Environment and Resource Management

Invasive plants and animals: Terrestrial plants

Author

Alexsis Wilson, Department of Primary Industries and Fisheries

Reviewer

Joe Scalan, Department of Primary Industries and Fisheries

Key findings

Indicators and summary of status


Indicator

Status of indicator

Current and potential extent, density and distribution of invasive terrestrial plants

Declared terrestrial plants are currently distributed throughout Queensland, although fewer species are present in the west than along the coast. There is considerable potential for many taxa to expand their distribution further west and north along the coast.

Impact on assets

Invasive terrestrial plants cost Queensland an estimated $600 million a year in lost production and the cost of control.

Number of local governments with pest management plans

At 30 June 2007, 119 of Queensland's 157 local governments have endorsed pest management plans in place.

Number of new biological control agents released

Two new biological control agents have been released since 2003. These are Agonosoma trilineatum for the control of bellyache bush (Jatropha gossypifolia), and Cometaster pyrula for the control of prickly acacia (Acacia nilotica).

Implementation of weed strategies

Four strategies are currently implemented: the Australian Weeds Strategy, the Queensland Weeds Strategy 2002-2006, the Queensland Weed Spread Prevention Strategy and the Queensland Mimosa Pigra Strategy. Seven terrestrial Weeds of National Significance are found in Queensland. Each has an individual national strategy accommodated by Queensland.

Number of new species outbreaks

Ten new weed species are estimated to enter Queensland each year. Approximately 12 species a year are classed as naturalised weeds and there are over 100 species of declared weeds in Queensland.

Importance

Environmental impacts

Weeds can adversely affect the function of natural ecosystems, limiting the sustainability of all the state's natural resources. Weeds can displace native species, reduce biodiversity, harbour pests and diseases, and increase fuel loads for fires.

Bellyache bush (Jatropha gossypifolia) competes directly with, and replaces, native plants, particularly in riparian habitats that may be important vegetation and wildlife corridors. Native animals such as parrots, possums, bats and large mammals do not appear to graze on bellyache bush. In addition, native insects do not consume bellyache bush foliage, which discourages visitation by insectivorous fauna such as birds and reptiles (Csurhes 1999). The overall effect is that the distribution of native animals is changed and their abundance is reduced.

Weed management practices can also have environmental impacts. Tillage can result in soil erosion and subsequent pollution of waterways.

Economic impacts

Weeds cost Queensland an estimated $600 million every year in lost primary production and cost of weed control (DNRW 2006 d).

Specifically, weeds have a negative impact on the Queensland economy by:

Just six declared weeds-parthenium (Parthenium hysterophorus), rubber vine (Cryptostegia grandiflora), prickly acacia (Acacia nilotica), mesquite (Prosopis spp.), parkinsonia (Parkinsonia aculeata) and lantana (Lantana camara)-cost the state more than $72 million each year.

Some weed species can have positive economic impacts. Before being declared a weed and having their sale prohibited, some species have been valuable to the horticulture industry as ornamentals. Certain grass species, such as hymenachne (Hymenachne amplexicaulis), were valued as pasture. The potential to commercially exploit weeds, for example as a biofuel, is often investigated.

Social impacts

Weeds can affect public health, safety and recreation and lower the aesthetic value of the natural landscape.

Parthenium (Parthenium hysterophorus) can cause health problems, particularly in heavily infested areas such as Queensland's central highlands. On contact with the plant or its pollen, some people suffer serious allergic reactions, which include dermatitis, hay fever and asthma (DNRW 2006b).

Weeds with thorns, such as the giant sensitive tree (Mimosa pigra) and prickly acacia (Acacia nilotica), can be hazardous to humans and animals. Thick stands of these plants can reduce public enjoyment of the environment, both physically and aesthetically (DNRW 2006c).

Pressure and condition

Climate

General climate warming may influence the spread and distribution of weeds in Queensland. Tropical weed species could extend further south while temperate species retreat. Summer-growing species could also become more prevalent in southern regions.

