Invasiveness Assessment - Wheel cactus (Opuntia robusta) 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 Wheel cactus.

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: Wheel Cactus
Scientific name: Opuntia robusta

Question	Comments	Reference	Rating
Establishment
Germination requirements?	“Seeds germinate at any time of the year”.	P & C (1992 p. 363)	H
Establishment requirements?	Occurs in open areas (See picture in P & c 1992 p. 363).	P & C (1992 p. 363)	ML
How much disturbance is required?	“Serious threat to lowland grassland and grassy woodland in Victoria.	Carr et al 91992)	MH
Growth/Competitive
Life form?	Erect succulent shrub. Other.	P & C (1992 p. 362)	L
Allelopathic properties?	No Allelopathic properties described.		L
Tolerates herb pressure?	“Opuntia spp. Are not usually grazed by stock because of the stout spines and bristles damage their tongues and lips, but in times of drought plants are eaten and animals appear to develop a craving for them”. (P & C 1992 p. 361).		ML
Normal growth rate?	“Seedlings produce small segments only a few centimetres in diameter each of which grow slowly…the first flowers do not develop until plants are at least three years old”. ‘Cactus Pears are slow growing”. (Muyt 2001 p. 203).	P & C (1992 p. 363)	ML
Stress tolerance to frost, drought, w/logg, sal. etc?	“All Opuntia species are drought resistant”. “Because of their high moisture content, plants are not easily burnt”.	P & C (1992 p. 361) P & C (1992 p. 361)	MH
Reproduction
Reproductive system	“reproducing by seed and from branch segments”.	P & C (1992 p. 362)	H
Number of propagules produced?	Seeds numerous in fruit (8 cm long and 6 cm diameter) and plants produce numerous fruits as shown in picture in P & C (1992 p. 363).	P & C (1992 p. 363)	H
Propagule longevity?	? – for seeds.		M
Reproductive period?	“Plants are long lived”. “Once established individual plants can persist for several decades”.	P & C (1992 p. 363) Muyt (2001 p. 203)	H
Time to reproductive maturity?	“The first flowers do not develop until plants are at least three years old”.	P & C (1992 p. 363)	ML
Dispersal
Number of mechanisms?	“As for tiger pear but in addition, wheel cactus produces viable seed which is spread in the droppings of birds, foxes and other animals”.	P & C (1992 p. 363)	H
How far do they disperse?	Birds and foxes may disperse seeds > 1 km.		H

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