Impact Assessment - Angled onion (Allium triquetrum) 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?	Although invading a significant number of environmental vegetation formations, A. triquetrum, as a low growing perennial herb (to 50 cm high), is would have minimal impact on human access.	Carr et al (1992) Muyt (2001)	L
2. Reduce tourism?	It is a persistent species capable of totally dominating ground flora. During leaf growth and flowering stage its presence is quite obvious resulting in a major negative impact on aesthetics. “The leaves and stems have a strong garlic-like aroma when crushed.” Some recreational activities may be affected as a result.	Muyt (2001)	MH
3. Injurious to people?	No known toxicity or harmful physical properties (burrs, spines, etc.). It has been used as a culinary herb.	Blood (2001)	L
4. Damage to cultural sites?	The obvious presence of the plant would produce a moderate negative visual effect.	Muyt (2001)	ML
Abiotic
5. Impact flow?	Terrestrial sp.	P & C (2001)	L
6. Impact water quality?	Terrestrial sp.	P & C (2001)	L
7. Increase soil erosion?	“Colonies dense, out-competes other herbaceous plants leaving bare ground in summer dormancy period, thereby increasing likelihood of erosion.”	Blood (2001)	MH
8. Reduce biomass?	“Dense stands will smother and crowd out any competing ground-flora while seriously impeding over-storey regeneration.” It is only active from mid-winter to early summer, thus leaving infested areas bare of vegetation for about six months of the year. Biomass would be decreased.	Muyt (2001) Blood (2001)	MH
9. Change fire regime?	Prefers moist environments. Dried plant material provides little fuel. Low probability of fire risk.	Muyt (2001)	L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=West Gippsland; Bioreg=Highlands–Southern Fall; VH CLIMATE potential. “…tenacious, persistent species capable of totally dominating the ground-flora wherever conditions are suitable.” Major displacement of dominant sp. within a layer.	Muyt (2001)	MH
(b) medium value EVC	EVC=Herb-rich foothill forest (D); CMA=Corangamite; Bioreg=Central Victorian Uplands; VH CLIMATE potential. “…tenacious, persistent species capable of totally dominating the ground-flora wherever conditions are suitable.” Major displacement of dominant sp. within a layer.	Muyt (2001)	MH
(c) low value EVC	EVC=Heathy woodland (LC); CMA=West Gippsland; Bioreg=Gippsland Plain; VH CLIMATE potential. “…tenacious, persistent species capable of totally dominating the ground-flora wherever conditions are suitable.” Major displacement of dominant sp. within a layer.	Muyt (2001)	MH
11. Impact on structure?	“Dense stands will smother and crowd out any competing ground-flora while seriously impeding over-storey regeneration.” Major effect on ground flora.	Muyt (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	Its presence is widespread, in medium to large populations, and it invades a large number of vegetative forms. It is thus likely to have a major negative effect on the habitat of non-threatened fauna.	Carr et al (1992) Blood (2001)	MH
15. Benefits fauna?	“Attachments on seeds [are] attractive to ants, which are important vectors.” Literature does not clarify native or introduces spp.	Blood (2001)	H
16. Injurious to fauna?	No toxic properties. Both humans and animals have eaten the plant.	Blood (2001)	L
Pest Animal
17. Food source to pests?	“Attachments on seeds [are] attractive to ants, which are important vectors.” Literature does not clarify native or introduced spp. Assume potential for both.	Blood (2001)	ML
18. Provides harbor?	As a bulbous herb, the plant only has foliage for six months. It would not provide any suitable, permanent harbor.	Blood (2001)	L
Agriculture
19. Impact yield?	A. triquetrum, “does not compete in strongly in crops and improved pastures.” Little affect agricultural yield.	P & C (2001)	L
20. Impact quality?	The plant, “imparts a strong onion flavour and an unpleasant odour to dairy products and meat, making them unfit for sale.” Contaminates product making it unfit for sale.	P & C (2001)	H
21. Affect land value?	Due to its significant impact on agricultural quality, the presence of A. triquetrum in paddocks would have a negative impact on land prices. However, the plant can be controlled with appropriate farm practices.	P & C (2001)	M
22. Change land use?	The plant can be controlled with straightforward cultivation techniques and the use of incrop herbicide sprays. Access by grazing animals would be restricted until weed was eliminated.	P & C (2001)	M
23. Increase harvest costs?	A known vector is contaminated mud on farm machinery and vehicles. Strict hygiene practices must be observed to prevent further spread. Potential to increase harvest costs through cleaning vehicles and machinery.	Blood (2001)	M
24. Disease host/vector?	None evident.		L