EPPO Global Database

EPPO Reporting Service no. 05 - 2008 Num. article: 2008/113

The Australian Weed Risk Assessment System

The Australian Weed Risk Assessment (WRA) system is a question-based scoring method that can be operated using a computer, or manually, using paper-based forms. The WRA system concerns the pathway of voluntary introduction for ornamental purposes. It applies to plants satisfying the IPPC definition of a quarantine pest: plants not yet present in the country, or, if present, having a limited distribution and subject to official control. The WRA system addresses risk assessment and does not evaluate management options; pathway analysis is not included. The scheme has been calibrated using 350 exotic alien plants that have been present for sufficient time in Australia to reveal their invasive potential. The system includes 49 questions dealing with biogeography and a range of biological and ecological attributes that are indicative of, or can contribute to the invasive character of the plant:

  1. Biogeography / History
  1. Domestication / cultivation
1.01 Is the species highly domesticated?
1.02 Has the species become naturalized where grown?
  1. Climate and distribution
2.01 Species suited to Australian climates (0-low; 1-intermediate; 2- high)
2.02 Quality of climate match (0-low; 1-intermediate; 2-high)
2.03 Broad climate suitability (environmental versatility)
2.04 Native or naturalized in regions with extended dry periods
2.05 Does the species have a history of repeated introductions outside its natural range?
3. Weed elsewhere?
3.01 Naturalized beyond native range
3.02 Garden/amenity/disturbance weed

  1. Biology / Ecology
4. Undesirable traits
4.01 Produces spines, thorns or burrs
4.02 Allelopathic
4.03 Parasitic
4.04 Unpalatable to grazing animals
4.05 Toxic to animals
4.06 Host for recognised pests and pathogens
4.07 Causes allergies or is otherwise toxic to humans
4.08 Creates a fire hazard in natural ecosystems
4.09 Is a shade tolerant plant at some stage of its life cycle
4.10 Grows on infertile soils
4.11 Climbing or smothering growth habit
4.12 Forms dense thickets
5. Plant type
5.01 Aquatic
5.02 Grass
5.03 Nitrogen fixing woody plant
5.04 Geophyte
6. Reproduction
6.01 Evidence of substantial reproductive failure in native habitat
6.02 Produces viable seed
6.03 Hybridises naturally
6.04 Self-compatible or apomictic
6.05 Requires specialist pollinators
6.06 Reproduction by vegetative fragmentation
6.07 Minimum generative time (years)
7. Dispersal mechanisms
7.01 Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)
7.02 Propagules dispersed intentionally by people
7.03 Propagules likely to disperse as a product contaminant
7.04 Propagules adapted to wind dispersal
7.05 Propagules water dispersed
7.06 Propagules bird dispersed
7.07 Propagules dispersed by other animals (externally)
7.08 Propagules survive passage through the gut
8. Persistance attributes
8.01 Prolific seed production (;2000/m2)
8.02 Evidence that a persistent propagule bank is formed (;1 year)
8.03 Well controlled by herbicides
8.04 Tolerates, or benefits from, mutilation or cultivation
8.05 Effective natural enemies present in Australia

For each plant assessed, the WRA system generates a score assisting Australian policy-makers to determine if a plant can be introduced. If the score is higher than 6, the plant is rejected. If the score is lower than 1, the plant is accepted, and in between these 2 thresholds, the plant is placed on an unable to complete assessment list. Placing a request to assess a species takes around 3 months to get a response.
Between 1997 and 2003, 1000 proposals of import of plants have been assessed: 30% of these were prohibited from entry into the country, 46% were allowed for entry and the remaining 24% required closer examination.

The WRA system has proven to be an effective and rapid decision-support tool in Australia for managing phytosanitary risks associated with proposals of new ornamental plants. As a matter of fact, the system has been officially adopted for use by the Ministries of Agriculture in New-Zealand and in Hawaii (US). In the Galapagos Islands, it is used by researchers to screen recent and future imports. Recent economic analysis of the WRA has suggested that its implementation was beneficial within a decade, and will save up to 1.8 M AUSD over 50 years in Australia. In addition, a recent study (Gordon et al., 2008) has showed that when compared with other systems, the WRA generally provided the most accurate results and that this accuracy remained consistent even when the system was applied to different geographical regions.


Gordon DR, Onderdonk DA, Fox AM, Stocker RK (2008) Consistent accuracy of the Australian weed risk assessment across varied geographies. Diversity and Distribution 14, 234-242.
Pheloung P (2005) Use of the weed risk assessment tool in Australia’s approach to pest risk analysis. In IPPC Secretariat - Identification of risks and management of invasive alien species using the IPPC framework. Proceedings of the workshop on invasive alien species and the International plant protection Convention, Braunschweig, Germany, 22-26 September 2003. Rome, Italy, FAO. P. 115-116. http://www.fao.org/docrep/008/y5968e/y5968e00.htm