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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. |
Question | Comments | Rating | Confidence |
Recreation | |||
1. Restrict human access? | Leafy tufted annual to c. 20 cm high (Stajsic & Albrecht 1992). Would not restrict human access. | L | MH |
2. Reduce tourism? | Low growing species. Hansford (pers coms) had difficulty locating the plant in amongst the taller growing grasses. Unlikely to affect tourism; weed not obvious. | L | M |
3. Injurious to people? | No toxic or harmful properties described. Leaves are described as smooth to touch (Stajsic & Albrecht 1992). | L | MH |
4. Damage to cultural sites? | A low growing annual sedge. The infestation in Melbourne is described as, “…locally abundant over an area of about 0.1 ha,” (Stajsic & Albrecht 1992). Particularly dense infestations may produce a moderately negative visual effect at certain times of year, but would also depend upon the form of other coexisting species. | L | MH |
Abiotic | |||
5. Impact flow? | Within it native range it inhabits, “[d]amp places on the flats from Maitland to Kenilworth,” (Adamson & Salter 1950). Not occurring in-stream; does not affect water flow. | L | MH |
6. Impact water quality? | See comment in Q5 above. | L | MH |
7. Increase soil erosion? | A low growing annual species, which germinates in June and dies off in January (CRC 2003). Where it occurs in the northeast of Melbourne it coexists with a range of native and exotic grasses and sedges, and while it is recorded as being abundant in a small area of 0.1 ha (Stajsic & Albrecht 1992), it is not noted as a dominant species. As it occurs in seasonally moist or boggy areas it may contribute to soil erosion if it were to exist as the dominant species and leave areas of soil exposed to heavy rainfall or flooding. | ML | MH |
8. Reduce biomass? | Low growing annual. May displace some annual grasses. Little or no change to biomass. | ML | L |
9. Change fire regime? | In Melbourne as in its native range (Stajsic & Albrecht 1992, Bond & Goldblatt 1984), found in moist areas, which are unlikely to be fire prone or support hot fires. Low growing sedge, would produce little fuel to establish or support fire. No change to fire risk. | L | MH |
Community Habitat | |||
10. Impact on composition (a) high value EVC | EVC=Swampy riparian woodland (E); CMA=East Gippsland; Bioreg=East Gippsland Uplands; Climate=VH. The current infestation in Melbourne, Victoria, which has been present for over 12 years (Stajsic & Albrecht 1992) does not appear to be affecting what is already a highly disturbed area (public reserve). The grassland area it infests is mown regularly (Hansford, pers coms), yet the plant persists. In a natural ecosystem it may eventually establish a more dense population perhaps minimally displacing a dominant or indicator species in the lower stratum. Minor impact on the lowest layer | ML | M |
(b) medium value EVC | EVC=Swampy riparian woodland (D); CMA=Port Phillip; Bioreg=Highlands Southern Fall; H CLIMATE potential. See comment in q10(a) above. Impact may be reduced due to High CLIMATE match only. | ML | M |
(c) low value EVC | EVC=Riparian forest (D); CMA=Port Phillip; Bioreg=Highlands Southern Fall; H CLIMATE potential. See comment in q10(a) above. It appears to tolerate a high level of shading (see Invasiveness assessment) and would possibly establish and survive in more open riparian forest areas. Impact may be reduced due to High CLIMATE match only. | ML | M |
11. Impact on structure? | The current infestation in Melbourne, Victoria, which has been present for over 12 years (Stajsic & Albrecht 1992) does not appear to be affecting what is already a highly disturbed area (public reserve). The grassland area it infests is mown regularly (Hansford, pers coms), yet the plant persists. It may displace some annual grasses or forbs. Minor impact on the lowest layer | L | M |
12. Effect on threatened flora? | No data documented. | MH | L |
Fauna | |||
13. Effect on threatened fauna? | No data documented. | MH | L |
14. Effect on non-threatened fauna? | No data documented. | M | L |
15. Benefits fauna? | Palatability of species not documented. Assume provides little or no support for fauna. | H | L |
16. Injurious to fauna? | No harmful properties described. No thorns or prickles. | L | L |
Pest Animal | |||
17. Food source to pests? | Palatability of species not documented. Assume provides little or no support for pest animals. | L | L |
18. Provides harbor? | Small leafy annual herb (CRC 2003). Not likely to provide harbour for pest species. | L | M |
Agriculture | |||
19. Impact yield? | Not known anywhere as a weed of agriculture. Consider minimal affect. | L | L |
20. Impact quality? | Not known anywhere as a weed of agriculture. Consider minimal affect. | L | L |
21. Affect land value? | No | L | L |
22. Change land use? | No | L | L |
23. Increase harvest costs? | No | L | L |
24. Disease host/vector? | No documented evidence of this species being a host or vector for disease of agriculture. | L | L |