Invasive Non-Native Species

Invasive non-native species (or INNS) are animals or plants that have been brought to an area in which they do not naturally occur.

Large overgrowing Himalayan balsam.
Himalayan balsam

Invasive species can spread rapidly and become dominant in the landscape. They also:

  • Increase our flood risk
  • Outcompete or spread diseases to native wildlife
  • Cause damage to the natural and man-made environment

The most problematic invasive species for flood risk in Calderdale are:

  • Himalayan balsam
  • Japanese knotweed
  • Giant hogweed

To learn more about these plants and how to identify them view the GB Non-Native Species Secretariat’s identification sheets.

Japanese Knotweed pictured with its small white flowers, zig zag stems and lush green colour.
Japanese knotweed
What do invasive species do to our landscape?

Invasive plant species negatively impact our landscape in Calderdale in a number of different ways:

Increase flood risk

Himalayan balsam and Japanese knotweed outcompete native species in summer but die back in the winter leaving riverbanks and valley sides bare and exposed. This means rainwater flows faster over these areas, increasing the likelihood of soil erosion, landslides and risk of flooding. This is a particular problem in Calderdale where we have such a steep landscape and need to try to slow the flow of water into our rivers.

Affect wildlife

Invasive plants can outcompete our native species and take over huge areas of land meaning that we don’t have the variety of plant life and habitats we need to support our wildlife.

Damage structures

Japanese knotweed can grow through small cracks and crevices in materials such as concrete, tarmac and bricks. This expands the gaps which weakens and damages structures including buildings, homes, footpaths and flood defences.

Affect our health

Giant hogweed has sap within the plant. If the sap comes into contact with people’s skin, the skin becomes incredibly sensitive to sunlight. Exposure can result in nasty burns and blisters.

A Giant Hogweed plant in flower
Giant hogweed
Stopping the spread

One of the key issues with invasive species is how quickly they can spread. This is often done unintentionally by people through their clothing, shoes and equipment.

We can all help stop the spread by being aware of invasives in our gardens and when we are out and about – walking, running, fishing, climbing, swimming or doing anything in the natural environment.

Be plant wise

This campaign helps us all to protect the environment while enjoying our gardens and land. Learn how to choose the right plants for your garden, pond and water features and dispose of your unwanted plants responsibly.

Check, Clean, Dry

Whenever you’re out in the countryside, remember to Check, Clean, Dry to help stop the spread of invasive plants and animals on land and  in water:

  • Check your clothing and any equipment, such as walking sticks and fishing rods, for live organisms and plant material including seeds or broken bits of plant. If you do come across anything it is important that you leave it where you found it.
  • Clean and wash all equipment, footwear and clothing thoroughly, paying particular attention to areas that have been in contact with water or mud, such as the soles of shoes.
  • Dry all equipment and clothing - some species can live for many days in moist conditions. Make sure you don't transfer water elsewhere.

This video from Yorkshire Water and Yorkshire Wildlife Trust gives more information on the invasives problem in Yorkshire and how to affectively check, clean, dry your footwear to stop the spread.

Useful resources

If you take part in recreational activities on our watercourses, you might find the following specialist training and resources useful:

We’re working hard to combat invasive species in Calderdale. To find out more about the actions being taken and how you can help, visit the Action on Invasives page.


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