The invasive shrub is most prevalent in Scotland, where it covers over 53,000ha. Of woodland managed by the Forestry Commission or its sister organisation Natural Resources Wales, over 18,000ha nationally, or 2.2 per cent, is under Rhododendron.
The rest is on private estates where the proportion is higher, with over 8 per cent of private woodland in the west of Scotland, the area of highest prevalence, having been invaded.
The data is taken from the NFI field survey conducted between 2009 and 2013. "It gives us the first reliable provisional estimate of the extent and location of R. ponticum in Britain's woodland and will provide a robust baseline of information with which to inform and monitor future rhododendron control strategies," a Commission representative said.
Introduced into gardens 250 years ago, R. ponticum "grows particularly well in the climate and soils of the British Isles", the Commission says, yet "has been shown to reduce the numbers of earthworms, birds and plants and regenerative capacity of a site", while established bushes "then act as a seed source for further invasions in adjacent areas, eradicating ground cover plants and interfering with the process of natural regeneration of trees".
Kay Haw, Woodland Trust conservation adviser, said: "The spread of rhododendron within woods is an example of how non-native invasive species can quickly get out of control. Managing rhododendron within our woods is both costly and time-consuming, but something which needs to be done to support wildlife and help increase biodiversity in the long-term."
See http://www.forestry.gov.uk/pdf/fcpg017.pdf/$file/fcpg017.pdf for guidance.