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Rhododendron ponticum might just look like a pretty pink flower you can spot in a garden or on a walk, but there’s so much more to the story. Did you know it’s an invasive non-native species destroying native wildlife and our temperate rainforests? Our Rainforest Advocacy Officer Erin Shott explains.
Imagine, it’s summertime and you’re enjoying a lovely afternoon walk, and you see this pretty pink Rhododendron flower everywhere, a stunning look across the landscape. Unfortunately, what you are seeing is an invasive non-native species known as Rhododendron ponticum.
First introduced to the UK in 1763 as an ornamental shrub, this plant, like many Victorian garden escapees spread across the UK until it could be found in just about every corner. There are many types of rhododendrons which are not invasive, but the ponticum variety is a particular problem.
The invasive Rhododendron ponticum is known for dominating the landscape, supressing the growth of young native trees and shading out internationally rare plant and lichen species. It also disconnects native woodlands from one another. It’s this characteristic that makes it a major threat to temperate rainforest and other native woodland habitats.
Once it’s established in the wild, removal of the plants is possible but not easy. Repeated rounds of control are necessary, taking anywhere from 3 to 5 years and costing huge amounts of money. In fact, £3.39 million was spent on Rhododendron ponticum control between 2015 and 2022 in England.
Rhododendron ponticum is a significant threat to the UK’s rainforest. As 1% of habitat, temperate rainforest is considered one of the rarest habitats globally. High rainfall and humidity along the UK’s west coast create perfect conditions for the greatest concentration of oceanic lichens and mosses in Europe.
But rainforests face a number of threats and challenges, including climate change, air pollution, inappropriate grazing (either too much or too little) and Invasive Non-Native Species (INNS) leading to a highly fragmented landscape in need of care and restoration.
We are dedicated to restoring the UK’s temperate rainforest. We are currently working with partners in removing this invasive species and restoring the environment, including through the Rainforest Restoration Project in Cumbria, the South West Rainforest Alliance, the Alliance for Scotland’s Rainforest and the Alliance for Wales’ Rainforests.
Every rainforest across the UK is threatened by INNS, specifically Rhododendron ponticum. In fact, every State of Rainforest Report published to date has listed Rhododendron ponticum as a major issue for the rainforest. The State of Scotland’s Rainforest report says that invasive Rhododendron ponticum is found in 40% of core rainforest sites. Similarly, the State of Wales’ Rainforests report released in 2023 also highlights the issue, calling it a significant threat to rainforest with 66% of sites requiring intervention on INNS.
The most recently published State of Temperate Rainforest in South West England report notes Rhododendron ponticum as the most widely problematic INNS in rainforest, found in 20% of lowland temperate rainforest sites.
Despite how widespread the issue is, there are still steps that can be taken to reverse impacts of invasive Rhododendron ponticum. The good news is that we can take action to reduce this threat:
The specific genetics surrounding Rhododendron ponticum are complex; after its introduction, it cross bred with 2 species from north America. This means that not all invasive Rhododendron is the same, some are a hybrid (a cross between the two species) and some are not.
At the moment invasive Rhododendron ponticum and any of its hybrids are listed as a Schedule 9 (Part II) species in the Wildlife and Countryside Act 1981. Section 14 of the Act ‘makes it an offence to plant or otherwise cause to grow in the wild any plant listed in Part II of Schedule 9 to the Act’.
Britain is home to one of the rarest habitats in the world – the temperate rainforest. But how would you know if you were walking in one?
Dave Lamacraft, Plantlife’s Lichen and Bryophyte Specialist, heads out to discover a wealth of extraordinary lichens which call Wales’ rainforests home.
Air pollution often poses the biggest danger to internationally rare habitats and nitrogen gases have the potential to destroy our temperate rainforests.
Meg Griffiths
Plantlife is building awareness of the threats that invasive species present to our native plants and animals.
We’re taking it right back to basics – explaining what makes an invasive plant species, and why they are becoming so problematic both in Wales, and globally.
Non-Native Species are species that, because of human activities, have become introduced in places beyond their native range. Physical barriers such as mountain ranges, oceans, rivers, and deserts mean that many ecosystems have evolved separately, creating distinct groups of species which are characteristic to certain places.
However, human activities like international trade and tourism now mean that species are being moved across these geographic barriers (either intentionally or otherwise). This shuttles species from the places where they evolved, into places where they have never been before.
Because non-native species evolved elsewhere, the new environments they enter haven’t yet developed ways of controlling their behaviour.
Some non-native species won’t be able to survive in our climate. Others will integrate with our habitats without damaging them (these are called ‘naturalised’ species). But certain species are able to thrive and dominate. These species are called Invasive Non-Native Species (INNS), and they present a serious problem not just to our ecosystems, but to our communities and our economies.
We are in a nature emergency. One in five species of UK vascular plant are now threatened with extinction, and the introduction of INNS is recognised as the second biggest threat to biodiversity after habitat loss. But how is it that these species are able to cause so much damage?
All of these factors mean that INNS are beginning to swamp many of our native ecosystems. This reduces the diversity of species present, which undermines the resilience of our habitats. When our ecosystems are vulnerable our economy is unstable. Natural Resources Wales now estimate that INNS are currently costing the Welsh economy at least £125 million a year. See below for some of Wales’ most destructive INNS to look out for, along with some information on how it is they are causing so much devastation.
Rhododendron now presents the single largest threat to our temperate rainforest ecosystems. This is especially a problem in Eryri, where it outcompetes native plants for nutrients and light, shading the forest floor and creating ecological dead zones. It also hosts a fungus-like disease-causing organism called Phytophthora. This causes the death of thousands of Larch trees in Wales each year and can also infect other species, such as Oak, Sweet Chestnut and Bilberry.
Now a familiar sight along riverbanks, the herbaceous annual Himalayan Balsam Impatiens glandulifera has become a serious problem species. Being an annual means the plant dies back in the winter, leaving the riverbanks bare and vulnerable to soil erosion. In the summer its rapid, swamping growth chokes out other riverbank species. Balsam also has the distinctive ability to fire its mature seeds out of ripe seedpods up to a distance of 7m, allow it to quickly colonize open areas.
Although not officially classed as invasive due to its use in forestry plantations, Sitka Spruce has all of the hallmarks of an INNS. It grows extremely fast in our climate and doesn’t support our native species. It also produces huge numbers of seeds that can disperse far and wide on the wind. The seeds from Sitka plantations are now spreading into priority habitats, altering their ecology. When Sitka seeds germinate in bogs, their roots take up too much water, causing the bog to dry out, they also shade out the rare and specialist plants that are present.
New Zealand Pygmyweed First seen in the UK in the 1970s this aquatic species has quickly spread across many of the waterways of southern England and Wales. The reason behind this rapid dispersal is vegetative reproduction – even a tiny section of stem broken from the mother plant can put down roots and form a whole new plant. Short stems break off easily and float, so these let the plant colonize new areas, and they’re easily transported between pools on livestock, dogs, clothing and even waterfowl. Once established the plant forms dense mats, shading out the water beneath and causing oxygen depletion.
Agricultural grasslands dominate Wales’ rural landscape. Finding ways to restore species-rich habitats to farms is a priority for Plantlife Cymru.
Chris Jones, the Warden of Kenfig National Nature Reserve, recently found the very rare fungus, during a routine survey.
Every day, our wild plants and fungi are put at risk from planning decisions, chemical sprays and more. Find out what you can do to help protect nature.
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