Impact Assessment - Water hyacinth (Eichhornia crassipes) 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 aquatic species, it does not restrict human access on land.	P & C (2001)	L
2. Reduce tourism?	“When densely established, water hyacinth makes swimming and pleasure boating impossible.” Major impact on recreation.	P & C (2001)	H
3. Injurious to people?	No toxic properties, however, infestations provide ideal breeding sites for mosquitoes and other animal vectors. “Decaying plants make water putrid and unfit for drinking by humans or animals.” Potentially harmful associations.	P & C (2001)	H
4. Damage to cultural sites?	“Floating rafts can be up to 1 metre deep and, in Florida, have become so large that wooden railway bridges are pushed over.” Potential threat to European cultural structures.	P & C (2001)	H
Abiotic
5. Impact flow?	“Water hyacinth chokes waterways reducing flow.” Minor impact on surface flow due to free-floating aquatics.	P & C (2001)	ML
6. Impact water quality?	“Dense growth removes considerable oxygen from water which, affecting the health of fish.” Moderate effect on O2 level.	P & C (2001)	MH
7. Increase soil erosion?	Aquatic species.	P & C (2001)	L
8. Reduce biomass?	Biomass significantly increased.		L
9. Change fire regime?	Aquatic species.	P & C (2001)	L
Community Habitat
10. Impact on composition (a) high value EVC	Aquatic species		L
(b) medium value EVC	Aquatic species		L
(c) low value EVC	Aquatic species		L
11. Impact on structure?	“Dense mats exclude other aquatic plants.” “In its native range, E. crassipes may be part of a mixed community of floating and emergent plants or grow as a monoculture.”	Muyt (2001) Groves et al (1995)	H
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“Dense mats…destroy habitat for native invertebrates, fish and birds.” Habitat changed dramatically.	Muyt (2001)	H
15. Benefits fauna?	No known benefits.		H
16. Injurious to fauna?	Not toxic.		L
Pest Animal
17. Food source to pests?	“Dense mats…destroy habitat for native invertebrates, fish and birds.” Habitat changed dramatically.	Muyt (2001)	H
18. Provides harbor?	No known benefits.		H
Agriculture
19. Impact yield?	“Losses are staggering, for example, in the Indian State of West Bengal, it causes an annual loss of paddy rice valued at 110 million rupees.” Serious potential to affect irrigated crops in Victoria.	P & C (2001)	H
20. Impact quality?	Aquatic species.	P & C (2001)	L
21. Affect land value?	In areas using irrigation, land values may be seriously affected. (See Q19 above.)		H
22. Change land use?	If water is not available for irrigation, infestations may lead to land being unusable for some agricultural activities. (See Q19 above.)		H
23. Increase harvest costs?	Does not affect harvest costs.		L
24. Disease host/vector?	“…water hyacinth has been reported to be an alternative host for the Asian corn borer, Ostrinia furnacalis Guenee and the rice root nematode, Hirschmanniella oryzae (van Breda de Haan) Luc and Goody.”	Groves et al (1995)	H

Impact Assessment Record - Water hyacinth (PDF - 30KB)
Impact Assessment Record - Water hyacinth (DOC - 58KB)
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