Impact Assessment - St Peter's wort (Hypericum tetrapterum) 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, to 1 m high. It is usually confined to moist areas adjacent to streams, swamps etc., from which it encroaches into moist pastures. The weed forms very dense stands and appears to be as strongly competitive as St John’s wort.” Its presence beside the banks of waterways may impede individual access.	P & C (2001)	ML
2. Reduce tourism?	It is usually confined to moist areas adjacent to streams, swamps etc. from which it encroaches into moist pastures. The weed forms very dense stands and appears to be as strongly competitive as St John’s wort.” Some water-based recreational activities may be affected due to access restrictions.	P & C (2001)	ML
3. Injurious to people?	Not documented to be toxic.		L
4. Damage to cultural sites?	Dense patches may create a moderated negative visual impact in cultural sites.		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?	“Extensive roots, no distinct taproot, numerous rhizomes.” As a perennial, it is unlikely to contribute to soil erosion.	P & C (2001)	L
8. Reduce biomass?	Plants grow to 1 metre high, and can form very dense stands. Biomass may increase.		L
9. Change fire regime?	Life cycle, “appears to be similar to that of St John’s wort.” Dead flower stems remain standing for some years; potential to increase the frequency of fire risk.	P & C (2001)	ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Creekline grassy woodland (E); CMA=Goulburn Broken; Bioreg=Victorian Riverina; VH CLIMATE potential. Medium to large populations in rare or localised infestations. Can form dense stands. Similar impact to St John’s wort. Mostly occurs close to water. Potential for major displacement of ground covers.	Carr et al (1992) P & C (2001)	MH
(b) medium value EVC	EVC=Riverine grassy woodland (E); CMA=Goulburn Broken; Bioreg=Victorian Riverina; VH CLIMATE potential. Impact as in 10(a) above.	Carr et al (1992) P & C (2001)	MH
(c) low value EVC	EVC=Moira Plain wetland (E); CMA=Goulburn Broken; Bioreg=Murray Fans; VH CLIMATE potential. Impact as in 10(a) above.	Carr et al (1992) P & C (2001)	MH
11. Impact on structure?	“The weed forms very dense stands and appears to be as strongly competitive as St John’s wort. To date, it only occurs close to water.” It occurs in medium to large populations (though only in rare or localised infestations in riparian vegetation). Potential to have a major effect on lower infested area.	P & C (2001) Carr et al (1992)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	It occurs in medium to large populations in rare or localised infestations, predominantly in riparian vegetation. Minor impact on fauna species.	Carr et al (1992)	ML
15. Benefits fauna?	No known benefits.		H
16. Injurious to fauna?	“St Peter’s wort is believed to be poisonous to stock and to cause photosensitisation similar to St John’s wort, but the infestations in Victoria are so limited that this has not been observed in the field.” Potentially harmful.	P & C (2001)	MH
Pest Animal
17. Food source to pests?	Not known as a food source to pests		L
18. Provides harbor?	Not known to provide harbor for pest animals.		L
Agriculture
19. Impact yield?	It can encroach into moist pastures, but its impact is not documented.	P & C (2001)	L
20. Impact quality?	No documented impact on agricultural quality.		L
21. Affect land value?	Not a weed of agriculture. Does not affect land value.		L
22. Change land use?	Not a weed of agriculture. Land use not affected.		L
23. Increase harvest costs?	Not a weed of agriculture.		L
24. Disease host/vector?	None evident.		L

Impact Assessment Record - St Peter's wort (PDF - 31KB)
Impact Assessment Record - St Peter's wort (DOC - 59KB)
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