Biodiversity is the diversity of life at various levels of organisation, ranging from genes, species, ecosystems, biomes and landscapes. As far as we can tell, the Earth just before the appearance of modern humans was the most biodiverse it has ever been during the three and a half billion years of life’s tenure on this planet, and before we began to upset things hosted a total of somewhere between 10 to 100 million species (Wilson 1992).  The fossil record shows us that there have been five mass extinctions in the last 500 million years or so, all due to natural causes such as meteorite impacts, flood basalt events, or possibly because of drastic internal reorganizations within biotic communities, but the most recent mass extinction is happening now and is entirely due to the economic activities of modern industrial societies. We are hemorrhaging species at a rate up to 10,000 times the natural rate of extinction (Wilson 2002), or, more prosaically, every day we are losing about 74 species (Wilson 1992), mostly in the great tropical forests because of our endless desires for timber, soya, palm oil and beef.  Coral reefs and the marine realm in general are not exempt from our destructive attentions either.  The list of atrocities which our culture has perpetrated on the living world makes for chilling reading. Hundreds of thousands of species wiil be driven to extinction in the next 50 years or so (Primak 2006).  According to the IUCN’s Red List, of Threatened Species, by the year 2000, about 11% of all bird species, 18% of mammals, 7% of fish and 8% of all the world’s plants were threatened with extinction. According to the Living Planet Index, in the period from 1970 – 2000, populations of forest species declined by 15%, those of freshwater species by a staggering 54%, and those of marine species by 35%.

Does the current mass extinction really matter? What does biodiversity do for Gaia, and for us?  To anyone who is deeply in touch with nature it is absurd to ask these questions – clearly the current mass extinction is a crime of vast proportions. Our intuitions and deep experiences of  belonging to the more than human world tell us that biodiversity gives us three key benefits: integrity, stability and beauty.  But what does science have to say about the importance of biodiversity?  To explore this question we need a systems diagram showing how biodiversity contributes to the well being of Gaia (figure 1)

Figure 1. The importance of biodiversity for the health of Gaia.

Firstly, human influences act directly on biodiversity, or indirectly by changing Gaian processes such as climate, biogeochemical cycles and other global processes.  Human induced changes to biodiversity could then affect aspects of ecosystem health, such as how well an ecosystem resists and recovers from disturbances, how well it recycles its nutrients and how reliably and how much biomass it produces over a given period of time.  These various aspects of ecosystem health could feed back to influence biodiversity, as changes in nutrient cycling or productivity impact on the species in the ecosystem.  Ecosystem health could also have big impacts on Gaian processes, such as the abundance of greenhouse gasses in the atmosphere and the overall albedo of the planet, both of which influence climate.  Every species has a preferred climate in which it feels most comfortable, so Gaian processes feed back to influence biodiversity.  Lastly, altering biodiversity could expose human activities to feedback from two directions: directly from changes to biodiversity, and indirectly if ecosystem health and Gaian processes have been affected.  Let’s look at each of these relationships.  Firstly, how are human activities influencing biodiversity?  The answer has been summarised in the famous acronym, ‘HIPPO’, which tells us that our lethal impacts on biodiversity are, in order of importance: Habitat destruction and fragmentation, Invasive species, Pollution, Population and Over harvesting.

Habitat Destruction : Before the beginning of widespread destructive human impact during the 19th century, Gaia was clothed with a continuous cover of wild habitats that melded gently into each other according to how climates varied over her surface.  If we had been standing in Britain after the last ice age was well and truly over some 10,000 years ago we could have walked all the way from the south coast of England to the north of Scotland without ever leaving the great mosaic of wild forest and natural meadows that covered most of the country.  We would have experienced the same continuum on each and every continent. Crossing the channel to France, we could have walked all the way across Eurasia to the great rainforests of Burma, Thailand and Vietnam without ever encountering a major disturbance to nature’s vast wild domain.  The abundance of flying, leaping, swimming beings in this pristine state astonished the first European settlers all over the world, who quickly set about logging, hunting, fishing and clearing for agriculture with a demonic destructiveness that beggars the imagination. (Pontin 2007)

