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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 | Reference | Rating |
Recreation | |||
1. Restrict human access? | “Forms impenetrable thickets” (Parsons & Cuthbertson, 1992). “Will encroach onto roadways” (DNRM, 2005). “Seeds germinated along forest paths” (Baret et al., 2003) and creekbanks (Parsons & Cuthbertson, 1992). People and/or vehicles access with difficulty. | MH | M |
2. Reduce tourism? | Where this plant invades creekbanks and forms impenetrable thickets (Parsons & Cuthbertson, 1992), access to waterways for recreational use will be affected | MH | MH |
3. Injurious to people? | “Sparse, recurved prickles to 5 mm” (Lingdi & Boufford, 2003) all year. | MH | H |
4. Damage to cultural sites? | Scandent shrub to 5 m with arching or climbing branches (Lingdi & Boufford, 2003) that can reach to the top of the canopy in forest (Baret et. al, 2003) and that forms impenetrable thickets (Parsons & Cuthbertson, 1992) will have a moderate visual effect at cultural sites. | ML | H |
Abiotic | |||
5. Impact flow? | Invades creekbanks (Parsons & Cuthbertson, 1992). Terrestrial species. | L | MH |
6. Impact water quality? | Invades creekbanks (Parsons & Cuthbertson, 1992). Terrestrial species. | L | MH |
7. Increase soil erosion? | The permanent root system formed by thickets of this plant (Parsons & Cuthbertson, 1992) is likely to decrease the risk of erosion. | L | MH |
8. Reduce biomass? | As this plant forms dense thickets, where it invades rainforest (Parsons & Cuthbertson, 1992), it is likely to directly replace biomass but where it invades pasture and roadsides (Parsons & Cuthbertson, 1992) it will increase biomass. | L | MH |
9. Change fire regime? | This species grows in rainforest in its natural range (Bean, 1997) and invades rainforest in Australia (Parsons & Cuthbertson), so is unlikely to change fire regime much. | L | MH |
Community Habitat | |||
10. Impact on composition (a) high value EVC | Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria. | L | H |
(b) medium value EVC | Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria. | L | H |
(c) low value EVC | Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria. | L | H |
11. Impact on structure? | Scandent shrub to 5 m with arching or climbing branches (Lingdi & Boufford, 2003) that can reach to the top of the canopy in forest (Baret et. al, 2003) and cover other plants (NAPPO, 2006). Invading “disturbed rainforest areas, wet gullies, creekbanks, perimeter of rainforest areas” (Parsons & Cuthbertson, 1992). Likely to have a major effect on the shrub and groundcover layers and a minor effect on the tree layer. | MH | MH |
12. Effect on threatened flora?12. Effect on threatened flora? | Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria. | L | H |
Fauna | |||
13. Effect on threatened fauna? | Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria. | L | H |
14. Effect on non-threatened fauna? | Scandent shrub to 5 m with arching or climbing branches (Lingdi & Boufford, 2003) that can reach to the top of the canopy in forest (Baret et. al, 2003) and cover other plants (NAPPO, 2006). Invading “disturbed rainforest areas, wet gullies, creekbanks, perimeter of rainforest areas” (Parsons & Cuthbertson, 1992). Likely to have a major effect on the shrub and groundcover layers and a minor effect on the tree layer. This may reduce the food and habitat available to fauna species, reducing their numbers. | MH | H |
15. Benefits fauna? | Berries are eaten by birds and animals (Parsons & Cuthbertson, 1992). | MH | MH |
16. Injurious to fauna? | “Sparse, recurved prickles to 5 mm” (Lingdi & Boufford, 2003) all year. | MH | H |
Pest Animal | |||
17. Food source to pests? | Berries are eaten by birds and animals (Parsons & Cuthbertson, 1992). | ML | MH |
18. Provides harbor? | Dense thickets (Parsons & Cuthbertson, 1992) are likely to provide permanent harbour to foxes and rabbits. | H | MH |
Agriculture | |||
19. Impact yield? | “Occurring as a weed…in newly sown or run-down pastures…Forms impenetrable thickets which reduce pasture productivity and may limit access to water.” (Parsons & Cuthbertson, 1992). Large infestations may reduce the carrying capacity of land by more than 5%. | MH | MH |
20. Impact quality? | No impact on quality recorded in Parsons & Cuthbertson (1992). | L | MH |
21. Affect land value? | As this plant can be controlled by cultivation (Parsons & Cuthbertson, 1992), it is unlikely to affect land value. | L | MH |
22. Change land use? | Following control by cultivation (Parsons & Cuthbertson, 1992) land can continue to be used for grazing. | L | MH |
23. Increase harvest costs? | Cultivation to control this plant involves the use of bulldozing, ploughing and ripping, the sowing of an annual crop, followed by more cultivation and the establishment of pasture (Parsons & Cuthbertson, 1992). This two year process involving the use of expensive equipment for several days would cause a major increase in labour and machinery costs. | H | MH |
24. Disease host/vector? | Not recorded as a disease host/vector in Parsons & Cuthbertson (1992). | L | MH |