Impact Assessment - Lagarosiphon (Lagarosiphon major) 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?	Aquatic species. Does not affect human access on land.	P & C (2001)	L
2. Reduce tourism?	An “aggressive freshwater weed,” it may affect some recreational activities such as swimming or boating.	P & C (2001)	MH
3. Injurious to people?	The physical properties of the plant are not harmful to humans, however, “it has the ability to accumulate considerable amounts of arsenic from the surrounding medium.” Tests conducted on sheep in New Zealand revealed the arsenic does not pose a serious threat to health.	P & C (2001) Lancaster et al1	L
4. Damage to cultural sites?	“in spite of one of its common names, oxygen weed, in a dense infestation of Lagarosiphon major there often is less oxygen present than in the surrounding water: thus dense infestations, ‘in such quantities confer no oxygen benefit on fish and other animals in the lake’.” Potential to obliterate the historic/cultural feature.	Ramey (2001)1	H
Abiotic
5. Impact flow?	Establishes in slow-moving streams and, “…in sheltered areas protected from wind and waves…it forms dense stands which impede water flow.” Major impact on subsurface flow.	P & C (2001)	MH
6. Impact water quality?	It, “interferes with water utilisation and shades out other plants.” “Heavy infestations of Lagarosiphon deplete oxygen levels in water, killing fish.” High effect on dissolved O2 levels.	P & C (2001)	H
7. Increase soil erosion?	Aquatic species.		L
8. Reduce biomass?	Dense stands would significantly increase biomass.	P & C (2001)	L
9. Change fire regime?	Aquatic species.		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?	“can form a light-blocking canopy so dense and thick (3 feet thick) that Lagarosiphon major easily out competes even tall non-canopy forming native species.” "Lagarosiphon major successfully out-competed native species wherever it has colonised New Zealand lakes in the depth zone 2-6 m--normally occupied by native milfoils (Myriophyllum spp.) and pondweeds (Potamogeton spp.)." Would have a major impact on the floral strata in aquatic situations.	Ramey (2001)	H
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“Heavy infestations of Lagarosiphon deplete oxygen levels in water, killing fish.” Its presence may also impact on waterbirds. Serious reduction in habitat.	P & C (2001)	MH
15. Benefits fauna?	No known benefits.		H
16. Injurious to fauna?	“it has the ability to accumulate considerable amounts of arsenic from the surrounding medium.” Tests conducted on sheep in New Zealand revealed the arsenic does not pose a serious threat to health. Unlikely to affect native fauna.	Lancaster et al	L
Pest Animal
17. Food source to pests?	In New Zealand, grass carp (Ctenopharyngodon idella) readily ate the plant in feeding trials. However, this species does not occur in Victoria.	Edwards (1974)	L
18. Provides harbour?	No		L
Agriculture
19. Impact yield?	Aquatic species.		L
20. Impact quality?	Aquatic species.		L
21. Affect land value?	Aquatic species.		L
22. Change land use?	Aquatic species.		L
23. Increase harvest costs?	Aquatic species.		L
24. Disease host/vector?	None evident.		L