site inspections in Brisbane
where it saw the widespread use of varieties of Duranta for hedges, landscapes and colour features on public and
private land. The Committee heard that many people who have planted Duranta in urban areas are not aware
that it is widely dispersed through the spread of seeds by fruit bats and birds
and is now naturalised from Cairns
to northern New South Wales,
outcompeting native vegetation.
The challenge of managing invasive species is
compounded by the fact that a number of invasive species have become
naturalised and native animals have learned to live with them. A case in point
for this is cane toads. At the public hearing in Brisbane Mr Craig Walton,
Senior Policy Officer, Ecology, Queensland Department of Natural Resources,
Mines and Energy stated that:
there have also been a number of native species and a number of
bird species that now feast on cane toads-they have now worked out how to roll
them over on their back and eat their stomachs, and cane toads are now a prey
Developing on this issue, Mr
Committee Member, Nature Conservation Society of South Australia, explained the
dependence of some native species on invasive species. Mr
Tucker stated that:
We also have quite a conundrum in that ... where we have weeds,
quite often native animals will use those weeds .... There is the nationally
endangered bandicoot, and if we were to eliminate the blackberries another type
of bandicoot would go extinct. It [invasive species management] is complex.
It has been recognised that:
This mutualism presents an intractable conservation management
Evidence supports claims that invasive species can play
a dual role. It has already been demonstrated that cane toads are a food source
for some native species and the killer of others. The same situation is
occurring with weed species. Weeds can harbour feral animals and diseases but
also provide a food source and protection to native species. An example of this
is blackberry (Rubus fruticosus) which
provides protection for rabbits. The
other role it plays is harbour native species, such as bandicoots.
Many invasive pest animals have become integrated into
the food chain. This has impacts on biodiversity when attempts are made to
reduce their numbers. Highlighting this is the fact that:
Dingoes have been integrated into established predator-prey
relationships and may play a constructive ecological role of regulating the
population of certain native fauna. The controlling influence of wild dogs on
marsupials and emus numbers is demonstrated by the difference in their
prevalence across the two sides of the barrier fencing (Pople et al. 2000).
There is also a case to argue that predation by wild
dogs of other introduced species of predators such as foxes, feral cats and
feral pigs counters their negative impact on native species. Mr
Vice President, AgForce Cattle, AgForce Queensland
explained this issue to the Committee.
For instance, some people will not bait for dogs and they do not
bait for feral pigs because they want the dogs to keep the pig population
down-that is, chase and get rid of the piglets. So, for that reason, they will
not bait for feral pigs. Sometimes it needs to be explained to people. While
people in the bush are well aware of feral pigs, wild dogs, foxes and so on,
some people probably need to go through a greater education process about just
what is happening to their overall profitability.
As a consequence of the dual role of many introduced
species the management of them needs to be carefully mapped to ensure that a
consequence of management plans is not further loss of biodiversity. Mr
Executive Officer, Animal and Plant Control Commission, told the Committee
simply removing the feral species is not going to achieve a good
outcome unless you know and plan what you want to achieve at the other end. So
we are suggesting that people really need to start planning for the outcome
they are trying to achieve, not just remove the weed.
The Committee heard evidence
that some of the small mammals and plants that have become extinct or are
threatened by invasive species are keystone species. A keystone species is a
species that is disproportionately important in the maintenance and balance of
its community's integrity. They interact with a large number of other species
in a community and because of those interactions, the removal of the species
can cause widespread changes to the community structure. The reduction in
keystone species has a significant impact as they are the cornerstone of the
ecological community in which they reside.
Examples of keystone species
are the small crabs on Christmas Island.
Robber, red and blue crab populations were significantly reduced in areas of Christmas
Island that were infested by yellow crazy ants in
the 1990s. The crabs play a key role in the forest ecology by digging burrows,
turning over the soil and fertilising the soil with their droppings. Once the
crab numbers declined the structure of the forest changed. Populations of other
ground and canopy dwelling animals, such as reptiles and other leaf litter
fauna also decreased. Increased densities of crazy ants led to increased
densities of scale insects, which led to increased light gaps in the canopy of
the rainforest. The light gaps and reduction in crab numbers led to change in
the ecology of the forest, resulting in an increase in seedlings and weeds
growing on the forest floor. With the introduction of control mechanisms for
the yellow crazy ants crab numbers were able to increase and biodiversity is
slowly being restored However, the longer terms impacts may not be evidenced
for some time.
