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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? | Grows up to 500 mm. Although found around creeks unlikely that the weed would impede access (CRC for Australian Weed Management 2003). Minimal or negligible impact. | L | M |
2. Reduce tourism? | Due to the areas the weed is known to grow (around creeks, agricultural areas) (CRC for Australian Weed Management 2003), weeds would not be obvious to the ‘average’ visitor. | L | M |
3. Injurious to people? | Weeds not known to be injurious to people. | L | M |
4. Damage to cultural sites? | Weeds not known to occur on cultural sites. | L | M |
Abiotic | |||
5. Impact flow? | Terrestrial species. | L | M |
6. Impact water quality? | Terrestrial species. | L | M |
7. Increase soil erosion? | Evergreen plant. ‘Roots are fibrous and the plant has an extensive rhizome system’ (CRC for Australian Weed Management 2003). Low probability of large scale soil movement. | L | M |
8. Reduce biomass? | Shows preference for damp open areas and rocky outcrops (CRC for Australian Weed Management 2003). Likely that the biomass would increase. | L | M |
9. Change fire regime? | Weed tends to grow in riparian areas. Unlikely that the weed would have any effect on fire risk. | L | M |
Community Habitat | |||
10. Impact on composition (a) high value EVC | EVC= Parilla Mallee (E); CMA=Mallee; Bioreg=Lowan Mallee; CLIMATE potential=H. Impact unknown. | M | L |
(b) medium value EVC | EVC= Grassy Riverine Forest (D); CMA=Mallee; Bioreg=Lowan Mallee; CLIMATE potential=H. Impact unknown. | M | L |
(c) low value EVC | EVC= Dune Field Heathland (LC); CMA=Mallee; Bioreg=Lowan Mallee; CLIMATE potential=H. Impact unknown. | M | L |
11. Impact on structure? | ‘Shows a preference for damp open areas or rock outcrops.’ In the Blue Mountains, it ‘grows beneath an overstorey of eucalypt along Yosemite Creek but will also grow in full-sun environments’ (CRC for Australian Weed Management 2003). Likely to have at least a minor impact on the lower stratum. | ML | M |
12. Effect on threatened flora? | No information available. | MH | L |
Fauna | |||
13. Effect on threatened fauna? | No information available. | MH | L |
14. Effect on non-threatened fauna? | No documented evidence that the weed has an effect on non-threatened fauna species. | L | M |
15. Benefits fauna? | Not known to provide benefits to indigenous fauna. | H | M |
16. Injurious to fauna? | Not known to be toxic to fauna. | L | M |
Pest Animal | |||
17. Food source to pests? | Not a known food source to pest animal species. | L | M |
18. Provides harbor? | Not known to provide harbour for pest species. | L | M |
Agriculture | |||
19. Impact yield? | ‘..has become a significant weed of crops of the East African highlands, in particular Kenya… seen as a potential threat to Australia’s environment and agricultural productivity’. ‘..locally common and important as a weed of crops in the highlands [of Kenya and Tanzania]’ (CRC for Australian Weed Management 2003). Insufficient information available to determine the extent of impact. Score medium. | M | M |
20. Impact quality? | No evidence to suggest that this weed would impact upon the quality of crops. | L | M |
21. Affect land value? | Not known to affect the value of land. | L | M |
22. Change land use? | Weed not documented to cause a change in priority of land use. | L | M |
23. Increase harvest costs? | No documented evidence to suggest that the weed increases the cost of harvest. | L | M |
24. Disease host/vector? | Not a known host or vector for disease. | L | M |