Impact Assessment - South African weed-orchid (Disa bracteata) 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 South African weed-orchid
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: South African weed-orchid
Scientific name: Disa bracteata
| Question | Comments | Rating | Confidence |
| Recreation | |||
| 1. Restrict human access? | Grows up to 50 cm tall (DNRE 2002). Weed would not restrict human access. | L | M |
| 2. Reduce tourism? | As the plant can out compete other species and is common in grassy paddocks and previously cleared areas (DNRE 2002), it is likely that the weeds would have a minor effect on the aesthetics of the land but would not inhibit activities. | ML | M |
| 3. Injurious to people? | Plant not documented to be injurious or toxic in any way. | L | M |
| 4. Damage to cultural sites? | Not known to occur at cultural sites. | L | M |
| Abiotic | |||
| 5. Impact flow? | Terrestrial species. | L | M |
| 6. Impact water quality? | Terrestrial species. | L | M |
| 7. Increase soil erosion? | The plant has tubers (1-3) and also fleshy side roots (DNRE 2002). Unlikely that the plant would contribute to soil erosion. | L | M |
| 8. Reduce biomass? | ‘Competes and excludes smaller indigenous flora including orchids, lilies and grasses’ (Muyt 2001). Biomass may increase. | L | MH |
| 9. Change fire regime? | Tuberous plant with fleshy stems (DNRE 2002) . Although deciduous, unlikely to change the frequency or intensity of fires. | L | M |
| Community Habitat | |||
| 10. Impact on composition (a) high value EVC | EVC=Herb-rich Foothill Forest (V); CMA=Glenelg-Hopkins; Bioreg=Victorian Volcanic Plain; CLIMATE potential=VH. ‘Competes and excludes smaller indigenous flora including orchids, lilies and grasses’ (Muyt 2001). Major displacement of some dominant species in the lower strata. | MH | MH |
| (b) medium value EVC | EVC=Herb-rich Foothill Forest (D); CMA=Glenelg-Hopkins; Bioreg=Victorian Volcanic Plain; CLIMATE potential=VH. ‘Competes and excludes smaller indigenous flora including orchids, lilies and grasses’ (Muyt 2001). Major displacement of some dominant species in the lower strata. | MH | MH |
| (c) low value EVC | EVC=Lowland Forest (LC); CMA=Glenelg-Hopkins; Bioreg=Victorian Volcanic Plain; CLIMATE potential=VH. ‘Competes and excludes smaller indigenous flora including orchids, lilies and grasses’ (Muyt 2001). Major displacement of some dominant species in the lower strata. | MH | MH |
| 11. Impact on structure? | ‘Competes and excludes smaller indigenous flora including orchids, lilies and grasses’ (Muyt 2001). Likely to have a major effect on the lower strata. | MH | MH |
| 12. Effect on threatened flora? | In South Australia ‘Monadenia bracteata has already been found in the close vicinity of nationally declared rare and endangered species such as Psoralea parva (small scurf-pea) and Drosera praefolia (Tepper’s sundew) (Prescott 1997). In Victoria, D. bracteata has been found in several locations including the Victorian Volcanic Plains, where threatened flora such as basalt greenhood and tough scurf pea exist (DPI 2003). | H | M |
| Fauna | |||
| 13. Effect on threatened fauna? | This species is not documented as posing an additional risk to threatened fauna. | MH | L |
| 14. Effect on non-threatened fauna? | Not documented to have an effect on fauna spp. | L | M |
| 15. Benefits fauna? | Not known to benefit fauna. | L | M |
| 16. Injurious to fauna? | Not known to be injurious to fauna. | L | M |
| Pest Animal | |||
| 17. Food source to pests? | Plant not known to be a food source to pests. | L | M |
| 18. Provides harbour? | Plant not known to provide harbour for pets species. | L | M |
| Agriculture | |||
| 19. Impact yield? | Not a weed of agriculture. | L | M |
| 20. Impact quality? | Not a weed of agriculture. | L | M |
| 21. Affect land value? | Weed not known to affect land value. | L | M |
| 22. Change land use? | Weed not documented to cause a change in priority of land use. | L | M |
| 23. Increase harvest costs? | Not a weed of agriculture. | L | M |
| 24. Disease host/vector? | Not a known host or vector for diseases of agriculture. | L | M |
This table can also be viewed as a PDF document (printer friendly).
Impact Assessment Record - South African Weed-orchid (PDF - 44 KB)
Impact Assessment Record - South African Weed-orchid (DOC - 125 KB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
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