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rain forests, temperate coniferous
forests, lakes, mangrove swamps,
and coral reefs. Of these, coral reefs
and tropical rain forests are under
particular threat from humankind.Rain forest clearance
Despite covering only 6 percent
of Earth’s land surface, tropical rain
forests represent the greatest
biomass of any terrestrial ecoregion,
and are home to about 80 percent
of land species. Every year, some^
54,000 sq miles (140,000 sq km) of
tropical rain forest is cleared—the
equivalent of a soccer field every
second. Logging is carried out for
firewood and construction materials,
and is also driven by the demand for
roads, settlements, and agriculture.
Globally, the rain forests that
are under greatest threat are in
West Africa, Central America, and
Southeast Asia. Indeed, only about
30 percent of the lowland rain forest
in Borneo now survives. In the
Amazon Basin, home to nearly
one-third of the world’s rain forest,
much of the clearance is for
agriculture, especially ranching.Once deforestation starts, the
problem quickly gets worse. When
rain falls on a forested slope, it is
mostly absorbed by vegetation.
But when the slope is cleared, the
rainfall erodes the soil, making it
useless for agriculture and
impossible to replant. It produces
silt runoff into rivers and lakes,
killing fish, and increases the risk
of flooding. The destruction of any
forest reduces its capacity toENDANGERED HABITATS
Palm oil trees are being planted on
a large scale in Indonesia and Malaysia,
where this is one of the main drivers
of deforestation. Orangutans are among
the species endangered as a result.absorb the greenhouse gas carbon
dioxide, thereby contributing to the
acceleration of climate change.Loss of coral reefs
Coral reefs are important ecoregions
and yet are especially endangered.
They support about 25 percent of
the planet’s marine species, and
are also nurseries for billions of fish.
Two-thirds of the world’s reefs are
under threat, and about a quarter
of them are likely damaged beyond
repair. Possibly the biggest threat
to coral reefs is increased acidity
caused by a greater uptake of CO 2
from the atmosphere. This impedes
the ability of many sea creatures
to build their shells, and induces
coral “bleaching,” which is a step
on the way to the reef dying.
In addition, coral reefs are being
destroyed by overfishing, and by
harmful practices such as cyanide
and blast fishing, and bottom
trawling. Sediment resulting from
coastal development blocks the
sunlight that reefs need. Chemical
pollution, coral mining, and careless
tourism all add to the burden
on this highly sensitive habitat.Wide-ranging impacts
All over the world, diverse natural
habitats are critically threatened by
human activity. Tropical deciduous
dry forest is easier to clear than
rain forest, and on Madagascar,
where dry forest was widespread,
less than 8 percent now remains. At
one time, tallgrass prairie stretched
across the US Midwest, but only
3 percent of it is left: the rest has
been converted to farmland. Many
wetlands have been drained forPressures include
storms, floods, wildfires,
volcanic activity, and
even meteor strikes.Pressures include
deforestation, urban
sprawl, mining,
industrialization,
pollution, and war.Humans can put
pressure on a habitat.Natural factors can put
pressure on a habitat.The habitat becomes endangered
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