The New Wild E-Book

Fred Pearce

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2015

Seitenzahl: 480

Beschreibung

Veteran environmental journalist Fred Pearce used to think of invasive species as evil interlopers spoiling pristine 'natural' ecosystems. Most conservationists would agree. But what if traditional ecology is wrong, and true environmentalists should be applauding the invaders? In The New Wild, Pearce goes on a journey to rediscover what conservation should really be about. He explores ecosystems from Pacific islands to the Australian outback to the Thames estuary, digs into the questionable costs of invader species, and reveals the outdated intellectual sources of our ideas about the balance of nature. Keeping out alien species looks increasingly flawed. The new ecologists looking afresh at how species interact in the wild believe we should celebrate the dynamism of alien species and the novel ecosystems they create. In an era of climate change and widespread ecological damage, we must find ways to help nature regenerate. Embracing the 'new wild' is our best chance.

Leseprobe

THE NEW WILD

THE NEW WILD

WHY INVASIVE SPECIES WILL BE NATURE’S SALVATION

FRED PEARCE

Published in the UK in 2015 by

Icon Books Ltd, Omnibus Business Centre,

39–41 North Road, London N7 9DP

email: [email protected]

www.iconbooks.com

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ISBN: 978-184831-834-2

Text copyright © 2015 Fred Pearce

The author has asserted his moral rights

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Contents

Acknowledgements

On language and acronyms

Introduction: Nature in a world of humans

PART ONE: ALIEN EMPIRES

1. On Green Mountain

2. New Worlds

3. All at Sea

4. Welcome to America

5. Britain: A Nation Tied in Knotweed

PART TWO: MYTHS AND DEMONS

6. Ecological cleansing

7. Myths of the Aliens

8. Myths of the Pristine

9. Nativism in the Garden of Eden

PART THREE: THE NEW WILD

10. Novel Ecosystems

11. Rebooting Conservation in the Urban Badlands

12. Call of the New Wild

Appendix: Latin names

References

Index

About the author

Fred Pearce has been environment and development consultant at New Scientist magazine since 1992, reporting from 85 countries. He has written fourteen previous books, including When the Rivers Run Dry and The Land Grabbers, which have been translated into 23 languages. He also writes for the Guardian and is a regular broadcaster on radio and TV. He won a lifetime achievement award for his journalism from the Association of British Science Writers in 2011, and was voted UK Environment Journalist of the Year in 2001.

Acknowledgements

The roll call of people who helped in this book goes back through most of my 35 years writing on science and the environment. Many are named and quoted in the text. But some deserve special mention for helping me on my travels. On Ascension Island, Stedson Stroud was a marvellous mentor and guide; Paul Lister invited me to Scotland’s Alladale Wilderness Reserve; Geoffrey Howard hosted me in East Africa; Nicola Divine McClain lured me to Montana; Peter Shaw took me to see his Essex ashpits and James Fraser helped me in Liberia. My thirst for the contrary has also been nurtured at successive meetings of the Breakthrough Institute in California, where several of the interviews here took place. So, my thanks to Michael Shellenberger and Ted Nordhaus for inviting me.

Many editors at New Scientist have helped fund my inquiries over the years. Kate Douglas sent me to Lake Victoria and David Concar to Sarawak. Thanks also to Jeremy Webb, Bill O’Neill, Michael Bond, Sumit Paul-Choudhury, Rowan Hooper and Graham Lawton. Other commissioners whose enthusiasms have helped develop my ideas on the new wild over the years include Brian Leith for Granada TV, Bruce Stutz at Audubon (who sent me to investigate the Mediterranean’s ‘killer algae’), Susanna Wadeson at Transworld, and Roger Cohn at Yale e360.

Many people gave me interviews while I worked on this book. They include Chris Thomas, Joseph Mascaro, Nicola Weber, Paul Robbins, Andrew Cohen, Melissa Leach, Erle Ellis, Stephen Pyne, Borgthor Magnusson, Jay Stachowicz, Ariel Lugo, Rick Shine, Peter Kareiva, Douglas Sheil, Stewart Brand, Joe DiTomaso, Sean Hathaway, Dick Shaw, Matt Shardlow, Jim Dickson, David Wilkinson, Susan Schwartz, Ken Collins, Jeffrey Sayer and William Laurance. Many others responded at length to my emails. Still more, some quoted and some forgotten, did the same for previous journalism that spun into this book. Thanks to them all.

On language

I have used a lot of words in this book to describe species moving to new places. Most frequently I call them aliens, not in a pejorative sense, but to describe their status. More for variety than anything else, I also call them vagabonds, invaders, carpetbaggers, migrants, interlopers, non-natives, incomers, and no doubt more. Some aliens were taken by humans deliberately or by accident; others arrived by more traditional means. I save the adjective ‘introduced’ for those taken by humans. For some ecologists, ‘invasive’ has a particular meaning. It applies to those aliens making waves and taking territory. Equally, when species settle down and appear at home, they will be termed by some ‘naturalized’. I generally follow both terms. But please judge the species I describe by what they do or don’t do, and not by the label attached to them.

Some people like the Latin names of plants and animals, and sometimes they are necessary to clear up confusion. But they do get in the way. So I have included Latin names in the main text for the main species and taxa when I first mention them, but not for bit-part players. For those, where the context allows me to be specific about individual species, and where I think readers may be interested, I have posted an appendix containing some common names and their Latin versions.

