Impact Assessment - Prairie ground cherry (Physalis viscosa) 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 25 cm to 60 cm high. It would not restrict human access.	P & C (2001)	L
2. Reduce tourism?	A summer growing plant of open grazing land, its presence would not affect tourism. Dense patches may create a negative visual effect.	P & C (2001)	ML
3. Injurious to people?	No	P & C (2001)	L
4. Damage to cultural sites?	Dense patches may create a moderate negative visual impact. More on agricultural land that has been cultivated		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?	Occurs in open grazing land. Perennial roots are deep and extensive. Not likely to contribute to soil erosion.	P & C (2001)	L
8. Reduce biomass?	Invader replaces biomass.		ML
9. Change fire regime?	Aerial growth dies in autumn. Little material left to establish or support fire. Green in summer		L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassland (E); CMA=Goulburn Broken; Bioreg=Victorian Riverina; VH CLIMATE potential. Occurs on open grazing land where it can form dense patches. Major impact on grasses/forbs. Possible Minor impacts as lots of space around plants	GMLN (1999)1	ML
(b) medium value EVC	Most commonly found in open grassland or disturbed situations. Does not appear likely to occur in medium value EVCs. (Possible Minor impacts as lots of space around plants )	GMLN (1999)	(ML)
(c) low value EVC	Most commonly found in open grassland or disturbed situations. Does not appear likely to occur in low value EVCs.	GMLN (1999)	L
11. Impact on structure?	“It is a perennial herb that is very invasive, forming dense coverages in pastures, crops and roadsides.” Likely to have a major impact on ground flora. 20 – 60%	GMLN (1999)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“…forming dense coverages in pastures, crops and roadsides.” In natural ecosystems, its presence would reduce available fodder for native species.	GMLN (1999)	ML
15. Benefits fauna?	No known benefits		H
16. Injurious to fauna?	“Prairie ground cherry is suspected of being poisonous but the foliage is rarely eaten by stock, however, sheep readily eat the ripe fruit, apparently without ill effect.” Not considered injurious.	P & C (2001)	L
Pest Animal
17. Food source to pests?	“The fruit is eaten by birds and foxes.”	P & C (2001)	H
18. Provides harbour?	“Aerial growth dies in autumn.” During summer it may provide limited harbour to minor pest species such as rodents.- not really dense enough to provide cover	P & C (2001)	L
Agriculture
19. Impact yield?	“…forms dense coverages in pastures and crops…reduces stock summer carrying capacities.” Likely to have a major impact on yield.	GMLN (1999)	MH
20. Impact quality?	“The distribution of hay cut from infested areas is an important means of dispersal.” Contaminated product may be unsuitable for sale. Original infestation in the Goulburn Valley of Victoria was through contaminated lucerne seed. Grain quality maybe reduced through water competition with PGC.	P & C (2001)	H
21. Affect land value?	Because of the deep root system control by cultivation is not effective. Chemical controls, while effective, are expensive over large areas. Due to persistence of the weed and its impact on both pastures and cropping, its presence may reduce land value. Not fussed	P & C (2001)	L
22. Change land use?	Land use could continue, though with reduced agricultural return.		M
23. Increase harvest costs?	“It interferes with crop harvesting.”	GMLN (1999)	M
24. Disease host/vector?	“Closely related species are known hosts of virus diseases affecting tomatoes in the United States but similar problems are not known in Australia.”	P & C (2001)	L