What is risk assessment?
An integral part of managing invasive species is determining the risks associated with potentially invasive species and alternative management options.
- Which species do I let into the country?
- Which naturalised exotic species are likely to result in environmental, economic or sociological impacts?
- Which habitats are likely to be threatened?
- Do I try to contain or eradicate the invasive species?
These are all questions that are considered under the umbrella of risk assessment.
The term encompasses identification, assessment and management of risks associated with the importation of animals, animal-derived products, plants and plant-derived products (AFFA 2001).
Risk assessment is a decision support tool used to communicate risk, typically the risk posed by an alien species. In the context of biological invasions, risk assessment is a type of ecological evaluation designed to meet specific regulations or legislation.
Risk assessments can also be applied to invasive species that are already present in the country. Typically they are geographically restricted i.e. to a country or state and their scope is defined to satisfy the regulation that triggered the risk assessment process.
Risk assessment can be divided into two types based on its intent:
- Quarantine or more broadly biosecurity.
- Mitigation: Typically attempting to minimise the impact of invasives that are already in the country eg. National weeds strategy.
Whether the risk assessment process is for prevention or mitigation, the aim is to identify future invaders and vulnerable communities or species. Australia is recognized as a world leader in developing a risk management framework (Standards Australia and Standards New Zealand, 1999).
For further information on Risk Assesment read Section 3.4 (Risk Assessmennt) in the GISP toolkit (Wittenberg & Cock 2001).
Risk assessment tools
A variety of tools have been used to facilitate and try and to keep the risk assessment process as objective as possible. Here we examine a collection of these that have been used for prevention and mitigation of the effects of invasive species. In this section we focus on plants, but, risk assessment tools & procedures have been developed for vertebrates, invertebrates and manufactured items.
For further information on plant and animal biosecurity visit the AFFA website.
Biosecurity Australia (BA) is part of the Department of Agriculture, Fisheries, Forestry Australia (AFFA) Market Access and Biosecurity Group. Biosecurity Australia regulates the importation of new plant species, following a decision-making policy consistent with relevant international treaties (eg. General Agreement on Trade and Tarriffs - GATT 1994; Sanitary and Phytosanitary Measures (SPS) agreement.)
All proposed new plant imports are assessed for weed potential before they are permitted entry in addition to examining the risk that they will carry exotic diseases or insects.
Below we introduce and explore several decision support systems/tools that have been used in evaluating the risk posed by alien plant species.
Quarantine Lists
Lists of potentially invasive species, based on their proven invasion ability overseas, is the simplest means by which quarantine agencies can decide what species they want to try and prevent from entry. These are known as "black lists"
This is now viewed as a very conservative goal for quarantine. A recent proposal is the use of "white lists" or the intermediate "pied lists".
Read the first three paragraphs in Section 3.3 (exclusion methods) of the GISP Toolkit to get an overview of how these lists could be used.
Climate-Based Models
Another risk assessment approach that that has been used for screening potentially invasive plants is climate based modelling.
This approach models the potential distribution of a species based on its climatic preferences. This is a very useful approach for continental scale evaluations of the potential distribution of a species and highlighting the need to keep certain species out.
However, the typically coarse resolution of the modelling and the failure to incorporate variables that interact with climate to produce actual distributions e.g. soils, vegetation, land use, limits the utility of this approach as a management tool, especially if attempting to manage naturalised species.
Australia's Weed Risk Assessment Tool (also known as the pre-border WRA)
Biosecurity Australia uses a Weed Risk Assessment (WRA) tool (Pheloung 1996) attempts to overcome some of difficulties of the above approaches, by using species attributes and habitat preference data.
Biosecurity Australia adopted this new system in 1996. The system is now used on all new plant imports whether they enter Australia as seeds, nursery stock or tissue culture and regardless of their use in Australia. The implementation of the WRA system is a component of the National Weed Strategy. The development of this tool has led Australia to be world leaders in weed prevention, and has been adapted by many other countries.
The Weed Risk Assessment (WRA) system contains a questionnaire that can be scored either manually or inputted into an Excel spreadsheet. Refer to the following to review the structure and content of the WRA:
Northern Territory’s Weed Risk Management System (a Post-border Weed risk tool)
Despite Biosecurity Australia’s WRA tool, many weeds are entering Australia. Furthermore, some weeds are present in some states but not neighbouring states which have suitable conditions for invasion. Therefore, the Australian States and Territories have been developing 'post-border' weed risk management systems.
These systems include WRA tools, but also include tools to guide management strategies. The NT system has been developed by CDU and the NT Government. It is described in (Setterfield et al 2009).