Acronyms

CBD

Convention on Biological Diversity

DDT

Dichlorodiphenyltrichloroethane, a pesticide

FAO

Food and Agriculture Organization of the United Nations

GCHQ

Government Communications Headquarters (UK)

IMO

International Maritime Organization

IPCC

Intergovernmental Panel on Climate Change

IUCN

International Union for Conservation of Nature

JK

Japanese knotweed

MEA

Millennium Ecosystem Assessment

MIT

Massachusetts Institute of Technology

NSA

National Security Agency (US)

RSPB

Royal Society for the Protection of Birds

TNC

The Nature Conservancy (US)

UC

University of California

UNEP

United Nations Environment Programme

UNESCO

United Nations Educational, Scientific and Cultural Organization

USGS

US Geological Survey

WRI

World Resources Institute

WWF

World Wildlife Fund

Introduction

Nature in a World of Humans

Rogue rats, predatory jellyfish, suffocating super-weeds, wild boar, snakehead fish wriggling across the land – alien species are taking over. Nature’s vagabonds, ruffians and carpetbaggers are headed for an ecosystem near you. These biological adventurers are travelling the world in ever greater numbers, hitchhiking in our hand luggage, hidden in cargo holds, stuck to the bottom of ships and migrating to keep up with climate change. Our modern, human-dominated world of globalized trade and messed up ecosystems is giving footloose species many more chances to cruise the planet and set up home in distant lands. Some run riot, massacring local species, trashing their new habitats and spreading diseases.

We all like a simple story with good guys and bad guys. And aliens always make easy enemies. So the threat of foreign species invading fragile environments and causing ecological mayhem gets our attention. Conservationists have for half a century been battling to hold back the tide of aliens. They call them the second biggest threat to nature, after habitat loss. Their concern is laudable. They want to protect native species and the ecosystems they inhabit. But do we fear these ecological outsiders too much? Is our fear usually little more than green xenophobia? Most of us are appalled when foreigners are treated as somehow intrinsically dangerous. Yet the orthodoxy in conservation is to demonize foreign species in just that way. Native is good, and alien is bad. But is this simple formula true? Or might we need the go-getter, can-do aliens? In fact, might their success be a sign of nature’s resilience in the face of the considerable damage humans have done to the planet?

I am an environment journalist. Even to ask such questions gets me treated in some circles as a conservation heretic. I have met incredulity and hostility in equal measure. To be clear, I am not accusing environmentalists of being closet xenophobes or misanthropes, still less racists. But I have found that I am far from alone in my concern that we have bought into some dangerous mythology about how nature works.

I am not questioning the motives – to strengthen nature – but the means. Many ecologists who actually study nature told me that they felt conservationists were, with the best of intentions, getting the aliens wrong. And worse, that their efforts to keep out all foreign invaders of ecosystems might often be counter-productive, weakening nature rather than strengthening it. I discovered that there is a scientific backlash going on against the simple formula that natives are good and aliens bad. The purpose of this book is to explore that new thinking, and to ask what it should mean for conservation.

My conclusion is that mainstream conservationists are right that we need a re-wilding of the Earth, but wrong if they imagine that we can achieve that by going backwards. We need a New Wild – hence the title of this book. But the new wild will be very different to the old wild. We have changed our planet too much, and nature never goes backwards. Nature’s resilience is increasingly expressed in the strength and colonizing abilities of alien species. They are often the new natives. And in the new wild, we need to stand back and applaud.

There are horror stories of alien takeovers, of course. Most of them happen on small, remote islands with only a few native species, where carnivorous rats, cats and others hop off ships and cause mayhem. But elsewhere, most of the time, the tens of thousands of introduced species usually either swiftly die out or settle down and become model eco-citizens, pollinating crops, spreading seeds, controlling predators, and providing food and habitat for native species. They rarely eliminate natives. Rather than reducing biodiversity, the novel new worlds that result are usually richer in species than what went before. Even the terror suspects of conservation, such as zebra mussels and tamarisk, Japanese knotweed and water hyacinth, often have a good side we rarely hear about.

After going on the trail of alien species across six continents, my conclusion is that their demonization says more about us and our fears of change than about them and their behaviour. Some ardent wildlife lovers show a dark side when it comes to aliens. I sometimes think the more ardent they are, the more likely they are to be rabid about alien species. Understandable love of the local, the native and the familiar – of an imagined pristine environment before humans showed up – too often becomes fear and hatred of the foreign and the unfamiliar.

This hostility is generally justified by outdated and ill-founded ideas about how nature works. We often think of life on Earth as made up of complex and tightly-knit ecosystems like rainforests, wetlands and coral reefs that are perfected and stable, with every species evolved to have a unique role. With that vision of nature, alien species are at best disruptive and at worse plain bad. But where did this idea come from? Darwin certainly never said it. He said natural selection allowed species to adapt and survive, but he said nothing about ecosystems evolving to some sort of perfect state. They were just a jumble of species making their way in the world.

And today, fewer and fewer ecologists believe nature is either stable or perfectible. Real nature, they say, is often random, temporary and constantly being remade by fire, flood and disease – with species coming and going, fitting in, adapting or losing out. Change is the norm, they say. In this vision of nature, alien species are just like any other. Whether brought by humans or in more traditional ways, they are not an intrinsic threat to ecosystems. They are part of nature doing its thing, constantly reordering itself, constantly submitting to random events. Aliens may or may not cause change, but if change is the norm then there is no harm in that. In any case, when invaded by foreign species, ecosystems don’t collapse. Often they prosper better than before. The success of aliens becomes a sign of nature’s dynamism, not its enfeeblement.

This new ecological thinking is critical for how we understand the meaning of conservation, and for what action to take in the name of protecting nature. If nature is perfected and vulnerable to outsiders, then conservationists have to man the barricades to keep out the interlopers and restore the balance of nature. That’s what most conservationists think, and for a long time I shared that view. But if it is wrong, then keeping out aliens serves no obvious purpose. More than that, it may be counter-productive. Nature’s desperados are proven colonists and exploiters of the ecological mess that humans leave behind them. So surely that makes them nature’s best chance of healing the damage done by chainsaws and ploughs, by pollution and climate change. Far from being nature’s destroyers, aliens may be its re-invigorators, its salvation. They may be a sign that nature is not done. That it can bounce back. If that thinking is right, then simple conservation is short-sighted and true environmentalists should be applauding the invaders.

I do not want to suggest that we should always welcome every alien species. We humans may sometimes want to protect the species we know and love – in the habitats that we are familiar with. There is nothing wrong with that. And where alien species cause us inconvenience – whether zebra mussels in American waterways, rats on oceanic islands or rabbits in Australia – we may want to try to halt their spread. Again, that is fair enough. We have a legitimate need to curb some of those excesses, and a legitimate desire to protect what we like best. But we should be clear that when we do this, it is for ourselves and not for nature, whose needs are usually rather different.

