Impact Assessment - Wild garlic (Opuntia robusta) 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 strong-smelling perennial herb, commonly 30 to 60 cm high.” Would not restrict human access.	P & C (2001)	L
2. Reduce tourism?	The strong garlic odour produced by the plant may discourage people from some recreational activities. Minor impact.	P & C (2001)	ML
3. Injurious to people?	No toxic or physically harmful properties	P & C (2001)	L
4. Damage to cultural sites?	Infestations may create a negative visual effect.		ML
Abiotic
5. Impact flow?	Terrestrial species.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	A shallow (to 60 cm deep), fibrous root system. It commonly occurs in cereal crops and pastures. Competitive properties in pasture not documented. Not likely to increase soil erosion.	P & C (2001)	L
8. Reduce biomass?	Commonly occurs in cereal crops and pastures. Invader replaces biomass.	P & C (2001)	ML
9. Change fire regime?	When aerial parts die in summer little material remains to establish or support fire. Assume no change to fire regime.	P & C (2001)	L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Creekline grassy woodland (E); CMA=Goulburn Broken; Bioreg=Central Victorian Uplands; VH CLIMATE potential. “Crow garlic is cold hardy, tolerant of wet soils and often occurs on poorly drained, heavy soils of pastures and streambanks.” Not known as a weed of natural ecosystems (Carr et al 1992). Competitiveness not documented.	P & C (2001)	L
(b) medium value EVC	EVC=Riverine grassy woodland (D); CMA=Goulburn Broken; Bioreg=Murray Fans; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	L
(c) low value EVC	EVC=Damp forest (LC); CMA=Goulburn Broken; Bioreg=Central Victorian Uplands; VH CLIMATE potential. Prefers open situations. Population density limited.	P & C (2001)	L
11. Impact on structure?	Data on population density or competitive nature of plant not available. Not known as a weed of natural ecosystems (Carr et al 1992).		L
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	Data on population density or competitive nature of plant not available. Grazing stock are known to eat the plant. Assume minor impact on food source for fauna species.	P & C (2001)	ML
15. Benefits fauna?	No benefits.		H
16. Injurious to fauna?	“There is little evidence that crow garlic is toxic to animals, although milk production is lowered on infested pastures and suspected cattle poisonings are reported occasionally in the British Isles.” Possible minor effect on fauna species.	P & C (2001)	ML
Pest Animal
17. Food source to pests?	Not known as a food source to pest animals.		L
18. Provides harbour?	Not known to provide harbour.		L
Agriculture
19. Impact yield?	Not known to affect yield.		L
20. Impact quality?	“Crow garlic…impart[s] a strong garlic odour and flavour to agricultural produce, particularly cereal grain, grain products, milk and meat.” Contaminated grain is rejected at grain silos, but may be sold as stockfeed at a reduced rate. Significant impact on quality of produce due to contamination.	P & C (2001)	MH
21. Affect land value?	Control of the plant is difficult. Considering the impact on agricultural quality, the value of infested land may be reduced slightly.		M
22. Change land use?	“Cultivation from late autumn to spring kills many plants but must be repeated for several years to ensure that all dormant bulbs have germinated and the resultant plants destroyed. Such a programmed is seldom practical because it requires the area to be virtually out of production for several years.” Potential threat to agricultural return for a time.	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 - Wild garlic (PDF - 31KB)
Impact Assessment Record - Wild garlic (DOC - 58KB)
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