Impact Assessment - Tangled hypericum (Hypericum triquetrifolium) 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 with tangled branches, to 45 cm high.” In dense patches, it may me somewhat of a nuisance due to the tangled branches.	P & C (2001)	ML
2. Reduce tourism?	Infestation densities not documented. “It is very competitive.” Dense patches my have a minor effect on aesthetics.	P & C (2001)	ML
3. Injurious to people?	Not known to be injurious to humans. However, as with H. perforatum, the plant may cause a contact rash in some people.	P & C (2001)	ML
4. Damage to cultural sites?	Dense infestations may create a moderate 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?	A perennial plant with deep vertical roots and horizontal rhizomes, it would improve soil stability. “It is very competitive and, where established in Victoria, it has eliminated most other vegetation.” Aerial growth dies off in summer no doubt leaving bare ground. Surface soil potentially affected by erosion where large patches occur.	P & C (2001)	ML
8. Reduce biomass?	“In Australia, it has very limited occurrence as a weed of open woodlands encroaching onto grazing land.” As it is very competitive, biomass may reduce slightly.	P & C (2001)	MH
9. Change fire regime?	No data available; assume little change to fire regime.		L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Grassy woodland (E); CMA=North Central; Bioreg=Goldfields; VH CLIMATE potential. “It is very competitive and, where established in Victoria, it has eliminated most other vegetation.” Small (2 ha), isolated infestation in Victoria. Contained and possibly kept in check by control efforts. Potential to affect all strata.	P & C (2001)	MH
(b) medium value EVC	EVC=Grassy dry forest (E); CMA=North Central; Bioreg=Goldfields; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	MH
(c) low value EVC	EVC=Riparian forest (E); CMA=North East; Bioreg=Highlands – Northern Fall; VH/H CLIMATE potential. Similar impact to 10(a) above. However, high CLIMATE potential only may restrict infestation.	P & C (2001)	MH/ML
11. Impact on structure?	“It is very competitive and, where established in Victoria, it has eliminated most other vegetation.” Invades similar habitats to H. perforatum. Potential to have a major effect on <60% of the floral strata.	P & C (2001)	MH
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	Considering its competitive nature, dense patches may reduce available fodder for fauna species.		ML
15. Benefits fauna?	No known benefits		H
16. Injurious to fauna?	Like H. perforatum, the plant contains hypericin, which causes photosensitivity in grazing animals.	Petazzi et al1	H
Pest Animal
17. Food source to pests?	Not known as a food source to pests.		L
18. Provides harbor?	Not known to provide harbour.		L
Agriculture
19. Impact yield?	“It is very competitive and, where established in Victoria, it has eliminated most other vegetation.” Potentially similar impact to H. perforatum by replacing useful vegetation. Additionally, as the plant contains hypericin, some stock losses may be indicated.	P & C (2001)	MH
20. Impact quality?	Not known to affect the quality of agricultural produce.		L
21. Affect land value?	Currently small (2 ha), isolated patch in Victoria. However, it is poisonous to stock and is very competitive. If it were to establish, land values may be affected.		M
22. Change land use?	No documented evidence to suggest land use would change.		L
23. Increase harvest costs?	“…in eastern Europe and the Mediterranean region [it] is considered a weed in orchards, vineyards and field crops.” The tangled branches of the plant may affect harvesting some crops. Potential increase in time taken to harvest.	P & C (2001)	M
24. Disease host/vector?	None evident		L