Impact Assessment - Annual ragweed (Ambrosia artemisiifolia) 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 Annual 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 - 1026 KB)
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: Annual ragweed
Scientific name: Ambrosia artemisiifolia
| Question | Comments | Rating | Confidence |
| Recreation | |||
| 1. Restrict human access? | Grows to 350 cm but usual height is between 50 and 200 cm. A much branched, hairy herb (Parsons & Cuthbertson 2001). The height may impede individual access – low nuisance value. | ML | MH |
| 2. Reduce tourism? | Most species are ‘so ordinary in appearance that they are rarely noticed despite their abundance’. However, as they are serious contributors to hay fever in US, some places advertise as ‘ragweed free’ (Parsons & Cuthbertson 2001). At certain times of the year, ragweed has the potential to have a major impact on recreation. | H | MH |
| 3. Injurious to people? | ‘Most important hay-fever producing plant in North America’. Also associated with asthma and can cause contact dermatitis (Parsons & Cuthbertson 2001). Serious problem in autumn and as an annual herb dies off after flowering. | ML | 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 a robust taproot system with ‘numerous branching fibrous roots’ (Parsons & Cuthbertson 2001). Unlikely that the species would contribute to large-scale soil erosion. | L | MH |
| 8. Reduce biomass? | Likely that biomass would slightly increase as ‘exhibits a high degree of morphological and reproductive plasticity in response to encroachment by neighbouring plants’ (Sprague 2002). | L | H |
| 9. Change fire regime? | Herbaceous plant. Unlikely that it would change the frequency or intensity of fires. | L | MH |
| Community Habitat | |||
| 10. Impact on composition (a) high value EVC | EVC= Low rises woodland (BCS =E); CMA=Wimmera; Bioreg=Lowan mallee; CLIMATE potential=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). Minor displacement of some dominant species within the lower stratum. | ML | MH |
| (b) medium value EVC | EVC= Shallow sands woodland (BCS =D); CMA=Wimmera; Bioreg=Lowan mallee; CLIMATE potential=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). Minor displacement of some dominant species within the lower stratum. | ML | MH |
| (c) low value EVC | EVC= Shrubby woodland (BCS =E); CMA=Wimmera; Bioreg=Lowan mallee; CLIMATE potential=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). Minor displacement of some dominant species within the lower stratum. | ML | 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). Likely to have a minor effect on plants in the lower stratum. | ML | MH |
| 12. Effect on threatened flora? | No information available. | MH | ML |
| Fauna | |||
| 13. Effect on threatened fauna? | No information available. | MH | L |
| 14. Effect on non-threatened fauna? | Annual ragweed is ‘unpalatable to horses’ (digester class) but cattle (fermenter class) can eat it so likely that native fauna (usually fermenters) can also (Parsons & Cuthbertson 2001). Tends to grow in ruderal sites so assume that there is no reduction in food for non threatened fauna. | L | MH |
| 15. Benefits fauna? | In the US the seed ‘provides food for pheasants, quail, dove, grouse, prairie chicken and songbirds..attract insects..provide browse for deer and rabbits’ (Scott 2001). Possible that provides some assistance to desirable species in Victoria e.g. quails, doves, ground-dwelling birds. | MH | H |
| 16. Injurious to fauna? | Beaked and spined seed attach to sheep and furred animals but no documented evidence that it impacts upon health of animal (Parsons & Cuthbertson 2001). | L | MH |
| Pest Animal | |||
| 17. Food source to pests? | In the US provides browse for rabbits (Parsons & Cuthbertson 2001). Therefore possible that rabbits also browse weed in Victoria. | MH | MH |
| 18. Provides harbor? | Not likely that it provides harbour for pest spp. | L | MH |
| Agriculture | |||
| 19. Impact yield? | In US, shown to impact upon sweet corn yield. Also serious competitor in ‘cereals, maize, vegetables, sunflowers, soybeans and tobacco’. Competes for nutrients in orchards. ‘Grows densely to detriment of crops and pasture’. ‘Annual ragweed densities in excess of 0.5 plants per metre reduce soybean yields significantly’ (Williams & Masiunas 2004). | H | H |
| 20. Impact quality? | Shown to effect several quality traits in corn (green ear mass, husked ear mass, ear length and width, kernel mass, depth and kernels per row) (Williams & Masiunas 2004). | MH | H |
| 21. Affect land value? | No information on whether or not the weed affects land value. Numerous studies on effect of annual ragweed on cropping systems but no references made to land values. | L | MH |
| 22. Change land use? | Even though the weed does affect crop yield and quality there is no reference made to a change in priority of land use. Assume that there would be little or no change. | L | MH |
| 23. Increase harvest costs? | Spined seeds difficult to remove from wool so added costs in acid carbonate used for removal (Williams & Masiunas 2004).. | MH | H |
| 24. Disease host/vector? | Acts as an ‘alternate host in the development of sclerotinia rot of cabbages’ (Scott 2001). | MH | MH |
This table can also be viewed as a PDF document (printer friendly).
Impact Assessment Record - Annual Ragweed (PDF - 23 KB)
Impact Assessment Record - Annual Ragweed (DOC - 52 KB)
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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