Killing Us Softly: Australia’s green stalker, is a 2020 vision statement to identify a way forward on the management of species that invade agricultural and native systems. After land clearing, this report identifies invasive species as the main cause of Australia’s plants and animals disappearing from areas where they were once common. This statement is open to debate, as statistics show that altered fire and grazing regimes (see Section 3.2d) have been linked to a greater number of threatened and endangered plants and fauna. Even so, weeds appear to be implicated in the extinction of at least four native plant species, and are known to be adding pressure to a further 57 now under threat. Of equal concern are changes to the structure and composition of native vegetation that environmental weeds can cause, which change habitat for plant and animal species, limiting opportunities for regeneration and potentially changing the patterns of fire and other ecological processes in the landscape. The insidious and relatively slow changes wrought by environmental weeds can make it hard for land managers to respond, but if they are left unmanaged an impoverished future for native vegetation and the people who enjoy and use it will result. Twenty Weeds of National Significance (WONS) have been identified, most of which represent threats to natural systems. WONS status brings a weed under national management for the purpose of restricting its spread and/or eradicating it from parts of Australia. To show real achievements in the prevention of incursions of these weeds requires the collection of consistent and reliable data. Developing a core set of data attributes was the purpose of a recent workshop and discussion paper released at national level that aims to manage the key threats imposed by these and other weed species more strategically. The Vegetation Assessment reported that in 2001 limited information was readily available on the distribution of weeds at a scale relevant to on-ground management. This situation has changed little in the intervening years. This makes the use of local or regional information on weed distribution and impacts essential for management. Introduced plants that have become naturalised in Australia now comprise about 10 per cent of the total Australian vascular flora. Not all of these become invasive, although many do. Weed Categories for Natural and Agricultural Ecosystem Management aims to categorise approximately 2,700 non-native plant species that are known to be naturalised in Australia into groups of major or minor threats to natural ecosystems or agriculture. Of this total, 798 species (about 30 per cent) were considered a major problem and 1,388 species (about half) a minor problem to managers of natural ecosystems. The 34 non-native species that are limited at present to one or a few populations in a defined geographic area are recommended for eradication from natural ecosystems (Table 10). If these species are found in regions you work in, then there is the potential to remove them as a risk. Those non-native species known to be having a direct impact on rare or threatened native plants numbered 49; most of these species are widely distributed across a number of States but eight within this group with more limited distributions are suggested as further candidates for eradication from natural ecosystems. This can be achieved at relatively low cost before the species become invasive and spread widely. Weed risk assessment has also been carried out at the State and regional level.
| | | | Action: 3.7 |
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| | Find out if the naturalised plants that have been identified as candidates for eradication occur in your area and plan an appropriate course of action. | | | COST |  | | | TIME |  | | | COMPLEXITY |  | | | | |
Concerns about the environmental weed risk of species promoted for revegetation, amenity plantings and farm forestry had been raised. This includes species native to one area of Australia that have been planted outside of their range and have become invasive, such as Acacia baileyana. A weed risk assessment has been developed in South Australia to rank the potential weed importance of plant species in different landuses. It has three main assessment criteria: invasiveness, impacts and potential distribution. - Invasiveness is used as an indicator of a weed’s rate of spread. Faster spreading weeds are considered more urgent for control and thus of higher priority. A score for invasiveness is calculated from five multiple choice questions, relating to a weed’s establishment ability, tolerance to routine weed control, reproductive ability and dispersal by natural and human-influenced means.
- Impacts relates to the economic, environmental and social effects of weeds, covering effects on establishment and growth of desired plants, reductions in product quality, effects on animal and human health, limits on physical movement, and effects on environmental health.
- Potential distribution considers the area at risk of invasion. This is best determined from a GIS analysis of climatic and soil preferences, overlaid with the locations of susceptible land uses/ecosystems.
| | | | Action: 3.8 |
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| | Assess the usefulness of the weed risk assessment system for species used in revegetation and farm forestry activities in your region. | | | COST | | | | TIME |  | | | COMPLEXITY |  | | | | |
This approach was used to assess the potential weed risk of 20 species used in revegetation, including trees, shrubs, grasses and a perennial herb. Table 10: The 34 naturalised non-native species that are impacting on natural systems (limited at present to one or a few
populations in a defined geographic area) for which eradication is recommended.
