Impact Assessment - Praxelis (Praxelis celmatidea) 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 Praxelis.

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)
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: Praxelis
Scientific name: Praxelis celmatidea

Question
Comments
Rating
Confidence

Recreation

1. Restrict human access? “Annual or short-lived perennial herb” (Waterhouse, 2003). “It can grow up to c. 1.2 m tall but most plants are c. 40-80 cm” (Csurhes, 1998). They have brittle stems (CRC Weed Management, 2003). Infestations of Praxelis would not impede pedestrian access as the plants would be easily pushed aside or crushed underfoot.
L
MH

2. Reduce tourism? “When crushed they [the leaves] emit a pungent odour similar to cat’s urine” (CRC Weed Management, 2003). “Unpleasant-smelling, softly-hairy herb, 20-80 cm tall…The flower colour is light violet…but can appear blue to purple” (Corlett & Shaw, 1995). “Forms monospecific stands, excluding other vegetation” (PIER, 2005). Flowering generally occurs from November to May but some flowers may appear at any time of the year (CRC Weed management, 2003). The brightly coloured flowers could be obvious to most visitors for much of the year and the smell would be off-putting to many people, but the presence of this weed would be unlikely to inhibit activity.
ML
MH

3. Injurious to people? “Anecdotal reports suggest that it may be poisonous to…humans if ingested” (Veldkamp, 1999) but there was no further record of the plant’s ability to injure people (CRC Weed Management, 2003). However, it is unlikely to be ingested.
ML
MH

4. Damage to cultural sites? The brightly coloured flowers could have a moderate visual effect for much of the year (see description from Q. 2).
ML
MH

Abiotic

5. Impact flow? “Grows vigorously along riverbanks” (CRC Weed Management, 2003), but there is no evidence that it invades the water.
L
M

6. Impact water quality? See Q. 5.
L
M

7. Increase soil erosion? “Can become the dominant herbaceous plant in open eucalypt woodlands.” In drier areas Praxelis dies off until the next rainy season and also “grows vigorously along riverbanks” (CRC Weed Management, 2003). There is the potential for large areas of soil to become bare when Praxelis dies off and with heavy rain and/or flooding of waterways, large scale soil movement is likely with major offsite implications.
H
M

8. Reduce biomass? As this plant can “become the dominant herbaceous plant in open eucalypt woodlands” and can seasonally die off in drier areas (CRC Weed Management, 2003), biomass may be slightly decreased where there was once a more permanent herbaceous cover.
MH
M

9. Change fire regime? This species is not noted for changes to fire regime. As an herbaceous annual or short-lived perennial that can invade grasslands (CRC Weed Management, 2003), it may reduce fuel load and flammability, thereby reducing the frequency and/or intensity of fires in these communities. Elsewhere, where it replaces similar vegetation it is likely to have little effect.
ML
M

Community Habitat

10. Impact on composition
(a) high value EVC Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.
L
H

(b) medium value EVC Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.
L
H

(c) low value EVC Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.
L
H

11. Impact on structure? Its ability to “become the dominant herbaceous plant in open eucalypt woodlands” (CRC Weed Management, 2003) could have a major effect on ground level vegetation.
MH
M

12. Effect on threatened flora? Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.
L
H

Fauna

13. Effect on threatened fauna? Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.
L
H

14. Effect on non-threatened fauna? “It can become the dominant herbaceous plant in open eucalypt woodlands” (CRC Weed Management, 2003). It is “not eaten by stock” (Pollock et al, 2004) and if this is true for other fauna it may reduce access to food, forcing them to seek food elsewhere.
MH
M

15. Benefits fauna? “There is some evidence that it may be poisonous to stock…if ingested” (CRC Weed Management, 2003), so it is unlikely to provide a food source for fauna and as an “annual or short-lived perennial herb” (Waterhouse, 2003) to 40 - 80 cm (Csurhes, 1998), would not provide much shelter either.
H
M

16. Injurious to fauna? “There is some evidence that it may be poisonous to stock…if ingested” (CRC Weed Management, 2003), so it may be poisonous to fauna when present.
MH
M

