Impact Assessment - Wards weed (Carrichtera annua) 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 Wards weed.

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: Wards weed
Scientific name: Carrichtera annua

Question	Comments	Rating	Confidence
Recreation
1. Restrict human access?	C. annua can form dense stands, to 60 cm in height (Cooke 2003: Weber 2003). C. annua would not restrict human access, minimal impact.	L	MH
2. Reduce tourism?	Orchard (1946) describes Carrichtera annua as an ‘evil smelling weed’ due to its pungent, penetrating odour. This may cause minor effects to aesthetics and tourism value.	ML	MH
3. Injurious to people?	C. annua is not reported having any toxic qualities or spines. Not described in the literature reviewed, to cause injury to humans.	L	M
4. Damage to cultural sites?	Unknown: No reviewed documentation suggests that C. annua causes damage to indigenous, european heritage sites or infrastructure.	M	L
Abiotic
5. Impact flow?	C. annua occurs in less dry habitats in desert situations (Loria and Noy-Meir 1979/80) where water runoff may occur, and is a tap-rooted, erect winter annual herb (Cooke 2003: Weber, 2003). The species does not occur within watercourses, little impact on surface or subsurface water flow.	L	H
6. Impact water quality?	No reviewed documentation suggests that C. annua impacts on water quality.	L	M
7. Increase soil erosion?	C. annua can form dense stands and has a deep taproot (Weber 2003) which may reduce soil erosion, although because C. annua can form dense stands and displace native plants (Cooke 2003) may increase the probability of soil erosion slightly. The annual species may leave bare patches that are exposed to soil erosion. Moderate probability of large scale soil movement.	ML	MH
8. Reduce biomass?	C. annua forms dense stands displacing both native plants and other weed species and can comprise up to an estimated 95% of total herbaceous biomass (Cooke 2003). Direct replacement of biomass by invader.	ML	MH
9. Change fire regime?	C. annua is a winter growing annual plant, following plant senescence, the dead plant remains upright over the summer months (Cooke 2003). Gat-Tilman (1995) describes C. annua as a ‘dry plant’ during the summer months. This suggests the plant may increase the risk of fire intensity. Minor change.	ML	MH
Community Habitat
10. Impact on composition (a) high value EVC	EVC= Semi-arid woodland (V); CMA= Mallee; Bioreg= Murray Mallee; CLIMATE potential=VH. C. annua can form dense stands becoming the dominant herbaceous plant. Across its range, C. annua displaces both native plants and other weed species and comprises up to an estimated 95% of total herbaceous biomass. C. annua could be considered as forming a monoculture in the Flinders Rangers National Park within a specific layer (Cooke 2003), although in other areas such as Willandra C. annua occurs with perennial competitors.	MH	MH
(b) medium value EVC	EVC= Semi-arid woodland (D); CMA= Mallee; Bioreg= Lowan Mallee; CLIMATE potential=VH. C. annua can form dense stands becoming the dominant herbaceous plant. Across its range, C. annua displaces both native plants and other weed species and comprises up to an estimated 95% of total herbaceous biomass. C. annua could be considered as forming a monoculture in the Flinders Rangers National Park within a specific layer (Cooke 2003), although in other areas such as Willandra C. annua occurs with perennial competitors.	MH	MH
(c) low value EVC	EVC= Shrubby Woodland (E); CMA= Wimmera; Bioreg= Greater Grampians; CLIMATE potential=VH. C. annua can form dense stands becoming the dominant herbaceous plant. Across its range, C. annua displaces both native plants and other weed species and comprises up to an estimated 95% of total herbaceous biomass. C. annua could be considered as forming a monoculture in the Flinders Rangers National Park within a specific layer (Cooke 2003), although in other areas such as Willandra C. annua occurs with perennial competitors.	MH	MH
11. Impact on structure?	Across its range, C. annua displaces both native plants and other weed species and comprises up to an estimated 95% of total herbaceous biomass. C. annua could be considered as forming a monoculture in the Flinders Rangers National Park (Cooke 2003) within the ground cover layer.	MH	MH
12. Effect on threatened flora?	Described by Cooke (2003), C. annua may form part of a succession of weed species, which appears to have succeeded hops (Rumex vesicarius) in the Flinders Rangers, which is now rare. This species is in the same genus as Glistening dock (Rumex crystallinus s.s.) a species classed as vulnerable in Victoria.	MH	L
Fauna
13. Effect on threatened fauna?	No reviewed documentation suggests that C. annua causes a threat to threatened fauna species.	MH	L
14. Effect on non-threatened fauna?	No reviewed documentation directly suggests that C. annua causes a threat to fauna species, although the ability of C. annua to form dense stands becoming the dominant herbaceous plant (Cooke 2003) may suggest a reduction in the available habitat for certain fauna species.	MH	MH
15. Benefits fauna?	The pod seed bank of C. annua forms a potential food source for vertebrate herbivores including goats, macropods, emus, sheep, cattle and rabbits. Ant species in semi-arid areas dominated by C. annua also use the seed of the species as an alternative food source (Cooke 2003 pg. 71).	MH	MH
16. Injurious to fauna?	No literature suggests that C. annua is injurious to fauna although the species is described by Orchard (1946) as being unpalatable to fauna because of its hairiness and pungent, penetrating odour.	L	MH
Pest Animal
17. Food source to pests?	C. annua provides a potential food source for vertebrate herbivores, including rabbits (Cooke 2003).	MH	MH
18. Provides harbor?	C. annua can form dense stands, to 60 cm in height (Cooke 2003: Weber 2003) which may suggest that the species has the capacity to harbour pest species, especially considering C. annua provides a potential food source for vertebrate herbivores including rabbits (Cooke 2003).	MH	MH
Agriculture
19. Impact yield?	C. annua is described as a major pastoral weed (Keighery 1991 in Cooke 2003 pg7) due to its ability to replace native vegetation following overgrazing. Orchard (1946) also describes that C. annua might choke out cereal crops entirely, if left uncontrolled.	H	H
20. Impact quality?	Reduced quality of meat and milk from animals feeding on C. annua has been recorded due to the strong odours of C. annua being transferred to the produce (Orchard 1946). Seeds of C. annua were also recognised as an impurity in wheat in Australia (Cooke 2003).	MH	H
21. Affect land value?	C. annua is unpalatable to sheep and cattle; it reduces the carrying capacity and so value of infested property (Cooke 2003). C. annua might choke out cereal crops entirely, if left uncontrolled. (Orchard 1946), causing a decrease in land value.	M	MH
22. Change land use?	C. annua is unpalatable to sheep and cattle therefore reduces the carrying capacity (Cooke 2003), C. annua may also choke out cereal crops entirely, if left uncontrolled (Orchard 1946) this may cause a downgrading of the priority land use, to one with less agricultural return.	MH	MH
23. Increase harvest costs?	Unknown: No reviewed literature suggests C. annua increases the cost of production.	M	L
24. Disease host/vector?	Unknown: No reviewed documentation suggests that C. annua acts as an alternative host or vector for disease of agriculture.	M	L

Impact Assessment Record - Wards weed (PDF - 71KB)
Impact Assessment Record - Wards weed (DOC - 63KB)
This table can also be viewed as a PDF document (printer friendly). To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).

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