Increased fire risk
A large number of pasture grasses were introduced to Australia
from Africa in the last century because they grew larger
and produced more feed for cattle than native grasses. Mr
Councillor, Invasive Species Council, told the committee that:
If they are not eaten by cattle they dry out into straw and
produce very hot bushfires-much hotter than Australia
has been used to. These are having a devastating impact all over Northern
Australia, changing vegetation structure, killing young trees and
eating into inland rain forest. Putting a cost to that ecological damage is
The Committee heard evidence from Mr
President, Weed Management Society of South Australia, that feral olive trees
burn faster and hotter than native trees, such as eucalypts. He advised that
this occurs because they have a greater biomass, consistent canopy and higher
oil content than natives. Concern was expressed regarding the bushfire risk
posed by the large number of failed olive plantation investment schemes in
areas of Australia that have a Mediterranean climate, especially those that are
in close proximity to urban areas.
The SA Government is seeking to address this risk. Mr
Executive Officer, Animal and Plant Control Commission, told the Committee
In South Australia,
under the policies of the risk assessment process we have implemented, if an
olive grove is not managed for two years, it can be proclaimed as a feral
planting and removal can be enforced. Obviously we are always concerned about
the fact that foxes and starlings spread olive seeds over large distances. When
we are looking at new applications, we request that they consult their local
boards and develop a management plan for those species. Providing a place for
the birds to defecate before they fly off is at least a good start, so we ask
the local boards to do something to manage the feral olives.
The Committee heard that olive trees were brought to
South Australia on the HMS Buffalo and
this has resulted in a situation in South Australia of there being:
both heritage listed olive trees and feral olives and we have an
industry that is trying to develop.
These different categories pose management challenges as
blanket management plans cannot be applied.
The difficulty in quantifying the social impacts of
invasive species was acknowledged by the Pest Animal CRC in its publication Counting the Cost: Impact of Invasive
Animals in Australia 2004. It wrote that:
Social impact is perhaps the most difficult element of the
'triple bottom line' framework to define and quantify.
The report sought to quantify the cost of 11 major
vertebrate pests on Australian agricultural industries and the environment. The
report was able to include annual cost values, including control and production
loss estimates. However, it acknowledged that many gaps exist in knowledge of
the social impacts of vertebrate pests and they were only discussed in
qualitative terms in the report.
Evidence received by the Committee indicated that the
social impacts of invasive species are significant. However, it was widely
acknowledged that there was difficulty in attributing an economic value to the
social impacts for all areas that are affected by invasive species.
A cross section of impacts
It is recognised that many introduced species do not
cause significant problems - it is worth recalling CSIRO's evidence cited above
that only 1 in 1000 species imported into Australia
end up being classified as invasive. For example, dogs and cats, tulips and
roses, have arguably made a significant positive contribution to Australian
social life. However, those that are invasive can have considerable social
impact on the community.
Social impacts of invasive species are considerable and
are not limited to rural areas. A cross section of impacts include:
vehicle accidents involving pest animals;
distress, fear and nuisance, eg. mice and
reduced rights of movement, for example in areas
that are undergoing invasive species management activities;
loss of aesthetic values and amenity, such as
with weeds, like Hymenachne amplexicaulis,
that clog waterways; and
impacts on lifestyle and heath, such as the
threat posed by red imported fire ants because of their aggressive nature,
large numbers and tendency to sting a number of times.
Although the economic cost of the social impacts of
invasive species is difficult to identify, the broad social impact of invasive
species was widely acknowledged in submissions and other evidence the Committee
received. The Bureau of Rural Sciences stated that:
Weed species, apart from impact on biodiversity, can also affect
recreational use of areas. For example, many introduced plants can form dense
infestations on or around coastline, such as bitou bush, and other water bodies
limiting or preventing their use, such as willows (Salix spp.) which can make
access along narrow rivers impossible. Many weeds grow densely and have
prickles or spines such as lantana (Lantana spp.) and blackberry, and can limit
or prevent access to areas.
Weeds can reduce the appeal of natural landscapes. This
can be seen in wetlands in the Northern Territory
which, which were initially havens for wildlife, but have now become overrun by
monospecific stands of Hymenachne
Impacts of aquatic weeds include:
blocking and polluting waterways;
reducing employment opportunities;
affecting drinking water; and
reducing recreational enjoyment.
