Impact Assessment - Leaf Cactus (Pereskia aculeata) in Victoria
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Assessment of plant invasiveness is done by evaluating biological and ecological characteristics such as germination requirements, growth rate, competitive ability, reproduction methods and dispersal mechanisms. Assessment of plant impacts, however, is determined by the extent to which a plant affects a land manager’s environmental, economic and social resources.
The relative importance of these resources varies depending upon the value people place on them and, as such, the assessment process is subjective. For example, a farmer is likely to place a higher emphasis on the impact of a plant on production (economic resource) than its impact on areas of natural vegetation occurring on the farm. Conversely, a Landcare or Friends group would value environmental or social resources more than economic resources.
Recognising that the value of resources vary between different land tenures, plant impact assessments allow a prioritisation of resources by land managers. Assessments can apply at a local, regional or state level, and the relative values of each resource identified may differ at each level.
The impact assessment method used in the Victorian Pest Plant Prioritisation Process uses three broad resource categories: social, environmental and agricultural, each with a number of related attributes. For example, social resources include such attributes as how the plant affects human access for recreation, or if it creates a health risk due to toxicity or by producing allergens.
| Each resource attribute, or criterion, is assessed relative to a list of intensity ratings. Depending upon information found in relation to each criterion, a rating of Low, Medium Low, Medium High or High is assigned. Descriptions of the impact criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the impact of Leaf 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)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
Common Name: Leaf cactus
Scientific name: Pereskia aculeata
| Question | Comments | Rating | Confidence |
| Recreation | |||
| 1. Restrict human access? | “The plant has a tendency to form large impenetrable clumps and its extreme thorniness makes control of large infestations difficult…Growing amongst riparian vegetation along the banks of rivers in Queensland and New South Wales” (CRC Weed Management, 2003). “Runners…also spread along the ground to make the whole area inaccessible” (de Beer, 1988). | H | H |
| 2. Reduce tourism? | Large, thorny, impenetrable thickets that are difficult to control and situated along riverbanks (see Q. 1) are likely to have a major impact on recreation in and around those rivers. | H | H |
| 3. Injurious to people? | The main shoots vigorously bear curved spines 4-8 mm long and 2-5 mm thick and straight spines 10-35 mm long and 0.5-1.5 mm thick and trichomes 1-2 mm long (Leuenberger, 1982). | H | H |
| 4. Damage to cultural sites? | As a large, thorny climbing shrub that clambers over trees (Moran & Zimmermann, 1991) this plant has the capacity to detract visually from cultural sites. | ML | H |
| Abiotic | |||
| 5. Impact flow? | Terrestrial species that “dislikes too much water” (CRC Weed Management, 2003). | L | MH |
| 6. Impact water quality? | Terrestrial species that “dislikes too much water” (CRC Weed Management, 2003). | L | MH |
| 7. Increase soil erosion? | This plant can smother vegetation (de beer, 1988) that might otherwise bind soil. In cool or drought conditions this plant loses its leaves (Leuenberger, 1986) and where it has killed the vegetation it has smothered, it will leave the soil bare and prone to erosion. It can form major infestations along riverbanks (pers. comm. photo from the Agricultural Research Council (ARC) in South Africa) making the likelihood of flooding, and large scale soil movement with major offsite effects highly likely. | H | MH |
| 8. Reduce biomass? | “Clambers over…trees…and may eventually kill them (Moran & Zimmermann, 1991). | H | H |
| 9. Change fire regime? | Burning is used to control this weed in South Africa (CRC Weed Management, 2003) however this appears to have been by dropping plant pieces into oil drums. This indicates that it is not very flammable. In subtropical eucalypt communities it has the potential to reduce the incidence and intensity of fires. | MH | MH |
