Himalayan Balsam (Impatiens glandulifera) was introduced to this country in Victorian times as a colourful annual with flowers now seen of various shades between almost white and near crimson though pinks predominate. There is no certainty that it was ever deliberately grown at Otterhead.
Himalayan Balsam at Otterhead close to the Royston Water stream August 2008.
Himalayan Balsam flowers and seed capsules at Otterhead close to the Royston Water stream August 2008.
Being an annual plant, Himalayan Balsam relies on propagation by seeds which are scattered from exploding seed capsules. The spread of the plant tends to be down slopes and down watercourses. It is therefore possible to eradicate the balsam by concentrating on the highest locations first.
If left, the fast growing Himalayan Balsam plants will in time crowd out native species and by attracting pollinating insects, tend to reduce pollination of other plants. In winter when the balsam plants have died, bare banks of watercourses are liable to be eroded especially in times of flood.
The current aim is to eradicate Himalayan Balsam from the Otterhead Estate and upstream along the Royston Water tributary of the River Otter and then to eradicate the plant from the River Otter in Somerset. Although it is possible to eradicate the plant from River Otter tributaries in Devon (where such operations, for example by the Tale Valley Trust and by Honiton Town Council, have been in progress for several years), eradication along the River Otter in Devon is reliant on eradication from the river upstream in Somerset where the Otterhead Estate Trust has been taking a lead since 2008.
The Blackdown Hills AONB launched Help Halt the Invasion - restoring our riverbank biodiversity, a four year project mainly targetting Himalayan Balsam, as part of The International Year of Biodiversity 2010.
Further Reduction of Himalayan Balsam within the River Otter catchment in Somerset in 2012:
There has been a further reduction in the numbers of Himalayan Balsam plants found and destroyed at the Otterhead Estate and upstream along the Royston Water valley. Surely very good news for anyone trying to control this invasive alien annual plant further downstream in Somerset and in Devon as the supply of seeds carried by the river will therefore have also been considerably reduced. Extensive reduction of Himalayan Balsam by members of the Otter Valley Association and others along the tributataries in the lower Otter Valley began this year.
And again in 2013:
The first survey this year for Himalayan Balsam at the Otterhead Estate in late May only found (and removed) seedlings very close to the banks of the Royston Water stream. The area colonised by this invasive plant has therefore been considerably reduced with a resultant reduction of seeds entering Devon transported by the River Otter.
The second survey of 2013 in June was over a wider area in the Royston Water catchment including roadside verges but again the only Himalayan Balsam encountered and removed was beside the banks of the stream between Little Royston Bridge and the confluence with the River Otter just above Royston Bridge on the Otterhead Estate. The continuing reduction in the number of Himalayan Balsam plants and the amount of land where the plants have been discovered seems to demonstrate the continuing success in reducing this invasive plant on the estate and upstream by other land occupiers.
Contractors for Wessex Water carried out construction work in late 2013 and early 2014. A short section of the Royston Water was dredged and large numbers of seedlings were dealt with where the dredgings had been deposited. A few seedlings were found and removed above the new pumping station all before flowering had taken place.
Seedlings only found at one location on the estate where 39 were removed from a valley slope above the Royston Water; a location where hundreds of plants had been dealt with a few years previously. The assumption is that at least one plant flowered and seeded hidden by bracken last year. One more seedling has since been found there and removed and on 28 May a group of Taunton Midweek Conservation Volunteers cut the young bracken on the slope to eliminate that hiding place for any Himalayan Balsam plants:
It is possible that the Otterhead Estate is now free from Himalayan Balsam excepting any seedlings from seeds carried down the Royston Water under Little Royston Bridge. The focus this year should therefore be to eradicate upstream from that bridge where the number of plants found has been considerably reduced during the last few years, so that no seeds are carried by the stream through the estate to the River Otter.
A third search for seedlings found five in the same area and bracken there has again been cut.
Four searches carried out three without finding any Himalayan Balsam seedlings and one during which four seedlings were found.
First search on 23 June did not find any Himalayan Balsam plants.
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