It’s not all bad news – Opportunities in tackling Rhododendron Ponticum

Why Rhododendron Ponticum is an invasive species that needs to be addressed. Learn how communities can lead the solution, with benefits extending beyond the ecological. This article is an informative opinion piece by Tom Lusink.

A Beautiful Killer on Raasay

The stunning pink and lilac flowers of Rhododendron Ponticum (referred to as Rhododendron) means the beginning of summer here on Raasay. A time when the island comes to life. And not just the plants, but the influx of people looking to visit the island or those seeking work here for the summer. 

While the beauty of this plant cannot be denied, are we living with a not-so-secret killer? Introduced to the UK in the mid-18th century. Plant-obsessed Victorians soon planted around the country. Is a plant that symbolises empire and globalisation.

Year-round thick, green waxy leaves, coupled with stunning flowers, made it a match made in heaven for large estates, being used as shelter belts for game, to mark boundaries or just as an ornamental. It didn’t take long to become a common sighting in peoples gardens.

Overview of Rhododendron Ponticum

• There are over 900 varieties of Rhododendron, but only the hybridised Ponticum variety spreads so prolifically.
• Rhododendron Ponticum is classified as an invasive species due to its aggressive growth.
• Native to isolated regions in Spain, Portugal, and the Black Sea, where it grows sparingly.
• The hybridised variety now thrives in:
  • Wet and mild climates, particularly those found on the west coast of Scotland.
  • Acidic soil conditions, which are common in this region.
• On Raasay, like many parts of the west coast of Scotland, Rhododendron Ponticum has become a widespread presence, overtaking much of the natural landscape.
• Every 20 years left untreated, the cost to tackle this invasive species doubles. 

insert picture of distribution (suggested: https://flourish.studio/)

What Impact Does Rhododendron Ponticum Have?

The spread of Rhododendron Ponticum creates a chain reaction of ecological damage:

1. Initial Growth: An isolated Rhododendron bush may not seem problematic at first.
2. Dense Clumps Form: As these bushes multiply, they form thick, dense clusters.
3. Light Blockage: The dense canopy prevents sunlight from reaching the ground, halting other plant growth.
4. Leaf Litter Accumulation: Thick layers of leaf litter accumulate, further stifling plant growth.
5. Soil Acidification: Over time, the soil becomes more acidic, creating inhospitable conditions for other plants.
6. Creation of Dead Zones: This results in “dead zones” where no other plants can seed or thrive, effectively displacing native plants and animals.
7. Exponential Spread: As bushes mature, the amount of seeds produced increases exponenetially, coupled with the right conditons leads to vigourous spreading akin to a run away train.

The bright lilac flowers of Rhododendron Ponticum release thousands of seeds that can spread hundreds of metres. As seen on parts of Raasay, a monoculture of Rhododendron takes over. Colonising land that could otherwise be used. Additional Rhododendron problems include:

• Host pathogens (such as phytotphthora) that cause diseases.
• Damage aquatic ecosystems near rivers/streams. Can even effect fish numbers!
• Poisonous to livestock (herbvores) and honey bees, making them immune to grazing pressure.

A subversive threat to biodiversity

The plants and trees that disappear are only the tip of the iceberg of the damage caused by Rhododendron. Think about the little bird that made its home on the arm of the now gone birch, or the vole that relied on the hazel nuts for food.  

Life relies on life.  Humans for example rely on bacteria living in us, which outnumber the amount of living cells. Similarly, plants do not grow in isolation. Nearly all plants rely on symbiotic relationships with fungi, bacteria and other organisms. Like all quality relationships, these take time to develop, thousands of years in these cases. Without one, the other collapses, causing an ecological clearance.

There will be places that are overrun by rhododendron, and those that overcome it. “It’s not hard to imagine Raasay being one big Rhododendron bush in 100 years!” said a woodland ecologist on their visit to the island said.

Raasay’s rich environment

Raasay’s varied landscape makes it a biodiverse place, with areas designated as Sites of Specific Scientific Interest. Over 3600 species are recorded here and we even have our very own rainforest!. A ‘Temperate Rainforest’ or the ‘Celtic Rainforest’, which is a globally rare and important habitat.  Rhododendron is classed as one of the biggest threats for its survival. The island also has rich cultural heritage. Gaelic poet, Sorley MaClean, who was a great communicator of natural wonders, comes from the island.

Rhododendron impact on carbon emissions

Beyond being a biodiversity catastrophe, Rhododendron is bad news for our carbon balance. Raasay’s Peatlands it’s largest emission source, are further degraded by the spread of Rhododendron, releasing more green house gas emissions.

The island’s forests, which use carbon do grow, are the islands our biggest carbon sequestering mechanism, again, Rhododendron threatens these. Think of a healthy forest. It has many layers and many plants within it, and is carbon rich from the trees to the soil. It’s this that environment rhododendron inhibits. Saying yes to Rhododendron is saying no many times over. 

A solution that does more than just tackle the Rhododendron invasion

The solution – Paying locals to remove Rhododendrons in winter months. Tackling Rhododendron can offer the spice of variety and offer employment when the seasonal employment dries up. For the effort to eradicate Rhododendron to be successful, it must be led by the community to be for the community. To take ownership of the problem and not just be at the mercy of it. The problem faced should not be viewed in isolation, and neither should the solution.

