Rhododendron ponticum, an Invasive Non-Native Species, currently poses a huge threat to Argyll's temperate rainforest and peatland habitats. Here's what we're doing about it and why. 

1. It outcompetes our native species

“Given enough time, Rhododendron ponticum can entirely outcompete the native woodland that it loves to colonise. It is particularly successful at getting a foothold in Argyll’s rainforest, where the dappled shade and wet, mossy understory provides ideal conditions for Rhododendron seed germination and growth,” explains Ian Dow, one of ACT’s woodland coordinators working to restore Argyll’s temperate rainforest.

When Rhododendron shrubs form dense thickets in and around rainforest habitats, they stop direct sunlight from hitting the forest floor and suppress the natural processes necessary for native plants and trees to grow. This action also impacts on the microclimate within rainforest habitat that enables Scotland's globally significant lichens and other lower plants to thrive.

“Once the Rhododendron canopy closes, natural regeneration of native plants and trees stops almost entirely,” says Ian. “This is due to many things in combination, including, competition for nutrients, persistent leaf litter, the conversion of soil biota to something less favourable to native woodland trees and plants, alongside other complex processes that we are yet to fully understand.”

Photo: Ian Dow/ACT, Rhododendron in Argyll rainforest. 

2. It likes acidic soils and bogs

Bog and other peatland habitats are particularly susceptible to invasion by Rhododendron ponticum because it can take root in slightly drier areas or in tiny patches of exposed peat, often disused peat banks or on the dry edges of drains. Rhododendron, once it takes hold, starts a cycle of further drying out the bog. 

“The bigger the Rhododendron, the more they soak up available water and outcompete the natural bog-loving plants like sphagnum moss that are key to a healthy peatland,” says Angharad Ward, ACT’s peatland initiative sites manager. “Once established, seeds can travel great distances, carried by the wind across the flat expanse of the bog, often from neighbouring woodlands.”

Photo: Katie Barnwell/ACT, Rhododendron on a peatland site in Argyll. 

3. It makes accessing our natural environment a challenge!

As well as outcompeting our native species, it's also challenging for us humans to access our natural environment because of Rhododendron! A mature Rhododendron thicket can create an impenetrable barrier, making accessing our rainforest almost impossible. Similarly, if a peatland site is surrounded by Rhododendrons, it is no longer visible and accessing a peatland site for surveys becomes very tricky!

If we are to celebrate, protect and enhance our rare habitats, then safe and unimpeded access is vital.  

Photo: Ian Dow/ACT, Rhododendron smothering native trees in Argyll. 

4. It's poisonous to many herbivores and insects

To protect itself from herbivores and insects, Rhododendron, like many other plants, produces a chemical defence. Herbivores, such as deer and sheep, are deterred from munching the leaves due to poisonous and unpalatable grayanotoxins in the leaves. Rhododendron can then spread unchecked by natural grazing or insect attack. A 2016 Royal Botanic Gardens Kew study found that these grayanotoxins are also present in Rhododendron pollen and these toxins can be disruptive or even deadly to some of our native bees. 

Photo: Katie Barnwell/ACT, deer on a peatland restoration site. 

5. It’s extremely hard to control

Rhododendron ponticum has the ability to keep on growing against all the odds. Chopping it to the ground encourages vigorous regrowth and removing it gives seeds the light they need to germinate. A large bush can produce several million seeds per year.

When tackling Rhododendron, it can take years to get under control and requires multiple methods and regular follow-up visits to keep new growth in check. Angharad explains the approach on a peatland site: “The first step is usually to tackle the seed sources, which could mean removing the shrub from nearby woodlands as well as around the bog. This takes multiple years, as mature plants are incredibly resistant and seedlings have a tendency to pop up just when you think you’ve cleared a site!”

Photo: Angharad Ward/ACT. Fresh Rhododendron growth on a peatland site on Islay.  

What we're doing about it 

Invasive Non-Native Species like Rhododendron ponticum pose a significant threat to biodiversity here in the UK and have a seriously detrimental impact on precious native habitats in Argyll, including our peatlands and rainforest. We keep ourselves informed on the latest methods and technologies to control species like Rhododendron ponticum and deliver projects to help tackle the spread. 

Julie Young, ACT’s chief executive explains: “It is worth every drop of blood, sweat and tears it takes to deliver these projects for Argyll’s globally significant temperate rainforest and peatland habitats.” 

Rainforest restoration

We’re currently working with landowners around Mid Argyll, Knapdale in particular, to create a plan for tackling Rhododendron ponticum in the area. Philippa McKee, ACT woodland coordinator, is leading this project, which is supported by The Scottish Government’s Nature Restoration Fund, a fund managed by NatureScot, and Scottish Forestry.

“We are working with landowners to establish a clear picture of where the problem areas are and how we might go about tackling rhododendron in a strategic and sustainable way,” says Philippa. 

“During the current phase, on the ground and using drones, we are surveying land around Mid Argyll to see the extent of Rhododendron ponticum spread. We will then quantify the amount of work required to tackle it and create a strategic plan for how this might be achieved.”

This survey work is ongoing, but we are thrilled with the level of positive engagement we have had from landowners in areas where Scotland’s Rainforest could benefit most from intervention. Philippa and Ian are ACT’s woodland coordinators, working to restore Argyll’s rainforest, as part of the Alliance for Scotland's Rainforest. 

Find out about our rainforest restoration in Argyll.

Photo: Ian Dow/ACT, Amanita muscaria, Fly agaric, in Argyll's rainforest. 

Peatland restoration

Deb Baker, ACT’s peatland initiative programme manager, worked on peatland restoration through the CANN – Collaborative Action for the Natura Network – project for five years. Over the course of that project, ACT removed Rhododendron on 113 hectares of land, both from peatland sites and in adjacent woodlands, which are often where the seeds spread from.

“These sites underwent multiple years of treatment to ensure this highly invasive plant was brought under control,” explains Deb. “Being able to return to a site annually to treat regrowth was vital and made a huge difference on sites previously infested with Rhododendron."

Based on Islay, Deb and Angharad are ACT’s peatland initiative team. ACT hosts a Peatland ACTION project officer role for Islay, Jura and Colonsay to work with NatureScot on Scottish Government-funded peatland restoration on the islands. The peatland initiative is also funded by Esmée Fairbairn Foundation, allowing us to go the extra mile in supporting smaller-scale landholdings through the restoration process.

Find out about our peatland restoration work around Argyll and the Isles 

Photo: Angharad Ward/ACT, peatland restoration site on Islay. 

How to support our work

By taking action to tackle Rhododendron ponticum and other invasive species, including spruce, we are securing the future of our precious Argyll peatland and rainforest habitats. You can support our work:

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