Should we be so precious about only growing native plants?
I frequently read about how dreadful it is to move plants around the world and to introduce alien species into our gardens. A bigger crime is to introduce them into the countryside and we certainly should not plant them into the wild.
A contrary view comes from ecologist Chris Thomas at the University of York. He is the man who predicted ten years ago that a global temperature rise of two degrees centigrade would perhaps over the next thousand years create species-loss of millions. This is on the scale of previous mass extinctions.
In a recent article in the New Scientist, Chris, who has not changed this view, argues that such extinctions have always created the conditions for massive bursts of new evolution. He argues that there is abundant evidence that this process has already started.
He says that contrary to popular opinion, when foreign invaders are introduced hybridisation will lead to valuable new species. Where Darwin made the analogy of evolutionary steps as new twigs on a tree, modern genetics sees rather speedier jumps in diversity when closely related species hybridise. Genes are more mobile than previously thought.
This is not to say we should not be concerned about the numerous documented cases where new introductions have invaded new habitats to the detriment of native ecology. More overlooked is where closely related species have given rise to plants and animals with beneficial selective advantages. This might not be obviously apparent where European rhododendrons have combined forces with native American species to create R. x super-ponticum. Nature does not pander to man’s ideas of how it should be. In evolutionary terms this rhododendron is a superior plant!
One problem with introduced species is that natural predators are often left at home. Japanese knotweed is no problem in Japan! Eventually new predators will arise or be imported by man. A new predator of invasive honeysuckle in North America has arisen by the natural hybridisation of two fruit flies. Actually, even Japanese knotweed is no threat to the wider British countryside. This has not stopped legislation that makes planting Fallopia sinense illegal in the wild. The not inconsiderable threat of knotweed, readily talked up by the extermination industry, seems to be restricted to man made environments such as old industrial sites, general wasteland and old cemeteries.
Japanese knotweed does hybridise with the thuggish climber called Russian Vine. Not the monster you might imagine. It’s not a good match, a woody climber mated with a herbaceous plant. No hybrid vigour here, more that of a wimp!
Chris Thomas regards the whole world as a gene pool that potentially has the capacity to counter mankind’s destruction. Rather than prevent transportation of animals and plants he argues for open corridors of movement. His university department have moved some of our own native butterflies further North than their previous distribution with very good effect.
|I do not know whether this strangling Costa Rican climber is native or not|
I have been reading an excellent book about weeds by ecologist Richard Mabey. In it he describes examples of harm caused by introduced plants. He never-the-less takes a benign view to growing and introducing none native plants. I have leaned heavily on his superb book in what follows.
Are there such things as native plants and natural native communities?
After each Ice Age, plants retreated back in different combinations. Ever since early man started to travel, plants and animals have moved and created new stable ecologies. New islands have arisen from the sea and have been randomly colonised with plants and animals of extremely diverse genetic origin. Such islands are evolutionary hotspots and their dynamic ecologies function extraordinarily well.
|Walking the beech in Costa Rica I imagined these ocean carried coconuts were colonising a new island. The lower one had success.|
Who are we to say what is native? Long before the Romans came to the UK bringing hundreds of plants now thought of as our own, new plants and animals were arriving. Early human activities, not least hunting, forest clearance and farming led to new landscapes. Over the past two thousand years new plants and animals have been brought to our shores. Nothing is completely stable. No environment is untouched by man.
|What could be more evocative of England than playing conkers on the village green? The horse chestnut was introduced from the Balkans 400 years ago.|
Even some of the as yet unspoiled parts of the Amazon jungle which we regard as pristine, grows on land cultivated by early indigenous communities. The Amazonian black earths, the man made terra preta soils, remain as evidence of land management more than a thousand years ago over South American regions that together total the area of France!
The movement of weeds.