Source: Groves RH, Hosking JR, Batianoff GN, Cooke DA, Cowie ID, Johnson RW, Keighery GJ, Lepschi BJ, Mitchell AA, Moerkerk M, Randall RP, Rozefelds
AC, Walsh NG, Waterhouse BM (2003) ‘Weed Categories for Natural and Agricultural Ecosystem Management.’ Bureau of Rural Sciences, Canberra ACT
State and Territory abbreviations: NT = Northern Territory, Qld = Queensland, NSW = New South Wales, Tas = Tasmania,
WA = Western Australia, Vic = Victoria, SA = South Australia.
Note: ? = information not available at time of publication of source reference
Diseases have the potential to significantly alter the structure and composition of native systems. They are one of the more insidious threats that regional managers have to face. Phytophthora cinnamomi, which is a soil-borne pathogen belonging to the water mould group (Oomycetes), has had the most resources allocated to its study and management, and is the only disease listed as a key threatening process at the national scale. It is found in most States of Australia, being identified as a major threat in south-west WA, Victoria, Tasmania and NSW. In NSW, it has also been listed as a key threatening process, where infection of native plants has been identified as a threat to a number of species and communities listed in Schedule 1 or 2 of the Threatened Species Conservation Act. The disease can kill plants through root declines and associated water stress, reducing habitat complexity. Phytopthora has been associated with the death of tropical rainforest patches in northern Queensland but the degree of threat the disease poses in these systems is still being determined. In Western Australia, the term dieback is generally used to describe the symptoms caused by Phytopthora. In eastern Australia, rural dieback is caused by a range of other factors such as tree clearance and insect attack, as described in Section 3.2b and Section 4.2e. The Threat Abatement Plan for Dieback Caused by the Root-rot Fungus Phytophthora cinnamomi, states that the colonisation of Australian landscapes by the disease is almost certainly in its second century in some areas. The disease is in the middle stages of its epidemic development and is now established in a mosaic over millions of hectares. As a result, the boundaries between infected areas and those free of infection may amount to hundreds of thousands of kilometres. Managing these boundaries is a problem that must be tackled at both regional and local scales. Susceptible species display a range of symptoms. Some are killed, some are damaged but endure, and some show no apparent symptoms. In some circumstances, Phytopthora cinnamomi may contribute to plant death where there are other stresses present (e.g. waterlogging, drought, and perhaps wildfire). Within a plant species there may be a variable response to infection. The Tasmanian 2003 State of the Environment lists plant disease as a significant threat to the conservation of native plant species in Tasmania, with Phytophthora affecting a number of species. The endemic disease Chalara australis (myrtle wilt) affects Nothofagus cunninghamii, the dominant tree in many cool temperate rainforests. Infection by the myrtle wilt fungus results in the death of the tree. In some areas localised disturbance, such as logging, thinning and roading of myrtle-dominated rainforest has led to increased myrtle wilt incidence. In the last 20 years, another disease has been identified across southern Australia that poses a threat to a wide range of native species in both natural stands and revegetated areas. Mundulla yellows is a progressive slow dieback and yellowing disease of many varieties of eucalypts, which has been reported on trees of all ages. Once symptoms appear, the affected trees do not recover, and die within a few years. The disease was first reported in South Australia, where it is thought to be present in an area exceeding 25,000 km2. The disease is also being monitored in south-western Western Australia and there are reports in other southern States. The cause of the disease is unknown, with both phytoplasmas (specialised bacteria that have not yet been grown in culture) and viruses suspected to be a possible cause. Understanding the nature of the Mundulla yellow disease is an active area of investigation. One line of questioning, based the basic epidemiology of the disease, has suggested that an infectious biotic pathogen is not the primary cause. This is based on the distribution of the disease, which is markedly associated with artificial landscape features such as roads, rails, drives, gravel paths and driveways. Consequently, the hypothesis has been put forward that poisons such as atrazine, that are applied to the soil to control weeds, are affecting susceptible trees such as red gum (Eucalyptus camaldulensis). These three examples, which are known to affect native vegetation often at large scales, demonstrate some of the challenges of identifying and managing diseases. Knowing what causes these diseases, how they spread, and what native vegetation is most threatened are the first steps in developing regional management plans. |
