Impact Assessment - Boneseed / bitou bush (Chrysanthemoides monilifera) 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?	Shrub 1 to 3 metres high and wide. It is highly invasive in many ecosystems including coastal dunes, and can dominate vegetation. “Dense stands can restrict recreational activities.”	Muyt (2001) Blood (2001)	H
2. Reduce tourism?	Dominant presence of weed and difficulty in accessing recreational facilities would have a major impact on tourism.	Muyt (2001) Blood (2001)	H
3. Injurious to people?	No prickles, spines or burrs. The fruit is edible.	Blood (2001)	L
4. Damage to cultural sites?	It is a shallow rooted plant with no distinct taproot. Infestations would seriously affect the aesthetics of a cultural site.	P & C (2001)	MH
Abiotic
5. Impact flow?	Terrestrial species. It does not tolerate waterlogged soils.	Muyt (2001)	L
6. Impact water quality?	Terrestrial species.	Muyt (2001)	L
7. Increase soil erosion?	Originally planted to stabilise disturbed sandy soils (due to sandmining). Dense, broad evergreen cover protects soil from wind erosion.	P & C (2001)	L
8. Reduce biomass?	It dominates native species such as Acacia longifolia (>2 m height), Correa alba (1.5 m height) , Leucopogon parviflorus (2 m height), potentially increasing biomass.	P & C (2001)	L
9. Change fire regime?	No data available that suggests infestations change the fire regime.		L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Grassy woodland (E); CMA=Corangamite; Bioreg=Otway Plain; VH CLIMATE potential “Dense stands [of C. monilifera] eliminate most indigenous ground-flora and prevent virtually all overstorey regeneration.” Displaces species across all strata with major impact on ground-flora.	Muyt (2001)	MH
(b) medium value EVC	EVC=Valley grassy forest (D); CMA=East Gippsland; Bioreg=East Gippsland Uplands; VH CLIMATE potential “…its ability to establish in areas of native vegetation ranging from mallee scrub to wet sclerophyll forests.” “Dense stands [of C. monilifera] eliminate most indigenous ground-flora and prevent virtually all overstorey regeneration.” Displaces species across all strata with major impact on ground-flora.	P & C (2001) Muyt (2001)	MH
(c) low value EVC	EVC=Lowland forest (LC); CMA=East Gippsland; Bioreg=East Gippsland Lowlands; VH CLIMATE potential Impact as in 10(a) above	P & C (2001) Muyt (2001)	MH
11. Impact on structure?	“Dense stands [of C. monilifera] eliminate most indigenous ground-flora and prevent virtually all overstorey regeneration.” In some areas of the NSW coast it now forms almost pure stands.	Muyt (2001) P & C (2001)	MH
12. Effect on threatened flora?	Direct threat to native orchid Pterostylis truncata (brittle greenhood) in the You Yang ranges. Threatens ANZECC rated rare or threatened native plant species	P & C (2001) Groves et al 2003	H
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	Dense stands destroy or drastically alter the habitat of native birds and animals. In NSW it has replaced plant species known to be important food sources for migratory birds.	P & C (2001)	MH
15. Benefits fauna?	May provide alternative food source.	P & C (2001)	MH
16. Injurious to fauna?	No evidence of the plant parts being toxic.		L
Pest Animal
17. Food source to pests?	Rabbits and foxes are both known to eat the fruit.	P & C (2001)	H
18. Provides harbor?	A dense, perennial and dominating shrub that is a source of food for both rabbits and foxes. It can provide harbor throughout the year.	P & C (2001)	H
Agriculture
19. Impact yield?	It does not affect agriculture detrimentally and is rarely found in pastures. It does not persist when grazed and trampled by stock nor when cultivated.	P & C (2001)	L
20. Impact quality?	Not a significant weed of agriculture.	P & C (2001)	L
21. Affect land value?	Not a significant weed of agriculture.	P & C (2001)	L
22. Change land use?	Not a significant weed of agriculture.	P & C (2001)	L
23. Increase harvest costs?	No evidence.		L
24. Disease host/vector?	None evident.		L