Invasive species week

Signal crayfish © Linda Pitkin/2020VISION

This week is invasive species week, 24-30th May. The week aims to raise awareness of the problems non-native invasive species cause, and ways we can all help prevent their spread. This week we will take a look at some of the invasive species that are most affecting habitats and wildlife in Hampshire and the Isle of Wight.

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.

American mink 

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.

Himalayan balsam

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.

Signal crayfish

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.