Impact Assessment - Gorse (Ulex europeaus) 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?	It is widespread in a broad range of vegetation communities in medium to large populations. Grown as a hedge plant and armed with numerous spines to 5 cm long, the plant forms dense impenetrable thickets that prevent access.	Carr et al (1992) P & C (2001) Muyt (2001)	H
2. Reduce tourism?	Because of its ability to form dense thickets that prevent access, infestations would have a significant impact on limiting recreational activities.	Muyt (2001)	H
3. Injurious to people?	The plant is armed with spines to 5 cm long throughout the year.	P & C (2001)	H
4. Damage to cultural sites?	An erect much-branched shrub to 3 metres that can form dense thickets. The root system is not vigorous and thus not likely to cause structural damage. The plant would have a moderate visual impact.	P & C (2001)	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?	The plant was recommended for sandbinding in coastal areas. Would not contribute to soil erosion.	P & C (2001)	L
8. Reduce biomass?	“Gorse forms dense, impenetrable thickets that eventually exclude all other indigenous vegetation and prevent any regeneration occurring.” Likely to increase biomass initially.	Muyt (2001)	L
9. Change fire regime?	“Furze burns readily and dense patches are a considerable fire hazard.” Not greatly changes but just moderate – fire frequency isn't necessarily increased because of gorse (David Boyle).	P & C (2001)	MH
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Valley grassy forest (V); CMA=West Gippsland; Bioreg=Highlands – Southern Falls; VH CLIMATE potential. Fixes nitrogen. “…exclude[s] all other indigenous vegetation and prevent[s] any regeneration occurring.” Major effect on species within low to mid strata.	Muyt (2001)	H
(b) medium value EVC	EVC=Damp heathland (R); CMA=West Gippsland; Bioreg=Gippsland Plain; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	H
(c) low value EVC	EVC=Heathy woodland (LC); CMA=Port Phillip; Bioreg=Gippsland Plain; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	H
11. Impact on structure?	“Forms dense impenetrable thickets that eventually exclude all other indigenous vegetation and prevent any regeneration occurring.” Would have a major effect on low to mid strata..	Muyt (2001)	MH
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	It eliminates native forage plants reducing food source for native fauna and restricts access. “Animals eat seedlings and young shoots, but mature plants are rarely eaten.” Overall reduction in habitat for native fauna.	P & C (2001) Muyt (2001)	MH
15. Benefits fauna?	“Gorse thickets often provide habitat for small native birds and mammals.”	Muyt (2001)	MH
16. Injurious to fauna?	The plant is armed with spines on leaf tips for all of the year. But is unlikely to be injurious	P & C (2001)	ML
Pest Animal
17. Food source to pests?	Birds and ants spread seeds. Possible pest species.	Blood (2001)	ML
18. Provides harbor?	“Dense furze growth provides excellent harbor for rabbits.”	P & C (2001)	H
Agriculture
19. Impact yield?	The plant restricts animal movement and access to other pasture species. Dense infestations severely reduce carrying capacity. In New Zealand, “it is a major problem in forestry, where it interferes with establishment operations and competes strongly with young trees.” Probable does decrease quantity but is not unviable to harvest probable less than 5%. Tolerance to the weed – put up with it for many/few years. Impact on yield is not significant.	P & C (2001) Panetta et al (1998)	ML
20. Impact quality?	Not known to impact quality of produce. Not a weed of cropping situations.		L
21. Affect land value?	“Control is made difficult by the vigour and competitiveness of the plant.” Seed banks can be as large as 100 million per hectare and seeds remain viable for several decades. Having this plant on agricultural land would reduce its value significantly due to the cost and duration of control activities.	P & C (2001) Blood (2001)	H
22. Change land use?	If left unmanaged, it would result in a major detrimental change to agricultural use. Animals do not graze mature plants and significant works are required to eliminate its occurrence in forestry situations. Tolerance to the weed – put up with it for many/few years.- some alteration but no major change – In New Zealand Canterbury plains and hillsides – move to forestry to suppress Gorse – but does not downgrade priority land use in Vic.	P & C (2001)	ML
23. Increase harvest costs?	No evidence of increased harvest costs.		L
24. Disease host/vector?	Not known as a vector/host for disease.		L