The largest coordinated Japanese knotweed clearance project in the UK – along a seven mile stretch of the Kenidjack Valley in West Cornwall – has been completed after three years of intensive clearance work.
The project used a technique developed by the National Trust which involves injecting the stem of the knotweed with herbicide before clearing the plant from the whole of the course of the stream in the valley.
In the first year 100 per cent of the knotweed in the valley was treated and removed, with follow-up monitoring and treatment in the second and third year.
Work now begins on monitoring any potential re-growth of the Japanese knotweed to stop it from re-spreading along the valley.
Simon Ford, Nature Conservation Adviser for the National Trust and the lead on invasive species, said: 'This is a classic example of how invasive plants can literally take over a site. It’s taken three years of hard work and monitoring to eradicate the majority of the Japanese knotweed and see the beginning of a return of native plant species. The next stage now involves monitoring the site to prevent it re-spreading along the river valley.'
Reaching this stage of such a major project comes on a ‘day of action’ across the National Trust to tackle invasive plants and raise the profile of their impact. The day coincides with the United Nation’s International Day for Biodiversity.
Japanese knotweed was introduced into the UK from Japan in the 1840s as an ornamental plant and is now the number one on the list of the UK’s most invasive plant species.
Its rapid growth – up to three metres in height - means that it overshadows native plant species and has a significant impact on wildlife. It has been estimated that it would cost in excess of £1.5bn to eradicate Japanese knotweed from the UK.
Scenic views that had been lost for decades have returned following the clearance of Japanese knotweed in the Kenidjack Valley and its likely that bluebells and wetland plants will return after years of absence.
A key part of the long term success of this project will depend on the ongoing monitoring of the site to make sure that Japanese Knotweed re-growth doesn’t take hold and action continues to be taken when necessary.
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The problem of invasive plants
Across the National Trust the five major invasive plants species are:
- Japanese knotweed
- Rhododendron ponticum
- Himalayan balsam
- New Zealand swamp stonecrop
- Laurel
Over the last 10 years the Trust has seen a major increase in the threat to rivers and lakes from invasive plants such as parrot’s feather, where small pieces float downstream increasing its spread, and New Zealand swamp stonecrop, which can spread rapidly and cover lakes.
There are many ways that invasive plants have spread. Fly-tipping of unwanted plants from gardens, the deliberate planting of Rhodendron ponticum as cover and seeds spreading on the wind are all causes of these plants spreading into the wild.
As part of the International Day for Biodiversity today the National Trust is running more than 30 events across England to highlight the real challenges of managing sites affected by invasive plant species.
Working in partnership with organisations such as Plantlife, the Environment Agency, Defra and Natural England, local councils and other landowners is essential to the management of invasive non-native plant species.
Hundreds of thousands of pounds and thousands of volunteer hours through working holidays are spent each year to clear and control these plants and minimise the impact on wildlife.
Simon Ford added: 'Trying to manage invasive plants is a bit like playing football with moving goalposts as the target keeps changing, as seen with the rise of invasive plants in rivers and lakes in the last decade. Add to that the reality of a changing climate and you have a serious problem for the natural world that is dependent on intensive action to control and manage the spread of invasive plants.'
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