Background

Implications

Regional aspects

Indicators

Management responses

Discussion

Future directions

Recommendations

Related issues

Related case studies

Background

A plant pest or weed can be considered as any plant that is having a negative impact on a valuable resource and requires some form of action to reduce that impact. See also the Introduced species issue for more information about plant species that are naturalised in Tasmania but are not considered weeds. There are also several significant diseases, mostly a result of fungal pathogens, that are known to adversely affect Tasmanian native vegetation.

In the case of weeds, most are introduced species that are able to out compete native plants, desirable pasture plants or crops due to either an absence of natural disease and pest controls or due to an aggressive capacity to dominate ground such as following soil disturbance.

Weeds are not restricted to the land - there are also many species that occur in water. For example Wakame/Japanese kelp (Undaria pinnatifidia) appears to have been accidentally introduced by commercial shipping, and is now infesting large areas of some of Tasmania's coastal areas. Another example is Canadian pond weed (Elodea canadensis), which occurs in freshwater. Infestations of Elodea may compete with desirable aquatic plants, resulting in modified aquatic flora assemblages and habitats.

Examples of weeds in Tasmania and their country of origin

Weed	Country of origin
Blackberries (Rubus fruticosus species aggregate)	Europe
Boneseed (Chrysanthemoides monilifera)	southern Africa
African boxthorn (Lycium ferocissimum)	southern Africa
Bridal Creeper (Myrsiphyllum asparagoides)	Africa
Gorse (Ulex europaeus)	Europe
Radiata pine (Pinus radiata)	North America
Spanish heath (Erica lusitanica)	Spain, Portugal, France
Canadian pond weed (Elodea Canadensis)	North America
Wakame/Japanese kelp (Undaria pinnatifidia)	Japan

Weeds are among the most serious threats to sustaining Tasmania's agricultural and forestry practices and conserving biodiversity. They have the potential to affect human and animal health. Weeds can be fire hazards; they can reduce recreational value, diminish aesthetic values and visibility and cause structural damage to facilities. Weeds may also damage the quality and quantity of water resources.

Weeds that affect the natural environment are termed environmental weeds and represent one of the most serious threats to Tasmania's biodiversity. Environmental weeds are plants that either escape or are deliberately introduced into the natural environment. They threaten the survival of native plants, animals and communities on land and in water.

In 2001 there were at least 64 introduced plant species considered to be key environmental weeds in Tasmania (a list of Tasmania's environmental weed species is available for downloading).

The key diseases known to cause native vegetation dieback, rot and decay in Tasmania include the introduced soil-borne cinnamon fungus (Phytophthora cinnamomi) and the naturally occurring myrtle wilt (Chalara australis). Armillaria species fungi also affects wet and dry eucalypts in Australia and natural defects from rot and decay increasingly occur in young eucalypt regrowth forests (particularly in swamp gum-Eucalyptus regnans).

Phytophthora is believed to have been introduced to Tasmania following European settlement and is now well established in many areas of moorland, heathland and dry Eucalypt forest in the State. The fungus has the potential to significantly alter the ecology of these vegetation types.

Phytophthora may spread with the movement of infected soil or plant material by people or animals and may be transported by water percolating through the soil or in creeks. People can transport the fungus to new areas on dirt adhering to vehicles, items they are carrying or footwear. Unfortunately this fungus is hidden from view within plant roots and its symptoms can be difficult to recognise in the field.

Early literature, aerial surveys and aerial photography indicated that myrtle wilt was endemic in at lease part (and possibly most) of the range of myrtle throughout Tasmania, but that in some areas, disease levels may have increased in the recent past (Packham 1994). In some areas localized disturbance, such as logging, thinning and roading, of myrtle-dominated rainforest has led to increased myrtle wilt incidence.

Implications

Weeds and diseases can have a large impact on natural diversity:

• major weed invasions and disease epidemics change the natural diversity and integrity of ecological communities;
   
• Diseases can cause root rot and dieback in native plants, change the composition of plant communities, and threaten the existence of rare and threatened plant species.
   
• Tasmania is fortunate to have a rich diversity of invertebrate and vertebrate wildlife. Weeds can affect the habitat opportunities of wildlife by changing food sources, thermal and escape cover, change water flow and availability to wildlife, and may reduce territorial space necessary for wildlife survival;
   
• weeds can displace native plants by using a range of strategies (faster growth, being unpalatable, reproductive swamping etc). In addition, they also survive better than native plants as they may not be affected by pests or diseases that would normally control them in their natural habitats; and
   
• weeds and diseases may reduce the biodiversity and health of remnant vegetation.
   