Dr Nicolas Bax, Senior Research Scientist, CSIRO Marine
Research told the Committee about an outbreak of caulerpa taxafolia in West Lakes in Adelaide, South Australia and
explained the impacts of the weed. He advised that caulerpa taxafolia:
is a green algae and it has caused a huge amount of trouble in
the Mediterranean, where it spread to cover 10,000
hectares. It has now invaded southern California
as well. It basically covers surfaces; it almost looks like an underwater golf course,
I think, when it comes. It covers reefs, it covers seagrass and it is basically
noxious to most species, so not many species eat it. It is seen as a major
threat to nursery areas-for fish, for example-so the South Australian
government went ahead and looked at various solutions to eradicate it from South
Australia. It is spread by the aquarium industry,
which is an interesting vector. Up until very recently it was still
available-you can still buy it on the Internet, for example-and up until very
recently it was exported from Queensland.
The cost of the eradication campaign was significant.
in South Australia
they spent $6 million to $8 million eradicating from West
Lakes through pumping freshwater
into those lakes. So it does appear that eradication is possible, especially in
areas where the environment is semi-closed...
He went on to explain that:
One thing that may be of interest about caulerpa is that,
whereas the national system and the cost sharing which has been set up by the
states and the Commonwealth addresses introduced marine pests, because it cannot
be demonstrated that caulerpa is introduced-and it appears that it comes from Queensland-it
falls outside of the whole cost-sharing arrangement.
Learning from other countries
is able to learn about the social impacts of invasive species that have yet to
become established in Australia,
from countries that have experienced an outbreak of the species. This is what
occurred when the red imported fire ant was discovered in Brisbane
in February 2001. Australia
looked to the United States
experience with the red imported fire ant, where it had been allowed to spread
beyond the point of eradication, and was able to conclude that inaction was not
an option. In the United States the social impacts of fire ants included
significant impact on public health due to their aggressive behaviour, their
tendency to sting repeatedly, their ability to cause anaphylaxis, and safety
risks for small children, the elderly and pets that may not be able to 'escape'
an attack. Other social impacts included the loss of ability to use yards as
places of relaxation and loss of amenity of other land, such as sporting
fields. A case study on the red
imported fire ant incursion is provided in Chapter 5.
The social impact of invasive species is often a
flow-on effect from the economic impact, especially if agriculture and industry
are involved. Mr Tim
Allen, National Coordinator, Marine and
Coastal Community Network demonstrated this point through the example of the
comb jellyfish in the Black Sea. He advised that:
It now constitutes up to 95 per cent of the biological mass of
the Black Sea. It led to the collapse of the Black
Sea’s fishery worth $250 million a year, causing massive social dislocation
and the complete collapse of that fishery.
A correlation can be drawn between the comb jellyfish
outbreak and the outbreak of the Northern Pacific Sea Star in Port
Phillip Bay. The Northern Pacific Sea Star was first identified in
Tasmanian waters in 1992. It is believed to have been present in Tasmanian
waters, but misidentified, since approximately 1986. By 1995 it had spread to Port
Phillip Bay and it has now extended beyond Port Phillip
Bay to near Inverloch, 100 kilometres to the east. It is estimated
that there are now 1200 tonnes of the Northern Pacific Sea Star in Port
Phillip Bay compared to 2700 tonnes of fish. The Committee heard
that the Northern Pacific Sea Star has the potential to spread east of Port
Phillip Bay due to prevailing currents, however, it will only spread west with
human assisted dispersal, for example through ballast water.
The Department of the Environment and Heritage noted
that there is evidence that the Northern Pacific Sea Star is affecting oyster
production on some marine farms in southeast Tasmania. It poses a threat to mariculture
through its direct predation on native species, its ability to out-compete
native species for food and its potential to occupy and dominate suitable
habitats from Sydney
to Perth. If it continues to spread
across Australian waters and increase in prevalence it has the potential to
cause significant social dislocation, resulting in job losses and reduced
income, to areas that rely on fishing and aquaculture as key economic sources.
The social impacts of invasive species are generally
localised. Mr Robert
Pietsch, President AgForce
Sheep and Wool and President
told the Committee that wild dogs are responsible for the slaughter of many
lambs and sheep and are one of the factors that have made it no longer viable
for people to run sheep in some areas of Queensland.
He also explained that cattle farmers have problems with losses from wild dogs,
a key source of losses being Neosposa
caninum, a disease which causes
bovine abortion. Mr Pietsch
told the Committee about the interrelation of the social and economic impacts.
He told the Committee that:
there is an enormous impact socially in places like old wool
towns where, because there are no longer shearing teams and all the rest of it,
the economic loss to those communities is enormous.