Ever since man started to cultivate the ground, unwanted plants have muscled in and natural selection over thousands of years has led to their superbly efficient strategies of survival in the garden and farm. Everywhere that man has gone he has been accompanied by weeds. Their well honed survival techniques have enabled many to outcompete native vegetation. 50% of New World weeds were brought over inadvertently by the settlers. Having survived many hundreds years of European farmers’ attempts at control, introduced weeds - or should I say wild flowers - easily outcompete native flora.
Despite their success, introduced plants have not lead directly to the actual extinction of native plants. It would be difficult to specify a plant lost to the UK because of introductions over the last 2000 years. That is not to say that plants have not been lost to man’s activities and changes in climate.
I liked Richard Mabey’s story of Kentucky Bluegrass.The grass has an image to us here in the UK as being American as American pie. Smooth stalked meadow grass was brought over from England!
Nettles, groundsel, sowthistle, knotweed, dandelion, chickweed, shepherd’s purse, mayweed and couch are just a few of Britain’s gifts to the world.
My friend Harry Kennedy was a merchant seaman in his youth and travelled the world. He tells me that what most impressed him was not the differences, but the similarities between plants from country to country. Our Victorian ancestors regarded it as their God-given duty to explore and redistribute plants. Kew gardens was a broker of plants that served the Empire. The world’s plants and social systems were changed with the transfer of rubber, sugar cane, tea, coffee and bananas. Plant explorer-collectors have imported plants for hundreds of years. World agriculture shares numerous crops. Many plants and animals deprived of their natural habitats by human activity have been conserved by their redistribution. The world is a better place for the sharing of plants.
His book ‘The Wild Garden’ published in 1873 created a sensation in Victorian times. He advocated using the wild flowers and weeds of the world to be planted naturalistically on the boundaries of country estates. He introduced from America, solidago and wild michaelmas daisies. He promoted wonderful Japanese knotweed and lovely yellow goat’s rue. Inevitably his plants escaped to the wild. Was William Robinson a visionary or a vandal?
So where do my musings take me?
Perhaps to reinforce prejudices! Here are some of them.
I will continue to fill my cemetery gardens and village plot with self seeding plants of the world.
I do not support the idea that when trees are planted in public places that they need to be native.
My prejudice against that vigorous intergeneric hybrid, the Leyland cypress remains.
I will continue to plant variegated plants and dahlias in my garden.
I will promote the use of insect and bee friendly plants on farmland whether they be ‘native’ or not.
I support efforts to maintain special landscapes whether they are deemed ‘natural’ or are relics of our forbears.
I am cynical about ‘offset arrangements’ when developers wish to develop ‘pristine sites’.
I will continue to point out that there are many instances of habitats for rare plants such as orchids on industrial wasteland that are bi-products of herbicide use. Clear examples of plants’ accommodation to man. Further, that enlightened use of herbicides has a place in land management.
I will continue to admire the fashionable colourful labour-intensive blobs on urban landscapes created as meadows with gaudy agricultural weeds. But they are too hard work for me.
I will also continue to look at the work of Piet Oudolf with a mixture of jealousy, envy and admiration. His methods are too expensive for me. I wonder how his landscapes will mature and how history will regard his skills.
Although it might be desirable to move animals and plants around the world there is still a place for governmental restriction and prescription.The only present permit from The European Commission for the import of a plant parasite is a psilid fly specific to Japanese Knotweed. Completely free transport would encourage the crooks who despoil natural habitats. Look what is happening to elephants now that the United Nations has allowed the worldwide sale of historic stored ivory. It has provided cover for their slaughter.
I am emboldened to argue against fashionable politically-correct notions of plants we must avoid. I think Himalayan balsam is a wonderful plant. An old rural name is the ‘bee-bum plant’ which is indicative of busy bumblebees deep in the flowers. It is a very pretty nuisance on wet sites already spoiled by man but in my view is no threat to nature.
What hat are you wearing today? Is it the one that maintains only ‘native’ flowers or the one that preserves insects and bees?