Japanese Knotweed Solutions Ltd. Blog "Growing Concerns"

Finger pointing

April 24th 2015

I’m always interested in finding out who actually introduced our various invasive non-native species to the United Kingdom? It is often difficult to put a specific name against a particular plant and say – ‘so and so’ was the person responsible for the introduction of ‘x’ plant on ‘insert date’. The name most associated with Japanese Knotweed would be Phillip F Von Siebold who reputedly sent samples of Fallopia Japonica to the Royal Horticultural Society at Kew in 1849 – starting an invasion that is still causing problems today.

More often these invasions take place gradually over a number of years – perhaps an accidental introduction then a gradual slow incremental spread – followed by a huge growth phase. Often these plants aren’t particularly on anybody’s ‘radar’ and it is only when someone takes notice that a problem is recognised. Himalayan balsam for example was first discovered in the wild in 1855 yet it took till 2006 for the first paper showing its negative impacts.

The example of the ruddy duck in Europe is a good example of what happens without early detection and response. First introduced to Britain from America it was allowed to escape and establish a breeding population as it was believed to have little local impact. With interbreeding and competition however it has become the biggest threat to the white headed duck in Spain. Failure to act and the consequences led to huge expenses being incurred with costs in excess of £5 million being spent in Britain alone where it had become widespread.

Many of our problem plant species in the UK were introduced by the Victorian gardeners who were intent on creating fantastic gardens full of exotic species from around the world.

King Louis XIV was known for his interest in botany, his legacy included more than thirteen hundred new species. Among this huge list was Rhododendron  ponticum first seen near the Turkish town of Pontus. This evergreen shrub appears to have been first brought to Britain from south western Spain in 1763 and was welcomed into all the best gardens.

The Victorian gardeners liberally planted R.ponticum as a rootstock on which to graft less vigorous and more exotic Rhododendron species. Rootstock suckered and spread and the prolific tiny seeds it produced helped it travel the length and breadth of Britain along railway embankments and taking up residence in woodlands.

There were originally two limiting factors in the spread of this evergreen invader;

It could not abide lime rich soils

It could not survive very cold winters


Whilst it still does not pose a problem in areas of calcareous soils …it has now naturalised up into the far north of Britain and has evolved a cold tolerance. Recent research has discovered that populations of R.ponticum in eastern Scotland contain genes from more cold tolerant species, Rhododendron catawbiense- this species was introduced from North America and can tolerate temperatures much colder than anything ever recorded in Britain.

Somewhere along the line R. ponticum evidently hybradized with R. catawbiense and has acquired genes from this source.This points to a further problem with invasive non-native species in their ability to become genetically modified.

Bad enough that invasions can happen and can be very serious – but even worse still, when genes move between species allowing plants to invade new habitats in which previously they were unable to survive.

This makes ‘naming’ the culprit who introduced a problem plant even more difficult as multiple factors have been involved…perhaps I could become an alien plant detective….???

 

Mike C

Ref Jonathon Silverton – Demons in Eden / ref The Royal Society of Edinburgh Discussion Forum Dr Niall Moore / Prof Chris Thomas