Impact Assessment - Uruguayan rice grass (Piptochaetium montevidense) in Victoria
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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.
| Each resource attribute, or criterion, is assessed relative to a list of intensity ratings. Depending upon information found in relation to each criterion, a rating of Low, Medium Low, Medium High or High is assigned. Descriptions of the impact criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the impact of Uruguayan rice grass
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
Common Name: Uruguayan rice grass
Scientific name: Piptochaetium montevidense
| Question | Comments | Rating | Confidence |
| Recreation | |||
| 1. Restrict human access? | “Forms dense tussocks to about 0.5 m high” (CRC Weed Management, 2003), which would not restrict human access. | L | MH |
| 2. Reduce tourism? | “can be difficult to identify because of its similarity to native grasses and Austrostipa species” (CRC Weed Management, 2003). This weed would not be obvious to the average visitor. | L | MH |
| 3. Injurious to people? | “The leaf blade is hairless but covered with minute rough protections” (CRC Weed Management, 2003), although these are not noted as sharp and so not likely to cause injury. | L | MH |
| 4. Damage to cultural sites? | See Q. 2, as a “native-looking” grass, this species would not detract from cultural sites, nor damage structures. | L | MH |
| Abiotic | |||
| 5. Impact flow? | Whilst this plant does invade streambanks (CRC Weed Management, 2003), the only documented occurrence in wet environments was in seasonally flooded, or “always” moist areas, rather than permanent waterways. This makes it unlikely to impact on water flow. | L | H |
| 6. Impact water quality? | See Q. 5, unlikely to impact on water quality. | L | H |
| 7. Increase soil erosion? | As “a perennial that forms tussocks” (CRC Weed Management, 2003), this plant should not increase erosion as it would not cause patches of exposed bare soil as dormant or annual species might. | L | MH |
| 8. Reduce biomass? | Similar habit to the dominant kangaroo grass (Themeda triandra) that it was found invading near Altona (CRC Weed Management, 2003; Albrecht et al (eds), 1991). Likely to replace tussock biomass in the grassland communities that it invades. | ML | MH |
| 9. Change fire regime? | As it is similar in habit to the vegetation that it displaces (see Q. 8) and “stimulated by fire” (CRC Weed Management, 2003) this plant is unlikely to change the fire regime in the communities that it invades. | L | MH |
| Community Habitat | |||
| 10. Impact on composition (a) high value EVC | EVC= Plain grassy woodland (E); CMA=Corangamite; Bioreg= Victorian Volcanic Plain; CLIMATE potential=VH. Formed a “dense sward” (Cunningham et al, 2003) where it invaded grassland in Victoria. Major displacement of some dominant species in the groundcover layer. | MH | H |
| (b) medium value EVC | EVC= Lowland Forest (D); CMA=Corangamite; Bioreg= Otway Plain; CLIMATE potential=VH. Formed a “dense sward” (Cunningham et al, 2003) where it invaded grassland in Victoria, however the forest canopy would be likely to reduce its density. Minor displacement of some dominant species in the groundcover layer. | ML | H |
| (c) low value EVC | EVC= Lowland Forest (LC); CMA=Glenelg Hopkins; Bioreg= Warrnambool Plain; CLIMATE potential=VH. Formed a “dense sward” (Cunningham et al, 2003) where it invaded grassland in Victoria, however the forest canopy would be likely to reduce its density. Minor displacement of some dominant species in the groundcover layer. | ML | H |
| 11. Impact on structure? | Formed a “dense sward” (Cunningham et al, 2003) where it invaded grassland in Victoria. It has the potential to have a major impact on ground flora. Its ability to affect the germination of flora from other strata is not known. | MH | H |
| 12. Effect on threatened flora? | No Information found. | MH | L |
| Fauna | |||
| 13. Effect on threatened fauna? | No Information found. | MH | L |
| 14. Effect on non-threatened fauna? | Has the potential to reduce the availability of ground flora as fodder (see Q. 11.) and is “resistant to grazing” so could reduce food sources where it invades, forcing some species to forage elsewhere. | MH | MH |
| 15. Benefits fauna? | See Q.14- would provide little food for desirable species. | MH | MH |
| 16. Injurious to fauna? | Despite its resemblance and close association to Chilean needle grass, the seeds on this grass are not sharp and barbed (see illustration CRC Weed Management, 2003). Not noted for toxicity. | L | MH |
| Pest Animal | |||
| 17. Food source to pests? | “Resistant to grazing” (CRC Weed Management, 2003) so not likely to provide a significant food source to pests. | L | MH |
| 18. Provides harbour? | As a perennial that “forms dense tussocks to about 0.5 m high,” (CRC Weed Management, 2003) this grass may provide harbour for entrances to rabbit warrens. | MH | MH |
| Agriculture | |||
| 19. Impact yield? | In Argentina this plant is a dominant understorey to Chilean needle grass and serrated tussock (David Maclaren, pers. comm.) indicating that it has the potential to form a significant component of invaded grassland. As a grassland invader that is resistant to grazing (CRC Weed Management, 2003), this tussock may displace stock fodder, reducing the carrying capacity of the land. The degree of impact is unknown, so a medium value was chosen. | M | L |
| 20. Impact quality? | Despite its resemblance and close association to Chilean needle grass, the seeds on this grass are not sharp and barbed (see illustration CRC Weed Management, 2003), so it doesn’t pose a meat contamination risk. The plant “will grow in crops” (CRC Weed Management, 2003) however, which may impact quality, however, again the degree of impact is unknown, so a medium value was chosen. | M | L |
| 21. Affect land value? | Affect on land value will depend on level of infestation and ease of control, both of which are unknowns for this species. | M | L |
| 22. Change land use? | Change in land use may occur if the carrying capacity of pasture is significantly reduced or if crop quality is too badly affected. Without any indication of the potential degree of impact, a medium value was chosen. | M | L |
| 23. Increase harvest costs? | Harvest costs may be increased if a large degree of weed control is necessary. | M | L |
| 24. Disease host/vector? | Not known as a disease host or vector, however there is not much information about this species. | L | L |
Impact Assessment Record - Uruguayan rice grass (PDF - 23KB)
Impact Assessment Record - Uruguayan rice grass (DOC - 64KB)
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