Tackling rhododendron together

In our latest blog we explore how lessons learned from Scotland’s rainforest helped to avert a serious threat from invasive rhododendron in Norway.

Scotland’s rainforest is home to some of the world’s rarest mosses, liverworts and lichens ©Lorne Gill/NatureScot/2020VISION

Scotland’s west coast is home to temperate rainforest habitat, which is scarcer than tropical rainforest and hosts some of the world’s rarest mosses, liverworts and lichens. NatureScot is a member of the Alliance for Scotland’s Rainforest, a partnership working to raise the profile of Scotland’s rainforest and ensure that it thrives again.

Awareness is continually growing that our rainforest is in trouble, and the main problems it faces are invasive rhododendron and pressure from herbivores. Rhododendron can be well-loved for its showy purple flowers and tolerance of our less than ideal climate, but its ability to thrive in damp, cool areas is now a major issue across large areas of woodland in western Scotland. It is shading out the rare and special plants associated with temperate rainforest and leading to long-term declines in biodiversity, along with severely reducing the potential for Scotland’s rainforest to regenerate and thrive in the long term.

An infestation of rhododendron ponticum ©Caz Austen / WTML

If there is a positive slant to this problem, it is that we have built up a really good understanding of the threats that invasive rhododendron poses, along with knowledge and experience of the best ways of tackling it. But outside the west of the UK and Ireland, the damage rhododendron can cause isn’t always so well recognised.

In 2017, a group of land managers and ecologists from Scotland, led by Duncan Halley of the Norwegian Institute for Nature Research (NINA), and including NatureScot Operations Officer Lorraine Servant, took part in an Erasmus+ study tour of southwest Norway. The main reason for the visit was to look at woodland and montane scrub and to highlight the potential for the expansion of these habitats in Scotland.

Young rhododendron regenerating at a previously treated rainforest site in Sunart Special Area of Conservation. ©Lorraine Servant/NatureScot

The group visited the Flekkefjord coastal region in the extreme southwest and were concerned to see rhododendron growing in and around gardens. On discussing the issue with various conservation and land use professionals, it became clear that the plant was not viewed as a serious threat in Norway. Duncan however, having seen the rhododendron problem in Scotland, was well aware of what could happen next and Lochaber-based Lorraine, who sees the harm caused by rhododendron on a daily basis, was also keen to act.

Discussions continued once the group returned home and Lorraine led some follow up work along with Dominic Driver (now with Natural Resources Wales) on a short paper to stress the importance of getting on top of the situation before the plant is allowed to spread. Due to the similar geology, soils and climate, rhododendron would be expected to become as invasive in southwest Norway as it has been in Scotland.

Duncan used this paper to push for a survey of rhododendron in 2018. This led to the discovery of a rather worrying incipient outbreak of a hybrid rhododendron at Svinvik, on a coastal fjord southwest of Trondheim. Several vigorously growing clumps were found out in the woods, over a thousand plants in all, and scattered individual bushes were found up to several kilometres from the original source: the garden of an early enthusiast collector which is now an arboretum.

First generation wild rhododendron on Tysnesøya. ©Duncan Halley/ NINA

This led to a website on how to remove new invasive populations, with case studies of outbreaks – Tiltak mot rømt rhododendron (nina.no). In 2021 a cooperation was started between Svinvik arboretum, NINA, and the local community, to remove the invasive form there, using British and Irish techniques and funded by the Norwegian Environment Directorate. It is estimated that at least 95 percent of the invasive form has been removed, and with it the vast majority of seed fall. This year follow up checks and treatments will be carried out, along with further survey work to remove any outlying bushes.

Duncan recently wrote with an update: “So thanks again – like I said last time, your initiative has probably saved SW Norway millions (GBP) a year, and justifies all your careers, and mine, by itself – at least in money saved the Norwegians! Also shows what Erasmus programme knowledge exchange can achieve.”

The Scottish group left Norway with eyes opened to the potential for how the landscape here could look, with much more woodland and montane scrub growing out onto the hills above the treeline. But the visit also did something very positive for nature in Norway by sharing knowledge across borders, highlighting the added value of Erasmus+ and the benefits of a replacement to this type of exchange programme.

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