Pest Animal

17. Food source to pests? Toxicity (CRC Weed Management, 2003) probably precludes this plant from being a food source to pests.
L
MH

18. Provides harbor? As an “annual or short-lived perennial herb” (Waterhouse, 2003) to 40 - 80 cm (Csurhes, 1998), this plant would not offer much shelter.
L
MH

Agriculture

19. Impact yield? “Forms monospecific stands, excluding other vegetation” (PIER, 2005), “not eaten by stock” (Pollock et al, 2004). “An abundant weed of…pastures…it encroaches upon sugarcane plantations and other cultivated areas (Waterhouse, 2003). “In Hong Kong and mainland China…it appears set to become a significant weed of dryland agriculture…There is some evidence that it may be poisonous to stock…if ingested” (CRC Weed Management, 2003). Large infestations may significantly reduce the carrying
capacity of pasture by forming poisonous monocultures and may reduce crop yields by encroachment.
MH
M

20. Impact quality? It is postulated that it was introduced to north Queensland as “a contaminant of pasture seeds imported from Brazil” (Waterhouse, 2003) and this suggests that it would be unlikely to be identified as reducing the quality of pasture seed crops. Whilst it invades other crops (CRC Weed Management, 2003) its bright flower colour (Corlett & Shaw, 1995) would make an infestation obvious and able to be avoided during harvest
L
MH

21. Affect land value? Reduced productivity may affect land value, see Q. 19, but probably not by more than 10%
MH
MH

22. Change land use? Increased costs of harvest (see Q. 23) and reduced quality of produce (see Q. 20) may make stocking and/or cropping less viable on infested land.
MH
MH

23. Increase harvest costs? “Could threaten, and significantly increase the costs of managing, such crops as bananas, other fruits and sugar cane’ (CRC Weed Management, 2003).
H
M

