Rhododendrons’ curse that lasts 30 years
THEY may be spectacular to look at but, as many gardeners know, rhododendrons can quickly take over.
Now scientists have discovered that the flowering shrubs have a devastating effect on native wildlife – even decades after they have been removed.
A study of sites where rhododendrons were eliminated 30 years ago found that native plants had still not returned.
Researchers studied a variety of woodland sites on the west coast of Scotland. Some had never been invaded by rhododendron, others were covered in dense thickets, and a third set of sites had been cleared of rhododendron at different times between 1984 and 2014.
They found that even 30 years after rhododendron removal, native plants had not recovered. Instead of primroses, violets, wild garlic, ferns and grasses, only dense mats of mosses and liverworts had returned.
Ecologists believe that the deep shade rhododendron casts is responsible for the impact on local flora.
Researchers from the James Hutton Institute, Aberdeen University and Scottish Natural Heritage say weed eradication programmes now need to be supplemented by reseeding for the original plant community to re-establish itself. Their research is published in the Journal of Applied Ecology.
Dr Janet Maclean, from Aberdeen University, said: ‘During the invasion, rhododendron dramatically reduces the amount of light reaching the woodland floor throughout the year, causing local extinction of native grasses and herbaceous plants.
‘Mosses and liverworts cling on because they can tolerate the darkness. When rhododendron is removed, common mosses and liverworts quickly recolonise.
‘But by the time grass and other plant seeds arrive, the thick mossy mat prevents them from germinating, so the site never recovers its previous rich flora.’
Rhododendrons were introduced to Britain by botanist Conrad Loddiges in 1763 to be used as a cultivated flowering plant in gardens and parks, and as a horticultural exhibit on estates.
Most of the invasive bushes are a hybrid species derived from rhododendrons from the Iberian peninsula.