Holly (Ilex aquifolium) – risk assessment notes
Originates from West Asia, North Africa, and South and West Europe (Kew Royal Botanic Gardens 2016)
Domestication/Cultivation
1.01.Species highly domesticated?
Yes
1.02.Naturalised where grown?
Yes
1.03.Weedy races?No, none known
Climate and distribution
2.01. Suited to Australian climates?Yes, naturalised in south-eastern Australia (including Tasmania, Victoria, New South Wales, and South Australia (Queensland Government 2016). Climatch modelling indicates very strong suitability to much of Tasmania(Figure 1) (DEPI 2014). Given naturalisations in four jurisdictions and the Climatch finding, Ilex aquifoliumis given a score of 2.
2.02. Quality of climate match data?Tasmanian Climatch assessmenthas been undertaken - see Figures 1. They indicate strong suitability to much of south-eastern Australia. Score of 2.
2.03. Broad climate suitability? Yes. Climatch modelling indicates suitability through a broad area of southern Australia – parts of Western Australia, South Australia, Victoria, New South Wales, and Tasmania.
2.04. Native/Naturalised in regions with extended dry periods?Yes, in its native region, the driest quarter of the year can average less than 50mm rainfall e.g. Fez, Morocco (World Weather Online 2016). ‘tolerates Mediterranean summer drought’ (Encyclopaedia of Life 2016).
2.05. History of repeated introductions outside natural range?Yes, naturalised in western USA, Hawaii, New Zealand and Australia (including Tasmania, Victoria, New South Wales and South Australia (Queensland Government 2016).
Weed elsewhere
3.01. Naturalised beyond native rangeYes, naturalised in western USA, Hawaii, New Zealand and Australia (including Tasmania, Victoria, New South Wales and South Australia (Queensland Government 2016).
3.02. Garden/amenity/disturbance weed?Yes, ‘English holly has escaped cultivation and become invasive …’ (DiTomaso and Healy 2007)
3.03. Weed of agriculture?No
3.04. Environmental weed?Yes, ‘regarded as a significant environmental weed in Victoria and as an environmental weed in South Australia, New South Wales and Tasmania (Queensland Government 2016).
3.05. Congeneric weed?Yes, other Ilex species (e.g. I. ambigua, I. decidua) recorded as weeds (Randall 2012).
Undesirable traits
4.01. Spines, thorns, burrs?Yes, spines on leaves
4.02. Allelopathic?No, no evidence of this found.
4.03. Parasitic?No, no documented evidence of this found.
4.04. Unpalatable to grazing animals?No. Palatable to cattle, sheep, goats, and deer (Blood 2001, Victoria State Government 2016)
4.05. Toxic to animals?No, no evidence of this.
4.06. Host to pests and pathogens?No, no documented evidence of this found.
4.07. Toxic to humans?Yes, berries ‘mildly poisonous to humans, causing vomiting’ (Encyclopaedia of Life 2016). ‘Toxic leaves and poisonous berries’ (Blood 2001).
4.08. Fire hazard?Unknown
4.09. Shade tolerant?Yes, ‘is tolerant of shade and often grows as a shrub in the understorey of woodlands’ (Encyclopaedia of Life 2016).
4.10. Grows in infertile soils?Yes,‘can grow in light, sandy soil, medium soil, and even relishes in heavy, clay soil. It can survive in extremely acidic environments …‘(University of Wisconsin – La Crosse 2016). ‘A rugged pioneer species that preserves and enriches the soil facilitating colonisation by others’ (Encyclopaedia of Life 2016).
4.11. Climbing or smothering habit?No, no documented evidence of this found.
4.12. Dense thickets?Yes, ‘forms dense thickets’ (Weber 2003).
Plant Type
5.01. AquaticNo
5.02. GrassNo
5.03. Nitrogen fixing woody plant?No
5.04. Geophyte?No
Reproduction
6.01. Reproductive failure in native habitat?No
6.02. Viable seed?Yes, (Blood 2001,Muyt 2001).
6.03. Hybridised naturally?Unknown
6.04. Self-compatible or apomicticNo, dioecious - male and female plants (Popay et al 2010)
6.05. Specialist pollinators?No, ‘pollination is generally performed by bees and other insects’ (Kew Royal Botanic Gardens 2016).
