Invasive Species

As part of my research I have been studying the proliferation of the landscape by invasive species introduced into the UK originally as ornamental species subsequently spreading into the wild often devastating the local native species. The species I am concentrating on in this blog are Giant Hogweed, Himalayan Balsam and Japanese Knotweed which were all introduced into the Uk at varying times in the 19th Century.

Giant Hogweed (Heracieum Mantegazzianum) were originally native to the Caucasus region of Eurasia. They were introduced into the Uk in 1893 as an ornamental curiosity. The plant is named after the mythological God Hercules (of robust size and strength). On account of its dense strands the hogweed can displace native plants and reduce wildlife interests whilst also contributing to erosion along riverbanks and streams.

Giant Hogweed (Heracieum Mantegazzianum)

A song was written by Genesis in 1971 entitled, The Return of the Giant Hogweed:

Turn and run! Nothing can stop them, around every river and canal their power is growing. Stamp them out! We must destroy them, they infiltrate each city with their thcik dark warning odour. 

They are invincible, they seem immune to all our herbicidal battering!

Long ago in the Russian hills, a Victorian explorer found the regal Hogweed by a marsh, he captured it and brought it home. Botanical creatures stir, seeking revenge. Royal beast he did not forget. He came home to London and made a present of the Hogweed to the Royal Gardens at Kew. 

Waste no time! They are approaching hurry now, we much protect ourselves and find some shelter strike by night! They are defenceless. They all need the sun to photosensitize their venom.

Still they're invincible, still they're immune to all our herbicidal battering.

Fashionable country gentlemen had some cultivated wild gardens, in which they innocently planted the Giant Hogweed throughout the lands. Botanical creatures stir seeking revenge. Royal beast did not forget. Soon they escaped, spreading their seed, preparing for an onslaught, threatening the human race.

Mighty hogweed is avenged. Human bodies soon will know our anger. Kill them with your hogweed hairs.

HERACLEUM MANTEGAZZIANI.

By 1870s, William Robinson, author of the Wild Garden, advocated seeding giant hogweed in rough places on the banks of rivers or artificial waters, islands, or any place where bold foliage is desired. He added that 'when established they often sow themselves so that seeding plants in abundance may be picked up around them; but it is important not to allow them to become giant weeds.'

Giant Hogweed can grow up to 18ft in the wild.

 A story taken from a newspaper article in 2013 tells the unfortunate tale of a walker and his wife who whilst on a walk in Whitley, Bay near Newcastle upon Tyne  spotted the plant in the undergrowth:

'We were walking the dog near the coast road when my wife stopped to admire a plant and she asked if we could have one for our garden.. the sap rubbed against me but I didn't realise as it didn't hurt. I just thought that I had been bitten. It was only when I got home that my right leg flared up and it started blistering.'

As a result of his injuries he was advised not to put his leg in the sun for the next seven years, as the injury had taken all the natural UV protection away in a condition known as phytophodermatis. 

Blistering due to skin contact with Giant Hogweed

 Japanese Knotweed (Fallopia Joponica) is a non native invasive species of plant introduced into the Uk in 1825 from the far east. In Japan it was kept in sway by natural predators, including insects and diseases. In Britain it had none.  Before long it had spread along watercourses, transport routes and infested waste areas. It is recognised as the most damaging and invasive weed in the country, forcing its way through cracks in walls and pavements, growing up to 13ft tall and destroying everything in it's path.

Japanese Knotweed being sprayed in Cornwall.

 When it was introduced Victorian gardeners took to it instantly: they loved tall, leafy architectural plant, especially those with heart-shaped leaves. William Robinson, the most influential writer of his day recommended planting it in clumps of two or three, describing it as:

 'large and noble tufts of lively green, which increase in beauty from year to year,' and 'a capital plant for the small town garden.' 

Japanese Knotweed spreading along a riverbank

  Richard Mabey, in his classic work Flora Britannica, describes what happened when the knotweeds powers of colonisation were realised:

 'when their formidable powers of colonisation were realised, they were thrown over the garden wall onto railway embankments and rubbish tips. From these strongholds they advanced even further, able to sprout from the smallest fragments of root as by the remorseless extension of their whole root systems.'

It hit the headlines when it was found rampaging along a footpath in Hampstead linking the houses of celebrities such as Thierry Henry and Esther Rantzen. Local resident Tom Conti called it the japanese secret weapon describing the invasion as the day of the triffids in Hampstead.

Japanese Knotweed, on a footpath in Hampstead

 Kenneth Mcrae killed his wife unlawfully before committing suicide, he had become increasingly 'obsessed' and 'possibly paranoid' about Japanese knotweed. In his suicide note he wrote:

'I believe I was not an evil man, until the balance of my mind was disturbed by the fact there is a patch of Japanese Knotweed which had been growing over our boundary fence on the Rowley Regis Golf Course.'

He believed the value of his mortgage free property would be dented by the knotweed. It has a reputation as being the cockroach of the plant kingdom and is so prevalent now that there is not a single six-mile square patch where it is not present. The cost of eradication is estimated at around £1.25 billion while clearing it from the 10 acres of the London Olympic site cost more than £70 million.

 Himalayan Balsam (Impatiens glandulifera) known as 'policeman's helmet' due to the shape of its flowers was introduced into the UK in 1839 at the same time as Giant Hogweed and Japanese Knotweed. All three species were promoted as having the virtues of 'herculean proportions' and 'splendid invasiveness' meaning that ordinary people could by them for the cost of a packet of seeds to rival the expensive orchids grown in the greenhouses of the rich. 

Himalayan Balsam at Bank Hall, Bretherton, Lancashire

 Himalayan Balsam grows up to 10ft (3m) tall and has colonised large areas beside rivers and woods throughout Britain, smothering any indigenous plants. On account of its aggressive seed dispersal coupled with high nectar production it attracts pollinators allowing it to out compete native plants. 

It invasion was aided by people. Miss Welch 1948 collected seeds in Sheffield and took them to the Isle of Wight and sprinkled them beside a river near Newport. Mrs Norris of camberley Surrey, spread them to local waste areas and woods, giving them to passers-by, sending seeds to Ireland and taking them on holiday to France and Spain.  

 

Himalayan Balsam spreading along a walkway