The concept of an alien species, and therefore one deemed fit for eradication, presupposes that the decision to classify such flora and fauna as invasive is made by ‘experts’ and therefore correct. There are currently 834 species on the ISSG database, a “global network of scientific and policy experts on invasive species, organized under the auspices of the Species Survival Commission (SSC) of the International Union for Conservation of Nature (IUCN)”, so where did they come from and why are they not invited? When Darwin finally published The Origin of Species in 1859, a document that had been sitting on his desk for at least a decade, readers marvelled at Darwin’s analysis and encouragement of adaptation and succession in the natural world. Since that time global trade and Victorian inquisitevness has seen a vast number of wierd and wonderful species land on our shores. The mitten crab hid in ballast imported from China in the 1900s, the ruddy duck escaped from Slimbridge reserve in 1956, the sycamore, considered an invasive, arrived here in the 15th century from mainland Europe. Therefore while we marvel, or otherwise, at the globalisation of finacial and travel markets somehow the globalisation of nature is unacceptable (it is worth noting here that twitchers welcome and subsequently chase birds with temporary visas obsessively). Two species of flora currently being given both barrels by conservationists are the giant hogweed and Himalayan balsam, both common within riparian landscapes. There are markedly different characteristics to this pair which brings into question the decision making on their future.
The first viable specimen of giant hogweed (Heracleum mantegazzianum) was imported as part of the Ibero-Caucasion garden at the Great Exhibition in 1851, and a further 5000 seeds were donated to Queen Victoria by the exhibitor and botanist Vakif Jalilabad. The subsequent planting formed a spectacle in the ‘Jardin Turc’ at Buckingham Palace but the plant escaped the walls of the palace and colonised large areas along the Regents Canal and south on Clapham Common. The plant is now widespread, favouring the moist soil along riverbanks and other natural or artificial water features, and considered a pest. Why?, because it creates a root system that compromises banking, leading to erosion, it creates a massive canopy that prevents other flora from growing and finally it has a venomous sap that can hospitalise those unfortunate enough to use the stems as pea-shooters.
The plant also has a stem covering of spines, which are unpleasant, therefore the giant hogweed has no redeeming features apart from looking impressive and monstrous. So how is this plant removed from our greenspaces? Well, it can be dug up, often requiring a JCB if the stand and root system is large, it can be poisoned and it can be decapitated to prevent the seed head forming. One extraordinary feature of the giant hogweed is that following poisoning and having its head chopped off it often quickly produces a seed head as its last act of defiance, this quickly disperses as the plant topples. As an invasive species it is without rival, however there are other species on the invasive hitlist that may be less deserving.
Himalayan balsam was introduced to Kew Gardens in 1839 and rapidly became a domestic garden favourite. The balsam we see in the wild is a garden escapee, in fact people still grow Himalayan balsam in the garden as it has attractive pink flowers which give the plant its common name of Policeman’s Helmet. It is a prolific seed producer with each plant producing 5000 seeds, or 600 per metre from the base. The downside to balsam is that it produces a canopy that crowds out other species while its nector production is such that it attracts the most pollinaters. Again, the Himalayan balsam prefers river banks and as such compromises the viability of berms and other substrates, thus increasing flood potential.
Recently, during a ‘balsam bash’ or balsam removal exercise over a number of weeks in London, participants were constantly reminded of balsam identification as other species were being pulled up in the process, such as natural balsam and figwort and assorted willowherb. The probability is that this was an act of innocence and enthusiasm but the need to pull balsam needs to be unwrapped. Himalayan balsam does prevent a succession of natural fauna from developing closer to the ground and has the potential to generate into large stands but it is certainly not an ugly plant, it is even edible (Balsam to eat) and happy to co-exist, albeit individually, amongst other species.
So really, what are we trying to protect by culling these flora? It seems that Darwin’s idea of natural selection and adaptation has been anthropomorphed into an archaic regime of man’s dominance over nature. This is a kind of Cartesian duality of our time, but if we are to aspire to lives closer to our environment then a more rigorous, and accepting, regime of ecology would surely allow these species to do what they want while we learn to coexist.