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The Vacuum Issue 5 spacer Issue 5
Aliens And Migrants In The Plant World
by Paul Hackney
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Native, alien and foreigner are terms people use everyday to reflect concepts of belonging, or otherness. Some people take pride in their families having lived in the same district or even house for several generations, or for having come over to England with William the Conqueror! Likewise we look down on 'blow-ins', foreigners, immigrants or aliens. They are rootless, they don't belong here.
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What happens when we look at the world of plants? Are these ideas still applicable? First of all is there such a thing as a truly native Irish plant? Biologists define an Irish native species as one which has reached Ireland by itself, by natural means of spread. Virtually no plant species survived the great Ice Ages which ended about 11,000 years ago; no plant could live here when the land was covered by a huge thick sheet of ice like the one that still covers Greenland. But when the ice started to melt, the newly exposed land surface became available for colonisation by plants from warmer regions further south in Europe that had escaped being engulfed by the ice sheets. Plant species migrated, over a period of hundreds of years, northwards and westwards from the continent of Europe, to which Ireland and Great Britain were still attached.
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Aliens And Migrants In The Plant World
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Perhaps the idea of a plant migrating seems odd. We can see how an animal species like fox or wolf could migrate; after all they have legs and can walk, and birds can fly. But how does an oak tree migrate? Of course, the individual trees don't, but their acorns are shed and spread around the parent tree and when these acorns grow to a mature tree and produce more acorns, they are spread out as well so that the net effect is a gradual shift of the oaks into previously uncolonised territory. Over several centuries the oak woods managed to spread hundreds of miles until they eventually covered most of these islands.
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While Ireland and Great Britain were still connected to each other and to the European mainland, there were no great impediments to plant migration. When the sea levels rose and Ireland and Great Britain became islands about 7,500 years ago, migration ceased. Because of this only a relatively small proportion of the total species available on the European continent managed to reach these islands. And Ireland fared worse than Great Britain - some plants got to the larger island but were prevented from reaching Ireland by the opening of the Irish Sea. Hence, although Great Britain has 1500 'vascular plant' species (this is the group that includes all the ferns, flowers and trees), Ireland has only about 1000. Botanists would say that it has an impoverished native flora. Among the species that got to Great Britain but not to Ireland are some of the great woodland trees such as beech and lime.
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However, it's quite obvious just looking around Ireland that beech and lime trees are actually very common. This is because they were deliberately introduced into the island by people. In fact there is a whole vast range of species which have been brought into the country from Great Britain, from the continent or even farther afield. Botanist class these plants as 'aliens' or 'introductions' or 'non-native species'. We can further classify these aliens by separating out those that were deliberately introduced like the beech and lime, because they are useful timber or ornamental species, from those species which were brought in by man accidentally, and which can include valueless or even harmful species. There are also some plants brought in because they had a perceived potential use as garden ornamentals, but which have turned out to be pests or nuisances.
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The actual number of alien plant species is huge: the total number of species of ferns and seed plants living on earth today is estimated at about 250,000. The total number of native plant species living in Ireland is probably only around 1000 at most. However, the total number of species cultivated in Northern Ireland is vastly in excess of this number, perhaps as many as 30,000. The total for the entire British Isles is probably about 55,000 - about a quarter or so of the entire world vascular plant flora! So in terms of sheer diversity, the aliens are vastly more important than the natives.
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Aliens And Migrants In The Plant World
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The aliens are also the economically important species. Not one of the principal human or animal food plants of Ireland is a native. Cabbage, turnip, carrot, swede, beet, wheat, barley, potato, tomato - all are introductions from abroad. There are native species which can be eaten, and were eaten before the introduction of agriculture about 3,000 years ago, but they form no part of the modern diet. The sole survivor of the old hunter-gatherer's diet is perhaps only the blackberry. The same applies to flax, once so crucial to Northern Ireland's industrial economy, but an introduction nonetheless.
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Most of our timber trees are introductions too: oak, ash and elm are native, but sycamore, lime, maple, spruce, Douglas fir are all aliens.
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Again, in our gardens, nearly all the ornamentals and vegetables we grow are from abroad - the story of the voyages of exploration and expansion of empire are readily traced in the dahlia, chrysanthemum and buddleia. We have a kind of inverted snobbery about garden plants; many gardeners look down their noses at the native species and praise the foreign exotics. Gardeners also make a clear if totally meaningless distinction between 'real plants' and what they call 'weeds'. Real plants require great care and skill to grow but weeds grow all too readily without help; real plants are attractive with showy flowers, weeds are nasty unattractive green things with no proper flowers - but what about the magnificent flower of the humble dandelion, that much-abused 'weed'?
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Quite a few plants which were brought in for gardens have spread into the wild. In a sort of botanical version of the Great Escape, they have tunnelled under the wire with their rhizomes or hurled their seeds over it and made off into the surroundings. There have been some notable successes in this category like buddleia, a Chinese shrub now found commonly in old quarries or on old masonry in towns, Japanese knotweed which is now a severe nuisance on many a river or roadside in that its dense growth obliterates every other wild plant or Himalayan balsam which is a beautiful but aggressively dominant plant of riverbanks and lakesides. One has to admire the sheer efficiency and vigour of these species - the Himalayan balsam for example has explosive fruits which throw the seeds many feet away from the parent plant - but they are the ultimate alien invaders, aggressive, pitiless exterminators of all vegetable opposition from our poor natives. Some cause so many problems it is actually illegal now to plant them in wild situations.
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The success of these aliens has not just been biological, many have accomplished cultural acceptance by our society. The fuchsia hedges of Co Antrim and other parts are frequently used as a sort of tourist totem for the Province. In fact most people never give it a second thought and don't realise that this beautiful shrub comes from far-away Chile. Likewise the floral badge of Northern Ireland is the flax flower, a plant of ancient middle-eastern origins.
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So our plant immigrants are a mixed bag: timber tree, ornamental garden plant, food plant; valuable, useless, nuisance. As with the introduction of people from other areas, our lives would now be impossible without them.
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Aliens And Migrants In The Plant World
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