And while we seek to protect what we like in nature, we should remember something else. There is very little that is truly natural in nature any more. They are very few, if any, pristine ecosystems to be preserved. Thanks to the activities of humans over thousands of years, no forests are virgin. They are all regenerating from past human invasions. We live in a new geological era, the Anthropocene, in which nothing is undisturbed and most ecosystems are a hotch-potch of native and alien species, often getting on in unexpected and productive ways.

Over my years as a journalist, I have written plenty of articles about how much harm alien species appear to do – about killer algae, marauding water hyacinth and many more. There was truth in them all, but they missed the bigger picture. This book is my journey to discover what conservation should really be about in the 21st century. It should not be about trying to preserve nature in aspic, still less about trying to recreate the past. That is both impossible and an affront to nature, like trying to turn the world into a giant zoo. In the 21st century, rather than fighting a losing battle to protect what we imagine to be pristine nature, we should be encouraging nature’s rebirth, often through the dynamism and invasive instincts of its alien species.

Nature is not there to do our bidding. While alien species may sometimes be a pain in the neck for human society, they are exactly the shot in the arm that real nature needs. Conservationists who want to cosset nature like a delicate flower, to protect it from the threat of alien species, are the ethnic cleansers of nature, neutralizing the forces of nature that they should be promoting. It is foolish to fear nature at its most dynamic – red in tooth and claw, rhizome and spore, root and branch. As true environmentalists, we should rejoice when species burst through the paving stones of our cities, or wash up on foreign shores. We should celebrate nature’s powers of recovery. We should let it run wild. How else are species to thrive and respond to the disruption of our activities, including climate change, if not by invading new territories, by becoming aliens? True nature-lovers should see that.

Harvard biologist Edward O. Wilson, the guru of biodiversity and rainforests, said the 21st century will be ‘the era of restoration in ecology’. I hope so. But we will not be going back to a supposedly pristine world. We cannot. We should be restoring nature’s wildness, and not trying to turn one moment in the past into an ossified museum relic. The new wild will be different, but no less dramatic and wonderful than the old wild. Alien species, and the novel ecosystems they inhabit, will be at the heart of it. We should bring them on.

*

This book begins with a look at the reality behind some of the invasions by alien species that have made headlines. Part One starts with islands, where some of the most dramatic stories have emerged. Those stories tell of places where species introduced by humans have created healthy ecosystems where none existed, as well as of places where introduced species have ransacked colonies of sea birds. Usually, however, the stories are more nuanced. In case after case, I found that the supposedly malign invaders were simply taking advantage of ecosystems that had already been wrecked by humans. They were opportunists, but also nature’s regenerators. They were often doing jobs that natives could not accomplish.

In Part Two, the story moves on to examine how our misplaced notions about aliens impact on the real world, and on how we do conservation. The results are often comical. Our efforts at ecological cleansing are rarely successful. They fail because conservationists have indulged ill-founded myths about aliens, pristine ecosystems and how nature works.

Having slain some myths, it is time to find some solutions. Part Three attempts to reboot our ideas about nature. Most of the world is now composed of novel mixtures of native and alien species, happily getting along together, enriching our lives, maintaining ecosystems and recharging nature’s batteries. This is the new wild. Nature is blossoming in the most unlikely places, such as logged-over forests and urban badlands. To make the most of that, we need to reboot conservation too. That means we need to lose our dread of the alien and the novel. It means conservationists must stop spending all their time backing loser species – the endangered and reclusive. They must start backing some winners. For winners are sorely needed if nature is to regroup and revive in the 21st century – if the new wild is to prosper.

PART ONE

ALIEN EMPIRES

All round the world, alien species are on the march, often with human help. But mostly they are moving into places we have messed up. They are often helping nature’s recovery.

1

On Green Mountain

Standing on the summit of an extinct volcano on Ascension Island in the tropical South Atlantic, I was at one of the most remote spots on the planet. I watched the British military plane that had delivered me there, midway between Brazil and Africa, take off and head on south to the Falkland Islands. I felt rather alone. Down below was a harsh, black and treeless moonscape of volcanic clinker, baking in the sun. Beyond was ocean for a thousand kilometres in every direction. But in the cool mountain air, I was surrounded by lush greenery. As noon approached, a lone cloud formed over the summit and then suddenly descended, shrouding me and the mountain in mist.

The Ascension locals – a mix of British contract workers, American service personnel, and families from St Helena, another remote South Atlantic island – call this oasis Green Mountain. The island’s British administrator has a bungalow up here, complete with a pair of old cannons pointing out across the ocean. But away from his lawns, where I later had afternoon tea, the mountain and its cloud forest felt primeval, a leftover perhaps from the days before sailors began visiting here five centuries ago.

My instincts couldn’t have been more wrong, however. The greenery was relatively new. When Charles Darwin visited Ascension Island in July 1836, homeward bound after his long journey aboard HMS Beagle, he had complained about its ‘naked hideousness’. The mountain where I now stood was ‘entirely destitute of trees’. Another visitor of the day, William Henry Webster, had called the island ‘an awful wilderness amid the solitude of the ocean’. Peering through the mist, my guide, the mountain’s genial warden Stedson Stroud, explained: ‘Nothing you see here is native. Except for a few ferns, everything has been introduced in the past 200 years.’ The cloud forest of Green Mountain is an entirely man-made ecosystem, a pot-pourri of foreign species shipped in by the British Navy during the early and mid-19th century at the whim of Victorian botanists. Every passing ship had delivered more trees for the local garrison to plant.

On our way up the mountain, Stroud and I had walked through stands of Bermuda cedar, South African yews, Persian lilacs, guava fruit trees from Brazil, thickets of Chinese ginger, New Zealand flax, taro from Madeira, European blackberries, Japanese cherry trees and screw pines that grow taller here than at home on the islands of the Pacific. The summit was improbably covered in a dense stand of Asian bamboo, and rattled like a huge wind chime in the brisk trade winds that suddenly blew the mist away.