Today, there is no habitat on Earth that has not been seriously degraded by humans. All the great biomes face increasing threats, including the mangrove swamps, the wetlands, the tropical dry forests, the tundra and the boreal forests – the future for all of them looks bleak.  When humans attack the great wild, they generally leave a few fragments of the original habitat here and there, perhaps out of laziness, or a because of a pang of conscience, or, most likely, because no money could be made out of them.  To begin with, these fragments are the last refuges for the great wild beings that once roamed freely over the untamed Earth, but they soon turn into death camps as the effects of fragmentation begin to bite.  Each fragment is an island, often surrounded by inhospitable habitats such as agricultural land, buildings and roads that for many creatures create insurmountable barriers to foraging, dispersal and colonisation – even a small road in a nature reserve can be a daunting obstacle to tiny insects. The refugees may not be able to find the food they need in their fragments, or a good mate, or even a good place to sleep.  Edge effects creep into the fragments, particularly the smaller ones, making things too dry or too hot or too cold. Pests and diseases can strike down the refugees more easily in the fragments, and even if there are enough breeding individuals to keep a population going, eventually lack of colonisation from outside can lead to seriously damaging inbreeding depression.

You never know who the big players are in the wild world – seemingly insignificant, the dung beetles of the Amazon are critically important for the health of the whole forest (Klein 1989).  Near Manaus, in the Amazon region of Brazil, a small dung beetle searches for food on the dry leafy floor of a small forest fragment left behind when the surrounding forest was cleared for pasture in 1982.  In the old days, when the forest was entire, a whole host of dung beetle species, large and small, killed off parasites, buried seeds and ensured that precious nutrients were quickly recycled as they fed their underground larvae on buried dung. But in the forest fragment there is little dung around, for most of the monkeys and birds that provided it in abundance before the forest was fragmented died or left a long time ago. Now there are fewer kinds of dung beetle, and those that remain are smaller and not very numerous. The dung beetle extinctions happened in many ways. Hot, dry winds searing in from the pasture outside the fragment wiped out several species by killing off their larvae.  For many species there just weren’t enough good quality mates to go around and the inhospitable pasture prevented beetles from colonising the fragment to boost numbers and bring in new blood.  The consequences for the fragment’s remaining denizens have not been good. There are more diseases amongst the few birds and mammals that remain, nutrients are washed away by heavy rains before roots can capture them and the seeds of many plants have not been able to germinate.  Seemingly insignificant, the dung beetles of the Amazon are major players in their ecological community – they are one of the keystone species of the forest.

Introduced species : These can cause extinctions even in areas where there has been very little habitat fragmentation and wipe out more species than pollution, population pressures and over harvesting put together.  They come from all over the world, the goats, pigs, cats, rabbits, and many others, brought to places they could never have reached without the help of humans. According to the USDA Forest Service, About 4,000 exotic plant species and 2,300 exotic animal species have been brought to the United States alone, threatening 42% of species on the endangered species list and causing about $138 billion of damage every year in sectors such as forestry, agriculture and fisheries.  Introduced species often do well in their new locales in the absence of their natural predators and diseases. Most don’t do much damage, but a small minority take hold and do massive harm.  Some are predators that exploit defenseless native prey species.  A famous example is the brown tree snake, Boiga irregularis, a native of the Solomon Islands, New Guinea, northern and eastern Australia and eastern Indonesia (Wilson 2002). Introduced to some of the Pacific islands, it has virtually wiped out many endemic bird species.  On Guam alone it is responsible for driving twelve to fourteen endemic bird species beyond the point of no return. Other introduced species are powerful competitors like the American grey squirrel, Sciurus carolinensis, that has pushed out the native red squirrel, Sciurus vulgaris,  in most parts of Britain (Reynolds 1985).

Pollution: Rachel Carson’s seminal book, Silent Spring, was instrumental in starting the green movement by bringing the dangers of pesticides to our attention in 1962.  Since then pollution of many kinds have become alarmingly widespread.  We are only too aware of gender bending chemicals in water and are well informed about atmospheric pollution such as acid rain from power stations and cancer causing soot particles. One of the most insidious pollutants today is carbon dioxide, which, strangely enough, is an essential nutrient for plants that they harvest from the atmosphere.  But it is also greenhouse gas, and too much of it causes the climatic mayhem that leads to extinctions (Lovelock 2006).

