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Invasiveness Assessment - Lacy ragweed (Ambrosia tenuifolia) 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.

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)
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Common Name: Lacy ragweed
Scientific name: Ambrosia tenuifolia

Question
Comments
Rating
Confidence
Establishment
Germination requirements?Seeds germinate in autumn (Parsons & Cuthbertson 2001). Requires seasonal temperatures.
MH
MH
Establishment requirements?Found principally in open areas (Parsons & Cuthbertson 2001). Limited establishment in shade.
ML
MH
How much disturbance is required?Primarily a plant of disturbed open areas… ‘occurs as weed of roadsides, railway reserves, sand dunes, cultivated fields, stubble paddocks , degraded pastures, and waste places ’ (Parsons & Cuthbertson 2001). Establishes 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. tenuifolia not documented to have Allelopathic properties (Parsons & Cuthbertson 2001).
L
MH
Tolerates herb pressure?Not documented to be eaten by animals or insects (Parsons & Cuthbertson 2001).
H
MH
Normal growth rate?Growth rate of A. tenuifolia is not documented. Others species have different growth rates. Therefore score as medium.
M
L
Stress tolerance to frost, drought, w/logg, sal. etc?Susceptible to fire and waterlogging. Drought tolerant. Due to the locations it can be found, it appears to have saline tolerance. No documented evidence of ability to withstand frost (Parsons & Cuthbertson 2001).
MH
MH
Reproduction
Reproductive systemReproduces sexually and vegetatively (Parsons & Cuthbertson 2001).
H
MH
Number of propagules produced?“All types (of ragweed) are prolific seeders … average about 3000 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 specific information on A. tenuifolia. Due to variation within genus, scored as medium.
M
H
Reproductive period?Other ragweed species known to live up to 10 years. Lacy ragweed can form dense colonies (Parsons & Cuthbertson 2001).
H
MH
Time to reproductive maturity?These three ragweed species reach 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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