I was on Ascension because the very existence of this forest is creating controversy. It is more than a patch of trees, more than a botanical garden. It is possibly the most cosmopolitan tropical forest in the world, and it is said to be the only one that is entirely man-made. Moreover, researchers who have visited herald it as a fully functioning ecosystem, created from scratch in little more than a century from fragments assembled at random from around the world. The vegetation, insects and other species interact in numerous ways, providing vital services for each other. Forest ecosystems are not supposed to happen like that. Conventional ecology says their complex interactions emerge only as a result of long-term evolution of species. As Stroud put it, in a paper with David Catling of the University of Washington, the species on Green Mountain ‘have bucked the standard theory that complexity emerges only through co-evolution’.1

Stroud had been tending the mountain for a decade, ever since he came here from St Helena to be the island’s conservation officer. He admitted that, as a conservationist, he should probably be rooting out all those foreign trees, in order to allow the natives to regain their terrain. But if he did, there would be almost nothing left. And in any case, he said, he was presiding over something profoundly interesting. This confected cloud forest was prime evidence in a growing movement among ecologists to reconsider many of their nostrums about how ecosystems function. It suggested that species with no previous contact can get along with each other much more intimately than assumed. It suggested that perhaps many more forests and other complex ecosystems around the world are the result of chance meetings rather than complex co-evolution. If that is true, it may hold vital clues for regenerating nature in the 21st century.

Ascension Island, which is almost twice the size of Manhattan, erupted from the Atlantic floor a million years ago. It was not barren for long. Remote as it was, some life soon arrived. Millions of seabirds occupied the lowlands, their spattered excretions turning the piles of black clinker white. Green turtles swam thousands of kilometres to nest on its sandy beaches. And the island’s mysterious land crabs arrived from who knows where – and who knows how – to make a life scuttling on the slopes of the volcano. But – apart from a few ferns and mosses on the mountain, and an endemic shrub called Ascension spurge along the shore – the black desert for a long time remained almost entirely devoid of vegetation.

The first known human visitors to Ascension Island were early Portuguese mariners who dropped anchor on Ascension Day 1503, on their way to the Indian Ocean. Hence the island’s name. But the first permanent occupation was by the British Royal Navy. It set up a garrison in 1815, to patrol the surrounding oceans and prevent the rescue of the most famous international prisoner of the day, the former French emperor Napoleon Bonaparte, whom the British had captured and incarcerated on St Helena, its equivalent of Guantánamo Bay, 1,300 kilometres to the south. After Napoleon’s death, the British used the island as a base for hunting down transatlantic slave ships, and to store fuel for warships heading to India, the ‘jewel’ in the British imperial crown.

Ascension Island has kept coming in handy. At the end of the 19th century, it became a hub for transatlantic telecommunications, with cables stretching to Europe, South Africa, Brazil and Argentina. These days, the island is peppered with aerials that track orbiting spacecraft, talk to nuclear submarines, and listen in secretly to cable and satellite-relayed communications. The electronic spies of Britain’s GCHQ are the biggest employers. The island’s band of temporary residents, who number about 800, say it has more antennae than people. It also has one of the longest airstrips in the world, built by the US Air Force during the Second World War to provide a secure stopping-off point for flights into Africa. When I arrived in early July 2013, I was amazed to see nine large US military aircraft sitting on the tarmac, all busy protecting President Obama during a visit to the continent.2

Inevitably, such human traffic has brought alien species, both accidental and deliberate. Recent arrivals on the lowlands include fast-spreading tobacco plants and Mexican thorn, or mesquite, which the BBC shipped here in the 1960s to brighten up gardens in a new settlement for operators of a transmission station serving Africa. Much was deliberately introduced. From the first, the naval garrison brought in species to make the remote outpost as self-sufficient as possible. Documents in Ascension’s archive, in the toy-town capital of Georgetown, show how it first established a farm on one of the few patches of natural soil on the mountain. The farm grew introduced fruit trees like guava from Brazil, Cape gooseberries from South Africa, bananas from the Far East and lychees from China. Then there were vegetables such as cabbages, spinach and potatoes, as well as some grains, herds of South African pigs, and cattle and sheep from England.

The farm operated until the 1990s and is now overgrown. But it is the trees that fascinate in the 21st century. Britain planted on this volcanic hulk specimens from across its global empire. In the early days, the sailors grew New Zealand flax to make rope for ships, and straight-trunked Norfolk pine for masts. British colonial botanist Sir Joseph Hooker – a friend of Darwin and future head of the famous botanical gardens at Kew in London – visited in 1843. He came up with the idea of growing trees to gird the mountain and green the arid island. The archive preserves a letter that Hooker wrote in 1847 with a long list of recommended introductions to ensure that ‘the fall of rain will be directly increased’. The new vegetation on the mountaintop would scavenge moisture from passing clouds, he promised. Further down the slopes, trees and bushes would encourage soil growth. Hooker’s ambition was nothing less than remaking the volcanic island – or ‘terra-forming’ it, as Stroud and Catling put it.

In 1845, a naval transport ship from Argentina delivered the first batch of seedlings. In 1858, more than 200 species of plants arrived from the Cape Botanic Gardens in South Africa. In 1874, Kew sent 700 packets of seeds, including those of two types of plants that especially liked the place: bamboo and prickly pear. The sailors got to work, planting several thousand trees a year. The bare mountain was soon verdant – and renamed Green Mountain. An Admiralty report in 1865 praised the new cloud forest. The island ‘now possessed thickets of upwards of 40 kinds of trees besides numerous shrubs’, it said. ‘Through the spreading of vegetation, the water supply is now excellent, and the garrison and ships visiting the island are supplied with an abundance of vegetables.’

