Invasive Aliens. Dan Eatherley

exaggerated, that we should stop worrying about non-natives and even welcome them for the benefits they can bring. At the other extreme, a growing band of conservationists is going beyond simple calls for the eradication of non-natives to campaign for the deliberate reintroduction of a menagerie of native British plants and animals which have become extinct at the hands of humans. To its critics, the ‘re-wilding’ movement is pure eco-nostalgia.

      For me though, most fascinating of all is that non-native organisms, invasive or otherwise, from rabbits to rhododendrons, mink to muntjac, hold up a mirror to our own species. Yes, the pace of invasion is higher than ever before but problematic non-natives aren’t a modern phenomenon: they’ve been with us from the outset, as unavoidable a corollary of the human way of life as cleared forests and piles of garbage. From the earliest settlement of our islands and first experiments with farming, through the Roman and medieval times, and the age of exploration by Europeans, to the current period of globalised free-for-all, the story of invasive species is the story of our own past, present and future.

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       First Invaders

       ‘But while men slept, his enemy came and sowed tares among the wheat, and went his way. But when the blade was sprung up, and brought forth fruit, then appeared the tares also.’

      King James Bible, Matthew 13:25–26

      For a million years a windswept peninsula in a corner of northwest Europe had seen various species of humans coming and going. The arrivals and departures were synchronised to the advance and retreat of continental glaciers, a dance choreographed by climatic change. They barely registered. A cluster of footprints here, a tidy pile of knapped flints there. Overwintering in caves, the people would emerge to gather shellfish from grass-fringed estuaries, pad through woodland in search of berries and nuts or pick at the carcasses left by lions and giant hyenas. The more ambitious, coveting the freshest meat, bone and fur, would rally family and friends in adrenaline-fuelled pursuits of deer, horse or mammoth.

      Make no mistake, even the earliest people were unusual. Britain had never welcomed visitors quite like them, and over the aeons these experiments in humanity forged in the evolutionary crucible of an African valley generated ever more sophisticated results: the grunts of the most obtuse of cavemen took on deeper meanings; people fashioned better weapons and perfected their hunting techniques; they got the hang of butchery and learned to tame fire. Humans would turn their new-found skills on each other from time to time. Yet, for a great sweep of history, these pioneers – Homo antecessor, Homo heidelbergensis and maybe others – were but minor players on a stage dominated by rhinoceros and sabre-toothed cat, bison and bear. A low profile was often the best strategy given the monsters with which the land was shared. People were no more masters of their destiny than were grains of pollen in the air. And, every time the cold rushed back in and the fragrance of the dwindling forest was lost once more to the bitterness of endless tundra, so would humans again retire to more hospitable refuges in southern and southeastern Europe, abandoning the briefly colonised outpost to musk ox, wolverine and ice.

      In the milder periods, when permafrost meltwaters inundated what would be known as the English Channel, the peninsula became an island. On one such occasion, some 125,000 years ago, humans found themselves shut out of the party altogether: things were warming up once again and a wealth of plant and animal species had spread back into Britain. But by the time people were on the scene, the land bridge from the continent had been claimed by the rising seas. Elephant, hyena, lion, deer, hippopotamus, elk and other animals had the place to themselves, enjoying a halcyon human-free interlude lasting 65,000 years.

      Even Homo sapiens, the most successful hominid – in population terms, at least – to arrive in Britain was no great shakes at first. Originating perhaps more than 200,000 years ago, modern humans took their time getting here. Not for millennia would the most substantial exodus from Africa occur, with one wave of migrants moving along the Indian Ocean coastline towards southeast Asia, and eventually Australasia; another meandering north and west across the Middle East and Europe. When, from around 40,000 years ago, small bands of nomads, each with its own distinctive material culture, started to reach our shores, perhaps in seasonal visits, they found they’d been beaten to it.

      Homo neanderthalensis had been eking out a living on Britain’s cold treeless steppes for at least the previous 20,000 years hunting, with flint-tipped wooden spears, woolly mammoth, woolly rhinoceros and probably quite woolly bison. The Neanderthals, with their heavy eyebrow ridges, flared nostrils and stocky physiques, were well suited to the hostile conditions. Yet their days were numbered, the British contingent vanishing within a thousand years of the arrival of modern humans. No one knows why.

      It’s tempting to equate correlation with causation and accuse Homo sapiens of behaving as the archetypal invasive species, outcompeting and eradicating a vulnerable native with cunning and violence, perhaps passing on some disease for good measure. But the story appears more complicated: the significant amount of Neanderthal DNA in the modern human genome suggests a peaceful, even romantic, coexistence between the two hominids across continental Europe dating back 100,000 years. Could it be that the two varieties of early human preferred to make love not war? In Britain, at least, it seems they had little direct contact, and in any case the argument is academic since dropping temperatures led to the most recent glacial maximum about 22,000 years ago. Any prospect of human existence was snuffed out for another ten millennia. The ice crept forward, smothering everything, wiping the sheet clean. Another fresh start.

      The people who returned to a warming Britain from around 15,000 years ago could still be classed as hunter-gatherers, but there was a greater sophistication about them, judging by the plethora of artefacts and art left behind. They were dog-lovers too, grey wolves having been domesticated to mutual advantage, possibly more than once, during or even before this most recent Ice Age. Moving along the Atlantic coast, the humans tracked herds of reindeer, horse, deer and elk north from their southern European refugia. Some perhaps crossed the English Channel in boats, while others may have sauntered through Doggerland, an expanse of terrain today submerged beneath the North Sea.

      These people exploited natural resources with unprecedented intelligence: flint-tipped arrows of hazel, fired from bows of elm, felled aurochs (wild ox), red deer and wild boar with accuracy; the slipperiest of fish were trapped in river weirs purpose-built from willow; birds and smaller mammals were noosed and snared; a wider range of plants was collected, stored and cooked than ever before. People were thinking ahead. Fire was used to manage woodland. Freshly burnt clearings, the ash festooned with appetising plant regrowth, could be used to lure hungry game, which was much easier than tracking a deer or boar through dense forest. Nevertheless, impacts on the landscape were minimal. As in previous migrations people travelled light and, save for the plant seeds brought as food or stuck to clothing and bedding, few in the way of new species were conveyed to Britain during this period. Things though were about to change.

      Danger. Tree felling in progress. A yellow warning sign greeted us as we approached the kissing gate. I had expected this: Hembury Hillfort’s website requested visitors to ‘observe cordoned off areas with red and white tapes’, and please to ‘not climb on timber stacks’. Thankfully, given my five-year-old daughter’s enthusiasm for outdoors rampaging, neither woodpiles nor tape were in evidence today. The works programme, aimed at reducing root damage to the site’s archaeology, was finished for the season. The tree clearance had a secondary function, to open up the view: that’s what partly drew us here. Hembury didn’t disappoint.

      Twenty minutes later saw us picnicking amid bluebells at its southernmost tip. From the 240-metre-high bluff we were offered stupendous views across the Otter river valley towards the coast at Budleigh (the sea itself was lost in haze). The landscape was a hodgepodge of greens, interrupted here and there with the dull copper of a newly ploughed field, a yellow patch of oilseed rape, and the occasional pale minaret of wood smoke. Just visible