Invasiveness Assessment - Tiger pear (Opuntia aurantiaca) 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 Tiger pear.

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: Tiger pear
Scientific name: Opuntia aurantiaca

Question	Comments	Confidence	Rating
Establishment
Germination requirements?	“Capable of rooting to form new plants, if it comes into contact with the soil (Zimmerman, 1978). “When joints are broken off they readily take root in most parts of the State during the greater part of the year” (Maiden, 1911). Opportunistically takes root.	H	H
Establishment requirements?	“This species is often difficult to see in long grass” (Auld & Medd, 1992), suggesting that it can grow under moderate cover.	MH	MH
How much disturbance is required?	Whilst this plant commonly invades highly disturbed areas, such as sparse drought-adapted plant communities (Zimmerman, 1978), riverbanks (Moran & Annecke, 1979), pasture land (Hosking & Deighton, 1981) and “areas from which erect prickly pear had been cleared by cactoblastis,” (Parsons & Cuthbertson, 1992); it is also noted as an invader of dense valley bushveld (Zimmerman, 1978) and lowland grassland & grassy woodland, (Carr et al, 1992), relatively intact ecosystems.	MH	MH
Growth/Competitive
Life form?	“Low-growing, many-jointed…cactus” (Moran & Zimmerman, 1991) with underground tubers (Moran & Annecke, 1979) that need to be grubbed out to control the plant (Parsons & Cuthbertson, 1992).	ML	H
Allelopathic properties?	None described in an extensive literature on this plant (e.g. Moran & Annecke, 1979; Hosking & Deighton, 1981; Maiden, 1911; Parsons & Cuthbertson, 1992).	L	H
Tolerates herb pressure?	“Opuntia species are not usually grazed by stock because the stout spines and bristles damage their tongues and lips, but, in times of drought, plants are eaten” (Parsons & Cuthbertson, 1992). Subject to several insect and pathogenic controls, some of which control the weed in “hot, dry conditions” and others that “usually fail to kill all joints [stems]” (Hosking, McFadyn & Murray, 1988). In South Africa “dense populations of the weed are presently confined to riverine bush and to higher rainfall regions where cochineal insects are relatively ineffective, as is the case in Australia” (Moran & Zimmerman, 1991).	ML	H
Normal growth rate?	“Was originally dwarfed by the masses of…common pear and…spiny pest pear…larger cactii” (Hosking & Deighton, 1979), however Tanner (2004a) claims that tiger pear “shoots can grow as long as 10 cm in a couple of weeks,” which will exceed most other ground flora.	MH	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	“All Opuntia species are drought-resistant” (Parsons & Cuthbertson, 1992). “Remarkable drought resistance” (Zimmerman, 1978). “Because of their high moisture content, plants are not easily burnt” (Parsons & Cuthbertson, 1992) so that in South Africa, “plants were collected, piled on firewood and later burned” (Moran & Annecke, 1979). Fire alone has not been suggested as a control method in comprehensive analyses of this pest (Hosking & Deighton, 1979; Parsons & Cuthbertson, 1992 or Zimmerman, 1978). This suggests that O. aurantiaca has some fire tolerance. This is also supported by Tanner (2004a)- “Tiger pear can be destroyed by fire. Tops of plants are easily killed, butts require extra heat.” “Common along watercourses in north-eastern New South Wales and south-eastern Queensland,” (Hosking, McFadyen & Murray, 1988); “subhumid to sermi-arid areas of warm-temperate and subtropical regions” (Parsons & Cuthbertson, 1992). This suggests that tiger pear is unlikely to tolerate frosts. Distribution in Australia is limited to areas far from the coast (see distribution map in Hosking & Deighton, 1981), suggesting that tiger pear may have low salt tolerance also. As a cactus, this plant is unlikely to tolerate waterlogging. This plant displays some tolerance to two stressors but is likely to be susceptible to at least two.	ML	H
Reproduction
Reproductive system	“The seeds of O. aurantiaca are not viable” (Hosking, McFadyn & Murray, 1988). Fruits are “filled with minute infertile seeds” (Zimmerman, 1978). “Tiger pear grows from segments and not from seed” (Hosking & Deighton, 1981).	MH	H
Number of propagules produced?	“The seeds of O. aurantiaca are not viable” (Hosking, McFadyn & Murray, 1988). Fruits are “filled with minute infertile seeds” (Zimmerman, 1978).	L	H
Propagule longevity?	“A detached segment has been known to survive indoors for 3 years” (Parsons & Cuthbertson, 1992). Viable seeds not produced (see Q. 9).	L	H
Reproductive period?	Plants are very long-lived (Parsons & Cuthbertson, 1992).	H	MH
Time to reproductive maturity?	Never reaches reproductive maturity as it does not produce viable seed (see Q.9).	L	H
Dispersal
Number of mechanisms?	“Small segments…attach to wool and hides of animals and to footwear and tyres of passing vehicles” (Parsons & Cuthbertson, 1992). “Another-and probably major-means of spread is by floodwaters” (Hosking & Deighton, 1981).	MH	MH
How far do they disperse?	“Widely dispersed as a result of adhering to stock, wild animals…Leaf-pads are also transported by runoff water” (Zimmerman, 1978). It is very likely that transporting stock and floodwaters have transported this plant many kilometres in the past (see Hosking & Deighton, 1981) and will continue to do so.	H	H

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