Impact Assessment - Blackberry (Rubus fruticosus agg.) 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?	“Blackberry forms dense, impenetrable thickets…often along watercourses.” Presents a major impediment to both human and vehicular traffic.	Muyt (2001)	H
2. Reduce tourism?	“It is the bane of bushwalkers and fishing enthusiasts.” Its dense form can seriously affect recreational pursuits.	Blood (2001)	H
3. Injurious to people?	Canes, which can grow up to seven metres in lengths, are covered in large, sharp prickles. Dead canes remain attached to the crown indefinitely. This presents a constant hazard to people.	Muyt (2001)	MH
4. Damage to cultural sites?	Although forming dense thickets, the root system is not extensive or highly vigorous. The plant is unlikely to cause structural damage to cultural features or structures, but would have a moderate visual impact.	P & C (2001)	ML
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 plant was initially recommended for soil stabilisation on riverbanks, but, “lack of other vegetation can eventually destabilised an area.” Potential for high probability of large scale soil movement.	Muyt (2001)	MH
8. Reduce biomass?	Many plants become deciduous during the cooler months and, as a dominant species, it would potentially decrease biomass. “As much as 70% of the mass of the clump may consist of dead canes.”	Muyt (2001) P & C (2001)	MH
9. Change fire regime?	“As much as 70% of the mass of the clump may consist of dead canes…and large clumps are a considerable fire hazard.”	P & C (2001)	MH
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Plains grassy woodland (E); CMA=Corangamite; Bioreg=Otway Plain; VH CLIMATE potential “…blackberry completely dominates the vegetation of an area in a very short time. Regeneration of native plants is seriously impeded.” Monoculture.	P & C (2001)	H
(b) medium value EVC	EVC=Grassy dry forest (D); CMA=Corangamite; Bioreg=Central Victorian Uplands; VH CLIMATE potential “…blackberry completely dominates the vegetation of an area in a very short time. Regeneration of native plants is seriously impeded.” Monoculture within mid stratum	P & C (2001)	H
(c) low value EVC	EVC=Lowland forest (LC); CMA=Corangamite; Bioreg=Central Victorian Uplands; VH CLIMATE potential “…blackberry completely dominates the vegetation of an area in a very short time. Regeneration of native plants is seriously impeded.” Monoculture within mid stratum.	P & C (2001)	H
11. Impact on structure?	“…it covers large areas with a dense canopy excluding light from the soil surface. Few other plants can compete and blackberry completely dominates the vegetation of an area in a very short time. Regeneration of native plants is seriously impeded.” Monoculture, or close enough!	P & C (2001)	H
12. Effect on threatened flora?	Threatens ANZECC rated rare or threatened native plant species	Groves et al (2003)	H
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	Because of its spreading habit, dominant nature, and spiny canes, it reduces the habitat for native fauna.	Blood (2001)	MH
15. Benefits fauna?	The native birds crimson rosella (Platycercus elegans), and the red browed finch (Neochima temporalis), and emus (Dromaius novaehollandiae) feed on the berries.	Panetta et al (1998)	MH
16. Injurious to fauna?	“Thorns are a problem for grazing animals.” A similar situation would exist for native fauna.	Blood (2001)	MH
Pest Animal
17. Food source to pests?	The berries are a food source for foxes and the introduced starling (Sturnus vulgaris L.) and blackbird (Turdus merula L.).	Panetta et al (1998)	MH
18. Provides harbor?	It provides harbor for rabbits, foxes and snakes.	P & C (2001)	H
Agriculture
19. Impact yield?	“In agricultural production the main industries affected are grazing and forestry.” Production of timber in forest plantations is reduced…natural regeneration of hardwood plantations can be prevented or reduced. Heavy infestations in pastures reduce carrying capacity because of access limitations and reduced availability of fodder.	Bruzzese & Lane (1996) 1 Panetta et al (1998) P & C (2001)	H
20. Impact quality?	No recorded level of impact on quality.		L
21. Affect land value?	Its ability to significantly reduce available pasture, and the high cost and time taken to control the plant suggest that land prices would be affected by more than 10%. “Some property values have been substantially decreased, due to heavy infestations of blackberry across the property.”	P & C (2001) 2	H
22. Change land use?	While heavy infestations limit carrying capacity, grazing of canes and stem damage through stock movement reduces tip-rooting and thus slow the spread of the plant. Paddocks can still be used, but with limited return. Neglected farming areas can be totally over-run with blackberry, effectively rendering the land useless.	P & C (2001)	H
23. Increase harvest costs?	The plant is recorded as occurring in orchards, however, no evidence exists of the impact on harvest costs. Not a significant weed of cropping.	P & C (2001)	L
24. Disease host/vector?	None evident		L