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Rhododendron ponticum

Identity

Common name: Rhododendron
Synonyms: R. speciosum, R. lancifolium
Origin: Asia, Southern Europe
Plant type: Shrub
Life cycle: Perennial
Code of conduct: Annex II
Invasive status (ISEIA protocol): Black list
Main ornemental function: Green screen • Ornamental shrub

Description

This evergreen shrub is densly branched growing to 5m. Flowers are violet to purple. Seeds are contained within a woody capsule. There are 2 subspecies : R. ponticum ssp. baeticum, native from Southern Europe, and R. ponticum spp. ponticum native from Turkey.

Spread

This species spread predominantly by seeds. Each flower can produce between 3000 and 7000 small seeds which can be dispersed up to 100m by wind and water under favourable open conditions, but often less far in closed canopy forest. Vegetative reproduction remains limited. The plant is able to sprout after cutting. Ends of branches may root if in contact with soil but such growth is usually only found at forest edge. Frequently planted as ornamental.

Habitat

Rhododendron ponticum invades deciduous forests (moninated by oak) and heaths. Preference for acidic soils. Sometimes grows on calcarous soils. Also found in coastal dunes, Nardus grassland and bogs. It is able to tolerate dense shade or even almost closed canopy conditions.

Impact

Species classified A2 in Belgium. Highly invasive in several regions in north-western Europe. Rhododendron may forms monospecific stands with a dense and permanent canopy preventing the development of native species. Rhododendron benefits from pollination by native insects. Competition is favoured by the production of allelopathic compounds. This species is poorly consumed by herbivores and its litter is hardly degraded by soil organisms. In invaded sites, R. ponticum is currently recognized as a threat to native communities, and a pest of forestry. First introduced in the British Isles, the species is now widespread in this country. Managing populations of R. ponticum cost 50 millions euros in one single invaded forest. The species is naturalized in France, Germany, Ireland, The Netherlands. In Belgium, invaded sites have been observed, both in Flanders and Wallonia. For more information, click here

Recommendation

(1) Avoid planting this species near heathlands and forests (acidophilous forests), especially in the vicinity of protected areas (natural reserves, Natura 2000 sites, etc.) ; (2) cut the flowers at the end of flowering and before fructification in order to avoid seed dispersal.

Possible native alternatives

Main ornemental function

Green screen
Ornamental shrub

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