Dealing with the problems caused by invasive non-native species costs the British economy in excess of £1.7 billion annually (CABI report, 2010)

What are invasive non-native species?

When the Ice Age ended over 10,000 years ago the ice that covered most of Britain retreated northwards. Following behind this retreating ice were waves of plants and animals that slowly colonised Britain as conditions warmed up. These plants and animals arrived in Britain naturally as there was still a connection attaching us to the European mainland. However as the ice melted, causing sea levels to rise, the connection was flooded. This effectively stopped any more colonisation by species that couldn't cross the water. All these plants and animals – the ones that established themselves in Britain naturally - are called native species.

Man first arrived back in Britain about 8,000 years ago and virtually all new land animals and plants that have become established since this date have been brought here by man. These are all non-native species.

However, we must not think that all non-native species are bad – indeed it is only a minority that has serious negative impacts on our native British species, our health or our economy. These species we call invasive non-native species.

How do they affect us?

The problems caused by invasive non-native species affect us all. They are an economic problem and a well known threat to our environment:

  • Reduction in population of our rarest species e.g. the impact of American mink on water voles
  • Competition with native species e.g. Harlequin ladybird
  • Reduction in biodiversity - invasive plants often form monocultures, taking over an area so that they are the only plant growing there e.g. Rhododendron (Rhododendron ponticum)
  • Impact on our health e.g. skin blisters from Giant Hogweed sap
  • Increased risk of flooding, difficulties with angling and reduced fish-stocks due to clogged waterways
  • Reduction in food availability for insects - non-native invasive plants are often unpalatable to native herbivores like invertebrates
  • Reduction in oxygen and light levels in water bodies as plants spread over the surface

Once a species has been introduced the problems persist and escalate as the species spreads further. Many invasive plants can re-grow from just a tiny fragment of plant matter left in the soil or water meaning it is often impossible to clear an area of unwanted plants in one go - it can take years to put right.

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