Impact Assessment - Wild watsonia (Watsonia meriana var. bulbillifera) 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 perennial herb, commonly 1.2 to 1.8 m high.” It is widespread in medium to large populations invading a broad range of vegetation formations including riparian areas and seasonal freshwater wetland. “Bulbil Watsonia forms dense stands.” May be a high annoyance to humans; makes access difficult.	P & C (2001) Carr et al (1992) Muyt (2001)	ML
2. Reduce tourism?	Some recreational activities such as fishing may be affected.		ML
3. Injurious to people?	“Poisoning of livestock has been reported overseas.” It is not considered harmful to humans.	Blood (2001)	L
4. Damage to cultural sites?	Dense stands would produce a negative visual effect.		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 root system is shallow and fibrous. Dense stands may provide cover. “All aerial growth dies in summer but dead plants often remain standing for several months.” Not likely to contribute to erosion.	P & C (2001)	L
8. Reduce biomass?	Occurs on, “heavy soils in moist conditions, becoming a weed of roadsides and neglected areas.” Biomass may increase as a result of dense clumping of plants.	P & C (2001) Muyt (2001)	L
9. Change fire regime?	“All aerial growth dies in summer but dead plants often remain standing for several months.” Increase in biomass due to dense clumping may increase the frequency of fire risk.	P & C (2001)	ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grass woodland (E); CMA=Port Phillip; Bioreg=Gippsland Plain; VH CLIMATE potential. A highly invasive species. Dominates ground flora and prevents most overstorey regeneration. Tolerates sun, semi-shade, moist conditions, flooding fore several weeks, most soil types. Major displacement of species in lower and mid strata.	Muyt (2001) Blood (2001)	MH
(b) medium value EVC	EVC=Wet heathland (D); CMA=West Gipplsand; Bioreg=Gippsland Plain; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001) Blood (2001)	MH
(c) low value EVC	EVC=Heathy woodland (E); CMA=Port Phillip; Bioreg=Gippsland Plain; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001) Blood (2001)	MH
11. Impact on structure?	“Bulbil Watsonia forms dense stands that dominate the ground-layer and prevent most overstorey regeneration occurring.” Infestations would have a major impact on the ground flora and affect mid-storey species..	Muyt (2001)	ML
12. Effect on threatened flora?	Threatens ANZECC rated rare or threatened native plant species	Groves et al (1995)	H
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	It invades, “dry coastal vegetation, heathland and heathy woodland, lowland grassland and grassy woodland, dry and damp sclerophyll forest and woodland riparian vegetation, freshwater wetland (seasonal), roadsides, unimproved pastures, gardens, wasteland and railway lines.” “Bulbil Watsonia forms dense stands that dominate the ground-layer and prevent most overstorey regeneration occurring.” Presence may lead to a reduction in habitat.	Blood (2001) Muyt (2001)	MH
15. Benefits fauna?	No known benefits.		H
16. Injurious to fauna?	“It is claimed to be poisonous to stock, and losses of horses have been reported overseas but this is not a problem in Australia. Animals do not graze mature plants but young shoots are eaten without any apparent effect.” Potentially mildly toxic?	P & C (2001)	ML
Pest Animal
17. Food source to pests?	Not known as a food source to pest animals.		L
18. Provides harbor?	Not known to provide harbor.		L
Agriculture
19. Impact yield?	“Wild watsonia does not invade improved pastures or cultivated land and, therefore, is of little agricultural importance.” Little or no impact on yield.	P & C (2001)	L
20. Impact quality?	“Wild watsonia does not invade improved pastures or cultivated land and, therefore, is of little agricultural importance.” Little or no impact quality.	P & C (2001)	L
21. Affect land value?	“Wild watsonia does not invade improved pastures or cultivated land and, therefore, is of little agricultural importance.” Not likely to affect land value.	P & C (2001)	L
22. Change land use?	“Wild watsonia does not invade improved pastures or cultivated land and, therefore, is of little agricultural importance.” Change in land use not required.	P & C (2001)	L
23. Increase harvest costs?	Does not affect harvesting.		L
24. Disease host/vector?	None evident.		L