Impact Assessment - Skeleton weed (Chondrilla juncea) 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?	“An erect, much branched perennial herb, commonly 60 to 90 cm high. The stem is much branched almost from the base and plants growing close together become entangled.” Such infestations may be a nuisance to people on foot.	P & C (2001)	ML
2. Reduce tourism?	In dense clumps the plant would have a minor negative impact on the aesthetics of an area.		ML
3. Injurious to people?	No	P & C (2001)	L
4. Damage to cultural sites?	Dense growth may produce a moderate negative visual effect.		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?	“Chondrilla juncea is essentially a weed of cultivation and of open, waste areas with disturbed soils.” The deep root system is likely to provide some soil stability. Not likely to contribute to soil erosion.	Groves et al (1995)	L
8. Reduce biomass?	Invader replaces biomass.		ML
9. Change fire regime?	“In autumn, aerial growth dies.” Little or no change to fuel load. Not likely to affect the fire regime.	P & C (2001)	L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassland (E); CMA=North Central; Bioreg=Victorian Riverina; VH CLIMATE potential. Occurs on temperate, sub-humid and semi-arid open scrublands. In Victoria, it occurs in small populations and is limited in distribution. Minor impact on ground-flora.	P & C (2001) Carr et al (1992)	ML
(b) medium value EVC	EVC=Hillcrest herb-rich woodland (D); CMA=North Central; Bioreg=Goldfields; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001) Carr et al (1992)	ML
(c) low value EVC	EVC=Heathy woodland (LC); CMA=Wimmera; Bioreg=Dundas Tablelands; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001) Carr et al (1992)	ML
11. Impact on structure?	“Chondrilla juncea is essentially a weed of cultivation and of open, waste areas with disturbed soils.” Optimum growth in open plant communities with a minimum of shadowing and root competition. In Victoria, its distribution is limited to small populations in mallee shrubland and lowland grassland & and grassy woodland. Affecting the lower stratum only.	Groves et al (1995) Carr et al (1992)	L
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“It is palatable and nutritious in the rosette stage and during flowering until the stems become lignified. Flowering stems are largely unpalatable.” Minor effect on fauna spp. through reduced food source.	Groves et al (1995)	ML
15. Benefits fauna?	The rosettes are palatable and nutritious. “Seed harvesting ants are known to remove skeleton weed seeds, although they are also known to consume many seeds.”	Groves et al (1995) P & C (2001)	MH
16. Injurious to fauna?	No	P & C (2001)	L
Pest Animal
17. Food source to pests?	Not known as a food source to pests.		L
18. Provides harbour?	Not known to provide harbour.		L
Agriculture
19. Impact yield?	“Competition for nitrogen and other nutrients by severe infestations is indicated by cereal yield losses as high as 50% in wet years and 80% in dry years.” Serious impacts on yield.	Groves et al (1995)	H
20. Impact quality?	“In most cases, cereal grain is harvested before skeleton weed produces seeds.”	P & C (2001)	L
21. Affect land value?	With the serious impact on agricultural yield in cropping areas and the difficulty in controlling the weed, the value of infested land may be seriously affected.		H
22. Change land use?	“The very deep root system and vigour of the plant makes skeleton weed difficult to control by the use of competing species. However, lucerne and other legumes are effective competitors in some areas and if a good stand can be established and carefully managed, the density of skeleton weed is considerably reduced over a number of years.” Land would be unavailable for a number of years for cropping activities.	P & C (2001)	M
23. Increase harvest costs?	“Light infestations can cause appreciable wear and tear to harvest machinery as well as delays through breakdowns, whilst heavy infestations can prevent harvesting because the stems are so entangled that many moving parts of the machinery become jammed.” Potential to affect harvest costs seriously.	Groves et al (1995)	H
24. Disease host/vector?	None evident.		L

Impact Assessment Record - Skeleton weed (PDF - 32KB)
Impact Assessment Record - Skeleton weed (DOC - 60KB)
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