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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 heathy plant can grow to between 1 and 3 m and dominate the shrub layer (Weber 2003). Therefore an impediment to individual access. | ML | MH |
2. Reduce tourism? | Can be mistaken for the native species E. impressa (Blood 2001). Introduced as an ornamental species, could alter the aesthetics. | ML | L |
3. Injurious to people? | No injuries reported. | L | M |
4. Damage to cultural sites? | Introduced as an ornamental species, could alter the aesthetics. | ML | L |
Abiotic | |||
5. Impact flow? | Terrestrial species | L | M |
6. Impact water quality? | Terrestrial species | L | M |
7. Increase soil erosion? | Competitive species with a strong root system (Blood 2001 and Weber 2003). Would therefore be equal to the displaced vegetation, if not reduce erosion by invading gaps. | ML | MH |
8. Reduce biomass? | Shrubby species that can dominate the lower stratum (Weber 2003). Displacement would be a direct or potentially an increase in the case of grassland or more open habitats. | ML | MH |
9. Change fire regime? | Has potential to increase biomass, and quickly regenerates after fire (Muyt 2001). This could alter both the fire intensity and frequency. | MH | M |
Community Habitat | |||
10. Impact on composition (a) high value EVC | EVC= Creekline Herb-rich Woodland (E); CMA= Corangamite; Bioreg= Victorian Volcanic Plain; VH CLIMATE potential. Can completely dominate the lower stratum, eliminating all native species and preventing regeneration (Weber 2003). | H | MH |
(b) medium value EVC | EVC= Wet Heathland (D); CMA= Corangamite; Bioreg= Otway Ranges; VH CLIMATE potential. Can completely dominate the lower stratum, eliminating all native species and preventing regeneration (Weber 2003). | H | MH |
(c) low value EVC | EVC= Wet Heathland (LC); CMA= Corangamite; Bioreg= Otway Plains; VH CLIMATE potential. Can completely dominate the lower stratum, eliminating all native species and preventing regeneration (Weber 2003). | H | MH |
11. Impact on structure? | Can completely dominate the lower stratum, eliminating all native species and preventing regeneration (Weber 2003). | MH | MH |
12. Effect on threatened flora? | Can completely dominate the lower strata and prevent regeneration (Weber 2003). | MH | M |
Fauna | |||
13. Effect on threatened fauna? | Unknown. | MH | L |
14. Effect on non-threatened fauna? | Alteration of habitat; eliminates native species (Weber 2003). Therefore altering habitat structure and potential food sources. | MH | M |
15. Benefits fauna? | Flowers profusely during in winter and spring (Muyt 2001). May therefore provide some resources for native species. | MH | M |
16. Injurious to fauna? | No evidence of this reported. | L | M |
Pest Animal | |||
17. Food source to pests? | Flowers profusely during in winter and spring (Muyt 2001). Therefore probably visited by bees. | ML | M |
18. Provides harbour? | Creates dense shrubby vegetation, could therefore harbour many different species (Muyt 2001). | M | M |
Agriculture | |||
19. Impact yield? | Invasive in weak pasture and not palatable to stock (Blood 2001). Therefore where it invades it can reduce the production capacity. | ML | MH |
20. Impact quality? | No evidence of this reported. | L | M |
21. Affect land value? | No evidence of this reported. | L | M |
22. Change land use? | No evidence of this reported. | L | M |
23. Increase harvest costs? | No evidence of this reported. | L | M |
24. Disease host/vector? | No evidence of this reported. | L | M |