Title: Opuntia stricta (Haw.) Haw.

Scientific Name:

Opuntia stricta (Haw.) Haw.

Common Name:

erect prickly pear



Source & more images (via ALA)

Habitat: The Prickly Pear (erect) prefers sub-humid to semi-arid areas in warm temperate and subtropical regions. It grows mainly along streams and banks from where it encroaches onto adjoining grazing land. The plant invades lowland grassland and grassy woodland, dry sclerophyll forests, riparian and rocky outcrop vegetation. It is drought resistant and does not burn easily.

Distribution:



Original source via CABI


Invasiveness Assessment

ESTABLISHMENT


1. Germination requirements? “Seeds germinate at any time of the year” (Parsons & Cuthbertson 1992)


2. Establishment requirements? “Growing well in both exposed and semi shaded situations”. (Parsons & Cuthbertson 1992. p.364)

3. How much disturbance is required? Invades lowland grassland and grassy woodland, dry sclerophyll forest and woodland and riparian vegetation (Carr et al. 1992).


GROWTH / COMPETITIVE


4. Life form? Erect succulent shrub. (Parsons & Cuthbertson 1992, p. 362)


5. Allelopathic properties? No Allelopathic properties described.

6. 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). “Today isolated plants and small patches are still found throughout much of the area originally infested but these are generally of no importance, being kept in check by the insects”. (Parsons & Cuthbertson 1992 p. 365).

7. 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).

8. 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”.

REPRODUCTION


9. Reproductive system? “Reproducing by seed and from branch segments” (Parsons & Cuthbertson 1992, p. 364)


10. Number of propagules produced? Seeds numerous in fruit (4-6 cm long) and plants produce numerous fruits as shown in picture (Parsons & Cuthbertons 1992 p. 365).

11. Propagule longevity? ? for seeds.

12. Reproductive period?“Plants are long lived”. “Once established individual plants can persist for several decades”

13. Time to reproductive maturity? “The first flowers do not develop until plants are at least three years old”.

DISPERSAL


14. 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” (Parsons & Cuthbertson (1992, p. 366).


15. How far do they disperse? Birds and foxes may disperse seeds > 1 km.


Impact Assessment

RECREATION


1. Restrict human access? An erect shrub commonly about 1 metre high. “Patches of Opuntia spp. grow densely forming an impenetrable barrier, hence their use as live fences in some areas.” However, O. stricta, while widespread, is not densely established in Australia. Most likely to be a high nuisance to people by restricting direct access (Parsons & Cuthbertson 2001).

2. Reduce tourism? Although not occurring in dense populations, its presence would be obvious and, due to the spiny nature of the plant, it may affect some recreational activities (Parsons & Cuthbertson 2001).

3. Injurious to people? Stems (cladodes) are regularly patterned with aureoles that bear very fine barbed bristles. Some aureoles also have 1 or 2 sharp spines about 2 to 4 cm long. The barbed bristles are obnoxious because they readily penetrate human skin causing sever irritation and are difficult to remove. Spines and bristles are present all year (Parsons & Cuthbertson 2001).

4. Damage to cultural sites? Stands of O. stricta would create a negative visual impact on cultural sites and seriously affect the aesthetics of an area. The root system is fibrous and shallow and unlikely to cause structural damage (Parsons & Cuthbertson 2001).

ABIOTIC


5. Impact flow? Terrestrial species (Parsons & Cuthbertson 2001).

6. Impact water quality? Terrestrial species (Parsons & Cuthbertson 2001).

7. Increase soil erosion? The root system, while shallow, is fibrous. In dense patches, aerial growth provides good ground cover. Not likely to contribute to soil erosion (Parsons & Cuthbertson 2001).

8. Reduce biomass? In Victoria, Australia, O. stricta occurs in small populations on lowland grassland and woody grassland, dry sclerophyll forest and woodland, and riparian situations. The plant would likely increase biomass (Carr et al. 1992).