Today, the island has around 300 introduced species of plants, says David Wilkinson, an eclectic botanist from Liverpool John Moores University who made a rare research visit to Green Mountain. Many are spreading. Above about 600 metres, Green Mountain is now completely vegetated. On my walk back down the mountain, Stroud pointed out coffee bushes, vines, monkey puzzle trees, jacaranda, juniper, bananas, buddleia, palm trees, clerodendrum, the pretty pink flowers of the Madagascan periwinkle and the bell-shaped blooms of the American yellow trumpetbush. He confirmed that the vegetation captures more cloud moisture on the mountain, just as Hooker had hoped. This even though there has been a decline in rainfall in the lowlands around.3

The Victorian terra-formers did not just bring plants. The island’s military inhabitants joined the 19th-century craze among expatriate Europeans to fill their new worlds with birds and animals from home. The regular ships to Ascension brought hedgehogs and rooks, ferrets and owls, bees to pollinate, and guinea fowl as quarry for hunting. Ascension never quite became the ‘Little England’ that they had hoped. Of the introduced birds, only the tropical canaries and mynas have stuck around. But the mammals did better. Rats and rabbits can still be found in numbers, along with feral sheep, cows and chickens let loose from the now-abandoned farm. And donkeys – descended from the beasts of burden that once carried water from mountain springs to the coastal garrison – still wander the landscape, eating mesquite fruit and getting hit by cars.

The introduced rats were trouble. They swiftly saw off a couple of local endemic birds, the Ascension crake and the Ascension rail, and possibly also a night heron.4 For a long time, there were also feral cats. Originally brought in to control the rats, they tyrannized the seabird colonies, forcing most to nest instead on a tiny offshore mound known as Boatswain Bird Island. Ornithologists began a cat-eradication programme, and the last cat was hunted down in remote Cricket Valley in 2006. Since then, boobies have begun returning to the main island. When I visited, the island conservationists were crossing their fingers for the survival of the first nest established by a returning pair of endemic Ascension frigatebirds.5 Meanwhile, 2013 saw a record nesting season for the green turtles – a great comeback after decades during which they were slaughtered for the pot. The last victim, they say, was fed to the Duke of Edinburgh when he visited back in 1957.6

The incomers have added hugely to the island’s biodiversity and now make up at least 90 per cent of its species. The local people like them. When, in the 1980s, the island authorities issued twelve postage stamps bearing pictures of local insects, all twelve were aliens. The national flower, dubbed the Ascension lily, actually comes from South America. Nevertheless, some would like to encourage the resurgence of native species by launching an eradication programme against foreign plants. They blame the environmental anarchy perpetrated by Hooker and his successors for the loss of three endemic ferns, and perhaps some insects that may once have depended on them – though the lost species may still be hiding here somewhere amid the steep valleys around the mountain. As we stood on one of the mountain paths, gazing south over an abandoned NASA tracking station, Stroud pointed out below us the cliff face where, in 2009, he rediscovered a single specimen of a fern species believed lost, Anogramma ascensionis, or Ascension Island parsley fern. It is now being propagated in the labs at Hooker’s old fiefdom in Kew, ready for reintroduction.

The British government’s environment policy for the island is to carry out the ‘control and eradication of invasive species’ in order to ‘ensure the protection and restoration of key habitats’. But this is dogma rather than considered policy based on research. A closer look would reveal that the ‘control and eradication’ of the aliens could now cause some natives, including endemic ferns, to go extinct. The ‘key habitats’ for some native species are provided by the alien trees on Green Mountain. Xiphopteris ascensionis, an indigenous fern that once clung to the bare mountainside, now lives only on the mossy branches of introduced plants. Bamboo is a favourite. ‘The ferns like the shade,’ says Stroud. ‘If it weren’t for the trees and other plants, I doubt if the ferns would be here any more.’

On our walk down the mountain, we saw native mosses clinging to an old stone wall, and alien insects and birds pollinating trees of a kind they had probably never encountered before arriving here. After the rains, we watched the distinctive yellow and pink land crabs – the island’s largest native land animals – rush out of their burrows to feast on the fruits of alien trees like the guava. The only researcher to have studied these endemic land crabs in recent times, Richard Hartnoll of the University of Liverpool, says that the foreign vegetation ‘increases the area of shade and shelter for crabs, and also provides a large resource of food’ – perhaps replacing their former scavenging on seabird colonies. Removing the aliens would likely have some nasty consequences for the natives.

You might think that this ecological snugness among species thrown here from across the world would be of some interest to conservationists. Yet, until now, they have shunned it, says Stroud. Most of the handful of researchers who have made the long journey to Ascension – the only practical way is aboard a British military flight – have concentrated on the island’s charismatic populations of seabirds and green turtles. A detailed study of the island’s flora conducted in the 1990s by the University of Edinburgh catalogued only the natives and characterized the rest – the great majority – as simply a continuing threat to them.7

As a result of this wilful blindness, simple but important ecological questions go unanswered. ‘As you walk through the forest, you see lots of leaves that have had chunks taken out of them by various insects’, Wilkinson says. ‘There are caterpillars and beetles around. But where did they come from? Are they endemic or alien? If alien, did they come with the plants on which they feed, or did they discover those plants on arrival?’

Wilkinson is among the scientists who propose that the complex ad hoc interactions between native species and aliens from many lands on Ascension are good evidence for an ecological theory that contradicts mainstream ideas about co-evolution. Ecological fitting, a term coined by US ecologist Daniel Janzen, holds that ecosystems are typically much more random. ‘The Green Mountain system is a spectacular example of ecological fitting’, Wilkinson says. ‘It is a man-made system that has produced a tropical forest without any co-evolution between its constituent species.’ Thomas Jones of the US Department of Agriculture in Logan, Utah, agrees. On Ascension, he says, plants gathered from across the world ‘self-organized by the mechanism of ecological fitting’.

This debate matters. It raises in practical form many of the questions I will explore in this book. What are ecosystems and how do they form and function? Are alien species ‘bad’ and natives ‘good’, or is this distinction false and scientifically unjustified? Could nature be far more resilient, and far less fragile, than we imagine? Have we messed with the environment so much now that places like Green Mountain, with their bizarre mixtures of natives and aliens, offer the best chance for nature’s survival in the 21st century and beyond? Is the success of aliens the most vivid expression of Darwin’s ‘survival of the fittest’? Should we – for the good of the natural world – learn to love the aliens?

