Impact Assessment - Camel thorn (Alhagi maurorum) 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?	Erect perennial shrub 40 to 100 cm high with rigid, much branched stems bearing numerous sharp spines 1.0 to 2.5 cm long. The spines can puncture human skin and break off in the wound. Dense infestations would restrict human access.	P & C (2001) Geoff Tyers1 pers coms	MH
2. Reduce tourism?	The size and spiny nature of the plant may reduce some recreational activities.	P & C (2001)	MH
3. Injurious to people?	Woody stems remain after the plant dies back in autumn. Spines present for most of the year. The spines can break off in the skin.	P & C (2001) Geoff Tyers CDFA 2	H
4. Damage to cultural sites?	The plant has an extensive and vigorous root system. In north-western Victoria “…shoots regularly break through a sealed bitumen road and the roots have extended the patch by a distance of about 6 metres.” It has the potential to cause serious structural damage to cultural sites.	P & C (2001)	H
Abiotic
5. Impact flow?	Terrestrial species.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	The aerial parts of the plant die back in autumn leaving the soil surface exposed in dense infestations. The extensive and deep root system (2 m deep and 8 m laterally), provide good soil stability. Potential for low probability of large scale soil movement.	P & C (2001)	L
8. Reduce biomass?	In Australia, it is found in pastures and neglected areas. Likely to replace existing biomass.	P & C (2001)	ML
9. Change fire regime?	“Woody tissues persist after plant death.” Increase fuel load is likely to increase frequency of fire risk.	CDFA	ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassland; CMA=North Central; Bioreg=Victorian Riverina; VH CLIMATE potential “It is found mostly in pastures and neglected areas. It is strongly competitive with other plants. In Merbein [Victoria]…it has eliminated most other vegetation.” Major displacement of grasses/forbs.	P & C (2001)	MH
(b) medium value EVC	“It is found mostly in pastures and neglected areas.” Requires pH>6. Unlikely to occur in any medium value EVC in Victoria.	P & C (2001)	L
(c) low value EVC	“It is found mostly in pastures and neglected areas.” Requires pH>6. Unlikely to occur in any low value EVC in Victoria.	P & C (2001)	L
11. Impact on structure?	“It is strongly competitive with other plants and, in the Merbein infestation, has eliminated most other vegetation.” Is found mostly in pastures and neglected areas. Likely to have a major impact on the lower strata.	P & C (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	In Australia, cattle and sheep graze the plant. However, it is also unpalatable and injurious to some animals. A competitive plant, it may impact on the habitat of native fauna.	P & C (2001) WSNWCB 3	ML
15. Benefits fauna?	Cattle and sheep graze the plant. It may be a limited food source for some species.	P & C (2001)	MH
16. Injurious to fauna?	It is injurious to some animals. The spines are present for much of the year.	WSNWCB	MH
Pest Animal
17. Food source to pests?	“The plant is confined to the northern parts of Victoria usually associated with irrigation.” Rabbits are known to occur in this area and the plant may provide some limited food.	P & C (2001)	MH
18. Provides harbor?	Dense patches may provide limited harbor for rabbits.	P & C (2001)	MH
Agriculture
19. Impact yield?	Overseas, it is a troublesome weed in cereal and horticultural crops where repeated cultivation aids its spread. It has an extensive root system and strongly competes with other plants. Likely to have serious impacts on yield.	P & C (2001)	MH
20. Impact quality?	No documented impact on quality. In the United States the plant is a potential alfalfa seed contaminant.	WSNWCB	MH
21. Affect land value?	Where it occurs in pasture situations it is unlikely to affect land value. Sheep and cattle graze the plant without apparent harm (from the spines).	P & C (2001)	L
22. Change land use?	In cropping situations cultivation spreads the weed and may increase shoot density. Land use would have to change until the plant was controlled. Change from cropping to permanent pasture.	CDFA	M
23. Increase harvest costs?	No evidence.		L
24. Disease host/vector?	None evident.		L