Rhododendron has started to take over in a short space of time, there is no promise of a quick fix for this. Communities like Knoydart have nearly eradicated Rhododendron, and have been at it for years. The same steady long-term approach is needed on Raasay, involving local residents rather than external contractors. This reinvests in the community while offering new skills and experience.

Effective Control Methods: When Less is More

Traditional methods like “cut and burn” often involve heavy equipment, chemicals, and fires. While this method can deliver visible results, and without follow up treatment is often infective. Many residents will remember huge efforts previously done that are a testament to this.On top of the negative environmental impact, extensive equipment and training is needed. A promising method, suited to community led removals, exists though. 

Stem treatment, or ‘drill and drop’ approach. This technique involves applying a small, targeted amount of herbicide(weedkiller) directly to the stem of the plant. With minimal equipment, just an axe or cordless drill, high success rates can be achieved. Best of all, it’s well-suited for the winter months when midges are dormant and other plants have died back, plugging the islands employment gap.

Ideally no chemical would be needed, though general consensus is now that for effective control some amount must be used. The stem injection minimises the amount of herbicide needed and if done diligently none should leave the bush, eventually breaking down as the bush decomposes. 

Whats happening on Raasay

Rhododendron removal is only the first step in a larger plan to restore and protect Raasay’s habitats. Japanese knotweed is prevalent. Even more so is bracken, which while native, is spreading rampently, liekly due to historic changes to how land is used. Bracken prevents trees from reseeding and takes over grazing pasture. It is said to often grow where trees once stood. (Raasay likely historically had much more woodland).

Mapping the spread is a first step. Ecologists from Great Glen Ecology and Tracks Ecology 

have been assisting with ground and aerial surveys using drones and machine learning. As summer turns to autumn, CNI hopes to offer locals training, with removal work beginning after, pending a funding application for £75k that’s been submitted. If granted, will allow the first steps to restoring habitats in a way that benefits the community and those who live off the land to begin this year.

Separate from CNI, Raasay House is taking steps to remove Rhododendron from its woodlands with works beginning this Autumn.

Tackling Rhododendron Ponticum requires specialist knowledge, making expert input essential. Fortunately, we benefit from local expertise, fromthose who work the land to botanists. We have also received support from the Environmental Science Department at Tennessee University, whose team visited Raasay earlier this summer. Their expertise is helping us to better understand the spread of invasive species and to map the problem using environmental data visualisation.

We’re not the first to ring the bell

“Proud tonight the pine cocks
crowing on the top of Cnoc an Ra,
straight their backs in the moonlight –
they are not the wood I love.

I will wait for the birch wood
until it comes up by the cairn,
until the whole ridge from Beinn na Lice
will be under its shade.”
– Hallaig by Sorley Maclean

Sorley Maclean’s poem Hallaig, written about the cleared township where he was born on Raasay, poignantly expresses the devestating effect of the clearances, but also of deep love of a place—where life was abundant, and people, trees, and animals coexisted as one. This delicate, symbiotic balance is now under threat from the spread of invasive species on the island. Sorley, far ahead of his time, even voiced disdain for invasive species in the same poem: ‘Proud tonight the pine cocks’ referring to non native pines.

On a national scale, this cause will require millions. If done poorly, it could mean millions wasted with little to show for it. However, if done well, with communities leading, our precious habitats can be protected while also offering opportunities for communities, leveraging this problem as both an ecological and economic solution for struggling rural areas.

As a community, we can either allow this ecological disaster unfold in front of us, or we can take ownership and look to protect what is valuable to us while providing opportunity.

References and Further Reading

In creating this article various sources we’re drawn from. These are listed below along with further reading.

• A critical review of work undertaken to control invasive rhododendron in Scotland
• https://treesforlife.org.uk/into-the-forest/habitats-and-ecology/forest-restoration-techniques/rhododendron-control/ 
• Publication 2019 – SNH Research Report 1157 – The effect of clearing invasive Rhododendron ponticum on the native plant community of Atlantic oak woodland.pdf (nature.scot)
• https://static1.squarespace.com/static/5d121ae120f35b0001f8abb0/t/620236e59426aa1a612f116e/1644312296037/CWA+info+note+21+-+Controlling+and+Eradicating+Rhododendron+ponticum.pdf
• rhododendron_poisons_the_soil.pdf (slef.org.uk)
• https://savingscotlandsrainforest.org.uk
• https://lostrainforestsofbritain.org/
• Five reasons we’re tackling rhododendron ponticum in Argyll (act-now.org.uk)
• https://www.nature.scot/professional-advice/land-and-sea-management/carbon-management/restoring-scotlands-peatlands 
• Publication 2019 – SNH Research Report 1157 – The effect of clearing invasive Rhododendron ponticum on the native plant community of Atlantic oak woodland.pdf (nature.scot)
• https://www.heraldscotland.com/news/13165435.destroy-rhododendrons-scotland
• https://www.agriland.ie/farming-news/over-three-quarters-of-tams-tranche-2-applications-approved/