Impact Assessment - Rope cactus (Cylindropuntia imbricata) 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 Rope cactus - Devil's rope 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 - 1 MB)

Common Name: Rope cactus - Devil's rope pear
Scientific name: Cylindropuntia imbricata

Question	Comments	Rating	Confidence
Recreation
1. Restrict human access?	Is a many branched shrub like cactus with spines up to 30 mm long (Henderson 1995). Can occasionally form “nearly impenetrable thickets” (Kinraide 1978). Can interfere with moving livestock (Pierper 1971). Therefore the species would be oh high nuisance value making access by people difficult.	MH	H
2. Reduce tourism?	Unknown; as the species does not resemble native flora invasion by this species may have some negative influence on the aesthetics of an area. While rare the species is reported to be able to form impenetrable thickets which may have some impact on recreation activities.	M	L
3. Injurious to people?	The species has spines (Hubert 1980). Its spines can be up to 30 mm long (Henderson 1995).	MH	MH
4. Damage to cultural sites?	There is no data reported on the species potential to incur structural damage, invasion by the species could result in an impact on the aesthetics of a site, this has not however been reported.	ML	L
Abiotic
5. Impact flow?	The species is not reported to restrict flowing water and as a terrestrial species of semi-arid to arid environments it is unlikely to do so.	L	MH
6. Impact water quality?	The species is not reported to impact on water quality and as a terrestrial species of semi-arid to arid environments it is unlikely to do so.	L	MH
7. Increase soil erosion?	Reduces grazing pressure on an area, by restricting the movement of grazing species, and protecting the grasses/herbs in the immediate vicinity of its spines (Pieper 1971), therefore increasing the groundcover and reducing soil exposed to erosion.	L	MH
8. Reduce biomass?	Invading grassland C. imbricata creates a shrub layer. It has also been reported to potentially improve the microclimate for grasses, while also restricting grazing, increasing net biomass (Pieper 1971).	L	H
9. Change fire regime?	The species is reported to benefit from fire suppression (Halstead 2002). There is no evidence however of the species causing a reduction in fire frequency. By restricting grazing, the species could potentially increase the biomass of grasses (Pieper 1971). This may have some impact on fire intensity.	ML	MH
Community Habitat
10. Impact on composition (a) high value EVC	EVC= Plains Savannah (E); CMA= Wimmera; Bioreg= Lowan Mallee; VH CLIMATE potential. Can occasionally form virtually impenetrable thickets (Kinraide 1978). Therefore the species can become a dominant species and potentially cause some level of displacement.	M	MH
(b) medium value EVC	EVC= Semi-arid Woodland (D); CMA= Wimmera; Bioreg= Lowan Mallee; VH CLIMATE potential. Can occasionally form virtually impenetrable thickets (Kinraide 1978). Therefore the species can become a dominant species and potentially cause some level of displacement.	M	MH
(c) low value EVC	EVC= Lowan Sands Mallee (LC); CMA= Wimmera; Bioreg= Lowan Mallee; VH CLIMATE potential. Can occasionally form virtually impenetrable thickets (Kinraide 1978). Therefore the species can become a dominant species and potentially cause some level of displacement.	M	MH
11. Impact on structure?	In a grassland invasion by the species creates a shrub layer and reportedly may alter the microclimate for the grass and herb layer (Pieper 1971). Can occasionally form virtually impenetrable thickets (Kinraide 1978). Therefore the species can become a dominant species and potentially cause some level of displacement.	M	MH
12. Effect on threatened flora?	No specific data; however the species is reported to restrict grazing (Pierper 1971). This may protect species sensitive to grazing.	M	L
Fauna
13. Effect on threatened fauna?	Unknown.	MH	L
14. Effect on non-threatened fauna?	Unknown; If the species invades grassland, it creates a vegetation layer that previously didn't exist.	L	M
15. Benefits fauna?	May be a food source during drought (Endecott et al 2005). Eaten by rodents (Bunting. & Wright 1976).	MH	H
16. Injurious to fauna?	The species has spines (Hubert 1980). Its spines can be up to 30 mm long (Henderson 1995).	MH	MH
Pest Animal
17. Food source to pests?	In the united states the cactus is eaten by rabbits and rodents especially during drought periods (Bunting. & Wright 1976).	MH	H
18. Provides harbour?	Unknown; the species is a tree-like cactus it may provide some shelter.	M	L
Agriculture
19. Impact yield?	There is some conflicting evidence on the species impact on yield. While it may have little impact on the herbage production it can restrict grazing (Pierper 1971). It can however be used as an emergency fodder source in time of drought (Sawyer et al 2001).	M	M
20. Impact quality?	Reported to potentially reduce the quality of wool, unknown to what extent. (Pierper 1971).	M	M
21. Affect land value?	Unknown.	M	L
22. Change land use?	There is no specific evidence reported. If invasion by this reduces the effective area of production it may result in range land becoming more marginal.	M	L
23. Increase harvest costs?	Reported to interfere with the movement of stock (Pierper 1971). This may result in an increase in labour time.	M	H
24. Disease host/vector?	The fruit of the species may be affected by fruit fly (Blood 2001).	M	M

Impact Assessment Record - Rope cactus - Devil's rope pear (PDF - 92KB)
Impact Assessment Record - Rope cactus - Devil's rope pear (DOC - 56KB)
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