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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? | Poisonous, symptoms can present after just contact with the plant, also has thorny capsules (Parsons & Cuthbertson 2001). A definite impediment to individuals. | ML | MH |
2. Reduce tourism? | A shrubby herb with large ornate flowers, it would be noticed (Parsons & Cuthbertson 2001). However no reports of impacts on tourism. | M | M |
3. Injurious to people? | All parts of the plant are poisonous, especially seeds and fatalities have occurred after children have eaten seeds of the similar D. stramonium (Parsons & Cuthbertson 2001). Seed capsules are also thorny (Parsons & Cuthbertson 2001). | H | MH |
4. Damage to cultural sites? | Has larger root system than other Datura species, however no reports of it causing structural damage. Could alter the aesthetics with its large leaves and ornate flowers. | M | L |
Abiotic | |||
5. Impact flow? | Terrestrial species. | L | M |
6. Impact water quality? | Terrestrial species. | L | M |
7. Increase soil erosion? | Has a large root system, however it does die back during the winter months (Parsons & Cuthbertson 2001). | MH | M |
8. Reduce biomass? | Can often create a shrubby herb layer, however as it is a short lived perennial, which dies back annually (Parsons & Cuthbertson 2001). Therefore has little capacity for acting as a carbon sink. | ML | MH |
9. Change fire regime? | Impact on fire not reported. | M | L |
Community Habitat | |||
10. Impact on composition (a) high value EVC | EVC= Plains Grassy Woodland (E); CMA= Glenelg Hopkins; Bioreg= Glenelg Plain; VH CLIMATE potential. Most invasive in highly disturbed habitats, if present would compete for moisture light and nutrients (Parsons & Cuthbertson 2001). | L | MH |
(b) medium value EVC | EVC= Heathy Herb-rich Woodland (D); CMA= Glenelg Hopkins; Bioreg= Glenelg Plain; VH CLIMATE potential. Most invasive in highly disturbed habitats, if present would compete for moisture light and nutrients (Parsons & Cuthbertson 2001). | L | MH |
(c) low value EVC | EVC= Heathy Woodland (LC); CMA= Glenelg Hopkins; Bioreg= Glenelg Plain; VH CLIMATE potential. Most invasive in highly disturbed habitats, if present would compete for moisture light and nutrients may cause some minor displacement (Parsons & Cuthbertson 2001). | ML | MH |
11. Impact on structure? | Most invasive in highly disturbed habitats, if present would compete for moisture light and nutrients may cause some minor displacement (Parsons & Cuthbertson 2001). | L | MH |
12. Effect on threatened flora? | No reports of this, most invasive in highly disturbed environments (Parsons & Cuthbertson 2001). | L | MH |
Fauna | |||
13. Effect on threatened fauna? | No evidence documented. | MH | L |
14. Effect on non-threatened fauna? | Poisonous plant (Parsons & Cuthbertson 2001). Minor hazard | ML | MH |
15. Benefits fauna? | Only insects seem to be able to use the plant as a food resource and no native species reported using it (Hare & Smith 2005 and Raguso et al 2003). | H | MH |
16. Injurious to fauna? | Poisonous (Parsons & Cuthbertson 2001). | H | MH |
Pest Animal | |||
17. Food source to pests? | Bees can use the nectar (Parsons & Cuthbertson 2001). | ML | MH |
18. Provides harbor? | Shrubby herb that can cause poisoning symptoms from contact (Parsons & Cuthbertson 2001). Little evidence for potential harbour. | L | MH |
Agriculture | |||
19. Impact yield? | Competes with crops for light, nutrients and moisture. Can also cause stock death especially in pigs and poultry (Parsons & Cuthbertson 2001 and Haegi 1976). | MH | M |
20. Impact quality? | Seed contamination of sorghum has lead to downgrading or rejection of the crop, and reported to cause birth defects in pigs (Parsons & Cuthbertson 2001). | H | M |
21. Affect land value? | No evidence of this reported. | M | L |
22. Change land use? | Seed contamination can’t easily be removed from sorghum (Parsons & Cuthbertson 2001). Therefore a different crop rotation would need to be put into place to produce a marketable product. | ML | M |
23. Increase harvest costs? | Can interfere with harvesting equipment (Parsons & Cuthbertson 2001). | M | MH |
24. Disease host/vector? | Alternate host for Xylella fastidiosa, the bacterium cause of Pierce’s disease of grapes (Wistrom & Purcell 2005). Alternate host for pests and diseases of crops such as tomatoes, tobacco and potatoes (Parsons & Cuthbertson 2001). | H | MH |