Impact Assessment - Cape broom / montpellier broom (Genista monspessulana) 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?	Evergreen plant that can dominate the shrub canopy and grow to 3 metres high and wide. It grows in a variety of natural habitats including forest margins and riparian areas. It was used as a hedge plant. In dense infestations it would present a significant barrier to both humans and vehicles.	Muyt (2001)	H
2. Reduce tourism?	Infestations in natural ecosystems would restrict some recreational activities.	Muyt (2001)	MH
3. Injurious to people?	The seeds are highly poisonous.	Blood (2001)	H
4. Damage to cultural sites?	The root system is not vigorous and is unlikely to cause structural damage. “Brooms are highly invasive, commonly invading disturbed bushland margins before expanding into less disturbed areas.” The presence of G. monspessulana would be very noticeable particularly during flowering, which would seriously affect the aesthetics of a cultural site.	P & C (2001) Muyt (2001)	ML
Abiotic
5. Impact flow?	Terrestrial species. Although it does occur in riparian areas, there is no documented evidence of its affecting water flow.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	An evergreen plant that provides extensive vegetative cover; branched taproot with numerous shallow lateral roots. This plant would not contribute to soil erosion.	Muyt (2001)	L
8. Reduce biomass?	Generally invades disturbed. With its growth habit biomass may increase.	Muyt (2001)	L
9. Change fire regime?	It is a fire hazard in forest areas where it can form “an inflammable understorey at the edge of forests where fires are most likely to start.” High potential to change the frequency of fire risk.	P & C (2001)	H
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Valley grassy forest (E); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; VH CLIMATE potential. “Infestations shade and crowd out smaller shrubs and ground-flora species, eventually dominating the shrub canopy and severely impeding overstorey regeneration.” Serious impact on lower and mid strata.	Muyt (2001)	MH
(b) medium value EVC	EVC=Heathy woodland (D); CMA=Glenelg Hopkins; Bioreg=Central Victorian Uplands; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	MH
(c) low value EVC	EVC=Heathy Woodland (LC); CMA=Glenelg Hopkins; Bioreg=Glenelg Plain; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	MH
11. Impact on structure?	“Infestations shade and crowd out smaller shrubs and ground-flora species, eventually dominating the shrub canopy and severely impeding overstorey regeneration.” Potential to serious affect lower and mid-storey species.	Muyt (2001)	MH
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“Dense thickets exclude most other plants and thus affect the carrying capacity.” It is widespread in medium to large populations. Its capacity to invade a broad range of vegetative communities including grasslands, woodlands, heathlands, forests and riparian areas and its potential to dominate indicates the plant is likely to have a major impact on the food sources of native fauna.	Muyt (2001) P & C (2001) Carr et al (1992)	MH
15. Benefits fauna?	No recorded benefits. The plant may provide harbor for some species.	P & C (2001) Blood (2001)	MH
16. Injurious to fauna?	Seeds are highly poisonous.	Blood (2001)	H
Pest Animal
17. Food source to pests?	Not known as a food source to pest animals.		L
18. Provides harbor?	It “affords cover for pest animals such as rabbits.”	P & C (2001)	H
Agriculture
19. Impact yield?	Its effect in agricultural situations is limited as it mostly occurs in poorer pastures. In these situations, however, “it forms dense thickets, which exclude most other vegetation and thus affect the carrying capacity.” It would have at least a minor impact on yield.	P & C (2001)	ML
20. Impact quality?	The plant reproduces sexually and takes about two years to reach sexual maturity. The plant would not develop in cultivated situations.	Muyt (2001)	L
21. Affect land value?	On arable land control is easily effected by mechanical means. Not likely to affect land value.	P & C (2001)	L
22. Change land use?	Not a serious weed of agriculture. Control is easily effected by mechanical means.	P & C (2001)	L
23. Increase harvest costs?	Not known.		L
24. Disease host/vector?	None evident.		L