Invasive Non-Native Species Initiative

What are Invasive Non-Native Species? Some species have been introduced into the UK deliberately for use in forestry or agriculture, and others have arrived as a result of human activity via the transport of goods or brought in by botanists and explorers. It’s currently estimated that Britain has more than 3,000 non-native species. Many are harmless, but occasionally a species will be introduced that can post a threat to native biodiversity – these are Invasive Non-Native Species (INNS).

We are currently targeting the most prevalent, Japanese Knotweed, American Skunk Cabbage and Himalayan Balsam. It’s believed these were introduced as exotic garden plants and, finding our temperate climate favourable, they spread out into the countryside via watercourses and other means. Sale of Himalayan Balsam and Japanese Knotweed is banned and both are listed under Section 9, Wildlife & Countryside Act and categorised as controlled waste. American Skunk Cabbage is found across the UK, but still in fairly localised areas and, incredibly, it is still available to purchase!

What’s the problem? Yes, they might have striking foliage and pretty flowers, but they pose serious problems for our waterways and the wildlife that depends upon them. Common to our 3 species is that they spread rapidly along watercourses, often aided by flooding to reach new areas, grow fast and outcompete our less vigorous native plants. They then die back leaving the banks denuded of stabilising vegetation. This heightens the risk of bank erosion during peak flood flows, leading to habitat loss, soils washing into waterways, reduced water quality and smothering of aquatic habitats. With our biodiversity in catastrophic decline and flood events increasing in frequency and severity, you can understand why we’re taking this very seriously. Also the nectar-rich Himalayan Balsam attracts pollinators in abundance leaving native species at heightened risk of being unpollinated.

And of course, these INNS don’t solely impact our ecology, they negatively impact us too. In terms of the public purse, they are exceedingly labour intensive, and cost £billions each year, to remove. Japanese Knotweed can cause structural damage to buildings and infrastructure, and its presence has to be declared when selling a property due to the risk of damage and cost of removal. There are hidden costs too. For example, the increased sedimentation in rivers increases water companies’ costs of treating the water to make it safe for public consumption, and that translates into higher water bills. Not forgetting these species can significantly impact on our own outdoor enjoyment. They often grow so tall and densely along riverbanks – Himalayan Balsam is the largest annual plant in Britain –  that they impede visibility of and from the water, altering our landscapes and riverscapes. 

The Wye Valley AONB has been active in tackling these INNS in the lower Wye for the past few years through our Sustainable Development Fund (SDF) and through the Lower Wye Catchments Project.

Currently Japanese knotweed and American Skunk Cabbage treatment are proving manageable in targeted areas within the current level of resources. We’ve been working very closely with our local communities, tapping into the wealth of local knowledge to map locations of these plants on our geographic information system (GIS) once they’ve been ground-truthed, and to gain landowner consent for access and treatment. We then share this information with the specialist Habitats Team at the Wye and Usk Foundation (WUF) who carry out the appropriate treatment for each site.

As result of our increasing knowledge of the distribution of the knotweed and skunk cabbage, and by securing further funding, in 2020 we have been able to scale up the treatment from around 60 Japanese knotweed sites and 1 American Skunk Cabbage site in 2019 to working across 15 local communities, treating around 120 Japanese knotweed sites and 14 American Skunk Cabbage sites.

Himalayan Balsam is widespread across the wider Wye catchment along the banks of our waterways, along our highways, in our fields and woodlands, necessitating a completely different approach; a catchment-wide, community-led approach, working from the headwaters to the sea to reduce the risk of reinfestation. Unfortunately, we do not have the resource to coordinate at that scale, and instead we are focusing effort effectively at a local sub-catchment scale. Piloting this approach for us is the volunteer group, The Narth & District Footpath Group. In 2019 they mapped the extent of balsam across the White Brook catchment and have been strategically removing balsam, working from the upper catchment downstream. Their work through 2019 is estimated to have removed up to 90% of the balsam at 9 sites. In 2020 the group removed the remaining 10% and they’ve tackled a new area, removing over 5,500 plants! It certainly proves ‘where there is a will, there is a way’ and we are obviously keen to roll out this model in further sub-catchments when Covid-19 restrictions and funding allow.

You can help us to tackle INNS and stop the spread:

  1. Be Plant Wise – get familiar with these species and keep a look out when you’re out and about in the lower Wye valley – have a look at the web pages below and the ID sheets.
  2. Raise awareness within your local community about INNS and our AONB initiative.
  3. Manage it where appropriate – Himalayan Balsam can be pulled up gently with its roots intact. Ideally do this before it flowers as the seeds are categorised as a Controlled Waste and have to be disposed of very carefully. With American Skunk Cabbage we advise landowners to cut the flowers off in the spring, before they go to seed, to help reduce the spread. Unfortunately Japanese knotweed is a different ball-game altogether. Please do not attempt to cut, strim or mow Japanese knotweed as it increases the risk of spreading the plant and could constitute an offence. Repeatedly cutting with a mower will not kill it, the plant will simply re-grow from the root, and attempts at digging the plant out should also be avoided. Before you try any knotweed control method please do contact us to find out if we can add it to our schedule of treatment. 
  4. Report it – if you spot any INNS in the lower Wye Valley do email us your sightings at If you see Japanese knotweed along a road or in a park report it to us and to your local council (via the Monmouthshire App (under ‘grasses, trees & hedges’), or the Forest of Dean DC or Gloucestershire CC website reporting pages). If you see it on Forestry England, Woodland Trust or Natural Resources Wales estate do report it directly to them.
  5. Get active – if you’ve been inspired by The Narth & District Footpath Group’s initiative and you have some spare time to get active outside, there are a few things you can look into. The Wye Valley AONB has its own Volunteer Group, which, once Covid-19 restrictions allow, will be out and about – you’d be very welcome to join us. Your local community might also have a volunteer group you could join or, if you don’t have one, how about setting one up yourself? There’s support and resources available – do get in touch. 
  6. Support WUF – Give, fundraise or volunteer for the Wye and Usk Foundation

Useful information sources:

GB Invasive Species Secretariat: ‘Be Plant Wise’

Japanese Knotweed:

Himalayan Balsam:

American Skunk Cabbage:

If you would like to be involved or find out more about the Lower Wye Catchments project or this INNS Initiative please contact Nickie Moore at or call 07919 530432 (currently home working)

Japanese Knotweed ID sheet

Japanese Knotweed Identification sheet

American Skunk Cabbage Identification Sheet

American Skunk Cabbage Identification Sheet

Himalayan Balsam Identification Sheet

Himalayan Balsam Identification Sheet

Be Plant Wise Poster

Non-Native Species Secretariat poster