Weeds and diseases also negatively affect human activities as they:

• can impact on primary production (e.g. agriculture, horticulture, forestry, aquaculture) by reducing product quantity and quality;
   
• have the potential to affect human and animal health directly, as well as through the potential consequences of weed control (e.g. manual removal, the use of herbicides), and as a result of disease and pathogens linked with weeds;
   
• can reduce recreational value (e.g. bushwalking, camping and fishing);
   
• can be fire hazards; and
   
• they can diminish aesthetic values and visibility and cause structural damage to facilities. Aquatic weeds block irrigation and drainage channels and choke dams and waterways reducing water volume and flow.
   

In 1996 it was estimated that weeds cost Tasmania $33 million per year (Ministerial Working Group 1996) due to losses in primary production and the cost of weed control. The cost of weeds to the urban environment, amenity and health values, tourism and the conservation of biodiversity and natural ecosystems has been estimated by some biologists at $66 million per year (Ministerial Working Group 1996).

Regional aspects

The distribution of weed species in Tasmania is dependent on a range of factors including the species, availability of suitable habitats, period of naturalisation, opportunities for range expansion, introduction pressure etc. For example, some species are widespread (e.g. blackberries, broom, ragwort, boneseed).

The distribution of diseases thoughout the State is dependent on factors such as plant species type, other types of stresses (e.g. drought or land use disturbance) that weaken a plant and make it more susceptible to disease, and the spread of the pathogens (particularly the introduced pathogens) by humans.

Indicators

Plant Species Deaths Due to Disease and Distribution of Pathogens - at a glance

• Continued in depth

• Indigenous and exotic pathogens can adversely affect native vegetation as agents of disease. There is an ever-present threat of disease epidemics causing damage that is severe enough to adversely affect native vegetation health and vitality, as well as potentially cause changes in community composition in Tasmania.
   
• Root rot caused by the introduced soil-borne fungus Phytophthora cinnamomi is the most significant threat to conservation of native plant species in Tasmania. Rare, threatened or endangered plants are at greatest risk from the fungus, and at least 39 of Tasmania's threatened plant species are susceptible to Phytophthora root rot. Some threatened plant species in Tasmania are known to be declining as a result of this root rot and more threatened species could also be affected should the fungus be introduced to their populations (see DPIWE website).
   
• The impact of Phytophthora root rot over time in Tasmanian vegetation types is yet to be scientifically documented. To gain an accurate picture of impact requires monitoring over long time frames (20-30 years). This allows fluctuations in the balance between mortality and recruitment to be shown.
   
• Permanent monitoring plots have recorded appreciable mortality in selected rare or threatened species during the three-year period 1996-1999. This has included the death of an average of 48.4% of Epacris barbata, 33.2% of E. limbate, and 25.9% Pultenaea hibbertiodes threatened plant species within the plots (RPDC 2002).
   
• The vegetation types most affected in Tasmania are heathland, moorland, dry sclerophyll forest and scrub. These vegetation types occur within the climatically susceptible areas and contain susceptible plant species. Moorland and heath communities are perhaps the most severely affected as many of species present in these communities are susceptible to Phytophthora root rot
   
• There will be many other infected areas that have not been sampled. The size of the infected area or severity of infection will vary significantly from site to site.
   
• Myrtle wilt is the most significant disease of Nothofagus cunninghamii. It is caused by the endemic fungus Chalara australis and occurs in rainforests throughout Tasmania. In the 8 years between 1992 and 2000 the annual rate of mortality throughout Tasmania dropped significantly from the rate measured between 1989 and 1992 (RPDC 2002).
   

Introduced Species that are Naturalised - at a glance

• Continued in depth

• In Tasmania there are 744 naturalised vascular plant species of which 162 are considered weeds.
   


• In Tasmania there are seven known naturalised non-vascular plants (e.g. seaweeds, mosses, lichens). The seven species are all macro algae (i.e. seaweeds). However, Japanese kelp (Undaria pinnatifidia) is recognised as noxious on the Fisheries (General and Fees) Regulations 1996. There are no known naturalised species of moss or lichen.
   