Invasive species were identified by Dr
CEO, Pest Animal CRC as being one of the aspects that make farming unappealing
for people. Dr
Peacock showed the Committee footage of a
mouse plague and advised that:
If you have had to shake them [mice] out of your children’s beds
at night and that sort of thing, it is another thing that makes farming
unattractive for many people to participate in.
The Committee heard that invasive fish species, such as
carp, impact on anglers' recreational enjoyment. In some parts of Australia,
fishing has been banned as a result of carp presence:
Lake Crescent (Tasmania),
for example, which had 1,559 full season anglers who exclusively fished this
area, was closed until the current brown trout season. Aside from directly
affecting the well being of these fishermen, possible decreased expenditure by
these people would have affected support industries. Each freshwater angler is
estimated to spend around $535 on the sport (Henry
and Lyle 2000).
Public amenity has been affected by invasive marine
species. Impacts of invasive species have included:
reducing the attractiveness of dive sites;
reducing the productivity of recreational
increasing the maintenance requirements for
Invasive species also have the potential to impact on
the cultural identity of indigenous Australians. It has been recognised that:
The introduction of cane toads into traditional Aboriginal
areas, such as Kakadu, may result in the decline of dingo, snake and crocodile
numbers - threatening the nomadic hunter and gatherer lifestyle.
The Indigenous Land Corporation submitted that:
the impact of weed species on cultural activities can be
significant and must be included in the risk assessment of invasive species and
the development of a Threat Abatement Plan and any other management strategy.
Impacts on health - human and animal
Invasive species can have significant impacts on human
and animal health, which flows on to adversely affect social well being.
Invasive plants can have an impact on peoples'
wellbeing. For example:
the health of asthma and hay fever sufferers is
linked to rye grass;
it has been documented that Parthenium can cause severe respiratory problems and dermatitis,
prolonged exposure can cause severe allergic reactions; and
olives can be accountable for up to 40% of
air-borne pollen at flowering time in areas where there is an invasive problem.
The continued spread of certain invasive plants is
increasing the adverse impacts that they have on peoples' health. Many invasive
species that have become established can:
sting people (stinging nettles);
give people rashes (Rhus, green cestrum); or
irritate skin with caustic sap (petty scurge).
Other weeds present a barrier of spikes, needles,
thorns and prickles that can cause injury. Thornapple and castor oil seeds,
arum, lilly, blackberry and nightshade, are toxic.
Twenty-three common weed species are a serious
respiratory or toxic risk, especially to young children. However, amongst the
twenty-three that pose significant respiratory or toxic risk only Parthenium has received federal funding
Landholders are well aware of weed species that harm
stock and pet animals. Examples include:
As with humans, the thistles, spines and burrs on weeds
such as mimosa, mesquite and acacias can often cause injury to stock and pet
animals. This can have flow on economic effects.
Evidence indicated that some invasive species are
potential reservoirs of diseases. Dr Kevin
Doyle, Veterinary Director, Australian Veterinary
Association, advised that feral pigs carry a number of diseases which are
endemic in Australia;
including a number of insect-borne viral diseases that cause encephalitis. The role of feral pigs as carriers
of disease has a public health dimension as some diseases of concern, such as
Japanese encephalitis, are zoonoses.
One of the most significant impacts of pest animals is
that they can spread disease to humans, livestock and native animals. Examples
Rabbits which host tapeworm and liver fluke and
can also increase the prevalence of hytaids, paovirus, toxo plasmosis,
distemper, brucellosis, coccidian and leptospirosis.
Feral pigs which can transmit leptospirosis,
brucellosis, tuberculosis and other diseases. They are also reservoirs for exotic
diseases such as foot and mouth disease and Japanese encephalitis.
Wild dogs have the potential to be vectors for
rabies if it enters Australia.
Feral cats are vectors for toxoplasmosis and
sarcosporidiosis, which can be transmitted to native animals, humans and
domestic livestock. They also have the potential to be carriers of rabies.
Cane toads are poisonous to pets, especially to
dogs which attempt to eat them.
The social benefits of invasive species
The impacts of invasive species are not all negative.
Camels, rabbits, foxes, carp and goats are a significant factor in the
management costs for invasive species but also provide employment opportunities
in rural and regional Australia.
Export of feral camels to the Middle East is
worth more than $2 million per annum;
Export of fox pelts was estimated as being worth
about $8 million per annum in 1984.
More recent estimates are not available, although demand has reduced.
Commercial harvesting of carp was worth a gross
total value of $1.7 million in 2002.