*

Some regard such talk about alien species as nonsense. And it is true that not all alien species fit in like respectable ecological citizens. Some create bloody mayhem, especially within the simple ecosystems that occupy many remote islands. Gough Island is another volcanic hulk far out in the South Atlantic. Like Ascension almost 4,000 kilometres to the north, Gough Island was first discovered by Portuguese navigators but claimed only much later by the British. They raised the Union Jack there in 1938 and named it after Charles Gough, the first British sea captain to spot the island, 200 years before. Gough has no natural harbour. Climbing ashore is difficult. As a result, sailors have only ever set foot here about 250 times. That includes the seasonal change of its only current inhabitants, the South Africans who man the weather station. Yet 71 of the 99 species recorded here were introduced during those 250 visits. One of them is a big problem.

For as long as anyone knows, Gough Island has been dominated by millions of nesting sea birds. When Britain nominated the island as a World Heritage Site back in 1995, the Royal Society for the Protection of Birds (RSPB) called it probably the world’s most important seabird colony. Its 10 million avian inhabitants included 90 per cent of the endangered Tristan albatrosses (Diomedea dabbenena) and the entire world populations of both the ground-nesting Gough bunting and the flightless Gough moorhen. The island is now also the only known breeding ground for endangered Atlantic petrels (Pterodroma incerta). (The other colony, on Tristan da Cunha, got eaten out by invading rats.)

There are no trees on Gough Island, and vegetation is mostly lichens and ferns. So to escape from the wind and cold, the birds live in burrows. But this subterranean seabird megacity is under threat. For there are new masters on Gough Island – the descendants of English house mice (Mus musculus) that leapt ashore from Victorian whaling ships sometime in the 19th century. These are not normal mice, however. Not now. Over the decades of their windswept exile, they have doubled in size and turned carnivorous. These mutant mice now typically grow up to 25 centimetres long and eat up to a fifth of their body weight every day. With an estimated 2 million mice on just 6,500 hectares, that means they devour three tonnes of bird flesh every day from every hectare of the island.8

Cape Town ornithologists first detailed the carnage during a visit in 2001. They calculate that only a quarter of the 1.6 million petrel chicks that hatch each year on Gough make it to adulthood. Virtually all the rest are eaten by mice as they sit immobile in their underground nests. Even albatross chicks, which may be the size of geese, succumb to the night-time attacks by these marauding monsters, says an incredulous Ross Wanless, who has taken video of the gruesome scenes.9 ‘It’s like a tabby cat attacking a hippopotamus’, says Geoff Hilton of the RSPB, which wants to exterminate the mice.

How do you get rid of 2 million mice on a remote island? A feasibility study recommended hiring a helicopter to bomb the place with some 100 tonnes of brodifacoum, an anticoagulant poison widely used against rats, at a likely cost of £1.5 million. Even then, since many of the mice live in caves and volcanic lava tubes, complete eradication could not be guaranteed. And there was a risk the poison could instead end up killing off the Gough moorhen. Perhaps not surprisingly, the enterprise was on hold in early 2014.10 The supermice remained in charge, and may remain so until they run out of food.

Despite their atypical nature, simple island ecosystems such as Gough have become the test cases for what we think about aliens – perhaps because, surrounded by ocean, they provide understandable terrain for these battles to play out. The most discussed of all sites of invasions is Hawaii, where both those vehemently opposed to alien species and those who see their virtues are willing to make their cases. On one side is Daniel Simberloff of the University of Tennessee. A guru among invasion biologists, he is now in his 70s. He studied half a century ago under Harvard’s legendary forest ecologist and pioneer of island biogeography Edward O. Wilson. He says Hawaii is the site of an ‘invasional meltdown’.11 On the other side is Joseph Mascaro, a post-doc at Stanford University, 40 years younger than Simberloff, whose work in Hawaii was publicized in the groundbreaking book Rambunctious Garden by journalist Emma Marris. Mascaro says Hawaii is simply exhibiting some textbook examples of what he and other ecologists are now calling ‘novel ecosystems’.12

The Hawaiian Islands are the most northerly of the Polynesian islands in the central Pacific. They are an archipelago of volcanic islands. One volcano, Mauna Loa, still spews lava today. Others are long extinct and have been above the waves for 10 million years or more. Species reached the islands on the winds and waves, in the gullets of migrating birds and clinging to the trunks of floating trees. Coconuts came bobbing by. They all made themselves at home as best they could. Lichens turned the lava to soil; seeds took root; birds spread the seeds of plants. Evolution hit overdrive. Genetic mutations created new forms through the constant rolling of DNA dice; and the successful flourished. More than a hundred bird species evolved from maybe twenty arrivals. Finches, probably from Asia, evolved into 56 different species of endemic Hawaiian honeycreepers, almost half of which are still flying around, pollinating both native and alien vegetation.

Many other unexpected things happened. As environmentalist Louise Young noted in her book on islands: ‘Wingless and blind insects evolved … land snails became tree snails … unusual varieties of blooming trees [emerged] like lobelias, hibiscus and tree violets.’13 But this largely random collection of species also contained some big gaps. ‘Hawaii lacked reptiles, amphibians, flightless mammals and ants’, says Mascaro.14 Pollinating insects never got going there, leaving the role to the remarkable collection of birds.

