Impact Assessment - Spotted thistle (Scolymus maculatus) in Victoria
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Assessment of plant invasiveness is done by evaluating biological and ecological characteristics such as germination requirements, growth rate, competitive ability, reproduction methods and dispersal mechanisms. Assessment of plant impacts, however, is determined by the extent to which a plant affects a land manager’s environmental, economic and social resources.
The relative importance of these resources varies depending upon the value people place on them and, as such, the assessment process is subjective. For example, a farmer is likely to place a higher emphasis on the impact of a plant on production (economic resource) than its impact on areas of natural vegetation occurring on the farm. Conversely, a Landcare or Friends group would value environmental or social resources more than economic resources.
Recognising that the value of resources vary between different land tenures, plant impact assessments allow a prioritisation of resources by land managers. Assessments can apply at a local, regional or state level, and the relative values of each resource identified may differ at each level.
The impact assessment method used in the Victorian Pest Plant Prioritisation Process uses three broad resource categories: social, environmental and agricultural, each with a number of related attributes. For example, social resources include such attributes as how the plant affects human access for recreation, or if it creates a health risk due to toxicity or by producing allergens.
| Each resource attribute, or criterion, is assessed relative to a list of intensity ratings. Depending upon information found in relation to each criterion, a rating of Low, Medium Low, Medium High or High is assigned. Descriptions of the impact criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the impact of Spotted thistle
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1026 KB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
Common Name: Spotted thistle
Scientific name: Scolymus maculatus
| Question | Comments | Rating | Confidence |
| Recreation | |||
| 1. Restrict human access? | “Because of its spininess, dense patches of this weed become impenetrable to stock.” As an annual herb with many branches to 50 - 100 cm (Parsons & Cuthbertson, 1992), dense patches of this plant may impede individual access at certain times of the year. | ML | MH |
| 2. Reduce tourism? | The tendency for this spiny shrub to invade disturbed sites (Parsons & Cuthbertson, 1992), including along pathways (Neuz & Bermejo, 1994) would make it obvious to the average visitor, but probably wouldn’t prevent recreational use of the area. | ML | MH |
| 3. Injurious to people? | Minor injury may occur from late winter to late summer, when the spiny branches of this plant are present (Parsons & Cuthbertson, 1992). | ML | MH |
| 4. Damage to cultural sites? | As an annual herb with many branches to 50 - 100 cm and yellow flowers (Parsons & Cuthbertson, 1992), dense patches of this plant may have a moderate visual effect at certain times of the year. | ML | MH |
| Abiotic | |||
| 5. Impact flow? | Terrestrial species (Parsons & Cuthbertson, 1992). | L | MH |
| 6. Impact water quality? | Terrestrial species (Parsons & Cuthbertson, 1992). | L | MH |
| 7. Increase soil erosion? | This plant has relatively sparse aerial growth that does not appear to shade out ground flora beneath its canopy (see picture in Parsons & Cuthbertson, 1992) so it is unlikely to leave bare patches of soil in summer when it dies off, having little or no impact on erosion. | L | MH |
| 8. Reduce biomass? | This plant has relatively sparse aerial growth that does not appear to shade out ground flora beneath its canopy (see picture in Parsons & Cuthbertson, 1992) so it is unlikely to have any net impact on biomass as a carbon sink. | ML | MH |
| 9. Change fire regime? | This annual plant has relatively sparse aerial growth that does not appear to shade out ground flora beneath its canopy (see picture in Parsons & Cuthbertson, 1992). However, since “nothing will either eat it or approach it” (Maiden, 1908), this plant may allow grassy fuel loads to increase in the absence of grazing, increasing the likelihood of fire. | ML | H |
| Community Habitat | |||
| 10. Impact on composition (a) high value EVC | EVC=Plains Grassy Woodland (E), CMA=Wimmera, Bioreg.=Wimmera, CLIMATE=M. This plant has relatively sparse aerial growth that does not appear to shade out ground flora beneath its canopy (see picture in Parsons & Cuthbertson, 1992), but its rapid growth may compete with low shrub and ground layer vegetation for space, water and nutrients. Sparse infestations. | L | MH |
| (b) medium value EVC | EVC=Box Ironbark Forest (D), CMA=Wimmera, Bioreg.=Goldfields, CLIMATE=M. This plant has relatively sparse aerial growth that does not appear to shade out ground flora beneath its canopy (see picture in Parsons & Cuthbertson, 1992), but its rapid growth may compete with low shrub and ground layer vegetation for space, water and nutrients. Sparse infestations. | L | MH |
| (c) low value EVC | EVC=Lowland forest (LC), CMA=Wimmera, Bioreg.=Wimmera, CLIMATE=M. This plant has relatively sparse aerial growth that does not appear to shade out ground flora beneath its canopy (see picture in Parsons & Cuthbertson, 1992), but its rapid growth may compete with low shrub and ground layer vegetation for space, water and nutrients. Sparse infestations. | L | MH |
| 11. Impact on structure? | This plant has relatively sparse aerial growth that does not appear to shade out ground flora beneath its canopy (see picture in Parsons & Cuthbertson, 1992). | L | MH |
| 12. Effect on threatened flora? | No information found. | MH | L |
| Fauna | |||
| 13. Effect on threatened fauna? | No information found. | MH | L |
| 14. Effect on non-threatened fauna? | “Dense patches…reduce available grazing…Even sparse stands are avoided by stock…because of the spines…further reducing the grazing area” (Parsons & Cuthbertson, 1992). “Nothing will either eat it or approach it” (Maiden, 1908). This plant may reduce the food available to grazing fauna, reducing numbers of individuals, but not causing local extinctions. | MH | MH |
| 15. Benefits fauna? | “Harbour vermin” (Parsons & Cuthbertson, 1992) and so may provide habitat for small native fauna also. | MH | MH |
| 16. Injurious to fauna? | From late winter to late summer the spiny branches of this plant are present (Parsons & Cuthbertson, 1992) which may injure fauna at some times of the year. | MH | MH |
| Pest Animal | |||
| 17. Food source to pests? | “Nothing will either eat it or approach it” (Maiden, 1908). Unlikely to be a food source to pests. | L | H |
| 18. Provides harbor? | “Harbour vermin” (Parsons & Cuthbertson, 1992). | MH | MH |
| Agriculture | |||
| 19. Impact yield? | “Dense patches…reduce available grazing…Even sparse stands are avoided by stock…because of the spines…further reducing the grazing area” (Parsons & Cuthbertson, 1992). Also grows in cornfields (PFAF, 2000) and its rapid growth may compete with crops for space, water and nutrients. | MH | MH |
| 20. Impact quality? | “Spiny seed head catches in wool or contaminates fodder” (Parsons & Cuthbertson, 1992). | ML | MH |
| 21. Affect land value? | Can be controlled by persistent and thorough cultivation through successive seed germinations or with common herbicides (Parsons & Cuthbertson, 1992). Unlikely to impact land value. | L | MH |
| 22. Change land use? | The ability to control this annual weed using conventional methods (Parsons & Cuthbertson, 1992) means that land use should not have to change much, if at all. | L | MH |
| 23. Increase harvest costs? | The ability to control this annual weed using conventional methods (Parsons & Cuthbertson, 1992) will cause a minor increase to the cost of harvest. | MH | MH |
| 24. Disease host/vector? | No record of this weed as an alternative host or vector for agricultural diseases in Parsons & Cuthbertson (1992). | L | MH |
Impact Assessment Record - Spotted thistle (PDF - 24 KB)
Impact Assessment Record - Spotted thistle (DOC - 64 KB)
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