Population : This refers to the explosive growth in the human numbers, especially since the industrial revolution.  The current world population stands at 6.4 billion, and is projected to level off at around 10 billion by 2150 (Wilson 2002).  People need land, water food and shelter, and have to satisfy these needs by destroying wild nature.  But it is not just a question of sheer numbers, for the amount of resources consumed by each person is what really makes a difference to our impact on the planet.  Paul Erlich devised his famous I=PAT equation (pronounced IPAT) to make this point (O’Neill  ‘I’ stands for impact; ‘P’ stands for population, ‘A’ stands for affluence and ‘T’ stands for technology.  Human impact is a product of the last three terms, so that it is possible to have a high population so long as people don’t have much money to spend on industrial products.  In the current economic climate all the terms on the right hand side of the equation are increasing alarmingly.  Today, the world’s middle class number about 20% of the population, but they consume about 80% of the available resources.  An oft-quoted fact uncovered by the New Economics Foundation in the UK : if everyone in the world were to consume as much as the average American, three to four extra planets would be required to provide the raw materials.  The huge pressures of the human population drive all the other causes of extinction, including the last of them all, over harvesting.

Over Harvesting: About one third of endangered vertebrates are threatened in this way.  Often the over harvesting is carried out by poor rural people left with no other means of surviving after they have been forced off their lands by global economic forces.  The rich countries of the North are also responsible for over harvesting and are especially responsible for driving several key fisheries to the point of extinction  – the Grand Banks and the North Sea cod fisheries are sad examples.  Many of the world’s great whales, the right, the bowhead and the blue had been pushed to the edge extinction by the early 20th century.  Detailed mathematical models designed to calculate ‘maximum sustainable yield’ for some of these species were spectacular failures that led to catastrophic declines (Gulland 1971).  Illegal whaling has been blamed for this, but the difficulties of observing and quantifying whale behaviour in the wild were also responsible.  Many whale species have been protected to some extent since 1946, and a few, like the Minke whale, are recovering, but many smaller cetaceans such as dolphins are killed every year when they become entangled in the nets of the fleets that are decimating the world’s fisheries.

Is it conceivable that the huge losses in biodiversity could feed back to influence the human enterprise in particular localities? To answer this question, we need to explore two questions.  Do organisms living in a specific place link up into an ecological ‘superorganism’ with valuable emergent properties such as climate regulation, better water retention, nutrient cycling and resistance to diseases, or are they are no more than collections of individually selfish organisms, each out to exploit as many of the available resources as possible, even to the detriment of the ecological community that enfolds them?  If the latter is true, then we will need to protect entire ecological communities in order to preserve the ecosystem services they provide. If the former is the case, then we need only bother to look after the key players, or to introduce those of our own choosing.

These questions occupied the minds of the founding fathers of ecology in the first half of the 20th century.  The American ecologist Frederick Clements, one the most influential ecologists of his day, studied how plants colonise bare ground.  He noticed that there was a series of stages beginning with an inherently unstable plant community and ending up in a stable climax community in balance with its environment.  In Devon, from where I write, bare ground is first colonised by annual herbaceous plants, then by brambles and shrubs and eventually by oak forest, which grows here because the mix of soil, temperature, rainfall and wind are just right.  For Clements, the development of vegetation resembled the growth process of an individual living being, and each plant was like an individual cell in our own bodies. He thought of the climax community as a complex organism in which the member species work together to create an emergent self-regulating network in which the whole is greater than the sum of the parts (Worster 1994).

Within the scientific community, a struggle ensued between the organismic views of Clements, and the objectivist approach of the Oxford botanist Sir Arthur Tansley and the American ecologist Henry Gleason.  Tansley declared that plant communities couldn’t be superorganisms because they are nothing more than random assemblages of species with no emergent properties.  Tansley found Clement’s views difficult to accept because they challenged our legitimacy as humans to remake nature as we liked. Tansley wanted to remove the word ‘community’ from the ecologist’s vocabulary because he believed, in the words of Donald Worster that “there can be no psychic bond between animals and plants in a locality.  They can have no true social order” (Worster 1994).