Drought can weaken native pasture systems, making them prone to weed invasion. Invasion by weeds that are toxic to stock can be particularly negative, as stock are more likely to consume toxic plants during drought when they are starving and normal feed is not available. Mother of millions (Bryophyllum spp.) poses this threat; its flowers are particularly toxic and flowering occurs during the drier months between May and October (DNRW 2006a).

Weed managers may use climate modelling increasingly in the future to predict weed distribution under changing climatic conditions.

Transport

Transport of people and goods is a major pathway for weed spread in Queensland. Seeds can 'hitchhike' to new sites in and on vehicles, on machinery and other equipment, and attached to clothing or the soles of footwear. The transportation of stock can facilitate weed spread, as seeds consumed at the animals' point of origin can be defecated at other sites, leading to weed establishment. Products such as hay, silage and seed for planting can also be contaminated with weed seed and facilitate weed spread.

More information on the spread of weeds can be found at www.nrw.qld.gov.au/pests/weeds/weed_spread/prevention.

Plants of value

The nursery trade is recognised as a potentially major source of new weeds. Approximately 70% of the nearly 2000 agricultural and environmental weeds in Australia are invasive garden plants (Groves et al. 2005). The trading of plants and seeds over the Internet by private citizens makes it particularly difficult to control the introduction of potentially invasive species. Plants cultivated for pasture or fodder may invade adjacent habitats. Prickly acacia was cultivated in Queensland from 1926 for shade and to provide fodder, but has since invaded several million hectares and is now recognised as a Weed of National Significance.

Invasive terrestrial plants

Each year, approximately 10 new species of invasive terrestrial plants (weeds) are introduced into the state. Currently, more than 1200 weed species are naturalised in Queensland, and approximately 12 additional species are classed as naturalised each year (G. Batianoff, pers. comm.). Naturalised weeds are subject to control rather than eradication programs and this may affect resource allocation and target priority.

Eighty-one genera and over 100 species of invasive terrestrial plants are declared weeds. These plants have or can have serious economic, environmental or social impacts. Table 8.2 lists Class 1 and 2 weeds and one Class 3 weed, lantana, present in the state; their current and potential distributions are shown collectively in species richness maps in Figures 8.6 and 8.7. The maps show that there is considerable potential for spread of these weeds outside south-east Queensland, their future distribution being concentrated along almost the entire coast.

The taxa listed in Table 8.2 currently occupy an average of 30% of their potential range. The highest density is found around Brisbane (22 weeds) and other major population centres along the coast such as Rockhampton, Townsville and Cairns, which each have 15-18 species. The potential distribution of the taxa in Table 8.2 could expand across the entire state, the most drastic increase in weed density being seen along the coast. The Great Dividing Range appears to act as a natural barrier, limiting the invasion and likely establishment of a number of weeds in western Queensland. A full list of declared plants in Queensland is available at www.nrw.qld.gov.au/factsheets/pdf/pest/pp1.

In 1997, the National Weeds Strategy identified 20 Weeds of National Significance from a list of over 3000 naturalised plants in order to focus on management of priority weeds and coordinate effort nationally. The species were selected according to their invasiveness, current and potential distribution, and their economic, social and environmental impacts. Queensland currently manages projects on seven terrestrial Weeds of National Significance:

Non-declared invasive plants can also have detrimental economic, environmental and social impacts. Plants that are not declared under state legislation may be subject to control requirements imposed by local governments.


Figure 8.6 Current distribution of declared terrestrial plants in Queensland
Source: DNRW

 
Figure 8.7 Potential distribution of declared terrestrial plants in Queensland
Source: DNRW

Table 8.2 Declared Class 1 and 2 terrestrial weeds in Queensland and lantana, a Class 3 weed

Class 1 plants

Bridal creeper

Asparagus asparagoides

Siam weed

Chromolaena odorata

Bitou bush w

Chrysanthemoides monilifera

Koster's curse

Clidemia hirta

Honey locust tree

Gleditsia triacanthos

Badhara bush

Gmelina elliptica

Miconia

Miconia calvescens

Mikania

Mikania spp.

Giant sensitive tree w

Mimosa pigra

Chilean needle grass w

Nassella neesiana

Thunbergia

Thunbergia spp.