Human interference on Hawaii probably began when Polynesian canoes rode ocean currents from the Society Islands onto the beaches of Hawaii some 1,500 years ago. The newcomers cut down lowland forests for farmland, while leaving intact the upland forests, which they regarded as sacred. They exterminated some meaty flightless birds. But they brought the first freshwater fish, as well as rats and pigs and the candlenut tree that they used to make canoes and provide nuts for lamps. The newcomer humans prospered, as did many of the species they had brought. When the English adventurer Captain James Cook first visited in 1778, there were several hundred thousand Polynesians there.15

Europeans brought many more alien species, like cats and mongooses to hunt down rats; pigs and giant African land snails for food; deer for hunting; guava and other useful trees. Out went a number of the islands’ unusually large range of bird species, including the Hawaiian rail, last seen in 1884. Nonetheless, each new invasion added biodiversity, since many more species arrived than were made extinct. Hawaii contains some 1,500 species of flowering plants found nowhere else, but also more than a thousand new plants have arrived. There are only 71 known extinctions. The estimated 2,500 introduced insect species have added 50 per cent to the native component. The avian tally is 66 bird species lost and 53 gained, though most of the losses were hunted to extinction by Polynesians before Europeans arrived. Some of the introductions were made to combat pests, like the worm-eating myna bird from Asia. Others, such as song birds and the American northern mockingbird, a notorious mimic, probably won passage for the sheer joy of their company.16

Whether adornments or not, most newcomers also provide ecological services. Alien birds such as the Japanese white-eye and the red-billed leiothrix, introduced from India a century ago, are today the mainstays for dispersing the seeds of native shrubs. ‘Introduced mangroves are straining sediment and building habitat that native fish utilize’, says Mascaro. Most ecologists do not spot these important services, he says, because they dismiss ecosystems containing alien species as damaged and degraded. Thus, they are beneath the attention of those who are searching for the truth about nature. This, he says, is a big mistake, because much of the truth about nature is bound up in these disrupted ecosystems.17 Getting rid of the alien birds would leave the understorey of many native Hawaiian rainforests bare, says Jeffrey Foster, now of the University of New Hampshire.18

Most controversial is the case of Morella faya (formerly Myrica faya), a myrtle tree sometimes called the ‘fire tree’. It was brought to Hawaii by Portuguese migrants a century ago from Atlantic islands like the Azores. It enjoys the sometimes harsh volcanic conditions and is the first plant to colonize newly created lava flows in the Hawaii Volcanoes National Park. It ‘fixes’ nitrogen from the air and uses it to turn the lava into soil, which no native plant can do. Many ecologists nonetheless think this skill is a bad thing. Princeton’s Andrew Dobson concluded in 1998 that by colonizing the lava flows, the myrtle ‘shuts out native species and leads to their subsequent extinction’.19 Ecologist Peter Vitousek of Stanford University took the same view, though he agreed that their nitrogen-fixing skills might eventually turn the lava into soils fit for native plants.20

I thought that, more than a decade on from these pronouncements, it would be interesting to know what happened. Did the fire tree pave the way for other species or crowd them out? But there is a dearth of published data. Nobody, it seems, has bothered to research the question. When I checked the International Union for Conservation of Nature’s Global Invasive Species database, it had no references to research into the impacts of Morella faya on Hawaii since 1991.21 Mascaro told me that from what he saw, the myrtle appeared to be receding from lava flows as native species colonize the soils it has created. He said the case was a perfect example of how conservationists can, through their love of native species and ecosystems, simply fail to recognize the services that aliens often provide to the wider environment. Novel ecosystems work.

*

Odd things happen on islands because their simple ecosystems have weak spots and tipping points beyond which dramatic changes can take place. Sometimes the arrival of outsiders triggers these tipping points. In the Indian Ocean, on Australia’s Christmas Island, the dynamic new ingredient was yellow crazy ants (Anoplolepis gracilipes) from West Africa. The ants have spread widely across the tropics, hitching lifts with passing trading ships, and are reckoned to have been on Christmas Island for the best part of a century. But they suddenly went on the rampage in the 1990s, creating ‘super-colonies’ of a kind never seen before. Nobody is sure why this happened, but they may have benefited from the spread of sap-sucking insects, since the ants eat the honeydew secreted by the insects. The ants and sap-suckers certainly seem to have formed a strong reinforcing relationship that ecologists call ‘mutualist’, even though one is alien and the other native.

The ant super-colonies extended for hundreds of hectares and contained billions of insects. As they grew, things got out of hand. The ants came into ever greater contact with the island’s previously dominant species, red land crabs (Gecarcoidea natalis), during their annual migration to the coast to breed. The ants adopted their normal defence mechanism, spraying formic acid around. The acid blinds and eventually kills the crabs. Since 1995, some 20 million crabs have been killed by the ants, equivalent to around a quarter of their total population. Though not much more than a tenth of the island has been invaded by ants, their impact has cascaded through the island’s ecosystems. Where the crabs have been eliminated, many more forest seedlings germinate, and parts of the forest have seen a massive increase in foliage in the understorey.22

Meanwhile, with fewer crabs to eat them, another longestablished invader, the rat-sized African land snail, is now also on the march across the island.23 And the ‘crazy’ ants – so-called because of their long-legged physique and frenetic behaviour – have won an instant place on the global list of the hundred most invasive species, drawn up by the IUCN.24 Actually, it is far from clear that they should be blamed. What caused the super-colonies to explode so suddenly after the ants had been on the island for so long? Nobody knows. But that may be the heart of it.

Ants can travel the world easily, and often thrive quite well on arrival – in part no doubt because they arrive in crowds. One recent study suggested that at least 600 different ant species may have made themselves at home in alien environments around the world. Notorious arrivals include South American raspberry crazy ants, now swarming inside electrical equipment in the US, and Argentine ants (Linepithema humile), which have been building super-colonies in Europe.25 But while invader ant populations sometimes boom, they also usually bust. The Argentine ant arrived in New Zealand in 1990 and marched across both the north and south islands in short order, killing chickens, invading orchards and pushing aside native ant species. ‘They can even squirm under the edge of screw top jars and follow the grooves until they reach the contents’, a government public warning advised. Officials set aside around $60 million a year to confront the ant army. Then in 2011, most of the known super-colonies collapsed. Why? Nobody is sure. But the panic is over, and native ants are recovering.26

*

Many remote islands have nurtured unique collections of species. The Seychelles in the Indian Ocean, for instance, have been isolated for more than 60 million years, gathering passing wildlife and turning the itinerant species into their very own. Aldabra, one of the Seychelles’ outer islands, is home to flightless birds like the white-throated rail, and some 100,000 giant tortoises, two-thirds of the world’s total. Aldabra remains remarkably unaltered, but the native species on many such islands have suffered. They have nowhere else to go, and the simple island ecosystems are wide open to outsiders with skills unknown to the naive locals. More than 90 per cent of the hundred-plus birds known to have become extinct over the past 400 years were endemic to islands, according to the World Conservation Monitoring Centre in Cambridge. Though many were hunted to extinction by humans, introduced predators have certainly taken their fill. Notoriously, ground-nesting birds with no experience of mammalian predators are suddenly confronted with mega-mice, cats or, most frequently, rats.

