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agriculture or urban development;
others are irreversibly damaged
by pollution. Nutrient runoff from
agricultural fertilizers has spoiled
many lakes and rivers. In many
countries, intertidal zones have
been destroyed by the building
of ports. Coastal development has
been largely responsible for the loss
of 35 percent of mangrove swamps.
In the tropics and subtropics,
overgrazing by domestic animals
such as goats has converted an
estimated^ 3.5 million sq miles
(9 million sq km) of seasonally dry
grassland and scrub into desert.Halting the decline
The destruction of these habitats is
not only a loss in terms of natural
beauty and biodiversity, but also
creates serious problems for people:
for example, poorer water quality,
declining fish stocks, crashes in
populations of pollinators, flooding
from increased rainwater runoff,
and faster buildup of greenhousegases. Conservation is now
paramount, and ecologists work
to refine their understanding
of the best ways to go about it.
Appropriate measures depend
on the situation, and range from the
creation of protected reserves or
“corridors,” to link areas that have
become fragmented, to projects
to recreate lost habitat. Sustainable
sources of fuel and timber for those
who are otherwise dependant on
forest wood are also important, as
is banning the trade in rain forest
hardwood. Since the impact of
habitat destruction is global,
international agreements and
cooperation are crucial. ■THE HUMAN FACTOR
Wetlands and intertidal zones are
important for marine invertebrates and
migratory shorebirds, but in many parts
of the world they have been drained for
industry and ports.Protected areas
National parks, wilderness
areas, nature reserves, and
sites of special scientific
interest (SSSIs) are all types of
protected habitats. Within
these areas, interference with
the natural environment is
prohibited or limited by some
kind of legal framework. They
must cover a specified
expanse of land or sea, but
they vary greatly in size and in
the level of protection given.
Just over 10 percent of Earth’s
land is protected, but only 1.7
percent of the oceans; though
marine reserves are essential,
they require local and national
governments to agree on key
issues such as fishing rights.
Marae Moana, the largest
protected area on Earth, is
772,000 sq miles (2 million sq
km) around the Cook Islands
in the Pacific Ocean. It is home
to sea turtles, at least 136
species of corals, and 21
whales and dolphins. The
biggest land reserve is the
Northeast Greenland National
Park, which covers almost
386,000 sq miles (1 million sq
km) of ice sheet and tundra.Muskoxen are Arctic herd animals
whose numbers were severely
depleted in the 19th century by
hunting. They now live on reserves
in Alaska, Norway, and Siberia.In every walk with
nature, one receives far
more than he needs.
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