Invasiveness Assessment - Italian buckthorn (Rhamnus alaternus) in Victoria

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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.

Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here.

The following table provides information on the invasiveness of Italian buckthorn.

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)
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Common Name: Italian buckthorn
Scientific name: Rhamnus alaternus

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Germination is reported to occur largely in spring and autumn if there is sufficient moisture (Blood 2001). Therefore the species is capable of germinating under natural seasonal conditions.	MH	MH
Establishment requirements?	Capable of establishing under low light conditions within existing vegetation (Blood 2001).	MH	MH
How much disturbance is required?	While the species is reported to prefer disturbed soil, it is capable of establishing within vegetation and is invasive in heathland (Blood 2001; Muyt 2001)	H	MH
Growth/Competitive
Life form?	Geophyte; has lignotuber, from which it can regrow (Blood 2001).	ML	MH
Allelopathic properties?	The plants leaves and fruits contain emodin at levels of 0.04% ± 0.05% d. wt, and 0.0017% ± 0.0006% d. wt, respectively. At levels of 10-100 mg l^-1 emodin can inhibit root and shoot growth of sunflower and corn (Izhaki 2002). Weber (2003) reports the levels of shade the species creates is thought to be the main agent in suppressing other species, however no studies on this species allelopathic ability have been reported. It is unknown to what level of impact any allelopathic properties Rhamnus alaternus might exhibit will have on other species.	M	M
Tolerates herb pressure?	The species’ leaves are reported to contain emodin which has been hypothesised as a deterrent against phytophagous insects (Izhaki 2002). The species is palatable to sheep and goats (Le Houérou 1980). A large amount of material is reported dumped due to the species fast growing nature and ability to sucker (Blood 2001). Therefore the species is considered capable of recovering from moderate grazing. However Aronne & Wilcock (1995) report that the fruit is formed on the one year old branches. Browsing may therefore have some impact on sexual reproduction but it would probably not eliminate it all together.	MH	MH
Normal growth rate?	Fast growing once established (Blood 2001). R.alaternus was shown to have an average relative growth rate after the first 6 months of growth in comparison with 9 other woody species native to the Mediterranean and almost double the average of the evergreen species (Ruiz-Robelto & Villar 2005). Therefore it is presumed to have equal growth to other competitive shrub species.	MH	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	Frost; tolerant -15ºC (Blood 2001). Tolerates drought (Blood 2001). Tolerates salt spray (Blood 2001). Can survive intense fire (Blood 2001). Tolerance to waterlogging is not reported, however the species preference for drier habitats may indicate a susceptibility (Polunin & Smythies 1973).	MH	MH
Reproduction
Reproductive system	Can reproduce sexually producing seed and vegetatively through root suckers (Weber 2003).	H	MH
Number of propagules produced?	Each fruit has between two and five seeds and while reportedly very variable fruit production per plant has been estimated at approximately 11,000 (Bas, Gómez & Pons 2005).	H	H
Propagule longevity?	Unknown.	M	L
Reproductive period?	Reported to be very long lived (Blood 2001). Therefore presumed to have a reproductive period greater than 10 years.	H	MH
Time to reproductive maturity?	Unknown.	M	L
Dispersal
Number of mechanisms?	The fruits have been reported to be eaten by starlings and blackbirds in New Zealand (Cole & Albrecht 1999 Produces fruits dispersed by birds, and possibly foxes and possums (Muyt 2001). Is also dispersed by ants in Europe (Aronne & Wilcock 1994; Gómez, Pons & Bas 2003).	H	H
How far do they disperse?	The fruits have been reported to be eaten by starlings (Sturnus vulgaris) in New Zealand (Cole & Albrecht 1999). The starling has been reported to have a seed dispersal range of 40 km (Spennemann & Allen 2000). The fruits of the species have been reported to contain emodin, which has been reported to potentially do two things, deter a bird from consuming too much and therefore reducing the possibility of seeds being excreted beneath the parent plant and shorten the bird’s digestion increasing the seeds viability but reducing the distance of dispersal (Izhaki 2002). The dispersal range of the species may therefore be less than the 40 km but still likely more than 1 km.	H	H

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