Geology Reference
In-Depth Information
H
abitat 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 mead-
ows that covered most of the country. We would have experienced a similar 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 set-
tlers all over the world, who quickly set about logging, hunting, fishing and clearing for
agriculture with a demonic destructiveness that beggars the imagination.
Today, there is no habitat on Earth that has not been seriously degraded by humans.
More than 50% of wild habitat has been destroyed in 49 out of 61 Old World tropical
countries. Tropical rainforests are being cut down so quickly that by 2040 virtually no
undisturbed rainforest will exist besides a few pitifully small protected fragments. 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 because of a pang of consci-
ence, 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 be-
gin 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 bar-
riers 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 mate, or even a good place to sleep. Edge effects creep into
the fragments, particularly the smaller ones, making things too dry, 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 reduced
colonisation from outside can lead to a seriously damaging lack of genetic diversity.
You never know who the big players are in the wild world—although they seem in-
significant, the dung beetles of the Amazon are critically important for the health of
the whole forest. 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
