Impact Assessment - Sweet briar (Dittrichia graveolens) in Victoria (Nox)

Back | Table | Feedback

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?	“Deciduous multi-stemmed shrub to heights and widths of 3 m. Plants commonly form thickets that prevent movement through areas.” It occurs in a broad range of native vegetation including riparian situations. Major impediment to human access.	Muyt (2001)	H
2. Reduce tourism?	“Deciduous multi-stemmed shrub to heights and widths of 3 m. Plants commonly form thickets that prevent movement through areas.” Thickets seriously reduce aesthetics and some recreational uses may be affected.	Muyt (2001)	MH
3. Injurious to people?	Older stems are rough and woody and bear numerous backward curving prickles of varying length to 1.5 cm. Prickles present all year.	P & C (2001)	MH
4. Damage to cultural sites?	A deciduous shrub, its presence would be obvious and create a moderate negative visual impact. Although the root system is stout and extensive, there is no evidence to suggest it would cause structural damage.		ML
Abiotic
5. Impact flow?	Terrestrial species. “It seldom establishes on poorly drained sites.”	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	A large deciduous shrub with a stout, extensive root system. Not likely to contribute to soil erosion.	P & C (2001)	L
8. Reduce biomass?	“It invades lowland grassland and grassy woodland, dry and damp sclerophyll forest and woodland, riparian, rock outcrop and alpine and sub-alpine vegetation, pastures and pine plantations.” It is widely distributed in Victoria in medium to large populations. Biomass may increase.	Blood (2001) Carr et al (1992)	L
9. Change fire regime?	Impact on fire regime is not documented; assume little change.		L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Dry valley forest (V); CMA=West Gipplsand; Bioreg=Highlands Southern Fall; VH CLIMATE potential. “Plants commonly…crowd out competing shrubs and prevent most overstorey regeneration.” Major displacement of species in the mid strata.	Muyt (2001)	MH
(b) medium value EVC	EVC=Montane grassy woodland (D); CMA=North East; Bioreg=Highlands – Northern Fall; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	MH
(c) low value EVC	EVC=Montane dry woodland (D); CMA=North East; Bioreg= Highlands – Northern Fall; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	MH
11. Impact on structure?	“Plants commonly form thickets that…crowd out competing shrubs and prevent most overstorey regeneration.” In dense patches would have a major effect on the lower and mid-storey species.	Muyt (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	In Victoria, it is widely distributed in medium to large populations. “It invades lowland grassland and grassy woodland, dry and damp sclerophyll forest and woodland, riparian, rock outcrop and alpine and sub-alpine vegetation, pastures and pine plantations.” Likely to reduce habitat for fauna leading to a reduction in numbers.	Carr et al (1992) Blood (2001)	MH
15. Benefits fauna?	No known benefits to fauna species.		H
16. Injurious to fauna?	Although the plant is prickly, it is not documented to cause injury to animals.		L
Pest Animal
17. Food source to pests?	Rabbits are known to graze the plant in its young stage.	P & C (2001)	MH
18. Provides harbor?	“…provides harbour for rabbits and foxes.”	Blood (2001)	H
Agriculture
19. Impact yield?	“The species has no fodder value and once clumps of the weed become numerous there is a considerable loss of pasture production because of competition with, and reduced space for, productive species.” Serious impact on pastoral activities.	P & C (2001)	H
20. Impact quality?	Not known to affect the quality of agricultural produce.		L
21. Affect land value?	“In some cases [in New Zealand] farms have been abandoned.” Serious infestations likely to lead to significantly devalued land.	P & C (2001)	H
22. Change land use?	“In some cases [in New Zealand] farms have been abandoned.” Change in land use would occur in some situations.	P & C (2001)	H
23. Increase harvest costs?	Not known to affect harvest costs.		L
24. Disease host/vector?	None evident.		L

Impact Assessment Record - Sweet briar (PDF - 31KB)
Impact Assessment Record - Sweet briar (DOC - 60KB)
This table can also be viewed as a PDF document (printer friendly). To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).

Feedback

Do you have additional information about this plant that will improve the quality of the assessment?
If so, we would value your contribution. Click on the link to go to the feedback form.