9. Change fire regime? A succulent, it would have a small or negligible effect on fire risk. “Because of their high moisture content, plants are not easily burnt.” (Parsons & Cuthbertson 2001).


COMMUNITY HABITAT


10(a) Impact on composition of high value EVC? EVC=Plains grassy woodland (E); CMA=North Central; Bioreg=Victorian Riverina; VH CLIMATE potential. Like other Opuntia spp., O. stricta grows densely forming impenetrable barriers. Stands can hinder growth of smaller shrubs and ground flora. Major impact on lower and mid strata (Parsons & Cuthbertson 2001; Muyt 2001).


10(b) Impact on medium value EVC? EVC=Riverine grassy woodland (D); CMA=Goulburn Broken; Bioreg=Murray Fans; VH CLIMATE potential. Impact as in 10(a) above (Parsons & Cuthbertson 2001; Muyt 2001).

10(c) Impact on low value EVC? EVC=Riparian forest (LC); CMA=West Gippsland; Bioreg=Highlands - Southern Fall; H CLIMATE potential. Similar impact as in 10(a) above, however, effect lessened due to high CLIMATE potential only.

11. Impact on structure? “Large stands can hinder the growth and regeneration of indigenous plants, particularly smaller shrubs and ground-flora.” Minor effect on the lower and mid strata (Muyt 2001).


12. Effect on threatened flora? This species is not documented as posing an additional risk to threatened flora.

FAUNA


13. Effect on threatened fauna? Unknown

14. Effect on non-threatened fauna? “Opuntia spp. are not usually grazed by stock because of the stout spines.” In dense patches, the plant could hinder access to water and reduce available fodder for fauna (Parsons & Cuthbertson 2001).


15. Benefits fauna? “Seed…is spread in the droppings of birds, foxes and other animals.” May provide limited food to desirable species (Parsons & Cuthbertson 2001).

16. Injurious to fauna? “Opuntia spp. are not usually grazed by stock because of the stout spines and bristles damage their tongues and lips.” Spines present all year (Parsons & Cuthbertson 2001).

PEST ANIMAL


17. Food source to pests? “Seed…is spread in the droppings of birds, foxes and other animals. Opuntia spp. are hosts to fruit-fly.” Food source to at least one serious pest animal at a crucial time of year (Parsons & Cuthbertson 2001).

18. Provides harbor? “Patches also provide effective harbour for pest animals such as rabbits.” Plants are long-lived, which would allow for permanent harbor (Parsons & Cuthbertson 2001).

AGRICULTURE


19. Impact yield? O. stricta was an aggressive invader of agricultural land in Queensland and NSW in the early 20th century. “Spread was helped, to some degree, in the 1902 drought when plants were cut and fed out as fodder.” Spread due to natural means is not documented. However, “Before the introduction of biological control agents it was the most serious weed in Australia and capable of growing in most parts of the continent.” Impact is now limited due to biological control with Cactoblastis cactorum. However, the effectiveness of control is sometimes reduced in colder climates. In those areas dense patches would limit carrying capacity (Parsons & Cuthbertson 2001).


20. Impact quality? Effect on quality of produce unknown. Not a weed of cropping or cultivated areas. Animals avoid the plants (Parsons & Cuthbertson 2001)


21. Affect land values? Biological control has reduced the potential for serious infestation. Land prices would not be affected (Parsons & Cuthbertson 2001).


22. Change land use? Biological control has reduced the potential for serious infestation. Land can still be used for intended purpose without loss (Parsons & Cuthbertson 2001).

23. Increase harvest costs? No impact on harvest costs.

24. Disease host/vector? None evident



Technical drawing by Audrey Peric-Low




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Assessment ratings originally made by the Victorian Department of Primary Industries.
The entry of this assessment was made possible through the generous support of The Weed's Network.






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Date: 21 November 2011; 10:59:20 PM AEDT

Author Name: David Low
Author ID: adminDavid