Rain Forest

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).