Impact Assessment - Spiny burr grass (Cenchrus longispinus) 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?	“An erect or spreading annual grass to 60 cm high. Inflorescence a spike-like panicle consisting of up to 40 burrs; spines sharply pointed, finely barbed, rigid to 7 mm long.” The plant would not present any restrictions to human movement except when burrs are present (December to April). High nuisance value during this time of year.	P & C (2001)	MH
2. Reduce tourism?	Some recreational activities may be affected; burrs remain on the ground for several months after the plant dies.	Barnard, T. (pers. comms.)1	MH
3. Injurious to people?	“Spines can easily puncture the skin of animals.” Similarly, may injure humans. Burrs present for much of the year.	P & C (2001)	MH
4. Damage to cultural sites?	An annual grass, it would have little effect on visual aesthetics or structure of cultural sites.		L
Abiotic
5. Impact flow?	Terrestrial species.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	An annual grass, “the weed grows well on disturbed road edges and infests neglected areas and summer crops.” Not likely to contribute to soil erosion in these situations.	P & C (2001)	L
8. Reduce biomass?	An annual grass, “the weed grows well on disturbed road edges and infests neglected areas and summer crops.” Biomass replaced by invader	P & C (2001)	ML
9. Change fire regime?	“Spiny burr-grass forms tussocks up to 60 cm and more across. Most plants die in autumn or early winter.” In dense patches the plant may increase the frequency of fire risk somewhat.	P & C (2001)	ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Heathy woodland (V); CMA=Wimmera; Bioreg=Goldfields; VH CLIMATE potential. Occupies open dry sandy conditions. Does not establish readily in pastures. Disturbance enhances invasiveness. Minor displacement of grass species.	P & C (2001)	ML
(b) medium value EVC	EVC=Sand heathland (R); CMA=Wimmera; Bioreg=Wimmera; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	ML
(c) low value EVC	EVC=Heathy woodland (V); CMA=Wimmera; Bioreg=Wimmera; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	ML
11. Impact on structure?	“Spiny burr-grass, which occupies open dry sandy situations and is a pioneer plant of disturbed sandy soils, also grows well under irrigation. Spiny burr-grass does not establish readily in pastures.” Minor effect on the lower stratum only.	P & C (2001)	L
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“Spiny burr-grass, which occupies open dry sandy situations and is a pioneer plant of disturbed sandy soils, also grows well under irrigation.” No fauna affected.	P & C (2001)	L
15. Benefits fauna?	No documented benefits.		H
16. Injurious to fauna?	“Spines can easily puncture the skin of animals.” Potential to injure fauna.	P & C (2001)	MH
Pest Animal
17. Food source to pests?	Not known as a food source to pests.		L
18. Provides harbor?	Not known to harbor pest animals.		L
Agriculture
19. Impact yield?	“Spiny burr-grass does not establish readily in pastures.” Although it does occur in summer crops, it is not documented to affect the yield.	P & C (2001)	L
20. Impact quality?	“The burrs become badly tangled in wool, lowering its value. Spines easily puncture the skin of animals thus affecting the value of the hides.” It occurs as a contaminant in dried fruit and may infest lucerne hay. Additionally, C. longispinus does not appear to cover large areas. “Heavy grazing with sheep prevents seeding but it is not always practical to confine sheep to small patches of the weed in the large paddocks common to Australia.”	P & C (2001)	MH
21. Affect land value?	Not known to affect land values.		L
22. Change land use?	Infestations can be controlled using a number of different techniques depending upon agricultural activities. Such techniques are: early cultivation; heavy grazing with sheep; establishing strong pasture growth particularly lucerne, which is very competitive against C. longispinus. Some temporary change may be necessary depending upon density of infestation and agricultural activity.	P & C (2001)	M
23. Increase harvest costs?	Burrs in wool, “make sheep difficult to handle, which results in penalty rates being paid to shearers.” “Penalty rates are also paid to abattoirs staff handling burr-infested sheep.”	P & C (2001)	M
24. Disease host/vector?	None evident.		L