Tansley represented a breed of ecologists who wanted to develop a completely mechanistic understanding of nature, in which, according to Worster, nature is seen as “a well-regulated assembly line, as nothing more than a reflection of the modern corporate state”.  For Tansley, agricultural fields were no better or worse than wild plant communities. To paraphrase Worster (1994), the reduction of nature to easily quantified components removed any emotional impediments to its unrestrained exploitation.  Ecology, he says, took on the economic language of cost-benefit analysis, but economic learnt nothing from ecology.

Which approach best describes biotic communities – organism or mechanism? Out in the flatlands of Minnesota, at a place called Cedar Creek, a long-term experiment is in progress that could have a bearing on these questions.  A strange chequerboard of meter square plots filled with prairie plants dots the landscape, tended by David Tilman, one of the world’s leading ecologists who has spent years investigating the relationship between biodiversity in his plots and the ability of the small ecological communities they contain to produce more biomass by capturing sunlight and to survive stress.  Tilman and his numerous assistants have set up hundreds of plots, each with a different number of species chosen from the native flora of the immediate locality.  Half way through one of these experiments, Minnesota experienced a severe drought, and to Tilman’s amazement the plots that survived best were those with the highest biodiversity (Tilman and Downing 1994).  This was evidence in favour of Clements and the organismic view, for the most diverse plots seemed to have developed a powerful emergent protective network as their various members melded their individual survival skills into a greater whole linked by tight bonds of the plant kind. But there were critics.  They pointed out that because Tilman had fertilised his plots with different amounts of nitrogen, the differences in drought resistance were due to this and not to the effects of species diversity (Huston 1997).

To eliminate this possibility Tilman established a more extensive experiment  using 489 plots of two sizes with different amounts of plant biodiversity seeded in identical soil and chosen from a maximum of four ‘functional groups’ : broad-leaved perennial herbs, nitrogen fixing legumes, warm season grasses and cool season grasses (Tilman et. al 1997).  This time, the more diverse plots produced more biomass, fixed more nitrogen, were better at resisting weed invasions and were less prone to fungal infections. The best plots were those that hosted a variety of species from each of the four functional groups.  Once again, here is evidence that diverse biotic communities resemble organisms with powerful emergent properties.  But the news was not all good, because Tilman found that the benefits of having extra species in the community peaked at around five to ten species.  Beyond that, extra species didn’t seem to improve ecological performance – what mattered most was having at least one member of each functional group. Some ecologists say that these results show that most species in wild ecosystems are dispensable, and that the extinction crisis gives us nothing to worry about.  But how are we to know which species are expendable and which aren’t?  Since we can’t tell which are the keystone species, it makes more sense to protect as many species as we can.  Furthermore, there is almost certainly an ‘insurance effect’ at work, in that more biodiverse communities are more likely to contain species that can take over the jobs left vacant by any keystone species that have disappeared, but which these are is difficult to predict.

Tilman’s approach was extended by the BIODEPTH project, in which plots with different amounts of native grassland biodiversity were set up in eight European countries, from the cold north to the warm south (Hector et. al, 1999).  Despite the wide range of climatic conditions, high biodiversity in each country was strongly correlated with improvements in many key ecological functions such as nutrient cycling, resistance to predators and biomass production – once again good evidence in favour of the organismic view (figure 2).  Up till now, the analysis of the BIODEPTH data has focused on the impact of biodiversity on each ecosystem function in isolation from the rest, but a new analysis by Hector and Bagchi (2007) has shown that in fact each species contributes to a wide variety of ecosystem functions simultaneously, so that focusing on isolated ecosystem functions seriously underestimates the level of biodiversity needed to maintain the health of ecosystems.

Figure 2. A key result from the BIODEPTH experiment.

