|Oxford Ragwort Senecio squalidus|
I well remember the excitement back in the 1970s that the late Dr Francis Rose showed when he first found Crassula helmsii in a small pond adjacent to Hatchet Pond in the New Forest. His excitement was caused by the fact that his initial identification of it was Elatine hydropiper, a very rare species that he had never seen before. Further research however put him right, and the truth was that he had had his first encounter with a most unpleasant alien. It did not take long for the whole of the bottom of that pond to be a one species carpet of Crassula helmsii with some important species crowded out completely.
The first occurrence of Crassula helmsii in the New Forest was recorded by the late and very able, deaf botanist Paul Bowman. His notebook showed that having found Crassula helmsii nearby, he then drove to Hatchet Pond. Circumstantial evidence suggests very strongly that a small piece of the plant may well have attached itself to his boot. This shows just what an invasive threat this species must be. The original source of the invasion is thought to have been an aquarist supply shop in Essex.
The story of Oxford Ragwort Senecio squalidus is fascinating. This species is now ubiquitous on the tops of walls and throughout Britain’s railway system. It is now completely taken for granted as part of the British flora. It is called Oxford Ragwort because it was grown in Oxford Botanic Gardens in the late 17th century having been collected from volcanic cinders on the slopes of Mount Etna. It was a small hop from its flower bed in Oxford to the walls of the Botanic Garden from whence it found the walls in the rest of the City and, from 1844, the cinders on the early railway tracks passing through the town. In no time at all, it had established itself throughout Britain on its fast expanding railway network.
|Rhododendron removed from one ownership but dense in a |
neighbouring one in Sussex
|Himalayan Balsam Impatiens glandulifera|
Discouraging the spread of aliens using non-native biological control may be fraught with difficulty. There are examples of non-native predators becoming a greater threat than the species they were designed to control. Where successful, such control may be very effective, but extreme caution is required before such biological control is implemented. Most conservationists shy away from the use of chemical control, however it seems that chemical methods are about the only armament available for the control of Japanese Knotweed. Invasive species are not confined to land, they can also cause havoc in marine habitat around our coast. The slipper limpet is a case in point as is Japweed Sargassum muticum which became established on the Isle of Wight in the early 1970s. It has now spread throughout western Britain as far north as south western Scotland, and is established in Ireland. In Britain, its long strands grow to the exclusion of all native marine algae where it has become established. Control of this menace was started too late for it to be very effective.
|Martagon Lily Lilium martagon|