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Alien Invaders in the Tamar Valley

Friday 22nd May is International Biodiversity Day and the theme for this year is Invasive Alien Species...

Right now, alien invasions are reaching beyond the realm of science fiction - creeping into our gardens and farms, emerging in our walls and waterways and breeding across our landscape to the detriment of the natives...
Invasive species of plants, fish, animals and other organisms are a global problem: one of the greatest threats to biodiversity and therefore the ecological and economic well-being of society and the planet.  Since the 17th century, invasive alien species have contributed to nearly 40% of all animal extinctions for which the cause is known! (Convention on Biological Diversity, 2006)
Here in the West Country, parts of our precious and beautiful environment are under attack by several virulent species of plants in particular.  Straddling the border between Devon and Cornwall, the Tamar Valley Area of Outstanding Natural Beauty is at the forefront of the invasives war, being the worst affected area in Cornwall with all three of the top offenders growing within its boundary.

Japanese Knotweed, Himalayan Balsam and Giant Hogweed are all are easily spread by water, so its no surprise that they settled so well in the Tamar Valley with its many tributaries.   Riverbanks and floodplains suffer the most damage, especially along the upper reaches of the Tamar.   Many of these areas are valuable habitats for wildlife, and when the aliens die back, they leave the banks more vulnerable to erosion.
Giant Hogweed is the attention-seeker of the group.  A relative of the carrot family, it can grow up to eight feet tall and is crowned with a massive white flower that can shed more than 50,000 seeds when ripe.  Anyone who has come into contact with this alien invader, will know how nasty it can be too: the leaves exude a toxic sap, that can burn the skin if exposed to sunlight.
Japanese Knotweed is the stubborn powerhouse of the gang.   The heart-shaped leaves and reddish colouring belie the fact that it grows each year from a huge underground root, so strong it can literally force its way through concrete. This is one of the most difficult invasives to eradicate.

Himalayan or Indian Balsam is the prettiest of the bunch, first introduced to the UK in 1839.  But don't be fooled by the lovely pink flowers, as this relative of Busy Lizzies spreads at a rate of two metres a year.  Also known as Jumping Jack and Policeman's Helmet, the seedpods 'explode' when ripe, allowing the weed to grow quickly and aggressively. Since 2000, a group of Tamar Valley environmental organisations has worked in partnership to control these alien species and work towards their extinction here in the south west.  Every year, the landscape is surveyed, checking for the invasive plants along 72 kilometres of riverbank, north of Cotehele.  Their positions are logged and then the plan of attack is implemented, which involves digging, spraying, pulling and treating with approved herbicides.

To avoid a real-life version of 'the day of the triffids', the crucial way to tackle these alien invaders is for
everyone to join forces.   The project team are urging any farmers and land owners to treat plants on their own land, or get in touch for help and advice.   Natural England, Environment Agency, Tamar Valley AONB and Cornwall Council are all on hand to help, and they have produced a useful leaflet on the subject.  For info or a copy of the leaflet, please call the AONB: 01822 835032 or email rteverson@tamarvalley.org.uk

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