Impact Assessment - St John's wort (Hypericum perforatum) 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 30 to 70 cm high.” Minimal or negligible impact.	P & C (2001)	L
2. Reduce tourism?	“St John’s wort forms extensive infestations excluding most other ground-flora.” Minor effects to aesthetics.	Muyt (2001)	ML
3. Injurious to people?	It can cause, “a contact rash in some people.” Mildly toxic.	P & C (2001)	ML
4. Damage to cultural sites?	“St John’s wort forms extensive infestations excluding most other ground-flora.” Likely to have a moderate negative visual effect.	Muyt (2001)	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?	“Main roots are stout and extend to 1 m deep.” “St John’s wort forms extensive infestations excluding most other ground-flora.” Unlikely to contribute to soil erosion.	P & C (2001) Muyt (2001)	L
8. Reduce biomass?	“It is considered to be a weed when it invades poorly managed grazing land, sparse bushland, roadsides, and neglected areas.” Dense infestations are likely to increase biomass.	P & C (2001)	L
9. Change fire regime?	“In late summer, the dry stems constitute a fire hazard in forest areas.” Moderate increase in the frequency of fire risk.	P & C (2001)	ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=West Gippsland; Bioreg=Gippsland Plain; VH CLIMATE potential. “St John’s wort forms extensive infestations excluding most other ground-flora and seriously impeding overstorey recruitment.” Major displacement of some species within different strata.	Muyt (2001)	MH
(b) medium value EVC	EVC=Grassy dry forest (D); CMA=Goulburn Broken; Bioreg=Central Victorian Uplands; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	MH
(c) low value EVC	EVC=Shrubby foothill forest (LC); CMA=Port Phillip; Bioreg=Central Victorian Uplands; VH CLIMATE potential. Impact as in 10(a) above.	Muyt (2001)	MH
11. Impact on structure?	“St John’s wort forms extensive infestations excluding most other ground-flora and seriously impeding overstorey recruitment.” Major effect on 20% of the floral strata. Minor effect on shrubs	Muyt (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“It is invasive in various native habitats including grasslands, grassy woodlands and forests, with the largest infestations in north-east Victoria and southern and central NSW. St John’s Wort forms extensive infestations excluding most other ground-flora and seriously impeding overstorey recruitment.” The plant is poisonous which can lead to loss of condition and eventually death. UNKNOWN	Muyt (2001)	M
15. Benefits fauna?	No benefits		H
16. Injurious to fauna?	“St John’s wort contains hypericin, which causes photosensitisation in any mammals that ingest it resulting in blisters on weakly pigmented parts of exposed skin.” UNKNOWN	Blood (2001)	M
Pest Animal
17. Food source to pests?	Not known as a food source to pest.		L
18. Provides harbor?	Not known to provide harbor for pest animals.		L
Agriculture
19. Impact yield?	“In pastures, H. perforatum is a weed because it replaces useful vegetation to an extent that can lead to the abandonment of formerly productive areas.” The plant, “reduces milk yield and causes abortions in animals.”	Groves et al (1995) P & C (2001)	H
20. Impact quality?	Not known to affect quality of agricultural production.		L
21. Affect land value?	“In pastures, H. perforatum is a weed because it replaces useful vegetation to an extent that can lead to the abandonment of formerly productive areas.” Land value may be reduced significantly if no longer available for agriculture. Unknown – or minimal impact on land values	Groves et al (1995)	L
22. Change land use?	In pastures, the plant can be readily controlled. “The greatest competition to the weed is provided by a mixture of subterranean clover and phalaris when sown on a prepared fallow. The developing pasture should be left ungrazed in the first year to allow the subterranean clover maximum chance to smother the St John’s wort.” Pasture is temporarily unavailable for grazing, however, no serious or permanent alteration of agricultural activity.	P & C (2001)	ML
23. Increase harvest costs?	Not known to affect harvest costs.		L
24. Disease host/vector?	None evident.		L