Impact Assessment - Wild teasel (Dipsacus fullonum) 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?	“An erect biennial herb to 2 m high.” It is widespread in medium to large populations in riparian vegetation and saline and subsaline wetland. Dense patches may make access to waterways difficult.	P & C (2001) Carr et al (1992)	MH
2. Reduce tourism?	“An erect biennial herb to 2 m high.” It is widespread in medium to large populations in riparian vegetation and saline and subsaline wetland. Its presence in dense patches may affect some recreational activities.	P & C (2001) Carr et al (1992)	MH
3. Injurious to people?	The stems are armed with slightly downward curved prickles, and stem leaves are toothed with prickles on lower side of midvein. In dense patches, the prickles may cause some discomfort to humans. Prickles present all year.	P & C (2001)	MH
4. Damage to cultural sites?	Dense patches would create a negative visual effect.		ML
Abiotic
5. Impact flow?	A terrestrial species, it does occur on streambanks. However, it is not known to affect water flow.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	A biennial with a fleshy taproot to 75 cm; large rosettes that remain until the following year. Dense patches not likely to affect soil erosion.	P & C (2001)	L
8. Reduce biomass?	It is widespread in medium to large populations in riparian vegetation and saline and subsaline wetland. Biomass may increase.	Carr et al (1992)	L
9. Change fire regime?	“…dead stems remain standing for many months, even years.” Dense patches may increase the frequency of fire risk.	P & C (2001)	ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Creekline grassy woodland (E); CMA=Glenelg Hopkins; Bioreg=Victorian Volcanic Plain; VH CLIMATE potential. Is widespread, occurring in medium to large populations. A biennial to 2 metres, the deep roots and large rosettes allow the weed to compete with other plants. Infestations may affect species in both lower and mid strata.	Carr et al (1992) P & C (2001)	MH
(b) medium value EVC	EVC=Sedgy riparian woodland (E); CMA=Glenelg Hopkins; Bioreg=Central Victorian Uplands; VH CLIMATE potential. Impact as in 10(a) above.	Carr et al (1992) P & C (2001)	MH
(c) low value EVC	Does not appear likely to occur in any low value EVC in Victoria.		L
11. Impact on structure?	“The deep roots and large rosettes compete with pasture plants for moisture and nutrients as well as for light.” In Victoria, it is widespread in medium to large populations. Dense patches are likely to have a major effect on lower stratum.	P & C (2001) Carr et al (1992)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“The deep roots and large rosettes compete with pasture plants for moisture and nutrients as well as for light, while the spines on leaves and stems discourage grazing by livestock.” Competition with other plants and prickly property of plant may reduce available fodder for fauna species.	P & C (2001)	ML
15. Benefits fauna?	No known benefits.		H
16. Injurious to fauna?	Not documented to cause injury. The prickly nature of the plant may cause some discomfort.		ML
Pest Animal
17. Food source to pests?	Not known as a food source to pests.		L
18. Provides harbor?	Not known to provide harbor.		L
Agriculture
19. Impact yield?	“The deep roots and large rosettes compete with pasture plants for moisture and nutrients as well as for light, while the spines on leaves and stems discourage grazing by livestock.” Effect on yield not documented, however, “It sometimes invades pastures, particularly on fertile damp soils, and this is the reason for its proclamation in Victoria.” Consider possibly minor impact (< 5%).	P & C (2001)	ML
20. Impact quality?	Not known as a weed of cropping or to affect the quality of agricultural produce.		L
21. Affect land value?	Limited infestations in Victorian agricultural situations. Ploughing is an effective method of controlling the plant. Not likely to affect land value.	P & C (2001)	L
22. Change land use?	With minimal impact on agricultural activity, change in land use not required.		L
23. Increase harvest costs?	No data available.		L
24. Disease host/vector?	None evident.		L

Impact Assessment Record - Wild teasel (PDF - 32KB)
Impact Assessment Record - Wild teasel (DOC - 60KB)
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