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Tackling invasive species

Landscape with gorge and a group of people walking in the distance
Stickle Ghyll Tarn Trail in the Langdales is popular with walkers. | © James Dobson

To help protect biodiversity and natural habitats in the Lake District our Ranger teams are delivering an ongoing programme of work to tackle non-native invasive species.

What are invasive species?

Invasive species generally refer to particular plants or animals that are by nature ‘invasive’, that is they invade spaces or areas within habitats, not necessarily where they are naturally found, and begin to compete with other species, often thriving and eventually dominating. Invasive species can be native to the natural environment/ecosystem or non-native, so long as they exhibit these traits.

However, invasives are most often associated with non-native species which have been introduced, and are not usual components of the natural ecosystem. A well known acronym is used to term these types of species; INNS (Invasive non native species) for exmaple Grey Squirrel or Himalayan Balsam. These species are native to other parts of the world but due to human interference have been purposefully brought into new ecosystems, upsetting the ‘status quo’. Often other native species have no experience of these non-native ones and do not have the inbuilt capacity to compete with them. These means that other species are threatened because of their existence. A good example of this is the native Red Squirrel being threatened by the non-native Grey.

How to identify non-native invasive species?

See images and descriptions to help you spot American skunk cabbage, Himalayan balsam and Japanese knotweed, which are the three main species we are focussing on in the the Langdale & Grasmere areas.

Plants growing outdoors near a small stream
Skunk cabbage growing next to a waterway in the Lake District. | © National Trust / Bethany Brown

American skunk cabbage (Lysichiton americanus)

Identification - Found in wet woodlands and around garden water features. Plants emit a strong, skunky odour. Big yellow flowers that look like wild arum (lords-and-ladies, cuckoo pint) with leathery leaves reaching 1m long. Management - Small plants can be dug up but the roots of larger ones can be huge. With large scale issue management is focussed on foliar application of herbicide in May.

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Himalayan Balsam in Langdale Valley

It is important that we manage invasive species. Especially INNS, as they directly threaten biodiversity. A good case study here in the Langdale valley is that of Himalayan Balsam; a familiar plant well known by many, it has purple/pink flowers that look like a police helmet and can grow up to 2m tall. It is usually found on wet, disturbed ground and thrives on riverbanks. However, due to it being an annual (grows and dies in one season) its entire survival strategy is to grow as fast and quick as possible and put out as much seed as it can. It’s seed heads when ready ‘pop’ and disperse thousands of seeds! It out competes everything around it, choking other plants of light, creating a monoculture. It has also been shown in studies to decrease species diversity of ground insects.

In Langdale we have a wet woodland designated a SSSI (Site of Specific Scientific Interest) due to its population of the very rare native balsam; Touch-me-not Balsam. This plant is the foodplant for the rare Netted Carpet Moth and as such, is at a direct threat from its foreign cousin. Many ranger hours are put in over the year to rid Himalayan Balsam from this SSSI woodland.

Why we manage bracken

An example of a native invasive species is Bracken, a typical woodland plant that due to excessive human disturbance i.e. the clearance of woodland, has become invasive in other habitats. For example, bracken is seen on fell sides in extensive beds that cover vast areas of space, but in reality this isn’t the natural state of affairs, wherever bracken is seen, in theory, woodland would have stood. In its natural woodland home, bracken is relatively sparse and grows along other typical woodland floor plants. Because it is light loving and thrives in canopy gaps, the vast clearance of woodland over time has opened up a whole new habitat and because it is quick growing with an extensive root system, it has out competed everything else in its way. Furthermore because it is toxic to grazing animals, it is left unchecked. As such this is why we see such extensive bracken on our fells, now that they are devoid of trees.

View of Elterwater village with hills in the background, Lake District
Bracken and wooded hills beyond at Elterwater Common, Great Langdale, Cumbria, looking towards Elterwater village. | © National Trust Images/David Sellman

What can you do to help?

You can help us to tackle invasive species in a variety of ways. Use the guidance in this article around the identification and removal of different species in your own outdoor spaces or if you are out and about in the countryside.

Report sightings

  • If you spot Skunk Cabbage, Himalayan Balsam or Japanese Knotweed you can report it using the INNS Mapping Tool.

Follow Check, Clean, Dry

  • If you are going on the water on paddleboard, boat, other watercraft follow this advice to help prevent the spread of invasives in our waterways.
  • Check your equipment, boat, and clothing after leaving the water for mud, aquatic animals or plant material. Remove anything you find and leave it at the site.
  • Clean everything thoroughly as soon as you can, paying attention to areas that are damp or hard to access. Use hot water if possible.
  • Dry everything for as long as you can before using elsewhere as some invasive plants and animals can survive for over two weeks in damp conditions.


  • Interested in doing a bit more? We run volunteer days to tackle invasive species see details below or follow us on social @NTLakeDistrict for updates on when they are running.

Volunteer Days: Balsam Bashing

Come along to one of our Balsam Bashing days with our Ranger team this summer.

  • 26 June
  • 2 July
  • 10 July
  • 18 July

Find out more about the events here.