Invasive Species Week 2023

15th May 2023 News

This week (15 – 21 May) is Invasive Non-Native Species Week, an opportunity to raise awareness of the impacts of invasive species on our environment.

Invasive species are animals or plants that have been brought to an area in which they do not naturally occur. They can spread rapidly and become dominant in the landscape. They also increase our risk of flooding.

In Calderdale, the most problematic invasive species for flood risk are:

  • Himalayan balsam
  • Japanese knotweed
  • Giant hogweed

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

  • Increase our flood risk – they die back in the winter leaving riverbanks and valley sides bare and exposed. This increases the likelihood of soil erosion, landslides and flooding.
  • Affect our wildlife – they 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 causing damage to 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.

The biggest difference you can make is to report sightings of invasive species. This is particularly important for Japanese knotweed and Giant hogweed as you should not try to remove them yourself – they require professional treatment. 

You could also volunteer to help to clear invasives and create natural flood management measures. The National Trust, in partnership with Slow The Flow, will be running volunteering days on the first Sunday of the month throughout summer. 

Invasive species can spread easily through clothing, shoes and equipment. Whenever you’re out and about remember to check, clean, dry


Invasive species warning sign

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