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average as well as greater ecological flexibility. In rainforests and other tropical
environments with their legions of finely adapted species, degradation of this kind
has deepened into catastrophe. Rainforests occupy about 9 million square kilometers
currently, down some 45% from the original cover before the coming of man. The
current area, then, is roughly equal to that of the United States. The forest is being
cut and burned at the rate of 100,000 square kilometers a year, roughly the area of
South Carolina—or, to use a more vivid measure, an area equal to a football field every
second. Employing simple models based on the
known relation of the area of islands and habitat
patches to the number of species that can coexist,
I have conservatively estimated that on a worldwide
basis the ultimate loss attributable to
rainforest clearing alone is from 0.2% to 0.3%
of all species in the forests per year. Taking a very
conservative figure of 2 million species confined
to the forests, the global loss that results from
deforestation is thus at least 4,000 to 6,000 species
a year. That, in turn, is on the order of 10,000
times greater than the naturally occurring background
extinction rate that prevailed before the
appearance of human beings.
Although 4,000 species a year extinguished
or doomed is a shocking figure, it is still almost
certainly a gross underestimate. When we consider
that the true number of plant and animal species
limited to the rainforests may well be in the tens
of millions, and that many, or even most, species
in these areas are very limited in distribution, even
small reductions in forest coverage can make them
MICRANTHEMUM (MICRANTHEMUM
MICRANTHEMOIDES ), A TINY RELATIVE OF
THE GARDEN SNAPDRAGON, ONCE
FLOURISHED ON THE MUDDY SHORES
OF ESTUARIES ALONG THE EAST COAST,
INCLUDING NEW YORK’S HUDSON
RIVER. IT HAS NOT BEEN SEEN IN SEVERAL
DECADES, AND IS PRESUMED TO BE
EXTINCT. ANOTHER RELATIVE OF THE
SNAPDRAGON, CHAFFSEED (SCHWALBEA
AMERICANA ), HAS A LIMITED RANGE
IN THE NORTHEAST AND HAS NOT BEEN
SEEN IN NEW YORK SINCE THE EARLY
NINETEENTH CENTURY, WHEN IT WAS
FOUND IN THE ALBANY PINE BUSH.
vulnerable to extinction. Add to this the species extinctions occurring in other habitats
worldwide, and the animal extinction rate could easily be 10 times higher—that is,
2% or more of all rainforest species, 50,000 or more species worldwide. A common
estimate among biodiversity specialists, one to which I subscribe, is that one-fourth
of the species of organisms on earth are likely to be eliminated outright or doomed to
B i o l o g i c a l
23 D i v e r s i t y