Impact Assessment - Bindweed (Convolvulus arvensis) 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 prostrate trailing and twining perennial herb. Would present minimal impact on human access.	P & C (2001)	L
2. Reduce tourism?	A strong competitor it can dominate in open areas. However, its prostrate form would not seriously affect recreation.	P & C (2001)	L
3. Injurious to people?	No toxic principles or harmful physical properties.		L
4. Damage to cultural sites?	The plant has a vigorous root system that, “…also allows shoots to push through asphalt paths.” This vigour could also have some impact on the structure of cultural sites or features.	P & C (2001)	MH
Abiotic
5. Impact flow?	Terrestrial species. Does not survive in waterlogged situations.	P & C (2001)	L
6. Impact water quality?	Terrestrial sp.	P & C (2001)	L
7. Increase soil erosion?	Perennial with tap root to three metres deep and numerous horizontal roots between 0.6 to 2 metres deep. Would not increase soil erosion.	P & C (2001)	L
8. Reduce biomass?	Occurring predominantly in agricultural situations where it, “…eliminates more valuable pasture species and smothers cereal crops.” Invader directly replaces biomass.	P & C (2001)	ML
9. Change fire regime?	Aerial growth dies off in autumn. In cropping situation, dry matter left with remnant material from harvest. Likely to have little effect on changing fire regime.	P & C (2001)	L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=Glenelg Hopkins; Bioreg=Glenelg Plain; VH CLIMATE potential The plant has a dominant growth habit in pasture and cultivated areas. While not a significant weed of natural ecosystems, where it does occur, it is likely to dominate the ground flora in low quality, open grassland areas. It does not grow well under the shade of other plants. Major effect on ground-flora.	P & C (2001) Holm et al (1977)	MH
(b) medium value EVC	EVC=Herb-rich heathy woodland (D); CMA=Glenelg Hopkins; Bioreg=Glenelg Plain; VH CLIMATE potential The plant has a dominant growth habit in pasture and cultivated areas. It does not grow well under the shade of other plants. Minor effect on ground flora/forbs in this EVC.	P & C (2001) Holm et al (1977)	ML
(c) low value EVC	EVC=Heathy woodland (LC); CMA=Glenelg Hopkins; Bioreg=Glenelg Plain; VH CLIMATE potential The plant has a dominant growth habit in pasture and cultivated areas. It does not grow well under the shade of other plants. Minor effect on ground flora/forbs in this EVC.	P & C (2001) Holm et al (1977)	ML
11. Impact on structure?	The plant has a dominant growth habit in pasture and cultivated areas. While not a significant weed of natural ecosystems, where it does occur, it is likely to dominate the ground flora in low quality, open grassland areas. It does not grow well under the shade of other plants. Likely to affect 20–60% of the floral strata.	P & C (2001) Holm et al (1997) 1	MH
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	“It occurs on roadsides, railway lines, and neglected areas in both urban and rural areas.” Its effect on the habitat of native fauna would be minimal.	P & C (2001)	ML
15. Benefits fauna?	The plant is eaten by stock and may provide some food source to native herbivores. However, it is regarded as having little fodder value.	P & C (2001)	MH
16. Injurious to fauna?	“It may be toxic or emetic and is suspected of causing photosensitisation in susceptible animals and of poisoning pigs after eating the roots.”	P & C (2001)	MH
Pest Animal
17. Food source to pests?	Birds are a known vector for seed, however, bird species are not recorded. Assume potential for pest species to forage	P & C (2001)	ML
18. Provides harbor?	The aerial parts of the plant die back in autumn leaving little cover for harbor. May provide limited harbor for mice or other small rodents during growth and flowering stages.	P & C (2001)	ML
Agriculture
19. Impact yield?	“It is a strong competitor with cereal crops in North America where crop reductions of 30% to 40% are not uncommon. In some years Kansas wheat and Canadian grain sorghum are reduced by 80%.”	P & C (2001)	H
20. Impact quality?	“Seeds contaminate grain for sowing, particularly wheat.” Plants can produce up to 500 seeds. Likely to have at least a minor impact on quality.	P & C (2001)	ML
21. Affect land value?	The plant seriously affects yield and it requires a concerted control program for several years to eradicate it. This would have a negative influence on price, depending upon type of agricultural activity.	P & C (2001)	M
22. Change land use?	“In California…some areas had been abandoned because of the weed.”	P & C (2001)	H
23. Increase harvest costs?	“The long stems twine through the maturing crop, which makes harvesting difficult or impossible.” Significant potential for increase harvest costs.	P & C (2001)	H
24. Disease host/vector?	“It is an alternative host for a number of viruses… and hosts several arthropods and nematodes of agricultural importance.”	P & C (2001)	H