Impact Assessment - Spiny broom (Calicotome spinosa) 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 much branched spiny shrub, commonly 1.5 to 2.5 metres high. Stems usually multi-branched from the base, armed with sharp rigid spines to 7.5 cm long. Spiny broom forms an effective hedge because of the dense growth of spiny branches. Dense patches limit access to watering points [for animals].” In dense patches, the plant would create a major impediment to human access, though not requiring significant works or closing tracks	P & C (2001)	MH
2. Reduce tourism?	Although the plant can occur in dense patches, it does so in small populations. Some recreational activities may be affected.	P & C (2001) Carr et al (1992)	MH
3. Injurious to people?	The stems bear rigid spines to 7.5 cm long, which could be a hazard to humans and likely to cause injury.	P & C (2001)	H
4. Damage to cultural sites?	Dense patches would create a negative visual impact.		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 shrub with a stout taproot, sometime forked. Dense stands (as hedges) provide ground cover. Unlikely to contribute to soil erosion.	P & C (2001)	L
8. Reduce biomass?	In Victoria, it invades lowland grassland & grassy woodland and dry sclerophyll forest & woodland. Biomass may increase where dense patches occur.	Carr et al (1992)	L
9. Change fire regime?	Not documented. However, the related plant Cytisus scoparius is known to be highly flammable and burn with an intense heat. Calicotome spinosa may also display similar fire response. Moderate change to the frequency and intensity of fire risk.	P & C (2001)	MH
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=Corangamite; Bioreg=Victorian Volcanic Plain; VH CLIMATE potential. Nitrogen fixing. Widespread, but in small populations. Minor displacement of ground covers/forbs/shrubs.	Carr et al (1992)	ML
(b) medium value EVC	EVC=Herb-rich heathy woodland (D); CMA=Glenelg Hopkins; Bioreg=Dundas Tablelands; VH CLIMATE potential. Impact as in 10(a) above.	Carr et al (1992)	ML
(c) low value EVC	EVC=Heathy woodland (E); CMA=Glenelg Hopkins; Bioreg=Dundas Tablelands; VH CLIMATE potential. Impact as in 10(a) above.	Carr et al (1992)	ML
11. Impact on structure?	Like Cytisus scoparius, the dense growth possibly shades out other plants and, as brooms fix nitrogen in the soil, establishment of native species may be prevented. The plant only occurs in small populations. Minor effect on the lower and mid strata.	P & C (2001) Carr et al (1992)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“Dense patches reduce grazing and limit access to watering points.” As it occurs in small populations, it is likely to have a minor effect on the habitat of fauna species.	P & C (2001) Carr et al (1992)	ML
15. Benefits fauna?	No known benefits to fauna.		H
16. Injurious to fauna?	“Young plants are claimed to be toxic but evidence of this is lacking.” Spines are present all year; may be dangerous to fauna.	P & C (2001)	H
Pest Animal
17. Food source to pests?	Not known as a food source to pests.		L
18. Provides harbour?	“Dense patches provide harbour for pest animals.”	P & C (2001)	H
Agriculture
19. Impact yield?	“Dense patches reduce grazing and limit access to watering points.” Minor impact on yield.	P & C (2001) Carr et al (1992)	ML
20. Impact quality?	Not a weed of cropping. Not known to affect the quality of produce.		L
21. Affect land value?	Small populations only. Not likely to affect land value.	Carr et al (1992)	L
22. Change land use?	Small populations only. Change to land use not required.	Carr et al (1992)	L
23. Increase harvest costs?	Not a weed of cropping.		L
24. Disease host/vector?	None evident.		L