| Community Habitat | |||
| 10. Impact on composition (a) high value EVC | EVC= Foothill Box Ironbark Forest (V); CMA=East Gippsland; Bioreg= East Gippsland Upland; CLIMATE potential=H. “Listed as a noxious weed in conservation areas in South Africa due to its formation of dense infestations” (CRC Weed Management, 2003). “It overshadows all other vegetation and even big trees could collapse under the mass of the tangled branches” (de Beer, 1988). Monoculture within the canopy layer. | H | MH |
| (b) medium value EVC | EVC= Riparian Forest (D); CMA=East Gippsland; Bioreg= East Gippsland Lowland; CLIMATE potential=H. “Listed as a noxious weed in conservation areas in South Africa due to its formation of dense infestations” (CRC Weed Management, 2003). “It overshadows all other vegetation and even big trees could collapse under the mass of the tangled branches” (de Beer, 1988). Monoculture within the canopy layer. | H | MH |
| (c) low value EVC | EVC= Lowland Forest (Lc); CMA=East Gippsland; Bioreg= East Gippsland Lowland; CLIMATE potential=H “Listed as a noxious weed in conservation areas in South Africa due to its formation of dense infestations” (CRC Weed Management, 2003). “It overshadows all other vegetation and even big trees could collapse under the mass of the tangled branches” (de Beer, 1988). Monoculture within the canopy layer. | H | MH |
| 11. Impact on structure? | “Listed as a noxious weed in conservation areas in South Africa due to its formation of dense infestations” (CRC Weed Management, 2003). “It overshadows all other vegetation and even big trees could collapse under the mass of the tangled branches” (de Beer, 1988). This vine has the capacity to form monocultures affecting all layers. | H | MH |
| 12. Effect on threatened flora? | No information found. | MH | L |
| Fauna | |||
| 13. Effect on threatened fauna? | No information found. | MH | L |
| 14. Effect on non-threatened fauna? | Dense infestations that smother native trees (CRC Weed Management, 2003) could reduce habitat and food for native fauna. | MH | MH |
| 15. Benefits fauna? | “It bears …edible fruits 25-45 mm in diameter, which are popular with birds” (CRC Weed Management, 2003). Its thorny branches may also protect small birds from predation. | MH | MH |
| 16. Injurious to fauna? | “Heavily spined” (Moran & Zimmermann, 1991). | H | H |
| Pest Animal | |||
| 17. Food source to pests? | May provide habitat and a food source for pest bird species (see Q. 15). | ML | MH |
| 18. Provides harbour? | May provide harbour for small birds (see Q. 15). | ML | MH |
| Agriculture | |||
| 19. Impact yield? | “Listed as a noxious weed in forestry in South Africa due to its formation of dense infestations” (CRC Weed Management, 2003). It “clambers over…commercially planted forest trees…and may eventually kill them” (Moran & Zimmermann, 1991). Given how difficult this plant is to control (CRC Weed Management, 2003), this could have a major impact on quantity of produce. | MH | MH |
| 20. Impact quality? | This plant is not noted as a weed of other agricultural systems in CRC Weed Management, (2003) and is not likely to impact on the quality of forestry products. | L | MH |
| 21. Affect land value? | The labour-intensive nature of controlling this species, due to dense infestations that are thorny and that can regrow from stumps, leaf and stem fragments (CRC Weed Management, 2003), would probably reduce the value of badly infested land. Photographs from ARC in South Africa (pers. comm.) show extensive infestations that have entirely smothered acres of land. | H | MH |
| 22. Change land use? | Commercial forests may no longer be viable in the presence of this weed (see Q. 19). | H | MH |
| 23. Increase harvest costs? | The South African experience has shown that infestations are difficult to remove, involve meticulous human labour, and require “a great deal of follow-up treatment” (CRC Weed Management, 2003). | H | MH |
| 24. Disease host/vector? | Not noted as a host for agricultural diseases (CRC Weed Management, 2003). | L | MH |
Impact Assessment Record - Leaf cactus (PDF - 19KB)
Impact Assessment Record - Leaf cactus (DOC - 48KB)
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