Impact Assessment - Khaki weed (Alternanthera pungens) 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?	A prostrate creeping perennial. Would not restrict human access.	P & C (2001)	L
2. Reduce tourism?	A prostrate perennial, the plant growth habit would not restrict recreational activities. However, “the sharp spines of the heads are a great annoyance to bare-footed children [and adults?] and fruit pickers.” As it commonly occurs in, “irrigated recreation areas and caravan parks,” it would affect some recreational activities.	P & C (2001)	MH
3. Injurious to people?	“The sharp spines of the heads are a great annoyance to bare-footed children…[and] it is claimed also to cause hay fever, asthma and dermatitis in some people.”	P & C (2001)	MH
4. Damage to cultural sites?	Khaki weed forms, “a dense ground cover [on]…bare or disturbed areas.” It has a deep, woody taproot only. Not likely to affect the structure of a cultural site but because of the dense ground cover, would create a moderate negative visual effect.	P & C (2001)	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?	“Roots form at stem nodes producing new plants and a dense ground cover.” The plant would not increase soil erosion.	P & C (2001)	L
8. Reduce biomass?	“Colonises bare or disturbed areas…[and] establishes occasionally in native pastures where it out-competes most other species.” Biomass may increase.	P & C (2001)	L
9. Change fire regime?	“Aerial growth dies off by late autumn.” Not likely to increase fuel load greatly. Small or negligible change to fire risk.	P & C (2001)	L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassland (E); CMA=North Central; Bioreg=Victorian Riverina; VH CLIMATE potential. “Establishes occasionally in native pastures where it out-competes most other species.” Would have a major impact on ground flora.	P & C (2001)	MH
(b) medium value EVC	EVC=Plains sedgy woodland (D); CMA=Glenelg Hopkins; Bioreg=Wimmera; VH CLIMATE potential. “Establishes occasionally in native pastures where it out-competes most other species.” Prefers open situations. Overstorey cover may limit impact. Would have a minor impact on grasses/forbs.	P & C (2001)	ML
(c) low value EVC	EVC=Heathy woodland (E); CMA=Glenelg Hopkins; Bioreg=Wimmera; VH CLIMATE potential. Impact as in 10 (b) above.	P & C (2001)	ML
11. Impact on structure?	“Establishes occasionally in native pastures where it out-competes most other species.” Would have a major impact on ground flora.	P & C (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“It occasionally invades native pastures on sandy soils but usually does not persist.” Where it does establish it, “out-competes most other species.” Animals rarely eat the plant. Would reduce food source for native fauna.	P & C (2001)	ML
15. Benefits fauna?	“Animals do not eat the plant; the heads cause mechanical damage to the feet and mouths of stock.” No benefits.	P & C (2001)	H
16. Injurious to fauna?	“The heads cause mechanical damage to the feet and mouths of stock.” “Khaki weed is believed to be poisonous to animals and to cause a skin ailment in cattle.”	P & C (2001)	H
Pest Animal
17. Food source to pests?	Not known as a food source to pest animals. Stock does not readily graze the plant.	P & C (2001)	L
18. Provides harbour?	A prostrate plant, though with dense ground cover. It may provide limited harbour for rodents.	P & C (2001)	ML
Agriculture
19. Impact yield?	Not known to affect agricultural yields greatly. “In New South Wales…it competes with both irrigated and dryland lucerne.” No similar impacts in Victoria.	P & C (2001)	ML
20. Impact quality?	It, “contributes to vegetable fault in wool and…in New South Wales…its burrs contaminate lucerne hay.”	P & C (2001)	MH
21. Affect land value?	Not a serious weed of agriculture in Victoria; not likely to affect land value.	P & C (2001)	L
22. Change land use?	No		L
23. Increase harvest costs?	Does not affect harvest activities; not a weed of cropping in Victoria.	P & C (2001)	L
24. Disease host/vector?	None evident.		L