Impact Assessment - Holly (Ilex aquifolium) 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 Holly.
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: Holly
Scientific name: Ilex aquifolium
| Question | Comments | Rating | Confidence |
| Recreation | |||
| 1. Restrict human access? | Forms dense thickets (Weber 2003). Has spiny leaves, therefore holly could be of high nuisance value restricting people and vehicles, however due to its slow growing nature it would be unlikely to cause tracks to become impassable. | MH | MH |
| 2. Reduce tourism? | Unknown | M | L |
| 3. Injurious to people? | Has poisonous berries, and leaves have spines (Blood 2001). The berries and leaves of the species are toxic, especially to children. Reported symptoms included nausea, vomiting, diarrhoea, collapsing and unconsciousness (Shepherd 2004). The spines on the leaves of holly are not however considered large and while toxic the fruit is not considered fatal and does not occur year round. | MH | MH |
| 4. Damage to cultural sites? | The species is reported to be valued in some historical situations (Blood 2001). Unknown if the species has any negative impact on infrastructure, cultural or heritage sites. | M | L |
| Abiotic | |||
| 5. Impact flow? | Terrestrial species, not reported to occur in flowing water. | L | M |
| 6. Impact water quality? | Terrestrial species not reported to impact on water quality. | L | M |
| 7. Increase soil erosion? | Unknown; The species is reported as strong rooted and from an early age develop a tap root (Muyt 2001). | M | L |
| 8. Reduce biomass? | Can create a taller shrub layer, therefore invasion by holly could increase biomass or result in direct replacement (Weber 2003). | ML | MH |
| 9. Change fire regime? | Unknown; After an intense fire damaged plants can regrow from the root stock (Peterken & Loyd 1967). | M | L |
| Community Habitat | |||
| 10. Impact on composition (a) high value EVC | EVC= Creekline Herb-rich Woodland (V); CMA= Corangamite; Bioreg= Central Victorian Uplands; VH CLIMATE potential. Holly can form dense thickets, creating a tall species poor shrub layer which also impacts upon the lower strata (Weber 2003). Therefore the species is capable of causing major displacement within a layer. | MH | MH |
| (b) medium value EVC | EVC= Lowland Forest (D); CMA= Corangamite; Bioreg= Otway Plain; VH CLIMATE potential. Holly can form dense thickets, creating a tall species poor shrub layer which also impacts upon the lower strata (Weber 2003). Therefore the species is capable of causing major displacement within a layer. | MH | MH |
| (c) low value EVC | EVC= Wet Forest (LC); CMA= Corangamite; Bioreg= Otway Plain; VH CLIMATE potential. Holly can form dense thickets, creating a tall species poor shrub layer which also impacts upon the lower strata (Weber 2003). Therefore the species is capable of causing major displacement within a layer. | MH | MH |
| 11. Impact on structure? | Holly can form dense thickets, creating a tall species poor shrub layer which also impacts upon the lower strata and can prevent regeneration (Muyt 2001; Weber 2003). Therefore the species is capable of causing major displacement within the shrub layer and possibly the lower strata and prevent the regeneration of canopy species. | MH | MH |
| 12. Effect on threatened flora? | Unknown. | MH | L |
| Fauna | |||
| 13. Effect on threatened fauna? | Unknown. | MH | L |
| 14. Effect on non-threatened fauna? | Unknown; The impact the species has on the vegetation of the invaded ecosystem could effect available habitat and alter food supply; however this is not specifically reported. | M | L |
| 15. Benefits fauna? | Fruits eaten by birds and possibly possums (Muyt 2001; Williams et al 2000). Forms thickets which may be used for shelter (Weber 2003). Unknown how important this can be to desirable species. | M | MH |
| 16. Injurious to fauna? | The leaves are spiny, the fruit is toxic to people not reported to effect birds or animals (Blood 2001). | MH | MH |
| Pest Animal | |||
| 17. Food source to pests? | Fruit eaten to some extent by foxes (Garcia, Martinez & Obeso 2007). Browsed by goats and deer (Obeso 1997). | MH | H |
| 18. Provides harbour? | Forms thickets which may be used for shelter (Weber 2003). It is not specifically reported to shelter pest species. | M | MH |
| Agriculture | |||
| 19. Impact yield? | It is reported to invade pasture and could occur in Forestry (Blood 2001). As grazing limits the species growth and it is reported to be slow growing it is unlikely to have significant impacts on product yield. | L | MH |
| 20. Impact quality? | It is reported to invade pasture and could occur in Forestry (Blood 2001). As grazing limits the species growth and it is reported to be slow growing it is unlikely to have significant impacts on product quality. | L | MH |
| 21. Affect land value? | Unknown. | M | L |
| 22. Change land use? | It is reported to invade pasture and could occur in Forestry (Blood 2001). As grazing limits the species growth and it is reported to be slow growing it is unlikely to cause a change in land use. | L | MH |
| 23. Increase harvest costs? | The species could occur in forestry and while it’s slow growing it is reported to form thickets (Blood 2001; Weber 2003). This may restrict access to plantations and slightly increase the time taken for maintenance. It is reported to invade pasture (Blood 2001). However as grazing limits the species growth it is unlikely to impact upon the cost of production. | M | M |
| 24. Disease host/vector? | Not reported to be a host or vector of pest species of agricultural crops. | L | M |
This table can also be viewed as a PDF document (printer friendly).
Impact Assessment Record - Holly (PDF - 75KB)
Impact Assessment Record - Holly (DOC - 58KB)
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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