Invasiveness Assessment - Californian / perennial thistle (Cirsium arvense) in Victoria (Nox)

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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 Californian / perennial thistle.

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: Perennial thistle
Scientific name: Cirsium arvense

Question	Comments	Reference	Rating
Establishment
Germination requirements?	Flowering occurs in December/January. New shoots produced in late winter and early spring.	P & C (1992)	MH
Establishment requirements?	Can establish under moderate canopy – occurs in forests/woodlands.	FEIS	MH
How much disturbance is required?	Establishes in minor disturbed natural ecosystems e.g. woodlands, forests, grasslands, natural communities. “It was not found in undisturbed areas”.	FEIS Thunhurst & Swearingen	MH
Growth/Competitive
Life form?	Geophyte. Buds on root produce new shoots in winter/spring.	P & C (1992)	ML
Allelopathic properties?	Produces allelopathic compounds, having an inhibitory effect on the growth of other plants.	P & C (1992)	MH
Tolerates herb pressure?	Stock avoid grazing in and around dense patches. “Unpalatable to livestock and wildlife”.	P & C (1992) FEIS	H
Normal growth rate?	“Growth is prolific”. It is strongly competitive in pastures and crops.	P & C (1992)	H
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerance to drought (occurs in desert shrub), frost (occurs in alpine areas), fire, water logging (occurs in wet areas).	FEIS - P & C (1992) Thunhurst & Swearingen	MH
Reproduction
Reproductive system	Reproducing by seed and from extensive creeping rhizome.	P & C (1992)	H
Number of propagules produced?	Between 5-6,000 seeds per plant under favourable conditions. (According to European studies).	P & C (1992)	H
Propagule longevity?	Small % remain viable in the soil for at least 21 years.	P & C (1992)	ML
Reproductive period?	“The deep roots grow horizontally and send up shoots along their length, forming dense colonies”.	Callihan & Miller	H
Time to reproductive maturity?	Some plants flower in their first year but this is not common.	P & C (1992)	MH
Dispersal
Number of mechanisms?	Wind, water, machinery, equipment.	P & C (1992)	MH
How far do they disperse?	Studies show wind disperses seeds only tens of metres. “Seeds travelling in irrigation canals and rivers causes new infestations far from the seed source. The parachuting effect of the pappus allows wind to carry Canada Thistle seed several hundred yards before settling”. (FEIS). “Canada thistle produces an abundance of bristly-plumed seeds which are easily dispersed by the wind”. (Thunhurst & Swearingen 1999).	P & C (1992) See p. 206	MH

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