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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? | A much branched, spiny herb with stems 30 to 60 cm long and well developed spines (Parsons & Cuthbertson 2002). Can occur in coastal sand dunes. May impede individual access. | ML | MH |
2. Reduce tourism? | Ornamental foliage (Parsons & Cuthbertson 2002). Can smother ground cover and occur in some recreational areas. Plant may have minor effect on aesthetics and inhibit some recreational activities. | ML | MH |
3. Injurious to people? | Plant has ‘well developed spines 5 to 10 mm long’ (Parsons & Cuthbertson 2002). Spines at most times of the year. | ML | MH |
4. Damage to cultural sites? | Ornamental foliage and can smother ground cover (Parsons & Cuthbertson 2002). May have moderate visual effect if occurs at cultural sites. | ML | MH |
Abiotic | |||
5. Impact flow? | Terrestrial species (Parsons & Cuthbertson 2002). | L | MH |
6. Impact water quality? | Terrestrial species (Parsons & Cuthbertson 2002). | L | MH |
7. Increase soil erosion? | Thick mat of tuberous roots. Plant doesn’t die back and leave bare soil exposed. (Parsons & Cuthbertson 2002). May help to bind soil. Low probability of large scale soil movement. | L | MH |
8. Reduce biomass? | ‘Smothers ground cover and can prevent regeneration of canopy species’ (Parsons & Cuthbertson 2002), but also produces a large mass of underground tubers (Vivian-Smith et al. 2006). The large underground biomass is likely to increase biomass. | L | MH |
9. Change fire regime? | The mass of underground organs completely suppresses other species (Parsons & Cuthbertson 2002), however flammability of this plant is unknown. Insufficient evidence to determine whether plant may alter fire regime. | M | L |
Community Habitat | |||
10. Impact on composition (a) high value EVC | EVC=Valley Grassy Forest (BCS =V); CMA=Glenelg Hopkins; Bioreg=Greater Grampians; CLIMATE potential=VH. ‘The mass of underground organs, together with the numerous seedlings produced, completely suppresses other species’ (Parsons & Cuthbertson 2002). Major displacement of some dominant spp. within the lower strata. | MH | MH |
(b) medium value EVC | EVC=Semi-arid woodland (BCS =D); CMA=Mallee; Bioreg=Lowan Mallee; CLIMATE potential=VH. ‘The mass of underground organs, together with the numerous seedlings produced, completely suppresses other species’ (Parsons & Cuthbertson 2002). Major displacement of some dominant spp. within the lower strata. | MH | MH |
(c) low value EVC | EVC=Lowan Sands Mallee (BCS =LC); CMA=Wimmera; Bioreg=Lowan Mallee; CLIMATE potential=VH. ‘The mass of underground organs, together with the numerous seedlings produced, completely suppresses other species’ (Parsons & Cuthbertson 2002). Major displacement of some dominant spp. within the lower strata. | MH | MH |
11. Impact on structure? | ‘The mass of underground organs, together with the numerous seedlings produced, completely suppresses other species’ (Parsons & Cuthbertson 2002). The area beneath mature asparagus fern can be devoid of other species (Breaden et al. 2006). Major effect on lower strata. | MH | MH |
12. Effect on threatened flora? | This species is a risk to threatened species in NSW (Downey 2006) but not documented to have an additional effect on threatened flora in Victoria. | MH | L |
Fauna | |||
13. Effect on threatened fauna? | Species not documented to have an additional effect on threatened fauna. | MH | L |
14. Effect on non-threatened fauna? | ‘The mass of underground organs, together with the numerous seedlings produced, completely suppresses other species’ (Parsons & Cuthbertson 2002). Effect on animals not documented although possible that the species may reduce habitat and food supply of non-threatened fauna. | ML | MH |
15. Benefits fauna? | Berries are eaten by native birds (Breaden et al. 2006). | MH | H |
16. Injurious to fauna? | Weed produces spines (Parsons & Cuthbertson 2002). May be injurious to fauna species. | MH | MH |
Pest Animal | |||
17. Food source to pests? | Species not documented as a food source to pest species. | L | MH |
18. Provides harbor? | Species not documented as a food source to pest species. | L | MH |
Agriculture | |||
19. Impact yield? | Not documented as a weed of agriculture in references that would be expected to report this, vis: Parsons & Cuthbertson (2001) or the ‘Asparagus weeds best practise manual’ (DWLBC 2006). | L | M |
20. Impact quality? | Not documented as a weed of agriculture in references that would be expected to report this, vis: Parsons & Cuthbertson (2001) or the ‘Asparagus weeds best practise manual’ (DWLBC 2006). | L | M |
21. Affect land value? | Not documented as a weed of agriculture in references that would be expected to report this, vis: Parsons & Cuthbertson (2001) or the ‘Asparagus weeds best practise manual’ (DWLBC 2006). | L | M |
22. Change land use? | Not documented as a weed of agriculture in references that would be expected to report this, vis: Parsons & Cuthbertson (2001) or the ‘Asparagus weeds best practise manual’ (DWLBC 2006). | L | M |
23. Increase harvest costs? | Not documented as a weed of agriculture in references that would be expected to report this, vis: Parsons & Cuthbertson (2001) or the ‘Asparagus weeds best practise manual’ (DWLBC 2006). | L | M |
24. Disease host/vector? | Not a known host or vector for disease of agriculture. Not documented in references that would be expected to report this, vis: Parsons & Cuthbertson (2002) or the ‘Asparagus weeds best practise manual’ (DWLBC 2006). | L | M |