This week is invasive non-native species week. A chance to highlight the problems that non-native species can cause to plants and animals when they are introduced or spread outside of their natural habitat. Today we are looking at woodlands, what invasive species are a threat here, and what can be done to protect Scotland’s rainforest.

There are three types of woodland in the world. Deciduous woodlands which lose their leaves in autumn, coniferous or boreal woodlands which are evergreen, and rainforests which are constantly wet and mild. These are areas dominated by trees, but which support many different species within them, from plants that grow on the ground, lichens and mosses growing on trees, and lots of insects, birds and mammals which all call the woodland their home.

Treecreeper on a tree trunk covered with moss and lichen

Woodlands are all special, they support huge numbers of species, they produce oxygen, and they lock away carbon, they are a great asset in fighting climate change.

But rainforests are very special. They are one of the most biodiverse habitats we have in the UK. Sadly, they face a lot of challenges, many of which are induced by humans. International trade has transported pests, diseases and invasive species to these habitats, and they also play a role in the decline of woodlands.

Work and campaigns to save and protect tropical rainforests, such as the Amazon, have been ongoing since the 1980s, but sadly we are continuing to lose this valuable habitat.

The relatively mild, and very wet conditions found on Scotland’s west coast makes the rainforest great for species that grow on trees, such as mosses, lichens, ferns and liverworts, known as epiphytes. These are what make the rainforest so special. They are rare, so the habitat is internationally important, they support migrant birds, such as pied flycatchers, wood warblers, redstarts and tree pipits, and they festoon the branches, creating a magical destination to lose yourself in.

Tiny songbirds fly thousands of miles to make this woodland their home each spring, while bluebells and primroses carpet the floor, and rare and beautiful ferns and mosses grow out of every nook and cranny.

Trees at Glenborrodale reserve with purple rhododendron flowers

But Scotland’s rainforest is at risk from an invasive, non-native species; rhododendron. Rhododendron, meaning ‘rose-tree’ was brought over to the UK from the Middle East in the 18th century. It’s thought the first rhododendron arrived in London in the 1760’s as a pot plant. The plant has large, brightly coloured flowers so was popular in gardens and on estates. However, it is very good at spreading itself, and its large leaves cast shade over native plants, meaning they die out while rhododendron thrives. The dense, shady bushes don’t allow the important mosses and lichens to grow, and it is also toxic, meaning no animals eat it or keep it under control.

So we must actively remove rhododendron from our native rainforest, to protect and restore this precious habitat.

It’s a tough plant, often requiring multiple treatments to make sure it is fully removed, and it is very good at growing on hard-to-reach cliff edges, making rhododendron control difficult and expensive.

There are several tried and tested, but all require follow up treatment and the best method varies depending on the age of the plant. The method with the least environmental impact is called ‘lever and mulch’ where plants are levered up at the base, any roots attacked with a hammer and plant is left to mulch and break down into the soil. Widespread spraying with herbicide is an option, but requires a lot of chemicals which, if it rains, can just wash off the shiny leaves. A better and more targeted option is, to drill into the plant and inject the herbicide directly.

This is a large task, which is why partnership projects, such as Saving Scotland’s Rainforest, a collaboration between conservation charities, local estates and communities, have the best chance of success. This project will set up local work teams focusing on eradication and growing locally sourced rainforest tree seedlings.

 Liverwort growing on tree trunk

Andy Robinson is a Senior Conservation Officer working with partners to restore part of Scotland’s Rainforest on the Morvern peninsula. He told us a bit about why woodlands are so special, and some things we can do to help protect them: “ Woodlands are special, not just because of the number of species that live in them, but in other ways too. Rainforests are described as “Earth’s lungs” producing oxygen and locking away carbon, a great double whammy to fight the nature and climate emergency.

My first real encounter with rhododendron was at university as a conservation volunteer, when we went to control the plant with “slash and burn” methods.

I’m not against rhododendron in itself, I’ve been fortunate enough to trek in Nepal, and the rhododendron forests there, such as in Poonhill, are wonderful to behold, especially accompanied by a dawn chorus of white collared blackbirds. It’s somewhat ironic that these rhododendron forests are also considered biodiversity hotspots and are facing serious habitat destruction. Like our rainforests, they need help to protect them.

We need to change our culture and policy and promote rainforests in Scotland (and woodlands worldwide) as a nature-based solution that can help tackle the nature and climate emergency.

Prevention is better than the cure where possible. We need to get everyone on board to ensure that ‘gardener-spread’ does not occur. It's still easy to buy rhododendrons at garden centres and online, and it can easily spread its prolific seeding from gardens out into the wild. It would be good if folk didn’t buy it, or if they did, were aware of the potential risks to their local and native nature.”