Impact Assessment - Greater bindweed (Calystegia silvatica) 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 Greater bindweed

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 - 1 MB)
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: Greater bindweed
Scientific name: Calystegia silvatica

Question	Comments	Reference	Rating
Recreation
1. Restrict human access?	Weed is found in waste places, roadsides and forest margins (Brummitt 2002). A creeper growing to 3 m or more. Because of the places it grows, and as it climbs over other plants, it would have a negligible impact upon access	L	H
2. Reduce tourism?	‘Very conspicuous even to a passing motorist’ (Brummitt 2002). ‘Strongly climbing stems and the large white flowers were very conspicuous’ (Brummitt 2002). Minor effects to aesthetics.	ML	H
3. Injurious to people?	Plant not documented to cause injury or be toxic to humans.	L	H
4. Damage to cultural sites?	‘Very conspicuous even to a passing motorist’ (Brummitt 2002). ‘Strongly climbing stems and the large white flowers were very conspicuous’ (Brummitt 2002). If plant occurred at a cultural site it would have a moderate visual effect.	ML	H
Abiotic
5. Impact flow?	Terrestrial species.	L	H
6. Impact water quality?	Terrestrial species.	L	H
7. Increase soil erosion?	‘.. shallow rhizomes spread for several metres under the soil surface, and root at the nodes’. ‘Aerial parts usually dying down in winter’ (Roy et al 1998) Occurs in already disturbed sites and would leave some soil exposed during winter but low probability of large-scale soil movement.	L	MH
8. Reduce biomass?	Found ‘in great abundance on waste ground over a distance of perhaps 100 m, swamping other vegetation and climbing to a height of 3 m’ (Brummitt 2002). Very vigorous habit and large glossy leaves. Likely to be an increase in biomass.	L	H
9. Change fire regime?	‘Aerial parts usually dying down in winter’ (Roy et al 1998). Climber with large glossy leaves occurring in waste places, roadsides and forest margins. Plant would have a small or negligible effect on fire risk.	L	MH
Community Habitat
10. Impact on composition (a) high value EVC	EVC= Plains grassland (BCS =E); CMA=Port Phillip; Bioreg=Gippsland Plain; CLIMATE potential=VH. Found ‘in great abundance on waste ground over a distance of perhaps 100 m, swamping other vegetation and climbing to a height of 3 m’ (Brummitt 2002). Major displacement of some dominant species within a strata.	MH	H
(b) medium value EVC	EVC= Riverine grassy woodland (BCS =D); CMA=Mallee; Bioreg= Murray mallee; CLIMATE potential=L. Found ‘in great abundance on waste ground over a distance of perhaps 100 m, swamping other vegetation and climbing to a height of 3 m’ (Brummitt 2002). Minor displacement of some dominant species within a strata.	ML	H
(c) low value EVC	EVC= Coastal tussock grassland (BCS =LC); CMA=Port Phillip; Bioreg=Gippsland Plain; CLIMATE potential=VH. Found ‘in great abundance on waste ground over a distance of perhaps 100 m, swamping other vegetation and climbing to a height of 3 m’ (Brummitt 2002). Major displacement of some dominant species within a strata.	MH	H
11. Impact on structure?	Found ‘in great abundance on waste ground over a distance of perhaps 100 m, swamping other vegetation and climbing to a height of 3 m’ (Brummitt 2002). Would have a major effect on the lower layers of the floral stratum	MH	H
12. Effect on threatened flora?	This species is not documented as posing an additional risk to threatened flora.	MH	MH
Fauna
13. Effect on threatened fauna?	This species is not documented as posing an additional risk to threatened fauna.	MH	MH
14. Effect on non-threatened fauna?	Weed not documented to have an effect on non-threatened fauna species.	L	MH
15. Benefits fauna?	Weed not known to facilitate the establishment of indigenous fauna.	H	MH
16. Injurious to fauna?	Weed not known to be toxic or have an effect on indigenous fauna.	L	MH
Pest Animal
17. Food source to pests?	Weed not known to provide a food source to pest animals.	L	MH
18. Provides harbor?	Weed not known to provide harbour for pest species.	L	MH
Agriculture
19. Impact yield?	In New Zealand, Calystegia silvatica grows in some asparagus crops ‘as their growth habits are somewhat similar to asparagus and herbicides do not provide adequate long term control’. ‘In asparagus.. weeds present during the growing season not only reduce the yield for the current season …but restrict replenishment of carbohydrate reserves in the crop for the next season’s growth’ (Rahman & Sanders 1996). Minor impact on quantity of produce.	ML	H
20. Impact quality?	Weed not documented in Rahman and Sanders (1996) to impact upon quality.	L	H
21. Affect land value?	Calystegia silvatica is ‘tolerant to most pre-emergent herbicides used in asparagus’ (Rahman & Sanders 1996). However, no evidence to suggest that presence of this weed would effect land value.	L	H
22. Change land use?	No evidence to suggest that this weed would cause a change in priority of land use.	L	H
23. Increase harvest costs?	‘Their sprawling climbing stems make harvesting of spears very difficult as they cover the rows and entwine the growing spears’ (Rahman & Sanders 1996). Minor increase in cost of harvesting – more time and labour would be required.	M	H
24. Disease host/vector?	Weed not known to act as an alternative host or vector for disease of agriculture.	L	H

This table can also be viewed as a PDF document (printer friendly).

Impact Assessment Record - Greater bindweed (PDF - 69KB)
Impact Assessment Record - Greater bindweed (DOC - 65KB)
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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