6.06. Reproduces by vegetative fragmentation?Yes, ‘vegetative reproduction can … occur where dislodged stem pieces contact moist soil’ (Muyt 2001).
6.07. Minimum generative time? First flowering 5+ years(Blood 2001)
Dispersal
7.01. Dispersed unintentionally?Yes, ‘spread by birds and animals (internal) and in dumped garden waste’ (Blood 2001).
7.02. Dispersed intentionally by peopleYes, ‘widely available in nurseries, garden centres and markets, and in florist shops’(Blood 2001).
7.03. Produce contaminant?No, no documented evidence of this found.
7.04. Wind dispersal?No
7.05. Propagules buoyant?Unknown
7.06. Bird dispersed?Yes (Blood 2001, Muyt 2001)
7.06. Dispersed by other animals?No – this question only relates to external dispersal
7.07. Propagules survive passage through gut?Yes (Blood 2001, Muyt 2001)
Persistence attributes
8.01. Prolific seed production (>2000/m sq.)Yes, 4-5 seeds per fruit (Blood 2001). Fruit production per tree in Spain was measured at approximately 10000 over a ten year period (State of Victoria 2016).
8.02. Persistent seed bank?No, ‘short-persistent seed bank’ (Arrieta and Suarez 2004).
8.03. Well controlled by herbicides?Yes (Muyt 2001).
8.04. Benefits from mutilation/cultivation?Yes, damage can produce suckering and vegetatively reproduces (Blood 2001, Muyt 2001).
8.05. Natural enemies in Australia?Unknown, no documented evidence of this found.
Figure 1. Climatch assessment for Ilex aquifoliumusing source locationdata from. Climatch conducted by Michael Noble 17 February 2016.
References
Arrieta, S. and Suarez, F. (2004). Germination and seed bank depletion of holly (Ilex aquifolium) in four microhabitat types. Seed Science Research 14(3), pp. 305-313.
Blood, K. (2001). Environmental weeds – a field guide for SE Australia. CH Jerram & Associates – science publishers, Mt Waverley, Victoria.
Carr, G.W., Yugovic, J.V. and Robinson, K.E. (1992). Environmental weed invasions in Victoria – conservation and land management implications. Department of Conservation and Environment, East Melbourne, Victoria and Ecological Horticulture Pty Ltd, Clifton Hill, Victoria.
Csurhes, S. and Edwards, R. (1998). National weeds program potential environmental weeds in Australia – candidate species for preventative control. (accessed 16 January 2016).
DiTomaso, J.M. and Healy, E.A. (2007). 'Weeds of California and other western states – Volume 1'. (University of California, Oakland, California).
Encyclopaedia of Life (EOL) (2016). Ilex aquafolium common holly. (accessed 17 February 2016).
Kew Royal Botanic Gardens (2016). Ilex aquafolium (common holly). (accessed 17 February 2016).
Muyt, A. (2001). Bush invaders of south-east Australia. R.G. and F.J. Richardson, Meredith, Victoria.
Popay, I., Champion, P. and James, T. (2010). An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand).
Queensland Government (2016).Holly Ilex aquifolium. 16 February 2016).
Randall, R.P. 2012. A global compendium of weeds (2nd Ed.). Department of Agriculture and Food, Western Australia.
University of Wisconsin – La Crosse (2016). English holly (Ilex aquifolium) (accessed 17 February 2016).
Victoria State Government (2016). Invasiveness assessment – holly (Ilex aquifolium) in Victoria. (accessed 16 February 2016).
World Weather Online (2016). Fez monthly climate average, Morocco. 17 February 2016).