Laboratory experiments also tend to support the idea that biodiversity improves the health of ecosystems.  Scientists at Imperial College, London, have developed the ‘Ecotron’, a series of chambers with controlled light, temperature and humidity levels which house artificially assembled ecological communities, each with differing amounts of biodiversity. The main result of this research is that more diverse communities fixed more carbon dioxide from the air (Naeem et. al. 1994). This may seem to be a fairly mundane finding, but it caused a stir in scientific circles by showing that biodiversity could have a key role to play in absorbing some of the vast amounts of the Earth-warming carbon dioxide gas that our economy is emitting into the atmosphere. In other words, terrestrial biodiversity may be of major use to us in helping to combat global warming, at least in the short term.  New work in the Ecotron mimicked the elevated carbon dioxide and temperature that are expected with climate change.  The surprising result was that climate change had little impact on the fauna and flora living above ground, but that the community of soil organisms was greatly altered.  More carbon dioxide in the atmosphere stimulated photosynthesis amongst the plants, which then transported some of this carbon to their roots as sugars.  The extra soil carbon changed the community of soil fungi, which in turn changed the community of fungus-eating spring tails (Jones et. al. 1998) .  These changes in below ground ecology could, if writ large, have a massive impact on nutrient feedbacks and carbon storage in soils, but as yet no one knows whether this means that soils will be able to hold more or less carbon.  The fact that there was a change is worrying and could have an effect on future strategies for dealing with climate change.

In another series of experiments, scientists created artificial ecological communities by seeding glass bottles containing water and nutrients with differing diverse communities of bacteria and their larger protozoan predators. In these experiments greater diversity led to less variability in the flow of carbon dioxide in and out of the community. (McGrady-Steed et al. 1997) The message here is that more diverse real-world communities could provide more predictable and dependable emergent ecological functions such as carbon capture and storage.

Mathematical modeling has also contributed to the new understanding of the relationship between biodiversity and ecological health. We now know from detailed fieldwork that ecological communities are replete with weak interactions, with many predators focusing on eating a few individuals from a fairly wide range of species. Models that take account of these insights show that virtual communities with realistic feeding relationships and abundant weak interactions are more stable than previously thought possible (McCann et. al. 1998).  Another group of mathematical models known as community assembly models work by creating a pool of virtual plants, herbivores and carnivores, each with its own body size and preferences for food and space.   One species at time is placed in an ‘arena’ where it interacts with other species that are already present.  After a while, an astonishing thing happens – persistent communities self-assemble with a final membership of about 15 species. As the number of species builds up, it becomes harder and harder for an invader to find a toehold in the nexus of interacting species. Communities that have existed for longer are harder to invade than newly established ones, strongly suggesting that communities develop an emergent protective network that becomes more effective as the community matures. Amazingly, the challenge for an invader lies with the community as whole. An inferior competitor in a mature, well-connected community has a better chance of surviving an invasion from a superior competitor than it does as a member of a less well connected more recently established community (Drake 1990).

All the research we’ve looked at so far, from field, lab and computer modeling tends to support Clements’ idea that ecological communities can indeed be thought of a superorganisms which function more smoothly and predictably as their biodiversity increases.  But perhaps Clements and Tansley were both right after all, perhaps each had seen different sides of the same coin.  If so, there is nothing inevitable about which species will colonise a bare patch of land, or indeed nothing inevitable about how a particular succession will progress (Tansley), but as soon as the species in a given place begin to web themselves together the whole community becomes a superorganism with powerful emergent properties (Clements).

So far we’ve looked at the effects of biodiversity on ecological health at the local level, but could there be a relationship between biodiversity and the health of the planet as a whole? This question, considered absurd by the scientific community as recently as ten years ago, is now beginning to loom large in the minds of scientists trying to understand how humans are changing the Earth, which they now recognise is a fully integrated system with life as a key player.

It is now generally agreed that life affects climate in at least two major ways: by altering the composition of the atmosphere and by changing how solar energy heats up the Earth’s surface and how this heat is distributed around the planet. But how could biodiversity be involved in making these globally important processes work more effectively? The Ecotron and BIODEPTH experiments have taught us that diverse ecological communities on the land can change the composition of our atmosphere by increasing the absorption of carbon dioxide. It is almost certain that biodiversity in the oceans also enhances this effect. Marine phytoplankton use carbon dioxide for photosynthesis much as land plants do, drawing it out of the air and into their tiny bodies. Dead phytoplankton sink, taking carbon that was once in the atmosphere with them to a muddy grave in the sediments below. This ‘biological pump’could also be more effective at removing carbon dioxide from the atmosphere if it is the case that larger phytoplankton are more often found in diverse communities, since it is known that these larger organisms increase the slow drift of carbon to the ocean depths (Fasham 2003).

