Invasiveness Assessment - Burr ragweed (Ambrosia confertiflora) in Victoria
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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.
| Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the invasiveness of Burr 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)
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Common Name: Burr ragweed
Scientific name: Ambrosia confertiflora
| Question | Comments | Rating | Confidence |
| Establishment | |||
| Germination requirements? | Germinates in autumn (Parsons & Cuthbertson 2001). Requires natural seasonal conditions. | MH | MH |
| Establishment requirements? | Prefers dryplains of temperate regions and is a weed of wastelands (Parsons & Cuthbertson 2001). Limited growth in shade. | ML | MH |
| How much disturbance is required? | Occurs in ‘run-down pastures, orchards, roadsides, wastelands and other disturbed areas’ (Parsons & Cuthbertson 2001). Established in highly disturbed natural ecosystems. | ML | MH |
| Growth/Competitive | |||
| Life form? | Perennial herbaceous plants (Parsons & Cuthbertson 2001). Life form – other. | L | MH |
| Allelopathic properties? | A. confertiflora not documented to have allelopathic properties (Parsons & Cuthbertson). | L | MH |
| Tolerates herb pressure? | A. confertiflora not known to be eaten by animals and insects | H | MH |
| Normal growth rate? | Seedlings grow at moderate rate during winter with growth rate increasing in spring (Parsons & Cuthbertson 2001). No indication that plant growth rate would equal competitive species of same life form. Therefore score as medium. | M | MH |
| Stress tolerance to frost, drought, w/logg, sal. etc? | ‘When dry periods occur in summer, aerial growth dies back and redevelops from the perennial roots in autumn’ Drought tolerant. Can be found in flood plains but no mention of ability to withstand waterlogging (Parsons & Cuthbertson 2001). Due to locations found, assume weed has some tolerance to salinity. | ML | MH |
| Reproduction | |||
| Reproductive system | Reproduces sexually and vegetatively (Parsons & Cuthbertson 2001). | H | MH |
| Number of propagules produced? | “All types (of ragweed) are prolific seeders … average about 3,000 seeds per year’ (Parsons & Cuthbertson 2001). | H | MH |
| Propagule longevity? | Annual ragweed propagule longevity is up to 40 years (Schmoll, Reigner & Harrison 2004). In contrast, giant ragweed is only viable for 6 weeks (Parsons & Cuthbertson 2001). No information on A. confertiflora. Due to variation within genus, scored as medium. | M | H |
| Reproductive period? | Not specified. Form large colonies and plants known to live up to 10 years (Parsons & Cuthbertson 2001). Therefore score as medium high. | MH | MH |
| Time to reproductive maturity? | A. confertiflora reaches maturity in approximately 9 months (Parsons & Cuthbertson 2001). | H | MH |
| Dispersal | |||
| Number of mechanisms? | Known to be dispersed by clinging to sheep, furred animals, bags, clothing, water, contaminated gravel and soil (Parsons & Cuthbertson 2001). | MH | MH |
| How far do they disperse? | Spreads ‘readily over long distances’. Hull provides buoyancy (Parsons & Cuthbertson 2001). Assume likely that some of the propagules will disperse greater than 1 km. | H | MH |
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