Skip to main content

What is an Invasive Non-Native Species?

Non-Native Species are species that, because of human activities, have become introduced in places beyond their native range. Physical barriers such as mountain ranges, oceans, rivers, and deserts mean that many ecosystems have evolved separately, creating distinct groups of species which are characteristic to certain places.

However, human activities like international trade and tourism now mean that species are being moved across these geographic barriers (either intentionally or otherwise). This shuttles species from the places where they evolved, into places where they have never been before.

Because non-native species evolved elsewhere, the new environments they enter haven’t yet developed ways of controlling their behaviour.

Some non-native species won’t be able to survive in our climate. Others will integrate with our habitats without damaging them (these are called ‘naturalised’ species). But certain species are able to thrive and dominate. These species are called Invasive Non-Native Species (INNS), and they present a serious problem not just to our ecosystems, but to our communities and our economies.

Why are INNS so dangerous?

We are in a nature emergency. One in five species of UK vascular plant are now threatened with extinction, and the introduction of INNS is recognised as the second biggest threat to biodiversity after habitat loss. But how is it that these species are able to cause so much damage?

  • No natural control mechanisms mean that INNS populations can grow without restriction. Many of our native herbivores choose not to risk eating unfamiliar plant species. Equally, our native pests, pathogens and parasites haven’t evolved to recognise the newcomers, so don’t infect them. This means that non-native species manage to escape the processes that normally restrict population expansion, letting them flourish excessively.
  • Fast growing INNS outcompete native species. Some INNS are extremely fast growing and well suited to our climate – these species crowd out slower growing natives, outcompeting them for resources like sunlight, water, nutrients, and space.
A young Sitka spruce (Picea sitchensis) which has spread from a plantation and germinated over a species rich pasture. Credit: Lizzie Wilberforce
  • INNS colonise over our natural habitats. Some INNS can spread their seeds in huge numbers over long distances. The germination of these seeds on our native habitats changes their species community structure, endangering these unique ecosystems.
  • New diseases can be brought in with the INNS. New pests and diseases are brought into the UK which our native species don’t have immunity to. This makes our native species highly susceptible to infection from INNS pathogens, resulting in widespread losses (such as with Ash dieback and Dutch Elm disease).
  • The changing climate is creating conditions which let some INNS flourish. Many of today’s invasive plants have grown in Wales for centuries without causing ecological damage. Climate change is now unlocking the conditions that allow these species to dominate over our native flora.

The result?

All of these factors mean that INNS are beginning to swamp many of our native ecosystems. This reduces the diversity of species present, which undermines the resilience of our habitats. When our ecosystems are vulnerable our economy is unstable. Natural Resources Wales now estimate that INNS are currently costing the Welsh economy at least £125 million a year. See below for some of Wales’ most destructive INNS to look out for, along with some information on how it is they are causing so much devastation.

Top Offenders

Wales Farming News
Black cow and white cow in Welsh Upland background trees and hills.

Wales Farming News

Agricultural grasslands dominate Wales’ rural landscape. Finding ways to restore species-rich habitats to farms is a priority for Plantlife Cymru.

Rare Fungus spotted at Kenfig National Nature Reserve
Brown topped fungus with yellow gills in a green grassy area.

Rare Fungus spotted at Kenfig National Nature Reserve

Chris Jones, the Warden of Kenfig National Nature Reserve, recently found the very rare fungus, during a routine survey.

How to Stand up for Wildlife and Protect Local Sites From Being Destroyed
Crop spraying.

How to Stand up for Wildlife and Protect Local Sites From Being Destroyed

Every day, our wild plants and fungi are put at risk from planning decisions, chemical sprays and more. Find out what you can do to help protect nature.