Japanese Knotweed.

This fast growing plant is ideally suited to the climate in the UK, has spread rapidly and can now be found in most regions in Britain. It produces underground runners that spread out and send out hollow shoots to the surface. These runners are very strong and can soon push up through stone walls, paving stones and even tarmac. These shoots form a dense growth and so cast a  lot of shade, while the runners fill the soil. Soon it is too dark beneath the canopy of knotweed leaves for anything else to grow.

Himalayan Balsam.

An attractive and fast growing waterside plant, Himalayan Balsam has spread across the UK partly because it has been ignored, partly because it has been actively encouraged as an ornamental plant and partly because of its own ability to spread its seed. The seeds develop in pods containing a long filament. As the seed pod dries in summer, the filament contracts and tries to form a coil like a spring, but it is held straight by the pods itself. When the seeds are ripe the pod finally breaks releasing the filament that quickly springs into a coil, flinging the seed out of the pod. Seeds can travel up to 5m away and are waterproof so they can be carried further along rivers and streams and to spread to new areas.

Rhododendron.

Large areas of woodland in the UK were purposely planted with Rhododendron as it provided cover for game birds on shooting estates. As an evergreen, it shades out native plants such as bluebells and snowdrops found in woodlands, while its fallen leaves and roots change the soil to make it difficult for other plants to grow. Its sparse branches provide little opportunity for nesting birds, and it does not produce seed for winter food.

American Mink.

The mink is a small but agile and adaptable predator. Since its release into the wild both by accident and on purpose, it has readily adapted to living in the UK. It can swim, run and climb and will eat a variety of other animals such as waterfowl, fish, ampihibians, small mammals and reptiles. Our native wildlife has never been exposed to such a successful and adaptable predator and so they have been unable to protect themselves. The mink is one of the principal causes of the massive decline in the number of water voles.  Water vole evade predators by swimming but the mink's ability to swim ensures they can make an easy meal of the water vole. The mink itself has no predators to regulate its numbers and now mink are common in most regions of the UK, although they are most often found near rivers or other water bodies. 

More information on the effects of Mink can be found here.

Grey Squirrel

The grey squirrel was introduced from north america and has adapted readily to life in the UK. It is very similar to our native red squirrel and lives in the same woodlands, eating the same food. However, the grey squirrel is larger and their numbers have grown quickly. This has left no room for the red squirrel and its numbers have plummetted. The red squirrel can now only be found in conifer plantations as these are not used by the grey squirrel.