In Sumatra, Indonesia, a Kubu tribesman contemplates a calcinated forest area, used
by generations for hunting and gathering medicinal plants.
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Forests precede people.Deserts
follow them.
François
René
de Chateaubriand,
French poet (1768-1848)
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The Russian forests are going
down under the ax. Millions of trees are perishing, the homes of wild animals and
birds are being laid to waste, the rivers are dwindling and drying up, wonderful
scenery is disappearing never to return. (…)
The climate is ruined, and every day the earth is growing poorer and more hideous.
Anton
Chekhov,
Russian writer (1860-1904)
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Many biologists believe
we are in the midst of one of the great extinction spasms of geological history.
This time however, human activity, not nature, is the culprit
 In the Amazon Basin the greatest
violence can begin as a flicker of light beyond the horizon. There, in the bowl of
the night sky, an approaching thunderstorm sends lightning bolts that illuminate
the wall of the rain forest. Spear-nosed bats fly through the tree crowns, palm vipers
coil in the roots of orchids, jaguars walk the river’s edge, and around them grow
800 species of trees, more than are native to North America. A thousand species of
butterflies, six per cent of the entire world fauna, wait for the dawn.
About the orchids, we know little. About the flies, beetles, and fungi we know almost
nothing. Rainforests like the Amazon with their myth-inspiring plants and animals
are still mostly unexplored. Biologists believe that they shelter more than half
of the world’s plant and animal species. Tragically, they are being quickly torn
down by human activity. It is difficult to assess quantitatively the loss of species
there and elsewhere because we do not know the precise number of species that exist
on earth. Probably fewer than 10 per cent of them have even been given a scientific
name. And extinction is hard to observe. We don’t see the last butterfly of its species
snatched from the air by a bird or the last orchid of a certain kind killed by the
collapse of its supporting tree.
We know from the fossil record that six great extinction events have occurred in
the past half billion years. The latest of these events, caused by a giant meteorite
strike near present-day Yucatan (Mexico) 65 million years ago, ended the age of dinosaurs.
These catastrophes variously obliterated 30 to 90 per cent of the world’s plant and
animal species. Afterward, evolution replaced the biodiversity very slowly, during
periods of millions of years.
Equilibrium
Biologists agree
that we are now in the earliest stages of a seventh mass extinction event, caused
not by an act of nature but entirely by human activity. The current rate of extinction
is generally estimated to be 100 to 1,000 times higher than it was before the origin
of modern humanity about half a million years ago. Throughout most of the geological
past, individual species and their descendants lived for an average of roughly one
million years, and disappeared naturally at about one species per million each year.
On a grand scale, new species replaced vanishing ones at about the same rate. No
more. Not only has the extinction rate soared, but also the birth rate of new species
is falling as the natural environment is reduced by human action.
According to estimates by the World Conservation Union (IUCN), about one quarter of the
world’s mammals and more than a tenth of its remaining birds are at a high risk of
extinction. One-fifth of all reptile species, a quarter of all amphibians and as
many as 34 per cent of all fishes (mostly freshwater species) are in similar jeopardy.
And these proportions only refer to species we know relatively well. In the less
studied groups, more than 500 insect species, 400 crustaceans and 900 molluscs are
also threatened, according to Iucn, figures that are surely vast underestimates.
Finally, about an eighth of the world’s flowering plants are edging toward extinction.
Human demographic success has brought the world to this crisis. Human beings have
become a hundred times more numerous than any other large land animal in the history
of life. By every conceivable measure, humanity is ecologically abnormal. Our species
appropriates between 20 and 40 per cent of solar energy captured in organic material
by land plants. There is no way we can draw upon the resources of the planet to this
degree without reducing many other species to rarity or extinction.
The leading cause of the decline is the destruction of natural habitats to make more
room for urban and farming areas and to extract timber, ore, and other natural resources.
Not many habitats in the world covering a square kilometre contain fewer than a thousand
species of plants and animals. Patches of rainforest and coral reef harbour tens
of thousands of species, even after they have been partly chipped away by human intervention.
But when an entire habitat is destroyed, almost all of the species specialized to
live in it are destroyed. Not just eagles and pandas disappear but also the smallest,
still uncensused invertebrates, algae and fungi, the invisible players that make
up the foundation of the ecosystem.
Celebrity
pandas
For years,
conservationists often focused on saving “star” species like pandas as opposed to
the entire ecosystem in which they live. Now, with a better understanding of the
extinction process, they have switched gears by, for example, focusing on the need
to protect particularly rich environments that contain numerous vulnerable species,
referred to as biodiversity “hotspots” (see page 21).
The second major cause of extinction is the invasion of alien species. When Polynesian
voyagers set shore in Hawaii around 400 A.D., the islands were a special kind of
paradise. Their lush forests and fertile valleys contained no mosquitoes, ants, poisonous
spiders nor snakes or plants with thorns or poisons. All these are now abundant.
Human commerce introduced invasive species, deliberately or by accident. As the natural
habitats were decimated and the alien invaders pressed on, the original fauna and
flora have retracted. Most are now rare or extinct.
The third major cause of decline is pollution. Freshwater faunas and floras, for
example, are especially vulnerable to the increasing flood of industrial and agricultural
pollution. The fourth agent of destruction, destined to rise in importance in the
future, is global warming, which itself is the result of pollution by excess greenhouse
gases. Among the more fragile environments most threatened are the arctic tundras
and the unique South African fynbos (scrubland) “trapped” on the tip of the continent.
Shrinking
rainforests
Just how fast
is diversity disappearing? We are far from an exact answer, except to say, “catastrophically
fast”. Yet it is possible to get a handle on the richest environment of all, the
tropical rainforests. By looking at the rate of reduction of the forest area, we
can roughly estimate the extinction rates of species. First, we must dispel the myth
of the regenerative power of rainforests, which are actually among the most fragile
habitats. More than half of the area of the forest surface worldwide consists of
acidic and nutrient-poor soil. When the forest is cut and burned by farmers, the
ash and decomposing vegetation flush enough nutrients into the soil to support vigorous
new herbaceous and shrubby growth for two or three years. But as the nutrient levels
decline, the land can no longer support healthy crops and forage. So the farmers
must add fertilizer or move on to slash-and-burn the next patch of forest.
In prehistoric times, the great forests–the greenhouses of planet Earth–covered 14
to 18 million square kilometres. Only about half of the original area remains. Much
of the destruction is recent, with about one million square kilometres cleared every
five to ten years. If this destruction rate continues, a quarter or more of the remaining
rainforest will be gone by 2025.
Now let’s conservatively assume that the forests presently shelter 10 million species
and focus exclusively on the impact of deforestation. We won’t even consider species
lost to over-hunting or those erased by new diseases, alien weeds and animals such
as rats. Within these cautious parameters, 27,000 species are doomed each year. In
other words, 74 will disappear or start their descent to endangered status every
day, three each hour.
If rainforests are as rich in diversity as most biologists think, their reduction
alone will eliminate at least five to ten per cent of all the species on earth. I
think that a far greater number of species are on the edge, perhaps irreversibly
so.
Clearly we are in the midst of one of the great extinction spasms of geological history.
Humanity needs a moral awakening together with all of the scientific and technological
ingenuity it can bring to bear, in order to avoid impoverishing the planet for all
generations to come. We can, we must find the way.
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