• Of the total naturalised plant species in Tasmania, 64 are considered to be significant environmental weeds (a list of Tasmania's environmental weed species is available for downloading). In February 2002, 30 of these species were listed on the Weed Mangagement Act.
   

Number of Declared Weeds - at a glance

• Continued in depth

• The number of weeds listed on the Tasmanian Weed Management Act provides an indication of management effort as once a weed has been declared a draft weed management plan must be compiled within 12 months. In 2001, 86 weed species/species aggregate were listed of which 50 are found in Tasmania.
   

Weeds of National Significance Present in Tasmania - at a glance

• Continued in depth

• In 2001, six of the 20 weeds of national significance were present in Tasmania.
   
• Alligator weed (Alternanthera philoxeroides), which is a weed of national significance, was found in Tasmania but was eradicated in 2000. Chilean needle grass (Nassella neesiana) has been found in Tasmania but is believed to be no longer present.
   
• Boneseed (Chrysanthemoides monilifera) is common in several coastal areas of Tasmania, especially along the north coast from Wynyard eastwards and on parts of the east coast. It is common in the Tamar Valley and in the cities and suburbs of both Launceston and Hobart. Elsewhere it occurs occasionally as a weed of disturbed bushland and coastal vegetation.
   
• Blackberry (Rubus fruticosus species aggregate), is found throughout the majority of Tasmania, especially in the wetter areas.
   
• There are four main infestations of bridal creeper (Asparagus asparagoides) in Tasmania: areas on Flinders Island, in the Tamar Valley, on the east coast from Binalong Bay to Falmouth and in the north-west from Leith to Ulverstone. These four areas include approximately 95% of the bridal creeper infestations in Tasmania. The other 5% is scattered throughout the State such as on King Island and on the east coast at Swansea.
   
• Gorse (Ulex europaeus) is a serious environmental weed. Once established, it competes strongly with native vegetation, alters fire regimes and reduces biodiversity. Gorse is present in most agricultural and urban areas throughout Tasmania.
   
• Serrated tussock (Nassella trichotoma) is restricted to the south-east of Tasmania and to southern King Island.
   
• Willows (Salix spp.) are found in most major river systems in the north, north-west, north-east, midlands, south and south-east.
   
• In aggregate, one or more of the six weeds of national significance that are present in Tasmania are found across an extensive range of vegetation communities and land uses.
   

Threatened Species and Communities Adversely Affected By WONS - at a glance

• Continued in depth

• Five of the six weeds of national significance present in Tasmania are known to be impacting upon 66 already threatened native plant species and 30 threatened and/or bioregionally important vegetation communities.
   
• Willows are currently impacting upon the most threatened species in Tasmania followed by gorse, boneseed, blackberry and then serrated tussock.
   
• Gorse is currently impacting upon the most threatened or bioregionally significant communities in Tasmania followed equally by willows, blackberries, serrated tussock and then boneseed.
   

Weed Alert Network - at a glance

• Continued in depth

• The number of Weed Alerts provides an indication of the number of significant new weed incursions into Tasmania. Between 1999 and 2001, 13 new alerts were identified of which seven are known to adversely impact biodiversity values.
   

Area Covered by Community Weed Strategies - at a glance

• Continued in depth

• Fifteen of Tasmania's 29 municipalities are fully covered by weed management strategies.
   
• Four municipalities are only partly covered by community weed management strategies: Break O'Day (55%), Central Highlands (75%), Meander Valley (100%) and West Coast (30%).
   
• Ten municipalities are currently without strategies: Brighton, Burnie, Central Coast, Devonport, Hobart, Kentish, Kingborough, King Island, Latrobe and Northern Midlands.
   

Management responses

• National Weeds Strategy launched in 1997. The strategy aims to reduce the detrimental impact of weeds on the sustainability of Australia's productive capacity and natural ecosystems.
   
• New Tasmanian weed management legislation was enacted in 1999: Weed Management Act. This provides for the control and eradication of declared weeds and promotes a strategic and sustainable approach to weed management in Tasmania. Eighty-six plants have been declared. Management plans to specify the restrictions or measures required for each of the declared weeds will be developed.
   
• Six of the 20 weeds of national significance (WONS) are found in Tasmania. For each WONS species a management strategy must be developed. All six of the WONS present in Tasmania have had draft plans developed. DPIWE has been a lead agency in the development of the National Gorse Strategy. By 2002 funding had been received for strategic control of bridal creeper, willows and biological control programs for gorse and boneseed. The DPIWE are also hopeful of receiving further funding for gorse, blackberry and serrated tussock management.
   
