Impact Assessment - Tree of heaven (Ailanthus altissima) 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.

Question	Comments	Reference	Rating
Recreation
1. Restrict human access?	“A medium to large tree to 25 m tall. Freely suckers from roots forming thickets.” Occurs in a broad range of vegetative communities including riparian areas, artificial waterways and urban areas. Access to recreational areas may be severely restricted where thickets establish.	Blood (2001)	H
2. Reduce tourism?	Some water-based recreational activities may be affected where plant has formed thickets in riparian areas.		MH
3. Injurious to people?	Direct contact with the bark and leaves can cause dermatitis in humans.	Blood (2001)	H
4. Damage to cultural sites?	“[It] is blamed for blocking sewers and disturbing foundations of buildings.” “In Greece and Italy it threatens ancient walls and other significant ruins.” Potential to lead to major structural damage.	P & C (2001) Blood (2001)	H
Abiotic
5. Impact flow?	Terrestrial species.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	Root system comprises a deep taproot as well as many shallow laterals. Not likely to increase soil erosion.	P & C (2001)	L
8. Reduce biomass?	As a medium to large tree, biomass would increase.	P & C (2001)	L
9. Change fire regime?	It occurs in medium to large populations, and in dense patches it may increase the frequency and intensity of fire risk. Doesn’t burn readily – fire suppression in dry schlerophyll forest	Carr et al (1992)	ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Lowland forest (E); CMA=West Gippsland; Bioreg=Gippsland Plain; VH CLIMATE potential. Tree to 20 m. “Important competitor for both nutrients and light, the latter being the more severe because of the very large leaves and density of foliage.” It often occurs in monospecific stands. Displaces most species in lower or mid strata.	P & C (2001)	H
(b) medium value EVC	EVC=Valley grassy forest (D); CMA=East Gippsland; Bioreg=East Gippsland Lowlands; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	H
(c) low value EVC	EVC=Riparian forest (LC); CMA=East Gippsland; Bioreg=East Gippsland Uplands; VH CLIMATE potential. Impact as in 10(a) above.	P & C (2001)	H
11. Impact on structure?	“Leaf extracts contain allelopathic substances which adversely affect the growth of other plants, which might help explain the occurrence of the plant often in monospecific stands.” Major effect on all layers.	P & C (2001)	H
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	Its potential to establish a monoculture within an infestation would have a serious impact on fauna species. However, its distribution in Victoria is rare or localised thus limiting the impact. Reduction in local habitat.	Carr et al (1992)	MH
15. Benefits fauna?	No known benefits.		H
16. Injurious to fauna?	“Stock feed on the lower leaves, and sheep poisoning in New South Wales is suspected, but not confirmed.” Potential to be harmful to fauna species. Unknown for fauna spp to feed on plant	P & C (2001)	M
Pest Animal
17. Food source to pests?	Not known as a food source to pests.		L
18. Provides harbor?	Not known to provide harbor.		L
Agriculture
19. Impact yield?	Primarily a weed of urban areas. It is known to occur on undisturbed grazing land, but its impact on agricultural output is not documented.	P & C (2001)	L
20. Impact quality?	See repines in Q19 above	P & C (2001)	L
21. Affect land value?	See repines in Q19 above	P & C (2001)	L
22. Change land use?	See repines in Q19 above	P & C (2001)	L
23. Increase harvest costs?	See response in Q19 above	P & C (2001)	L
24. Disease host/vector?	None evident.		L

Impact Assessment Record - Tree of heaven (PDF - 34KB)
Impact Assessment Record - Tree of heaven (DOC - 59KB)
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