Impact Assessment - Chilean cestrum (Cestrum parqui) 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?	An erect shrub 2 – 3 metres. It builds up large populations in moist habitats such as river flats, creekbanks and wetland edges. It has sometimes been planted as a hedge plant. High potential to block access to waterways.	Muyt (2001) P & C (2001)	H
2. Reduce tourism?	Due to its potential to build a large population in moist habitats, some associated recreational pursuits may be affected (e.g. swimming, boating, bird watching, etc).	Muyt (2001)	MH
3. Injurious to people?	“Plant material is poisonous to animals and humans if chewed or swallowed. Some people may develop skin rashes from handling plants.”	Muyt (2001)	H
4. Damage to cultural sites?	In dense infestations it would present a moderate visual impact. Although the plant reproduces vegetatively and has an extensive root system, there is no evidence to indicate it could affect the structure of cultural sites.	Muyt (2001) P & C (2001)	ML
Abiotic
5. Impact flow?	Although it invades creekbanks and wetland edges there is no indication it affects the flow of water.		L
6. Impact water quality?	Although it invades creekbanks and wetland edges there is no indication it affects water quality.		L
7. Increase soil erosion?	An evergreen shrub, it has an extensive though shallow root system. Unlikely to cause soil erosion.	P & C (2001)	L
8. Reduce biomass?	“It forms extensive stands along disturbed edges and openings preventing growth and regeneration by indigenous plants.” Infestations would increase biomass.	Muyt (2001)	L
9. Change fire regime?	The plant does not create a fire hazard in natural ecosystems. Small or negligible effect on fire risk.	PIER1	L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Alluvial terraces herb-rich woodland (E); CMA=Glenelg Hopkins; Bioreg=Victorian Volcanic Plain; VH CLIMATE potential. “The plant grows well on alluvial river flats often to the exclusion of most other vegetation.”	P & C (2001)	MH
(b) medium value EVC	“Green cestrum builds up large populations in moist habitats such as river flats, creekbanks and wetland edges.” Unlikely to occur in any medium value EVC in Victoria.	Muyt (2001)	L
(c) low value EVC	EVC=Montane damp forest (LC); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; H CLIMATE potential. “Green cestrum builds up large populations in moist habitats…on disturbed edges and openings.” CLIMATE potential distribution rating is HIGH in this EVC/CMA/bioregion; limited impact. Other EVCs less affected.	Muyt (2001)	ML
11. Impact on structure?	“The plant grows well on alluvial river flats often to the exclusion of most other vegetation.” “It forms extensive stands along disturbed edges and openings preventing growth and regeneration by indigenous plants.”	P & C (2001) Muyt (2001)	MH
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“The plant grows vigorously when neglected and is toxic to animals including cattle, sheep, horses, pigs and poultry.” Its ability to form dense stands, “preventing growth and regeneration by indigenous plants,” and its toxic property suggests the plant would reduce the habitat of desirable species.	P & C (2001) Muyt (2001)	MH
15. Benefits fauna?	The dense stands may provide harbor for birds. Birds are known to eat the fruit.	P & C (2001)	MH
16. Injurious to fauna?	“Plant material is toxic.”	Muyt (2001)	H
Pest Animal
17. Food source to pests?	Birds are a known vector, but it is claimed the plant is toxic to birds and bees.	P & C (2001)	ML
18. Provides harbor?	Dense stands may provide harbour for pest birds.		ML
Agriculture
19. Impact yield?	“The plant prefers moist habitats such as river flats, creekbanks and wetland edges.” However, animals are attracted to the plant and will graze it. Infested areas have to be fenced off to prevent stock losses. “In Auckland, New Zealand, stock losses have occurred in spite of attempts to restrict access to the plant.”	P & C (2001)	MH
20. Impact quality?	The plant takes several years to mature so would not become a weed of cropping. No seed contamination. Animals that eat the plant usually die; they do not end up in the food chain.	P & C (2001) Muyt (2001)	L
21. Affect land value?	The plant grows vigorously, and it reproduces sexually and vegetatively. It is difficult to control. Where it occurs in grazing land the value of the land would be affected.	Muyt (2001)	M
22. Change land use?	In grazing situations stock losses can be minimised by fencing off infested areas. The land use would not be compromised.	P & C (2001)	L
23. Increase harvest costs?	No		L
24. Disease host/vector?	None evident.	PIER	L