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DEFORESTATION
Before the dawn of agriculture
approximately 10,000 years ago, forests and open woodland covered about 15.3
billion acres (6.2 billion ha) of the globe. Over the centuries, however, about
one-third of these natural forests has been destroyed. According to a 1982 study
by FAO, about 27.9 million acres (11.3 million ha) of tropical forests are cut
each year-an area about the size of the States of Ohio or Virginia. Between
1985 and 1990, an estimated 210 million acres (85 million ha) of tropical forests
were cut or cleared. In India, Malaysia, and the Philippines, the best commercial
forests are gone, and cutting is increasing in South America. If deforestation
is not stopped soon, the world will lose most of its tropical forests in the
next several decades.
Reasons for Deforestation
Several factors are responsible
for deforestation in the Tropics: clearing for agriculture, fuelwood cutting,
and harvesting of wood products. By far the most important of these is clearing
for agriculture. In the Tropics, the age-old practice of shifting, sometimes
called "slash-and-burn," agriculture has been used for centuries.
In this primitive system, local people cut a small patch of forest to make way
for subsistence farming. After a few years, soil fertility declines and people
move on, usually to cut another patch of trees and begin another garden.In the abandoned garden
plot, the degraded soil at first supports only weeds and shrubby trees. Later,
soil fertility and trees return, but that may take decades. As population pressure
increases, the fallow (rest) period between cycles of gardening is shortened,
agricultural yields decrease, and the forest region is further degraded to small
trees, brush, or eroded savanna.Conversion to sedentary
agriculture is an even greater threat to tropical forests. Vast areas that once
supported tropical forests are now permanently occupied by subsistence farmers
and ranchers and by commercial farmers who produce sugar, cocoa, palm oil, and
other products.In many tropical countries
there is a critical shortage of firewood. For millions of rural poor, survival
depends on finding enough wood to cook the evening meal. Every year more of
the forest is destroyed, and the distance from home to the forest increases.
Not only do people suffer by having to spend much of their time in the search
for wood, but so does the land. Damage is greatest in dry tropical forests where
firewood cutting converts forests to savannas and grasslands.The global demand for tropical
hardwoods, an $8-billion-a-year industry, also contributes to forest loss. Tropical
forests are usually selectively logged rather than clear-cut. Selective logging
leaves the forest cover intact but usually reduces its commercial value because
the biggest and best trees are removed. Selective logging also damages remaining
trees and soil, increases the likelihood of fire, and degrades the habitat for wildlife species that require large, old trees-the ones usually cut. In addition,
logging roads open up the forests to shifting cultivation and permanent settlement.In the past, logging was
done primarily by primitive means-trees were cut with axes and logs were moved
with animals such as oxen. Today the use of modern machinery--chain saws, tractors,
and trucks -makes logging easier, faster, and potentially more destructive
.Endangered Wildlife
Forests are biological communities-complex
associations of trees with other plants and animals that have evolved together
over millions of years. Because of the worldwide loss of tropical forests, thousands
of species of birds and animals are threatened with extinction. The list includes
many
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unique and fascinating animals, among them the orangutan, mountain gorilla, manatee, jaguar, and Puerto Rican parrot. Although diverse and widely separated around the globe, these specles have one important thing in common. They, along with many other endangered species, rely on tropical forests for all or part of their habitat.Orangutans (Pongo pygmaeus) are totally dependent on small and isolated patches of tropical forests remaining in Borneo and Sumatra, Indonesia. Orangutans spend most of their time in the forest canopy where they feed on leaves, figs and other fruit, bark, nuts, and insects. Large trees of the old-growth forests support woody vines that serve as aerial ladders, enabling the animals to move about, build their nests, and forage for food. When the old forests are cut, orangutans disappear.The largest of all primates, the gorilla, is one of man's closest relatives in the animal kingdom. Too large and clumsy to move about in the forest canopy, the gorilla lives on the forest floor where it forages for a variety of plant materials. Loss of tropical forests in central and west Africa is a major reason for the decreasing numbers of mountain gorillas (Gorilla gorilla). Some habitat has been secured, but the future of this gentle giant is in grave danger as a result of habitat loss and poaching.The jaguar (Leo onca), a resident of the Southwestern United States and Central and South America, is closely associated with forests. Its endangered status is the result of hunting and habitat loss.The Puerto Rican parrot (Amazona vittata), a medium-sized, green bird with blue wing feathers, once inhabited the entire island of Puerto Rico and the neighboring islands of Mona and Culebra. Forest destruction is the principal reason for the decline of this species. Hunting also contributed. Today, only a few Puerto Rican parrots remain in the wild and their survival may depend on the success of a captive breeding program (fig. 9).
In addition to species that
reside in tropical forests year round, others depend on such forests for part
of the year. Many species of migrant birds journey 1,000 miles or more between
their summer breeding grounds in the north and their tropical wintering grounds.
These birds are also threatened by tropical forest destruction.
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