Biodiversity may also improve the absorption and distribution of energy from the sun. It could be that more diverse communities on land and in the ocean are better at seeding clouds, possibly via the emission of more diverse cloud seeding chemicals, but this remains to be established. What is more certain is that a greater diversity of land plants could enhance cloud-making and energy distribution in two other important ways – by transpiring more water from the soil through roots and out into the air from pores on the undersides of leaves, and by providing more leaf surfaces from which rainwater can evaporate directly.

A big rain storm has just finished watering several hundred square kilometers of Amazon forest. The leaves are all wet, and those at the top of the canopy glisten in the early afternoon sun.  Some of the energy in the sunlight passes deep into the leaf where it fuels photosynthesis, but a fairly large portion is absorbed directly by the recently arrived film of water on the leaf surfaces.  As the water molecules receive their gift of solar energy they begin to gyrate like inspired dancers, and when sufficiently energised they dance their way into the air as water vapour.  This is evaporation. In the case of a leaf drying in the sun, solar energy which might have heated the leaf is transferred to water vapour, and as this is swept away by the wind, the leaf is kept cool, just as we are when we sweat.

The energy held in water vapour can be released as heat whenever condensation converts it back into liquid water. This energy is called ‘latent heat’ because it remains ‘invisible’ until condensation happens.  On the other hand, any solar energy absorbed by the surface of the leaf causes the molecules there to vibrate and to immediately re-emit the energy as sensible heat, which you can detect directly with your skin or indirectly if you have an infrared sensor.

But it is not just rain water that evaporates from the surface of a leaf, so does water that has travelled from the soil into the plant through tubes leading all the way from the roots to the thousands of microscopic pores beneath a leaf’s surface. This water, carrying with it life-giving nutrients from the soil, eventually passes through the leaf pores into the air, a process known as transpiration.  Amazingly, plants keep the flow of water going without the kind of muscular contraction seen in animal circulatory systems. They do this by continually and deliberately leaking water through the pores, thereby creating a mysterious kind of ‘suction’ that draws in new water all the way down at the roots.  On warm days water entering a leaf from the soil is heated up by the sun’s rays, and passes out of the leaf pores as water vapour.  The summed effect of evaporation of water from leaf surfaces and transpiration of water from within the plant is considered to be a single process known as evapotranspiration, which is vitally important for Gaia’s climate. Because of it, a huge amount of solar energy is stored as latent heat in water vapour that can travel long distances before condensing to release its energy as heat, sometimes thousands of kilometres away.  But evapotranspiration also has local effects.  In the southern boreal forests of western Canada, where the deciduos trembling aspen (Populus tremuloides)  is abundant, temperature rises steeply in the early spring when, unimpeded by aspen leaves the sun’s rays warm the ground. But as the aspen leaves unfurl and swell out to their full size the rate of temperature increase drops dramatically because evapotranspiration cools and moistens the air (Hogg et. al. 2000)..

Foliage is thus very important in regulating the surface climate. In general, the more leafy a forest, the more evapotranspiration and so the more cloud production, local rainfall, local cooling and plant matter production by photosynthesis (Bonan 2002). A more diverse flora could well improve transpiration by providing a bigger and more varied mat of below-ground root structures with better water trapping abilities, and it could also enhance evaporation by providing a larger and more complex total leaf surface area from which rainwater can evaporate. Both of these effects would send more water vapour into the air for cloud-making.  Some plants evapotranspire more than others. Because they have far fewer leaf pores, needle leaf trees pass less water into the air than their broadleaved cousins, thereby keeping themselves warmer – an advantage in the high latitudes (Bonan 2002).

