Impact Assessment - Poverty weed (Iva axillaris) in Victoria (Nox)

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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.

Question	Comments	Reference	Rating
Recreation
1. Restrict human access?	A perennial herb commonly 20 cm to 30 cm high. It would not restrict human access.	P & C (2001)	L
2. Reduce tourism?	It produces dense aerial growth and its presence would be obvious. The leaves produce an unpleasant aromatic odour when crushed. This aspect of the plant may limit some recreational activities.	CDFA1	ML
3. Injurious to people?	“it causes contact dermatitis in some people while its abundant pollen has exacerbated hay-fever problems.”	P & C (2001)	MH
4. Damage to cultural sites?	As a strong competitor with dense aerial growth. It would create a negative visual effect seriously affecting the aesthetics of a site.	P & C (2001)	ML
Abiotic
5. Impact flow?	Terrestrial species	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	An extensive perennial root system to 2.5 metres deep consisting of both vertical and horizontal roots. Colonises cultivated land or overgrazed pastures. Aerial growth dies in autumn leaving the potential for surface soil erosion.	P & C (2001)	ML
8. Reduce biomass?	Invader replaces biomass.		L
9. Change fire regime?	Aerial growth dies in autumn. Little matter remains to establish or support fire.		L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=Wimmera; Bioreg=Wimmera; VH CLIMATE potential. In the U.S., it occurs mostly in grassland (rangeland) situations. It sometimes forms large clonal colonies on disturbed sites where it is difficult to eradicate. Major displacement of grasses/forbs in open situation. Effect in woodland situation may be limited.	P & C (2001)	MH
(b) medium value EVC	Distribution limited to northwest of Victoria. Limited data on EVC available. It does not appear to affect any medium value EVCs.		L
(c) low value EVC	As in 10(b) above.		L
11. Impact on structure?	“With its extensive root system and dense aerial growth, poverty weed competes strongly with other plants. Almost no crop is produced in heavily infested areas. Poverty weed is allelopathic.” Occurs in open disturbed or neglected areas. Likely to have a serious impact on the lower stratum in open situations.	P & C (2001)	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	It, “competes strongly with other plants…and large areas of infested pasture in western Canada have little or no grazing value.” As it is not grazed by livestock, its presence would lead to a reduction in available food for native species.	P & C (2001)	ML
15. Benefits fauna?	No known benefits.		H
16. Injurious to fauna?	In Canada “there have been reports that poverty weed is a selenium accumulator and may be toxic to livestock when ingested. However, this is very rare due to the unpalatable nature of the plant.” Not considered toxic.	CDFA	L
Pest Animal
17. Food source to pests?	No known as a food source to pests.		L
18. Provides harbour?	Low growth habit of plant would not provide harbour.		L
Agriculture
19. Impact yield?	“It is highly competitive when established in agricultural fields and may significantly reduce crop yields.” “Almost no crop is produced in heavily infested areas.” Major impact on production.	CDFA P & C (2001)	H
20. Impact quality?	“Its seeds are a common contaminant of legume and grass seed crops in some areas.” Impact not documented, though contaminated crop may be difficult to sell due to the competitive nature of the weed.	P & C (2001)	MH
21. Affect land value?	Its impact on yield in both grazing and cropping situations, and the difficulty in controlling the plant, suggest land value may be seriously affected.		H
22. Change land use?	“…cultivation and repeated workings over 3 years in Canada did not eliminate the weed…herbicides offering the only effective treatment. Large areas of grazing land in Canada have little or no grazing value.” Potential for significant agricultural loss.	P & C (2001)	H
23. Increase harvest costs?	No known effect on harvest costs.		L
24. Disease host/vector?	None evident.		L