24. Disease host/vector? Not noted as a disease host or vector in CRC Weed Management, 2003.
L
M

Impact Assessment Record - Praxelis (PDF - 24KB)
Impact Assessment Record - Praxelis (DOC - 68KB)
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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Question	Comments	Rating	Confidence
Recreation
1. Restrict human access?	“Annual or short-lived perennial herb” (Waterhouse, 2003). “It can grow up to c. 1.2 m tall but most plants are c. 40-80 cm” (Csurhes, 1998). They have brittle stems (CRC Weed Management, 2003). Infestations of Praxelis would not impede pedestrian access as the plants would be easily pushed aside or crushed underfoot.	L	MH
2. Reduce tourism?	“When crushed they [the leaves] emit a pungent odour similar to cat’s urine” (CRC Weed Management, 2003). “Unpleasant-smelling, softly-hairy herb, 20-80 cm tall…The flower colour is light violet…but can appear blue to purple” (Corlett & Shaw, 1995). “Forms monospecific stands, excluding other vegetation” (PIER, 2005). Flowering generally occurs from November to May but some flowers may appear at any time of the year (CRC Weed management, 2003). The brightly coloured flowers could be obvious to most visitors for much of the year and the smell would be off-putting to many people, but the presence of this weed would be unlikely to inhibit activity.	ML	MH
3. Injurious to people?	“Anecdotal reports suggest that it may be poisonous to…humans if ingested” (Veldkamp, 1999) but there was no further record of the plant’s ability to injure people (CRC Weed Management, 2003). However, it is unlikely to be ingested.	ML	MH
4. Damage to cultural sites?	The brightly coloured flowers could have a moderate visual effect for much of the year (see description from Q. 2).	ML	MH
Abiotic
5. Impact flow?	“Grows vigorously along riverbanks” (CRC Weed Management, 2003), but there is no evidence that it invades the water.	L	M
6. Impact water quality?	See Q. 5.	L	M
7. Increase soil erosion?	“Can become the dominant herbaceous plant in open eucalypt woodlands.” In drier areas Praxelis dies off until the next rainy season and also “grows vigorously along riverbanks” (CRC Weed Management, 2003). There is the potential for large areas of soil to become bare when Praxelis dies off and with heavy rain and/or flooding of waterways, large scale soil movement is likely with major offsite implications.	H	M
8. Reduce biomass?	As this plant can “become the dominant herbaceous plant in open eucalypt woodlands” and can seasonally die off in drier areas (CRC Weed Management, 2003), biomass may be slightly decreased where there was once a more permanent herbaceous cover.	MH	M
9. Change fire regime?	This species is not noted for changes to fire regime. As an herbaceous annual or short-lived perennial that can invade grasslands (CRC Weed Management, 2003), it may reduce fuel load and flammability, thereby reducing the frequency and/or intensity of fires in these communities. Elsewhere, where it replaces similar vegetation it is likely to have little effect.	ML	M
Community Habitat
10. Impact on composition (a) high value EVC	Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.	L	H
(b) medium value EVC	Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.	L	H
(c) low value EVC	Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.	L	H
11. Impact on structure?	Its ability to “become the dominant herbaceous plant in open eucalypt woodlands” (CRC Weed Management, 2003) could have a major effect on ground level vegetation.	MH	M
12. Effect on threatened flora?	Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.	L	H
Fauna
13. Effect on threatened fauna?	Climate modelling shows that this species is not likely to occur as an invasive plant in Victoria.	L	H
14. Effect on non-threatened fauna?	“It can become the dominant herbaceous plant in open eucalypt woodlands” (CRC Weed Management, 2003). It is “not eaten by stock” (Pollock et al, 2004) and if this is true for other fauna it may reduce access to food, forcing them to seek food elsewhere.	MH	M
15. Benefits fauna?	“There is some evidence that it may be poisonous to stock…if ingested” (CRC Weed Management, 2003), so it is unlikely to provide a food source for fauna and as an “annual or short-lived perennial herb” (Waterhouse, 2003) to 40 - 80 cm (Csurhes, 1998), would not provide much shelter either.	H	M
16. Injurious to fauna?	“There is some evidence that it may be poisonous to stock…if ingested” (CRC Weed Management, 2003), so it may be poisonous to fauna when present.	MH	M
Pest Animal
17. Food source to pests?	Toxicity (CRC Weed Management, 2003) probably precludes this plant from being a food source to pests.	L	MH
18. Provides harbor?	As an “annual or short-lived perennial herb” (Waterhouse, 2003) to 40 - 80 cm (Csurhes, 1998), this plant would not offer much shelter.	L	MH
Agriculture
19. Impact yield?	“Forms monospecific stands, excluding other vegetation” (PIER, 2005), “not eaten by stock” (Pollock et al, 2004). “An abundant weed of…pastures…it encroaches upon sugarcane plantations and other cultivated areas (Waterhouse, 2003). “In Hong Kong and mainland China…it appears set to become a significant weed of dryland agriculture…There is some evidence that it may be poisonous to stock…if ingested” (CRC Weed Management, 2003). Large infestations may significantly reduce the carrying capacity of pasture by forming poisonous monocultures and may reduce crop yields by encroachment.	MH	M
20. Impact quality?	It is postulated that it was introduced to north Queensland as “a contaminant of pasture seeds imported from Brazil” (Waterhouse, 2003) and this suggests that it would be unlikely to be identified as reducing the quality of pasture seed crops. Whilst it invades other crops (CRC Weed Management, 2003) its bright flower colour (Corlett & Shaw, 1995) would make an infestation obvious and able to be avoided during harvest	L	MH
21. Affect land value?	Reduced productivity may affect land value, see Q. 19, but probably not by more than 10%	MH	MH
22. Change land use?	Increased costs of harvest (see Q. 23) and reduced quality of produce (see Q. 20) may make stocking and/or cropping less viable on infested land.	MH	MH
23. Increase harvest costs?	“Could threaten, and significantly increase the costs of managing, such crops as bananas, other fruits and sugar cane’ (CRC Weed Management, 2003).	H	M
24. Disease host/vector?	Not noted as a disease host or vector in CRC Weed Management, 2003.	L	M