Jungle and rain forest are terms that are often used
synonymously but with little precision. The more meaningful and
restrictive of these terms is rain forest, which refers to the
climax or primary forest in regions with high rainfall (greater
than 1.8 m/70 in per year), chiefly but not exclusively found
in the tropics. Rain forests are significant for their valuable
timber resources, and in the tropics they afford sites for
commercial crops such as rubber, tea, coffee, bananas, and
sugarcane. They also include some of the last remaining areas
of the Earth that are both unexploited economically and
inadequately known scientifically.
The term jungle originally referred to the
tangled, brushy vegetation of lowlands in India, but it has
come to be used for any type of tropical forest or woodland.
The word is more meaningful if limited to the dense, scrubby
vegetation that develops when primary rain forest has been
degraded by destructive forms of logging or by cultivation
followed by abandonment.
Types of Rain Forest
Rain forests may be grouped into two major types: tropical and
temperate. Tropical rain forest is characterized by broadleaf
evergreen trees forming a closed canopy, an abundance of vines
and epiphytes (plants growing on the trees), a relatively open
forest floor, and a very large number of species of both plant
and animal life. The largest trees have buttressed trunks and
emerge above the continuous canopy, while smaller trees
commonly form a layer of more shade-tolerant species beneath
the upper canopy. The maximum height of the upper canopy of
tropical rain forests is generally about 30 to 50 m (100 to 165
ft), with some individual trees rising as high as 60 m (200 ft)
above the forest floor.
The largest areas of tropical rain forest are in the Amazon
basin of South America, in the Congo basin and other lowland
equatorial regions of Africa, and on both the mainland and the
islands off Southeast Asia, where they are especially abundant
on Sumatra and New Guinea. Small areas are found in Central
America and along the Queensland coast of Australia.
Temperate rain forests, growing in higher-latitude regions
having wet, maritime climates, are less extensive than those of
the tropics but include some of the most valuable timber in the
world. Notable forests in this category are those on the
northwest coast of North America, in southern Chile, in
Tasmania, and in parts of southeastern Australia and New
Zealand. These forests contain trees that may exceed in height
those of tropical rain forests, but there is less diversity of
species. Conifers such as REDWOOD and Sitka spruce tend to
predominate in North America, while their counterparts in the
southern hemisphere include various species of EUCALYPTUS,
Araucaria, and Nothofagus (Antarctic beech).
Ecology
Rain forests cover less than six percent of the Earth’s total
land surface, but they are the home for up to three-fourths of
all known species of plants and animals; undoubtedly they also
contain many more species as yet undiscovered. Recent studies
suggest that this great diversity of species is related to the
apparently dynamic and unstable nature of rain forests over
geologic time. The fact is that despite their appearance of
fertile abundance, rain forests are fragile ecosystems. Their
soils can quickly lose the ability to support most forms of
vegetation once the forest cover is removed, and some soils
even turn into hard LATERITE clay. The effect of forest removal
on local climates is also often profound, although the role of
rain forests in world climatic changes is not yet clear.
Humans and Rain Forests
Throughout history, human beings have encroached on rain
forests for living space, timber, and agricultural purposes. In
vast portions of upland tropical forest, for example, the
practice of “shifting cultivation” has caused deterioration of
the primary forest. In this primitive system of agriculture,
trees are killed in small plots that are cropped for two or
three seasons and then abandoned; if the plots are again
cultivated before primary vegetation has reestablished itself,
the result is a progressive deterioration of the forest,
leading to coarse grass or jungle. Lowland forests are
similarly being reduced in many areas; on the island of Java,
the lowland primary forest has been almost totally removed and
replaced with rice fields or plantation crops such as rubber.
In the 20th century these incursions on rain forests have grown
rapidly, and numerous organizations are now attempting to
reduce the rate of the loss.
Bibliography: Caufield, Catherine, In the Rainforest (1985);
Forsyth, Adrian, and Miyata, Ken, Tropical Nature: Life and
Death in the Rain Forests of Central and South America (1984);
Sutton, S. L., et al., Tropical Rain Forest: Ecology and
Management (1984); Whitmore, T. C., Tropical Rain Forests of
the Far East, 2d. ed. (1984).
