All in the name
Before we look at their impacts, there is a lot of terminology around non-native species which can make it a confusing topic.
Native species are any plant or animal that have naturally come to live in and be part of an ecosystem. They have natural predators and controls, so their populations are unlikely to grow hugely. Non-native species are those that are introduced to an ecosystem, purposefully or accidentally, by humans. Many of these species pose no threat to native wildlife, but around 10% become invasive. Non-native invasive species cause damage to natural ecosystems and are often a huge financial burden to remove.
As our climate changes, these definitions will become more fluid. Some species are moving into new locations as the climate becomes suitable for them, without human intervention. As native species go extinct, these newcomers may be filling a role that has been lost. But they could also add extra pressure to an ecosystem already under pressure from climate change, habitat degradation or a whole range of other factors.
Escapees and releases from fur farms have made the American mink a pervasive threat to British wildlife, particularly freshwater creatures. The water vole, in particular, has suffered from predation from the American mink, disappearing from some areas because of this. The Trust controls mink populations on some of our nature reserves where important populations of water vole live.
Many plants can become invasive, and waterways provide the perfect medium for their seeds to spread further. Himalayan balsam is very fast-growing, smothering other plants, and as it dies back in winter, leaving banks bare, it can contribute to bank erosion. Nesting sites are lost for water voles and kingfisher when this happens. The Trust’s volunteers regularly pull balsam as part of our New Forest Non-native Plants Project.
Introduced for food, these crayfish are far more aggressive than the native white-clawed crayfish. They eat the small animals and plants in the river, damage banks and also carry a fungal plague. The Trust is setting up ‘ark sites’ for the native species, isolated from the invaders, and monitoring their populations across the county.