Impact Assessment - Hawthorn (Crataegus monogyna) 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 deciduous, dense shrub or small tree to 7 metres high and wide. Forms dense thickets that seriously impede movement. It invades a broad range of vegetation communities including riparian and coastal areas. Infestations likely to be a major impediment to humans.	Muyt (2001) P & C (2001)	H
2. Reduce tourism?	Dense infestations would have a major impact on tourism. It seriously impedes movement and has a major impact on bushland habitats.	Muyt (2001)	H
3. Injurious to people?	“…many stout branchlets terminating in spines, armed with thorns 5 to 25 mm long.” Spines present all year.	P & C (2001)	H
4. Damage to cultural sites?	C. monogyna forms dense thickets, which have a major impact on bushland habitats. It presence would create a moderate negative visual impact on the area. The root system is deep and spreading and may cause some structural damage.	Muyt (2001)	MH
Abiotic
5. Impact flow?	Terrestrial species.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	The deep spreading root system would effectively bind soil. Although deciduous, the dense growth habit of the plant still provides significant soil cover. Not likely to contribute to soil erosion.	P & C (2001)	L
8. Reduce biomass?	Where it occurs in thickets along roadsides, forest margins, and poorly managed pastures, the dense vegetative growth would increase biomass.	P & C (2001)	L
9. Change fire regime?	In forest margins dense infestations may create an increased risk to the frequency of fire risk. The flammability of the plant is not documented.		ML
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=West Gippsland; Bioreg=Gippsland Plain; VH CLIMATE potential. “When climate and soil are suitable it…forms dense stands.” It shades out ground-flora, “affecting the growth and regeneration of overstorey plants. Major impact on species within different layers.	P & C (2001) Muyt (2001)	MH
(b) medium value EVC	EVC=Montane grassy woodland (D); CMA=West Gippsland; Bioreg=Highlands – Southern Fall; VH CLIMATE potential. Similar impact as above.	P & C (2001) Muyt (2001)	MH
(c) low value EVC	EVC=Riparian forest (LC); CMA=West Gippsland; Bioreg=Gippsland Plain; VH CLIMATE potential. Similar impact as above.	P & C (2001) Muyt (2001)	MH
11. Impact on structure?	“Dense thickets…have a major impact on bushland habitats, shading out ground-flora and affecting the growth and regeneration of overstorey plants.” Has a major effect on the floral strata.	Muyt (2001)	MH
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	It has a major impact on bushland habitat. Spines deter grazing animals. Dense stands would significantly reduce habitat of native fauna.	Muyt (2001) P & C (2001)	MH
15. Benefits fauna?	Birds, possums and wallaroos are known to eat the fruit. Provides habitat and food for smaller native animals.	P & C (2001)	MH
16. Injurious to fauna?	Spines all year round; may injure larger grazing animals. “Some species of Crataegus contain hydrocyanic acid [and] should be considered potentially hazardous.”	P & C (2001)	H
Pest Animal
17. Food source to pests?	Birds and foxes are known to eat the fruit of C. monogyna.	P & C (2001)	H
18. Provides harbor?	“Dense patches provide good cover for rabbits and other pests.”	P & C (2001)	H
Agriculture
19. Impact yield?	“Dense stands reduce grazing capacity by direct competition and because the spines deter grazing animals. It is known that milk yields are reduced in the British Isles when cows graze hawthorn foliage.” Potential to establish dense patches would have a major impact on yield.	P & C (2001)	MH
20. Impact quality?	Not a plant of cropping. No documented effect on animal produce.	P & C (2001)	L
21. Affect land value?	Removing large infestations demands a major effort. Likely to have an impact on land value.	Muyt (2001)	M
22. Change land use?	It colonises poorly managed pastures. Depending upon the density of infestation, availability of land may be restricted until plant is controlled.	P & C (2001)	M
23. Increase harvest costs?	Not a plant of cropping; would have no impact on harvesting costs.	P & C (2001)	L
24. Disease host/vector?	“In the British Isles, hawthorn is an important reservoir of the fire blight bacterium which affects pears and apples.” “It hosts Mediterranean fruit fly and light brown apple moth.”	P & C (2001) Blood (2001)	H

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Impact Assessment Record - Hawthorn (PDF - 31KB)
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