The black rat (Rattus rattus) has been causing trouble ever since it left India for Europe some 5,000 years ago. If nothing else, it brought Europe the fleas that carried the Black Death. The Polynesian rat (Rattus exulans) has been similarly troublesome across the Pacific. It is now being blamed for the mysterious crash of the once grand civilization on Easter Island in the remote south-east Pacific, whose collection of giant stone statues of humans has long mystified explorers. The theory used to be that the Polynesian Rapa Nui people who made the statues deforested their island to death. With the trees gone, the island ecosystem collapsed, and the islanders could no longer make the boats they needed to go fishing. The once-proud island people were reduced to a small emaciated rabble. It was ecocide, a warning to the world about the folly of mankind’s environmental sins. Jared Diamond asked in his book Collapse: ‘Are we about to follow their lead?’27

But now it seems that when the Rapa Nui arrived on the island a thousand years ago, they also brought seed-eating Polynesian rats. Rather than humans destroying the forests with axes and fire, it was the rats that delivered the coup de grâce, says Terry Hunt, an anthropologist at the University of Oregon. The rats ate the seeds of the island’s palm trees, so the trees did not reproduce. Virtually every palm seed shell dug up on the island has been gnawed by a rat, Hunt says. ‘It was rats, more than humans, that led to deforestation.’28

Henderson Island is a British-run World Heritage Site in the Pacific that has been uninhabited since the Polynesians left in the 1600s. Unfortunately, they left behind Polynesian rats, which have overrun the place and are currently eating their way annually through some 25,000 seabird chicks, including endemic petrels. A million-pound effort by ornithologists to poison the island’s rat population in 2011 failed. Zoological explorer Mike Fay, whose exploits in Africa we will hear more about in Chapter 8, spotted one while tramping across the island the following year.29 A reconnaissance group sent out by the RSPB in 2013 found that a small population was still there, probably happily breeding. RSPB’s Jonathan Hall told me there would be ‘a further eradication attempt’.

More rarely, snakes turn small islands into horror movies. Until 1950, the only snake on Guam in the Western Pacific was the Brahminy blind snake, a small slow-moving worm-like reptile that could not see where it was going and mostly lived in termite mounds. Then the American military showed up. Somewhere aboard the ships and planes moving equipment from wartime bases on the Admiralty Islands of Papua New Guinea to the new US Pacific headquarters on Guam, came a contingent of brown tree snakes (Boiga irregularis).30

On their home islands, brown tree snakes were just one element of a diverse reptilian menagerie. But on Guam they had an electrifying effect from the moment they slithered off into the bushes. They proliferated fast, colonizing half the island by the mid-1960s and most of the rest by a decade later. In places, there were soon 100 snakes per hectare. Fanged and venomous, with large head and bulging eyes, they were very different from the blind and harmless native. They travelled everywhere, climbing trees and invading buildings during their nocturnal hunting expeditions. They ate almost anything, from dog food to lizards and birds to animal carcases. Ten of the island’s native forest bird species, along with several species of native bats and lizards, went locally extinct after the arrival of the brown tree snake. Brought in to work out why, avian pathologist Julie Savidge concluded that the snakes were to blame. Gordon Rodda, who works on invasive snakes for the US Geological Survey, says there could at one time have been as many as four snakes for every bird. 31

The snakes’ notoriety grew. They got a reputation for entering houses and taking a nip at babies in their cots. There were more than a hundred hospitalized cases.32 The invaders climbed wooden poles carrying power lines, presumably mistaking them for trees, and slithered along the wires looking for snoozing birds. Growing up to three metres long, they were heavy enough to drag down the lines, causing hundreds of power cuts.

There are many theories as to why this previously little-noticed snake caused such a stir on Guam. It certainly stumbled on a place where snakes were a novelty. Local victims had no idea how to defend against the newcomers. But equally, it may have found an island ecosystem in crisis and wide open to takeover. Guam had only fragments of its old forests. Most had long-since been cleared for coconut plantations. Much of the island had been bombed by the US and Japanese as they fought over it during the Second World War. It had then been washed with DDT to rid it of malaria. By the time the carpetbagging snake showed up, the remains of the native forests were rapidly being cleared for the runways, houses, golf courses and other infrastructure needed to satisfy tens of thousands of US troops on an island less than a sixth the size of Long Island.

Such changes – by disrupting existing ecosystems, removing other species and creating numerous ways for the incomers to prosper – must surely have contributed to both the wildlife decline and the conditions that allowed the remarkable spread of this hungry and crafty snake. The snake cannot be blamed for the loss of several species of birds that had all but gone before it showed up. The nearby US-run island of Rota, which was at the time free of snakes, has shown a similar decline in native forest birds, which ornithologists attributed to habitat loss.33 Without the snake, there would undoubtedly be many more birds on Guam today; but without the massive disruption caused by the arrival of the US military in particular, the snake is unlikely to have prospered so well.

The heyday of the brown tree snake on Guam may be past, however. Its numbers have fallen to roughly half the 4 million estimated during its marauding 1980s peak. Perhaps it has simply been too successful in eating the available food. But the US military is taking no chances. In spring 2013, it dropped thousands of dead mice into the forests of Guam. Each mouse carcase was stuffed with tablets containing paracetamol and kitted out with a tiny parachute made of green tissue paper. The mice floated into the branches, where the plan was for them to be gobbled up by the snakes, for whom the painkiller is lethal.34 Will the programme succeed in wiping out the snake? We shall see.