• RETICLE weed mapping database launched in 2001. This provides a simple accurate system to help land managers record weed occurrences throughout Tasmania, and to store and share this information with others. The database helps with planning and conducting more effective weed control works on a local, regional and Statewide scale. More information can be obtained from the Weed Management Section, DPIWE.
   
• Publication of a new weed management book Weeding roadsides: a guide to the effective weed management on roadsides (Goninon 2001).
   
• Development and implementation of a legal procedures training program for weed inspectors.
   
• The prevention of Phytophthora cinnamomi (root rot) from infecting large disease-free areas of susceptible native vegetation, highly susceptible species which are declining, and threatened species susceptible to the disease has been recognised as the main course of action required in Tasmania. This is because there is practically nothing that can be done to control the natural spread of Phytophthora root rot or to destroy it in the native plant communities of the State. As part of the actions for prevention:
   
• Management areas and prescriptions have been selected and developed for the 39 threatened species that are currently identified for protection from Phytophthora root rot in Tasmania. This is being developed by Forestry Tasmania under a program funded by Environment Australia.
   
• Phytophthora cinnamomi is listed as a threatening process in the Commonwealth Endangered Species Protection Act 1992. A Threat Abatement Team has been established to support the development of plans and actions to minimise the impact of Pythophthora root rot in Tasmania. The team's priority is to establish monitoring and management programs for selected populations of susceptible threatened species.
   
• In relation to threatened species that have already been infected by Phytophthora root rot, a line of research is being investigated in Australia that involves the application of fungicides to increase the ability of treated plants to resist Phytophthora root rot, but the action does not kill the fungus.
   
• There are guidelines and prescriptions included within the Forest Practices Code 2000 (source=324!;) that aim to minimise the disturbance to myrtles from forestry activities that can often lead to the increased infection and death of trees by the fungus Chalara australis (myrtle wilt).
   

Discussion

A weed can be considered as any plant that is having a negative impact on a valuable resource and requires some form of action to reduce that impact.

The magnitude of the weed problem in Tasmania is significant and trends and changes indicated by, for example, weed alert data highlight the potential risks to agricultural productivity and biodiversity values (between 1999 and 2001, 13 new weeds were identified of which seven are known to adversely impact biodiversity values, and 12 of the 13 are known to affect agricultural production).

Positive developments since the last SoE report have included the significant improvement in systems for monitoring and reporting weed incursions and threats. The introduction of the Tasmanian Weed Management Act 1999 has established a strategic and consultative process for weed management.

The data highlight the importance of whole-of-community approaches to weed management; all land uses and tenures, whether on public or private land, are affected.

Future directions

• The State is continuing to pursue the following three critical weed management goals, which are underpinned by the need to promote the sharing of weed management responsibilities amongst all tiers of government and members of the community and the strategic use of limited resources.
   


• To prevent the development of new weed problems;
   


• to reduce the impact of existing weed problems of State significance (i.e. those listed on the Weed Management Act 1999); and
   


• to provide the framework and capacity for ongoing management of weed problems of State significance.
   
• WeedPlan, which is Tasmania's weed management strategy, was developed in 1996. The strategy is being reviewed in 2002. One of the key strategic actions of WeedPlan is to develop a procedure and program for ensuring WeedPlan is reviewed at appropriate intervals. The review is to take place in the context of both the current situation and future trends in weed management and natural resource management at the national, State and regional levels. The outcomes of the review will assist in defining the future direction of weed management in the State.
   


• Explore options for controlling all plant importation into the State except where permitted under a weed risk assessment process.
   


• Explore options for stabilising long-term funding support for coordinated community action on weeds.
   

Tasmania Together and the RMPS

Relevant Tasmania Together goals and standards for 'Biodiversity' are listed in the linked file. The Tasmania Together Progress Board reported on progress toward targets for benchmarks set (Tasmania Together Progress Board 2003). Indicators, targets and baseline data are available in the latest Progress Report June 2003. Further information, including progress report updates, is available from Tasmania Together.

Involvement of the community, and the fair and orderly use of resources are also fundamental principles of the RMPS. The RMPS objectives have been developed to advance the principles of sustainable development.

Recommendations

Related issues

Related case studies