Tropical
forests are characterized by the greatest
diversity of species. They occur near the equator, within the area bounded
by latitudes 23.5 degrees N and 23.5 degrees S. One of the major characteristics
of tropical forests is their distinct seasonality: winter is absent,
and only two seasons are present (rainy and dry). The length of daylight
is 12 hours and varies little.
Temperature
is on average 20-25° C and varies little throughout the year: the
average temperatures of the three warmest and three coldest months do
not differ by more than 5 degrees.
Precipitation
is evenly distributed throughout the year, with annual rainfall
exceeding 2000 mm.
Soil
is nutrient-poor and acidic. Decomposition is rapid and soils are subject
to heavy leaching.
Canopy
in tropical forests is multilayered and continuous, allowing little
light penetration.
Flora
is highly diverse: one square kilometer may contain as many as 100 different
tree species. Trees are 25-35 m tall, with buttressed trunks and shallow
roots, mostly evergreen, with large dark green leaves. Plants such as
orchids, bromeliads, vines (lianas), ferns, mosses, and palms are present
in tropical forests.
Fauna
include numerous birds, bats, small mammals, and insects.
Further subdivisions of this group are determined by
seasonal distribution of rainfall:
evergreen rainforest:
no dry season.
seasonal rainforest: short
dry period in a very wet tropical region (the forest exhibits definite
seasonal changes as trees undergo developmental changes simultaneously,
but the general character of vegetation remains the same as in evergreen
rainforests).
semievergreen forest: longer dry season (the
upper tree story consists of deciduous trees, while the lower story
is still evergreen).
moist/dry deciduous forest (monsoon): the
length of the dry season increases further as rainfall decreases (all
trees are deciduous). More than ½ of tropical forests have already
been destroyed.
The Layers of the Rainforest
The rain forest is divided into four main layers. Different kinds of
trees, flowers, and other plants grow in each layer. These layers are
called the emergent layer, the canopy, the understory, and the forest
floor.
Emergent Layer - The Top Layer
These huge trees rise above all other trees in the forest and grow to
150 ft. tall. They receive the most sunlight.
Canopy - The Next Layer
A canopy (or cover) of very tall trees is the next layer of the rain
forest. The treetops, or crowns, grow very close together and form a
lush green garden in the air. The canopy is rich with plants, animals
and insects. Many beautiful birds, butterflies, hummingbirds, and flowering
plants live here. Monkeys, bats, reptiles, and other animals swing,
swoop, and climb through the canopy.
Understory - The Middle Layer
Smaller trees, bushes, and plants such as ferns, live in the understory.
Not much sunlight reaches here, because the canopy blocks the sun. Still,
many birds and animals make their home in the understory. Forest wildcats,
such as the leopard, are excellent tree climbers. They will chase monkeys
and squirrels through the understory for food.
Forest Floor - The Bottom Layer
Few plants grow on the forest floor because almost no sunlight reaches
here. But the leaves and plants which drop from the upper layers provide
food and shelter for animals and insects who live on the forest floor.
Mice, frogs, snakes and insects look for food. Larger animals, such
as wild boar and deer, also make the forest floor their home.
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