It looks beautiful, but this common Rhododendron is an invasive species that is spreading throughout western Scotland and is destroying our native biodiversity. Read more about invasive species in this issue, which has lots of articles on nature. Photo: James Merryweather
The climate crisis is also a biodiversity crisis. Invasive non-native species are one of the five main causes of biodiversity loss globally; they put significant pressure on Scottish biodiversity across land, sea and freshwater habitats, and have economic impacts. Scottish Environment Link recently published a report on invasive non-native species in Scotland, highlighting the need for the Scottish government to take actions, and setting out principles and plans on how to tackle these species.
Invasive non-native species were introduced to gardens and estates whence they have escaped into the wild, or they were imported accidentally by road, sea freight or air, often in consignments of other products. A widespread invasive plant is the pink/purple-flowering Rhododendron (Rhododendron ponticum) seen in gardens and landscapes across Skye, Raasay and Lochalsh, and up and down the west coast of Scotland. Other serious problems are caused by giant rhubarb (Gunnera), Himalayan balsam, Japanese knotweed and ash dieback fungal disease. Invasive mammals include grey squirrels and mink. Invertebrates include New Zealand flatworm, Acorn barnacle and North American signal crayfish. Rhododendron ponticum thrives in our wet, mild climate, spreading by prolific seeding and then layering of branches. This eventually forms a closed canopy that shuts out most light and overwhelms other plants. It is particularly damaging in Scotland’s rainforest, which occurs along Scotland’s west coast, including on Skye. Invasive Rhododendron affects woodlands, waterways, heathlands and bogs, is toxic to most herbivores including sheep and deer, and can carry the Phytopthora fungus-like disease that can seriously impact other tree species. If you see small seedlings, pull or lever them out and leave the plants upside down for the roots to dry out and die. Established plants and larger areas need specialised treatment for effective eradication.
Read more about Rhododendron here, or listen to a report on the BBC’s Good Morning Scotland (from 49:30 – 55 minutes). The Community Woodlands Association held a workshop on the longterm sustainability of Rhododendron control, which you can view here.
Gunnera (giant rhubarb), often grown in gardens as an ornamental, is another invasive plant that thrives in our wet, mild climate. Both Gunnera tinctoria and G. manicata are invasive if allowed to escape from gardens, out-competing native plants, and blocking drainage ditches and access tracks. These two species are now banned from sale in the UK. If you have Gunnera in your garden but don’t want to remove the plant entirely, you can cut off the flower heads each summer before they set seed, and either burn them or put them into an effective compost heap.