Impact Assessment - African feather grass (Pennisetum macrourum) in Victoria (Nox)

Back | Table | Feedback

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?	“Perennial grass generally 1 to 1.8 m high.” “…dense growth…prevents access to streams.”	P & C (2001)	MH
2. Reduce tourism?	With a capacity to invade “riparian vegetation and freshwater wetlands,” the plant would have a major impact on visitor activities to these areas.	Blood (2001)	MH
3. Injurious to people?	No recorded toxic properties.		L
4. Damage to cultural sites?	Noticeable presence of infestation, but as a shade intolerant grass it is unlikely to affect cultural structures or features.	Blood (2001)	ML
Abiotic
5. Impact flow?	In Tasmania, “Large plants are also capable of totally blocking waterways and channels by trapping silt and debris.”	DPIWE (Tas) (2002) 1	H
6. Impact water quality?	No known effect on water quality. However, with the potential to block waterways and channels, P. macrourum would negatively affect water quality.	DPIWE (Tas) (2002)	ML
7. Increase soil erosion?	“Perennial grass with fibrous roots extensive, to depth of 1 m. Stout rhizomes to 2 m long.” Unlikely to cause soil erosion.	Blood (2001)	L
8. Reduce biomass?	“Weed of lowland grassland and grassy woodland.” Potential to suppress overstorey regeneration in grassy woodland areas. Biomass would likely decrease slightly.	Blood (2001) Carr et al. (1992)	MH
9. Change fire regime?	“Dense infestations are a fire hazard.”	DNRE (1998) 2	H
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=Glenelg Hopkins; Bioreg=Goldfields; VH CLIMATE potential Invades lowland grassland & grassy woodland, riparian vegetation and seasonal freshwater wetland. When occurring in, “…dense clumps…[it] virtually eliminates all other plants. Plants dislike shading and rarely establish under forest canopies.” Major displacement of grass species.	P & C (2001)	MH
(b) medium value EVC	EVC=Sedge-rich wetlands (D); CMA=Glenelg Hopkins; Bioreg=Greater Grampians; VH CLIMATE potential. It is recorded in Carr, et al. (1992) as occurring in freshwater wetland (seasonal) and it usually occurs in medium to large populations. Assume major displacement of grasses/forbs	Carr, et al. (1992)	MH
(c) low value EVC	Not a significant weed in low value EVCs. Mostly occurs in endangered grassland situations.		L
11. Impact on structure?	When occurring in, “…dense clumps…[it] virtually eliminates all other plants.” Occurs in open grasslands; affects grass and forbs.	P & C (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“…under suitable conditions strong growth produces dense clumps within a few years.” Low palatability may result in reduced food source for non-threatened fauna.	P & C (2001)	ML
15. Benefits fauna?	See comment in Q16 above. Provides little support. “…leaves have low palatability (for stock).”	P & C (2001)	H
16. Injurious to fauna?	No known toxic or hazardous effects.		L
Pest Animal
17. Food source to pests?	Not known as a food source for pest animals.		L
18. Provides harbor?	“dense growth provides harbor for rabbits.”	P & C (2001)	H
Agriculture
19. Impact yield?	“once established, improving the pasture alone does not control (the weed).” “under suitable conditions,…dense clumps virtually eliminate all other plants.” Has affected softwood industry in Casterton, Victoria.	P & C (2001) 3	H
20. Impact quality?	“Because of their bristles, seeds are equipped to cling to the wool and hair of animals.” Potential to reduce the quality of wool.	P & C (2001)	MH
21. Affect land value?	With the potential to dominate in pasture grasses, grazing land could be seriously affected by price reduction due to low palatability of plant.	P & C (2001)	H
22. Change land use?	Infested areas unusable for grazing purposes without significant control activities. “…once the weed is established, improving the pasture alone does not control it.” Where dense infestations occur in pastures, the land use would need to be changed. e.g. agroforestry. “Requires full sun: rarely will a dense infestation occur within a shady bushland environment.”	P & C (2001) DPIWE (Tas) (2002)	H
23. Increase harvest costs?	No known effect on harvesting costs. It is predominantly a weed of pasture, not cropping. (Cultivation is effective in controlling the plant.)	P & C (2001)	L
24. Disease host/vector?	Not evident.		L