Impact Assessment - Cutch tree (Acacia catechu) 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	Rating	Confidence
Recreation
1. Restrict human access?	Trees range from 3 to 15 metres with average height when fully grown between 10 to 15 metres (CABI 2005). Trees have a light feathery crown. Forms ‘dense impenetrable stands and the sharp thorns .. can impede the movement and mustering of stock’. When fully grown, stems up to 30 cm diameter (CRC for Australian Weed Management 2003). As common on riverbanks and watersheds, plant would be a major impediment to access waterways.	H	MH
2. Reduce tourism?	As the weed can be found on riverbanks and watersheds, it is possible that some recreational uses may be affected e.g. swimming, fishing, boating (World Agroforestry Centre 2005).	MH	MH
3. Injurious to people?	The branchlets have ‘twin hooked prickles’. These prickles are present throughout the year (CABI 2005).	H	MH
4. Damage to cultural sites?	Not likely that the plant would do any structural damage but due to size and potential to spread (CABI 2005), would have moderate visual effect.	ML	MH
Abiotic
5. Impact flow?	Terrestrial species (CABI 2005).	L	MH
6. Impact water quality?	Terrestrial species (CABI 2005).	L	MH
7. Increase soil erosion?	‘..apart from checking soil erosion. On steep slopes, its roots bind the soil and prevent landslides or excessive erosion’. Tree has a strong primary root (up to 2 metres deep) which is long and wiry with lateral short, fibrous roots (CABI 2005). Does not replace ground cover so unlikely to leave ground exposed. Low probability of large scale soil movement.	L	MH
8. Reduce biomass?	As the plant likes open woodlands and grasslands with a tendency to invade degraded areas (CRC for Australian Weed Management 2003), biomass may increase.	L	M
9. Change fire regime?	Deciduous tree. Although ‘the wood is excellent firewood’, and would burn well once ignited there is nothing to indicate that the tree would change the frequency or intensity of fires (CABI 2005). In Australia, the known distribution of Acacia catechu is sparse so wouldn’t contribute to either intensity or frequency.
Community Habitat
10. Impact on composition (a) high value EVC	Potential distribution of Acacia catechu excludes Victoria. No impact on EVCs in Victoria.	L	H
(b) medium value EVC	Potential distribution of Acacia catechu excludes Victoria. No impact on EVCs in Victoria.	L	H
(c) low value EVC	Potential distribution of Acacia catechu excludes Victoria. No impact on EVCs in Victoria.	L	H
11. Impact on structure?	Found with other dry deciduous species, and grasses. Can occur in both open grasslands and also within dry forests (CABI 2005). ‘Occurs as a weedy shrub on overgrazed grasslands’ (Parsons & Cuthbertson 2001). Therefore, it may exclude understorey species e.g grasses. Will affect only one of the stratum.	L	MH
12. Effect on threatened flora?	The potential for Acacia catechu to establish and naturalise in Victoria is highly unlikely due to ecoclimatic limitations. No impact on threatened flora in Victoria.	L	H
Fauna
13. Effect on threatened fauna?	The potential for Acacia catechu to establish and naturalise in Victoria is highly unlikely due to ecoclimatic limitations. No impact on threatened fauna in Victoria.	L	H
14. Effect on non-threatened fauna?	‘The sharp thorns .. can impede the movement and mustering of stock’ (CRC for Australian Weed Management 2003). In agricultural situations the plant may be a problem but in natural situations may not hinder or affect fauna e.g. access to water, but may have a minor effect	ML	M
15. Benefits fauna?	In India it is known to be ‘an excellent source of food for wildlife’ (CABI 2005). May provide an alternate food source for native fauna.	ML	MH
16. Injurious to fauna?	‘The bark is toxic and contains an alkaloid’ (CABI 2005). However, it is a common fodder species within its native range for both wild and domesticated animals so toxicity likely to have little effect. Forms ‘dense impenetrable stands and the sharp thorns .. can impede the movement and mustering of stock’ (CRC for Australian Weed Management 2003).	ML	MH
Pest Animal
17. Food source to pests?	‘Is a useful fodder species.. browsed by cattle, rhinoceros, deer and elephants’. Rodents are also reported to damage the tree’ (CABI 2005). May supply food for one or more minor pest spp.	ML	MH
18. Provides harbor?	No evidence in CABI (2005) that the weed provides harbour for pest spp.	L	MH
Agriculture
19. Impact yield?	Dense patches ‘impede stock movement and access to other pasture plants’ (Parsons & Cuthbertson 2001). Could impact stock access to water with potential to have minor impact on quantity of produce.	ML	MH
20. Impact quality?	Not known to effect quality of produce.	L	MH
21. Affect land value?	No documented evidence that weed would affect land value.	L	MH
22. Change land use?	No evidence to suggest that the weed would cause a change in priority of land use.	L	MH
23. Increase harvest costs?	No evidence to suggest that the weed would increase the cost of harvest.	L	MH
24. Disease host/vector?	Not a known host or vector for diseases of agriculture.	L	MH