Impact Assessment - Ragwort (Senecio jacobaea) in Victoria (Nox)

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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.

Question	Comments	Reference	Rating
Recreation
1. Restrict human access?	Erect biennial or perennial herb commonly 45 to 60 cm high. Primarily associated with disturbed habitats in which it can form dense infestations. In such situations it may be a nuisance to people.	Muyt (2001)	ML
2. Reduce tourism?	During flowering, the plant’s presence would be obvious, as would dense patches. It may have a serious impact on the aesthetic of an area. Minor impact – photos taken – soft leaf – no threat		ML
3. Injurious to people?	“Ragwort pollen is believed to produce an allergic reaction in some people but this is not well documented.” “Probably poisonous to humans.” Toxic properties throughout the year. Impact may only occur sometimes of year	P & C (2001) Blood (2001)	MH
4. Damage to cultural sites?	Dense patches would create a moderate visual impact. Negligible		L
Abiotic
5. Impact flow?	Terrestrial species.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	The plant has perennial roots, slightly fleshy to 15 cm long and many fibrous roots extending deeper into the soil. Not likely to contribute to soil erosion.	P & C (2001)	L
8. Reduce biomass?	Invader replaces biomass.		ML
9. Change fire regime?	“In autumn, the flower stems die back.” Little dry matter remains to establish or support fire. Negligible change to fire risk.	P & C (2001)	L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Valley grassy forest (V); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; VH CLIMATE potential. “Dense infestations develop over disturbed ground, smother other ground-flora and impeding overstorey regeneration.” Major displacement of ground-flora.	Muyt (2001)	MH
(b) medium value EVC	EVC=Grassy woodland (D); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; VH CLIMATE potential. “Dense infestations develop over disturbed ground, smother other ground-flora and impeding overstorey regeneration.” Major displacement of ground-flora.	Muyt (2001)	MH
(c) low value EVC	EVC=Damp forest (LC); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; VH CLIMATE potential. “Dense infestations develop over disturbed ground, smother other ground-flora and impeding overstorey regeneration.” “Scattered populations occur in shade.” Minor displacement of ground-flora or mid stratum spp.	Muyt (2001)	ML
11. Impact on structure?	“Dense infestations develop over disturbed ground, smother other ground-flora and impeding overstorey regeneration.” Major effect on lower and mid strata. 1st year affects ground covers, grass not much impact on overstorey impacts.	Muyt (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“When firmly established, ragwort dominates an area almost to the exclusion of all other plants.” “It is mostly found in open, sunny locations.” Reduction in habitat for fauna species. Minor primarily weed of agric land not of native habitat reduction	P & C (2001) Muyt (2001)	ML
15. Benefits fauna?	“Ragwort is poisonous to grazing animals.” No known benefits.	P & C (2001)	H
16. Injurious to fauna?	“Ragwort is poisonous to grazing animals. The plant is more palatable but equally toxic when dry.” Unknown	P & C (2001)	M
Pest Animal
17. Food source to pests?	Not known as a food source to pest species.		L
18. Provides harbour?	Not known to provide harbour for pest species. Dense infestations may provide temporary harbour for minor pest species such as rodents.		ML
Agriculture
19. Impact yield?	“When firmly established, ragwort dominates an area almost to the exclusion of all other plants and, because it has low grazing value, the production from such areas is considerably reduced.” Serious impact on yield. Not viable to have stock – 50% reduction but not reduce yield – Ragwort strategy	P & C (2001)	MH
20. Impact quality?	“Whilst ragwort does not generally occur as a crop weed in Australia, it is occasionally found in lucerne in Tasmania. It is also troublesome in lucerne in New Zealand and North America.” Potential contaminant. Produce may not be fit for animal consumption; unable to sell crop. “It is reported from New Zealand and North America that ragwort imparts a taint to honey making it unfit for sale.” Too many assumptions	P & C (2001)	M
21. Affect land value?	The plant’s potential impact on yield may reduce the value of grazing land.	P & C (2001)	M
22. Change land use?	“Some of the land on which it occurs is marginal for agriculture – it is steep, has a short growing period and is prone to competition from pests such as rabbits, blackberry and bracken.” One recommended method of control is afforestation with Pinus radiata. This would lead to a significant change in land use with potential agricultural loss. As dairy area – much more effective to clean ragwort and run dairy cattle	P & C (2001)	ML
23. Increase harvest costs?	Not known to increase harvest costs.		L
24. Disease host/vector?	None evident.		L

Impact Assessment Record - Ragwort (PDF - 26KB)
Impact Assessment Record - Ragwort (DOC - 59KB)
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