Interim profile, incomplete information
Taxonomic name: Rhododendron ponticum L.
Synonyms: Rhododendron lancifolium Moench, Rhododendron speciosum (Willd.) Sweet.
Common names: common rhododendron (English), Pontian rhododendron (English), rhododendron (English)
Organism type: shrub
Rhododendron ponticum often simply called rhododendron, is an evergreen shrub that has been widely cultivated as an attractive ornamental species. In ideal conditions R. ponticum can form dense stands which can inhibit the regeneration of native species and alter plant and animal communities. Control of R. ponticum is best achieved using a combination of physical and chemical methods, however this is usually an expensive and labour intensive process due to the high numbers of wind dispersed seed produced and the ability to resprout vigorously from its stumps and roots.
natural forests, planted forests, range/grasslands, scrub/shrublands, urban areas
Rhododendron ponticum is tolerant to a wide range of temperatures and to shade, but is intolerant to drought; it grows best in uniformly damp climates (Hulme, 2006; Maguire et al., 2008). R. ponticum is capable of thriving on peaty, sandy or acidic soils (Maguire et al., 2008) and while seedling recruitment is inhibited in areas where there is an existing continuous ground cover by native species, R. ponticum is able to establish readily in disturbed areas where a gap is present (Hulme, 2006). Distribution modelling has shown that fallen logs or tree stumps with light moss levels also provide establishment opportunities for R. ponticum in areas of existing ground cover (Stephenson et al., 2006).
Native Range: Rhododendron ponticum displays a disjunct native distribution, with R. ponticum ssp. baeticum found in south-west Spain and southern Portugal, and R. p. ponticum found in Turkey, Lebanon, Bulgaria and the Caucasus (Hulme, 2006).
Known Introduced Range: Rhododendron ponticum is known to have naturalised in the United Kingdom, Ireland, Belgium, France and Netherlands with an increasing invasion trend in continental Europe. It is also reported to be naturalised in New Zealand (USDA-ARS, 2010) and present in Austria (Hulme, 2006).
Introduction pathways to new locations
For ornamental purposes: Rhododendron ponticum has been widely distributed in the British Isles as an ornamental plant (Dehnen-Schmutz, et al., 2004).
Horticulture: Rhododendron ponticum was used as a rootstock species for less hardy Rhododendron species and cultivars (Edwards, 2006).
Landscape/fauna "improvement": Rhododendron ponticum was historically planted as game cover in woodland habitats as a suitable habitat for pheasants (Dehnen-Schmutz, et al., 2004).
Local dispersal methods
Natural dispersal (local): Rhododendron ponticum is able to propagate itself through vegetative means, both by suckering from roots and by layering wherever branches touch the ground (Maguire et al., 2008).
On animals: A single mature Rhododendron ponticum individual is capable of producing a million tiny seeds per year which are easily dispersed by wind or on animal fur (Tabbush & Williamson, 1987; in Green, 2003).
Wind dispersed: A single mature Rhododendron ponticum individual is capable of producing a million tiny seeds per year which are easily dispersed by wind or on animal fur (Tabbush & Williamson, 1987; in Green, 2003). Strong winds are thought to be able to disperse seeds effectively over distances of about 100 m and very occasionally 1000 m or more (Shaw, 1984; in Stephenson et al., 2007).
Preventative measures: Preventing the establishment of Rhododendron ponticum should vary according to the major colonising strategy in the area and may include eradication of seed sources, minimising soil disturbance, reducing moss formation, relaxing fire exclusion policies and preserving plant cover (Esen et al., 2006a); or the regulation and planning of forest activities to reduce disturbance levels (Colak, 1997; in Esen et al., 2006a).
Prioritisation: Prioritisation of control sites is important for the long term control of R. ponticum with different best practice guides recommending he prioritisation of different infestation types based on the age and condition of the infestation and nearby seed sources (Barron, undated; Edwards, 2006).
Physical control: Physical control can include the hand pulling of seedlings and smaller plants, which may involve the use of handtools (Edwards, 2006). Above ground material can also be removed with handtools or chainsaws with cut material either removed, chipped or burnt to enable necessary follow up work to continue (Barron, undated; Edwards, 2006; Maguire et al., 2008). Heavy machinery can also be used to removed material, and while faster, it requires road access, is expensive and may cause damage to the soil and environment (Walter, 2005; Esen et al., 2006a; Maguire et al., 2008). Follow up treatments are always required for the stumps of R. ponticum as resprouting will occur otherwise (Edwards, 2006). In terms of physical control, this can be achieved by digging out the stumps either by hand or with heavy machinery and can be a very labour intensive process (Barron, undated; Maguire et al., 2008).
Chemical control: Stumps of R. ponticum are more commonly treated with herbicides with a number of different applications including painting or spraying freshly cut stumps and stem injection techniques; foliar application through spraying or weed wiping is also possible and are preferred in some situations (Walter, 2005; Edwards, 2006; Maguire et al., 2008). There are a number of different herbicides used at different rates which may be used successfully, their use and the application method utilised depending on a number of factors (Edwards, 2006)
Biological control: The indigenous wood-rotting fungus Chondrostereum purpureum has been recognised as a potential bioherbicide option in the UK, allowing for the controlled distribution of a biological control agent without the risk of harming other cultivated, ornamental and non-invasive Rhododendron species (Green, 2003).
Please follow this link for details on the management and control of Rhododendron ponticum.
Compiled by: IUCN SSC Invasive Species Specialist Group (ISSG) with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
Last Modified: Tuesday, 8 June 2010