Class 2 plants

Prickly acacia wq

Acacia nilotica

Annual ragweed

Ambrosia artemisifolia

Groundsel bush

Baccharis halimifolia

Mother of millions

Bryophyllum spp.

Rubber vine wq

Cryptostegia grandiflora

Tobacco weed

Elephantopus mollis

Harrisia cactus

Eriocereus spp.

Telegraph weed

Heterotheca grandiflora

Bellyache bush

Jatropha gossypifolia

African boxthorn

Lycium ferocissimum

Giant sensitive plant

Mimosa invisa

Prickly pear

Opuntia spp.

Parkinsonia wq

Parkinsonia aculeata

Parthenium weed wq

Parthenium hysterophorus

Mesquite wq

Prosopis spp.

Fireweed

Senecio madagascariensis

Sicklepod

Senna spp.

Weedy sporobolus grasses

Sporobolus spp.

Chinee apple

Ziziphus mauritiana

Class 3 plants

Lantana wq

Lantana camara

Weeds of National Significance species; q management coordinated from Queensland by DNRW.

Response

Weed strategies

In 2007 the National Weeds Strategy has been replaced by the Australian Weeds Strategy and the Queensland Weeds Strategy 2002-2006 will be updated. Development of these strategies involved public consultation and input was sought from key stakeholders. Both strategies recognise the need to identify and deal with pathways for weed introduction and spread. The risk of spread of weeds needs to be assessed and the ability of various management actions, including greater awareness, to reduce that risk needs to be determined. Queensland has developed a Weed Spread Prevention Strategy which, among other aims, will develop innovative, practical and cost-effective solutions to minimise weed spread.

Blueprint for the Bush is a ten-year partnership plan, announced in 2006, between the Queensland Government, AgForce Queensland and the Local Government Association of Queensland. Reclaim the Bush, a Pest Offensive is an $11 million funding initiative under the Blueprint for the Bush to attack priority pest animals and weeds (DNRW 2006 d). The plan will target 20 significant woody weeds, including mesquite, prickly acacia, parkinsonia and pond apple (Annona glabra). Reclaim the Bush will provide eight new or improved wash-down facilities to limit weed spread by vehicles and machinery.

The National Four Tropical Weeds Eradication Program has been running since 2002 and has been extended until 2012. It has made significant progress towards eradicating Clidemia hirta, Limnocharis flava, Mikania micrantha and Miconia spp. All known plants have been treated, reductions in seedling recruitment have occurred, and hygiene practices have been introduced to reduce the risk of further spread. In 2006 the program was independently reviewed by the Australian Weeds Committee, which saw no impediment to the program's long-term goal of eradication.

State pest management plans and strategies can be viewed on the Department of Natural Resources and Water website, www.nrw.qld.gov.au.

Legislation

The Land Protection (Pest and Stock Route Management) Act 2002 (Qld) provides a framework and powers for enforced control of weeds. Through this Act, weeds are assessed and may be declared as Class 1, 2 or 3. All landholders, including local governments and state agencies, are required to control Class 1 and 2 pests on their land. Class 1 pests are subject to eradication programs if present in the wild in the state. There is an obligation on landholders to control Class 3 plants only where they affect an environmentally significant area. It is an offence under the Act to introduce, keep (Class 3 weeds excepted), supply or release a declared pest without a permit.

Declaration is reserved for serious weeds with current or potentially widespread impact. Given finite resources, it is important to prioritise taxa for management action. Some plants that are not declared under state legislation can still have significant detrimental economic, environmental or social impacts. However, they may already be widespread, with few practical options for control. Alternatively, they may be localised and subject to control requirements imposed by local governments. Other species (such as Leucaena leucocephala) have benefits and are perhaps best managed through a combination of local declaration and codes of practice.

Declaration also removes weeds from sale, but the weeds need first to be identified as a problem. An alternative approach to the present prohibited list is to develop a permitted list of plants that can be sold (Csurhes et al. 2006): plants are automatically prohibited from trade unless they are on the list. To be listed, taxa would need first to be formally assessed for their potential invasiveness.

