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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? | “An erect shrub, commonly about 1 m high.” Occurs, “…on damp, shaded sites and forest edges.” “Infestations spread rapidly and often form dense closed stands.” Herbaceous species; may be a nuisance to humans. | ML | |
2. Reduce tourism? | “An erect shrub, commonly about 1 m high.” Occurs, “…on damp, shaded sites and forest edges.” “Infestations spread rapidly and often form dense closed stands.” Some recreational activities may be affected. | P & C (2001) Muyt (2001) | ML |
3. Injurious to people? | Not considered injurious to humans. | L | |
4. Damage to cultural sites? | Dense stands would create a negative visual effect. | ML | |
Abiotic | |||
5. Impact flow? | Terrestrial species. | P & C (2001) | L |
6. Impact water quality? | Terrestrial species. | P & C (2001) | L |
7. Increase soil erosion? | A shrub with numerous shallow roots to 30 cm deep, a few deeper. Not likely to increase soil erosion. | P & C (2001) | L |
8. Reduce biomass? | “Tutsan is a serious weed in moist forests, woodlands and riparian areas. Infestations…often form dense closed stands that smother ground-flora and smaller shrubs.” Biomass may increase slightly. | Muyt (2001) | L |
9. Change fire regime? | Effect on fire regime not documented, however, as a semi-deciduous plant, it may have little impact on fire risk. | L | |
Community Habitat | |||
10. Impact on composition (a) high value EVC | EVC=Cool temperate rainforest (V); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; VH CLIMATE potential. Establishes in disturbed and undisturbed bushland. Tolerates deep shade and can establish in open, sunny locations. Smothers ground flora and smaller shrubs. Major displacement of species in lower strata. | Muyt (2001) | MH |
(b) medium value EVC | EVC=Warm temperate rainforest (R); CMA=East Gippsland; Bioreg=East Gippsland Uplands; H to VH CLIMATE potential. Impact as in 10(a) above. | Muyt (2001) | MH |
(c) low value EVC | EVC=Wet forest (LC); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; VH CLIMATE potential. Impact as in 10(a) above. | Muyt (2001) | MH |
11. Impact on structure? | “There is an area near Mansfield, in Victoria, where it extends as the dominant species from a roadside for several hundred metres into native bushland greatly reducing the density of native species.” Serious impact on lower strata. | P & C (2001) | ML |
12. Effect on threatened flora? | |||
Fauna | |||
13. Effect on threatened fauna? | |||
14. Effect on non-threatened fauna? | In Victoria, it is widely distributed in damp and wet sclerophyll forest, riparian vegetation, warm and temperate rainforest. As the plant is unpalatable and rarely eaten and it forms dense close stands, it may have a some impact on reducing fodder. | ML | |
15. Benefits fauna? | No known benefits. | H | |
16. Injurious to fauna? | “It is suspected of poisoning cattle in New Zealand, and of causing skin ailments in sheep and cattle although this is not well documented.” However, the plant is unpalatable and rarely eaten. | P & C (2001) | ML |
Pest Animal | |||
17. Food source to pests? | Not known as a food source to pest animals. | L | |
18. Provides harbor? | Not known to provide harbor | L | |
Agriculture | |||
19. Impact yield? | “…tutsan encroaches onto semi-improved areas or pastures which have been severely overgrazed when, in Victoria, whole hillsides may be covered to the exclusion of most other vegetation.” These infestations greatly reduce the pasture available to stock. | P & C (2001) | MH |
20. Impact quality? | Not known as a weed of cropping or to contaminate agricultural produce greatly. | L | |
21. Affect land value? | Not considered a significant weed of agriculture. Little effect on land value. | L | |
22. Change land use? | Not considered a significant weed of agriculture. Where it occurs on steep hillsides or in the presence of other vegetation in pasture situations, herbicides provide some degree of control. Change in land use not required. | P & C (2001) | L |
23. Increase harvest costs? | Not known as a weed of cropping. | L | |
24. Disease host/vector? | None evident. | L |