Another climatically important characteristic of vegetation is its roughness, a measure of how much resistance plants give to the wind (Bonan 2002).  When wind blowing over the land surface encounters plants such as trees, grasses and shrubs it transfers some of its energy to the leaves, making them dance about. This sometimes frenzied leafy dance mixes the air, making both evapotranspiration and the transfer of sensible heat from leaf to air much more effective than on a perfectly still day. The higher up the canopy you go, the more efficient are these transfers of energy from wind and sun to leaf.  A dense rainforest canopy, with its high roughness, transfers much more energy to the air than the far less leafy, low roughness grasses in a savannah. The intricate leaf surfaces of a more diverse flora could create a rougher land surface that increases air turbulence, and this might well increase the transfers of heat and moisture to the air, influencing weather patterns on both local and global scales.

These impacts of biodiversity on local and global climates in turn feed back to influence biodiversity itself. Clouds seeded by chemicals emitted by the Amazonian vegetation keep the forest cool and recycle its water, thereby allowing the forest to persist and preventing the encroachment of the nearby drought-tolerant savannah (Artaxo et. al. 2001). The heat released when the clouds condense helps to configure the Earth’s climate system as a whole into a state that favours forest growth in the Amazon region.  Herein lies a great lesson for living in peace with Gaia, namely that the very structure of an ecosystem, namely which species are present, the depths of its roots, the extent of its leafiness, its albedo and its release of cloud seeding chemicals to the air all have massive effects not only on climate both locally and globally, but also on the great cycling of chemical beings around the planet.

We have seen how biodiversity is a key player in creating habitable conditions on the Earth, including a climate that favours our own existence. Biodiversity also provides us with a host of other benefits such the stabilisation of soil, recycling of nutrients, water purification and pollination. These benefits have been called ‘ecosystem services’ by a new breed of economists who are attempting to calculate how much these services are worth in financial terms. The results are staggering – in 1997 global ecosystem services were worth from one to two  times the global GDP (Costanza et. al. 1997).  Recently, the results of the most comprehensive survey of the state of the world’s ecosystem services were made public. The Millennium Ecosystem Assessment (2005), compiled by 1360 scientists from 95 countries, deliberately took the approach of looking for the interconnections between human well being and ecosystem health.  The results make for sobering reading – in all, 60% of the ecosystem services investigated have been degraded. Human activity has changed ecosystems more rapidly in the past 50 years than at any other time in human history.  About 24% of the planet’s land surface is now under cultivation; a quarter of all fish stocks are over harvested; 35% of the world’s mangroves and 20% of its coral reefs have been destroyed since 1980; 40%-60% of all available freshwater is now being diverted for human use; forest has been completely cleared from 25 countries and forest cover has been reduced by 90% in another 29 countries; more wild land has been ploughed up since 1945 than during the 18th and 19th centuries put together; demands on fisheries and freshwater already outstrip demand; and fertilizer runoff is disturbing aquatic ecosystem services. The report makes it abundantly clear that the UN’s Millenium Development Goals of halving poverty, hunger and child mortality by 2015 cannot be met unless ecosystem services are nurtured and protected, because it is the poor who are most directly dependent on these services, particularly for freshwater and protein from wild fish and game.  Furthermore, it has become abundantly clear from a handful of successful projects that the way forward lies with encouraging local people to become involved in protecting their own ecosystem services.  This has worked well in Fiji, where local fishermen established restricted areas that reversed serious declines in fish stocks, and in Tanzania where villagers now harvest food and fuel from 3,500 square kilometers of degraded land that they were allowed to reforest (Giles 2005).

All of this should be enough to convince the most hard-headed amongst us that it is very much in our own interest to maintain as much of our planet’s native biodiversity as possible, but these utilitarian arguments for protecting biodiversity may not prevent it from being seriously degraded, for ultimately, in the words of Stephen Jay Gould, we may not be able to save what we do not love. If we are ever to develop a world view which has any chance of achieving genuine ecological sustainability we will need to move away from valuing everything around us only in terms of what we can get out of it, recognising instead that all life has intrinsic value irrespective of its use to us (Naess  1990).  Scientific and economic arguments such as those we have been exploring for protecting biodiversity can help a great deal, but on their own they are not enough. We need, as a matter of the utmost urgency, to recover the ancient view of Gaia as a fully integrated, living being consisting of all her life-forms, air, rocks, oceans, lakes and rivers if we are ever to halt the latest, and possibly greatest, mass extinction.


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