Export of feral goats was worth a gross value of
$29 million in 1993.
While noting the positive contribution of pest animals
to rural and regional Australia,
the beneficial outcomes need to be discounted by the potential impact on
biodiversity. The Pest Animal CRC's report noted that in most cases the
benefits are relatively minor in comparison to the cost of pest impacts.
In light of the disparity between the contribution and
the cost of pest animals the Committee notes that compensation may be payable
to people whose livelihoods are affected by the release of control methods.
A case that highlights this is the recent ruling that
requires the Commonwealth Government and CSIRO to pay $1.5 million in
compensation to a small group of shooters and wholesalers who made their
livelihoods from the wild rabbit industry. The grounds for the suit were that
the Government and CSIRO were negligent in failing to prevent the release of
the calicivirus from a testing station on an island in the Spencer Gulf of South
Australia in 1995.
Challenges in addressing social impacts
The extent to which invasive species are able to be
effectively managed is dependent upon whether key stakeholders have been
engaged and acknowledge problems and support programs to address them. It is
essential that landowners be engaged as they bear the majority of costs
associated with invasive species and their support is required if management
activities seek to incorporate their land and neighbouring land.
Management of invasive species can be hindered by
negative attitudes amongst some members of the community to some management
activities. In relation to invasive plants, there may be objections to what are
seen to be beautiful plants, such as duranta or willow trees. In relation to
pest animals, objections are primarily focused on the method of reducing the
pest animal population or objections to the killing of animals on humane
grounds. This issue is very complex and has been acknowledged by researchers
and authorities responsible for the management of invasive species. The Committee was told that, on South Australia's Kangaroo Island, the koala population is in danger of starving
to death, simply because there is no palatable public policy to deal with the
A backlash against proposed ariel baiting in the Kosciuszko
National Park to control wild dogs
highlights this issue. The Humane Society International advised that:
Under no circumstances does HIS support the use of 1080 baiting
as a method of pest control. It is inhumane and indiscriminate in the species
Four animals over which the management of the pest
populations have been the recipient of heated debate are kangaroos, koalas,
dingoes and wild horses. Reasons for objections to reducing their numbers
an iconic status being attached to them;
the animals being internationally recognised
symbols of Australia and the attraction of international media attention on
attempts to cull populations; and
the animals being a source of eco tourism, such
as wild horses on the NSW highlands, dingoes on Fraser Island and koalas on
told the Committee that invasive species are not the first issue for farmers.
He said that:
The fact that it [invasive species management] is a second- or
third-order level of magnitude means that it is an issue that goes between the
cracks a little bit.
If landowners do not see invasive species as a problem
that warrants attention then the issue will not be effectively managed. To
highlight this point, Dr Peacock
told the Committee that:
the horticulture industry does virtually no vertebrate pest work
and does not recognise it as an issue, but if you talk to a grape grower who is
grape netting about what they are doing every night to keep vertebrate pests off
their crops, it has a huge impact.
Educating stakeholders about the issue is key to
obtaining support for management programs. Mr
highlighted the role of education when he told the Committee about a project to
return yellow-footed rock wallabies. He told the Committee that:
when we went up there first, the local people were a bit
scathing about the idea of putting the wallabies back in the wild-more than
scathing; they were a bit rude about the idea. However, once we got going, one
of our young female vets went to the school and spoke to the children and the
children became very enthusiastic. At Christmas time that year, they had the
Wallaby Hop. The children all dressed up in wallaby outfits with tails and they
did the Wallaby Hop. They went home to their parents and the parents were
sucked in to getting involved. The pastoralists who did not want to do any
baiting ended up being almost forced by moral pressure from the children. It
started off with a 10-kilometre wide radius around the outside of the
sanctuary. The result was that lambing percentages increased, so all of a
sudden it has now been increased to a 30-kilometre wide radius. Once you can
get the children on board, you can work through the children to get to the
The flow on from this was that:
The other thing that happened is that when they got enthusiastic
they formed a biodiversity group up there in the Flinders
Ranges. They got money from the NHT
to eradicate weeds and to keep on eradicating foxes and rabbits, particularly,
as well as dogs and cats.
Another program that demonstrates the benefits of
education campaigns is Weed Buster Week. This is a national education and
awareness campaign that started in Queensland.
A review of Weed Buster Week in 2003:
showed that for every dollar invested in education initiatives
pertaining to weed control there is $43.80 worth of benefits generated by weed
control activities throughout the state.
The value of engaging the community in management projects
is discussed in Chapter 8.