Impact Assessment - English broom (Cytisus scoparius) 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?	“Dense stands seriously impede movement.”	Muyt (2001)	H
2. Reduce tourism?	“English broom is a devastating species capable of totally transforming invaded habitats. It simplifies the structure and diversity of the ground-flora…eventually preventing overstorey regeneration.” The weed would have a major impact on recreational activities.	Muyt (2001)	H
3. Injurious to people?	The plant does not have spines or burrs, however, the seeds are poisonous if eaten in quantity.	Blood (2001)	H
4. Damage to cultural sites?	The root system does not appear to be vigorous, however, the notable presence of the plant would have a moderate negative visual impact.		ML
Abiotic
5. Impact flow?	Terrestrial species. It will not grow in swampy places.	Blood (2001)	L
6. Impact water quality?	Terrestrial species.	Blood (2001)	L
7. Increase soil erosion?	The plant provides dense coverage, and it has been planted to stabilise sand dunes and to bind soil in road cuttings or following fire. It would not contribute to soil erosion.	Panetta et al (1998)	L
8. Reduce biomass?	“It simplifies the structure and diversity of the ground flora, and crowds or shades out shrubs and tree seedlings, eventually preventing overstorey regeneration.” Broom infestations left undisturbed can prevent the re-establishment of overstorey eucalypts.	Muyt (2001) Panetta et al (1998)	H
9. Change fire regime?	“English broom…burns with intense heat.” Once established it makes the native vegetation much more susceptible to fire because of its flammability and the intense heat with which it burns.	P & C (2001)	H
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Sub-alpine grassland (V); CMA=East Gippsland; Bioreg=East Gippsland Uplands; VH CLIMATE potential. “Once established, [it]…dominates the vegetation of an area, smothering quite large shrubs and preventing re-establishment of native species.” Fixes nitrogen. Major displacement of dominant species within different strata.	P & C (2001)	MH
(b) medium value EVC	EVC=Grassy woodland (D); CMA=East Gippsland; Bioreg=East Gippsland Uplands; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	MH
(c) low value EVC	EVC=Sub-alpine woodland (LC); CMA=East Gippsland; Bioreg=East Gippsland Uplands; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	MH
11. Impact on structure?	“It simplifies the structure and diversity of the ground-flora, and crowds or shade out shrubs and tree seedlings.” Major effects lower and mid strata.	Muyt (2001)	MH
12. Effect on threatened flora?12. Effect on threatened flora?	Threatens ANZECC rated rare or threatened native plant species	Groves et al (2003)	H
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	Habitat is significantly reduced. C. scoparius infestations dominate ground-flora and can prevent access to water.	Muyt (2001)	MH
15. Benefits fauna?	The seed is spread by a number of animals (ants, cattle, horses and pigs), and seedlings have been found growing along wallaby tracks. Possible minor food source for native fauna.	Panetta et al (1998)	MH
16. Injurious to fauna?	“The seeds are thought to be poisonous if eaten in quantity.”	Blood (2001)	H
Pest Animal
17. Food source to pests?	Possible food source to pest animals such as birds or ants.	Blood (2001)	ML
18. Provides harbor?	It provides harbour for pest animals including feral pigs and blackbirds.	P & C (2001) Panetta et al (1998)	H
Agriculture
19. Impact yield?	Although a significant weed of natural ecosystems it is also a serious weed in orchards and pastures in some areas. “It establishes very rapidly after forests are harvested and out competes naturally regenerating as well as planted species.” In forestry situations it is likely to have a serious impact on yield.	P & C (2001) Panetta et al (1998)	H
20. Impact quality?	Not known to affect the quality of produce.		L
21. Affect land value?	“Eliminating English broom infestations can take several years due to the large number of long-lived seeds that accumulate in the soil.” Attempted broom control in pasture areas in the Barrington Tops and elsewhere have proved expensive and largely ineffective. Presence of the plant is likely to reduce land value.	Muyt (2001) Panetta et al (1998)	M
22. Change land use?	Presence of the plant may dictate a temporary change in land use. “Dense patches have been eliminated by bulldozing and repeated disc cultivations over 2 years.”	P & C (2001)	M
23. Increase harvest costs?	Not known to affect harvest costs.		L
24. Disease host/vector?	None evident.		L