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Impact Assessment - Lacy ragweed (Ambrosia tenuifolia) in Victoria

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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.

The following table provides information on the impact of Lacy ragweed

A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:

Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).

Common Name: Lacy ragweed
Scientific name: Ambrosia tenuifolia

Question
Comments
Rating
Confidence
Recreation
1. Restrict human access?Grows between 30 to 60 cm high . Forms dense colonies but unlikely to have impact on human access (Parsons & Cuthbertson 2001).
L
MH
2. Reduce tourism?Most species are ‘so ordinary in appearance that they are rarely noticed despite their abundance’. All species noted for allergens (Parsons & Cuthbertson 2001). Some recreational uses affected.
MH
MH
3. Injurious to people?‘Most important hay-fever producing plant in North America’. All species are noted for their allergens and are a major contributor to hay fever in US, with some places advertising as ‘ragweed free’ (Parsons & Cuthbertson 2001). Also associated with asthma and dermatogenic properties. Major component in allergies.
MH
MH
4. Damage to cultural sites?Not known to cause structural damage. Little or negligible effect on aesthetics.
L
MH
Abiotic
5. Impact flow?Terrestrial species (Parsons & Cuthbertson 2001).
L
MH
6. Impact water quality?Terrestrial species (Parsons & Cuthbertson 2001).
L
MH
7. Increase soil erosion?Plants have ‘creeping runner-like roots’ (Parsons & Cuthbertson 2001). Aerial growth dies off but unlikely that the species would contribute to large-scale soil erosion.
L
MH
8. Reduce biomass?Occurs principally in open areas or waste lands (Parsons & Cuthbertson 2001). Likely that biomass would slightly increase.
L
MH
9. Change fire regime?Herbaceous plant (Parsons & Cuthbertson 2001) so assume that it would have small or negligible effect on fire risk.
L
MH
Community Habitat
10. Impact on composition
(a) high value EVC
EVC=Plains Grassy Woodland (E), CMA=Glenelg-Hopkins, Bioreg.=Dundas Tablelands, CLIMATE=VH.
Weed

doesn’t occur in healthy, well-established ecosystems. Occurs mostly in open, disturbed areas where less than 3 strata are present (Parsons & Cuthbertson 2001). Very little displacement of any indigenous species.
L
MH
(b) medium value EVCEVC=Coastal Alkaline Scrub (D), CMA=West Gippsland, Bioreg=Gippsland Plain, CLIMATE=H.
Weed doesn’t occur in healthy, well-established ecosystems. Occurs mostly in open, disturbed areas where less than 3 strata are present (Parsons & Cuthbertson 2001). Very little displacement of any indigenous species.
L
MH
(c) low value EVCEVC=Coastal Tussock Grassland (LC), CMA=West Gippsland, Bioreg.=Gippsland Plain, CLIMATE=H.
Weed doesn’t occur in healthy, well-established ecosystems. Occurs mostly in open, disturbed areas where less than 3 strata
are present (Parsons & Cuthbertson 2001). Very little displacement of any indigenous species.
L
MH
11. Impact on structure?Weed doesn’t occur in healthy, well-established ecosystems. Occurs mostly in open, disturbed areas where less than 3 strata are present (Parsons & Cuthbertson 2001). Usually only affecting one of the strata.
L
MH
12. Effect on threatened flora?No information available.
ML
L
Fauna
13. Effect on threatened fauna?No information available.
MH
L
14. Effect on non-threatened fauna?Tends to grow in rural sites so assume that there is no reduction in habitat/food/shelter for non threatened fauna species.
(Parsons & Cuthbertson 2001).
L
MH
15. Benefits fauna?Lacy ragweed not documented to provide benefit to non-threatened fauna species.
H
MH
16. Injurious to fauna?Not documented to be injurious to fauna species (Parsons & Cuthbertson 2001).
L
MH
Pest Animal
17. Food source to pests?Not documented to provide a food source to pest species.
L
MH
18. Provides harbor?Not likely that it provides harbour for pest species.
L
MH
Agriculture
19. Impact yield?Occurs in cultivated fields, stubble paddocks and degraded pastures but not documented to impact agricultural yield (Parsons & Cuthbertson 2001).
L
MH
20. Impact quality?Not documented to impact quality of yield (Parsons & Cuthbertson 2001).
L
MH
21. Affect land value?No information on whether or not the weed affects land value. Weed can be controlled by herbicides (Parsons & Cuthbertson 2001).
L
M
22. Change land use?Weed can be controlled by herbicide (Parsons & Cuthbertson 2001). Often found on degraded lands. Assume no change in priority of land use.
L
MH
23. Increase harvest costs?No documented evidence to suggest that harvest costs would increase due to the presence of lacy ragweed.
L
MH
24. Disease host/vector?None evident.
L
MH

Impact Assessment Record - Lacy ragweed (PDF - 69KB)
Impact Assessment Record - Lacy ragweed (DOC - 62KB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).

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