Weed Hygiene Declarations are used to provide information on whether a supplied item such as fodder or grain is contaminated by any of six species of Class 2 weeds.

Biological control

Biological control research in Queensland has led to three new biological control agents being released since 2003. One of these was a gallfly, Cecidochares connexa, released onto Siam weed (Chromolaena odorata) infestations in Papua New Guinea (PNG). The gallfly established in all 12 provinces of PNG and caused substantial damage at some sites. Because of the geographical proximity of PNG to Queensland, controlling the weed there minimises the risk of further introductions of Siam weed into this state.

Six traditional biological control agents for lantana, prickly acacia and rubber vine have continued to be released. Long-term monitoring of rubber vine infestations has shown positive signs of control by the rust Maravalia cryptostegiae and the moth Euclaster gigantalis. Evaluations of the effect of the seed-feeding beetle Penthobruchus germaini, which was released prior to 2003 on parkinsonia populations, suggest it has an insufficient impact, causing low levels of seed mortality.

Applications for the release of four new biological control agents, two for lantana and two for cat's claw creeper (Macfadyena unguis-cati), another Class 3 weed, are currently being sought (DNRW 2006e).

Detailed information on biological control in Queensland can be found at www.nrw.qld.gov.au/alan_fletcher/biocontrol.

Education

Two education programs, Weed Warriors and Weedbusters, are currently being run in Queensland schools. Both programs promote weed awareness and action. Weed Warriors partners natural resource practitioners and other weed specialists with local schools and incorporates the biological control of local weeds. Both programs are important for the long-term control of weeds because they encourage people to become weed specialists in the future and give people the skills and knowledge needed to make informed decisions.

Government extension officers play an essential role in the distribution of research and education to landholders and other stakeholders, which leads to the practical application of weed prevention and control. The reciprocal communication between extension officers and landholders is also useful for pre-empting and overcoming problems with control methods and education.

References

Csurhes, S.M. 1999, Bellyache bush Jatropha gossypifolia in Queensland: pest status review series, Land Protection, Department of Natural Resources, Brisbane, viewed 4 January 2007, www.nrw.qld.gov.au/pests/management_plans/pdf/bellyache_bush_psa.pdf.

Csurhes, S.C., Randall, R., Goninon, C., Beilby, A., Johnson, S. and Weiss, J.E. 2006, Turn the tap off before you mop up the spill, Exploring a permitted-list approach to regulations over the sale and interstate transport of potentially invasive plants in the states and territories of Australia, in Preston, C., Watts, J.H. and Crossman, N.D. (eds), Proceedings of the 15th Australian Weeds Conference, Weed Management Society of South Australia, Adelaide.

DNRW 2006a, Mother of millions Bryophyllum spp.: pest series, Land Protection, Department of Natural Resources and Water, Brisbane, viewed 10 January 2007, www.nrw.qld.gov.au/factsheets/pdf/pest/pp33.pdf.

DNRW 2006b, Parthenium weed Parthenium hysterophorua: pest series, Land Protection, Department of Natural Resources and Water, Brisbane.

DNRW 2006c, Prickly Acacia, Acacia nilotica: pest series, Land Protection, Department of Natural Resources and Water, Brisbane, viewed 10 January 2007, www.nrw.qld.gov.au/factsheets/pdf/pest/pp9.pdf.

DNRW 2006d, Reclaim the Bush, a Pest Offensive, Department of Natural Resources and Water, Brisbane, viewed 15 December 2006, www.nrw.qld.gov.au/blueprint/pdf/infosheet_2_reclaim.pdf.

DNRW 2006e, Technical Highlights: weed and pest animal research 2005-06, Department of Natural Resources and Water, Brisbane, viewed 4 January 2007, www.nrw.qld.gov.au/alan_fletcher/pdf/tech_highlights_zerofive_zerosix.pdf.

Groves, R.H., Boden, R. and Lonsdale, W.M. 2005, Jumping the garden fence: invasive garden plants in Australia and their environmental and agricultural impacts, CSIRO report prepared for World Wildlife Foundation, Sydney.

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Last reviewed 18 May 2011
Last updated 13 February 2008

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