Download Tropical Rainforests of Madagascar Madagascar is home to some of

Tropical Rainforests of Madagascar
Madagascar is home to some of the richest rainforests on Earth. Well over half of Madagascar's species
are found in these forests, which lie on the east coast of the island.
A rainforest is a tropical biome characterized by regular rainfall (exceeding 100 inches -- 250 cm -- per
year), and a high canopy consisting of a dense ceiling of leaves and tree branches formed by closely
spaced evergreen trees.
The Canopy
An estimated 70-90% of life in the
rainforest exists in the trees, above
the shaded forest floor. Primary
tropical rainforest is vertically divided
into at least five layers: the overstory ,
the canopy, the understory, the shrub
layer, and the forest floor. Each layer
has its own unique plant and animal
species interacting with the ecosystem
around them. The overstory refers to
the crowns of emergent trees which
soar 20-100 feet above the rest of the
canopy. The canopy is the dense
ceiling of closely spaced trees and
their branches, while the understory is
the term for more widely spaced,
smaller tree species and juvenile
individuals that form a broken layer
below the canopy. The shrub layer is
characterized by shrubby species and
juvenile trees that grow only 5-20 feet
off the forest floor. The forest floor is
the ground layer of the forest made up
of the trunks of trees, fungus, and low
growing vegetation. These layers are
not always distinct and can vary from
forest to forest, but serve as good
model of the vegetative and
mechanical structures of the forest.
The overstory is characterized by scattered emergent trees that tower above the rest of the canopy, the
tops of some species exceeding 210 feet (65 m). Below the over-story trees, the canopy stretches for
vast distances, seemingly unbroken when observed from an airplane above. However, despite
overlapping tree branches, canopy trees rarely interlock or even touch. Instead they are separated from
one another by a few feet. Why the branches of these trees do not touch is still a mystery, but it is thought
that it might serve as protection from infestations from tree-eating caterpillars and tree diseases like leaf
blight. To survive, canopy dwellers must have the ability to negotiate these gaps by climbing, leaping,
gliding, or flying.
The billions of leaves of the canopy, acting as miniature solar panels, provide the source of power for the
forest by converting sunlight to energy through photosynthesis. Photosynthesis is the process by which
plants convert atmospheric carbon dioxide and water into oxygen and simple sugars. Since the rate of
photosynthesis of canopy trees is so high, these plants have a higher yield of fruits, seeds, flowers, and
leaves which attract and support a wide diversity of animal life. Besides attracting a broad array of wildlife,
the canopy plays an important role in regulating regional and global climate because it is the principle site
of the interchange of heat, water vapor, and atmospheric gases. In addition to collecting solar energy and
regulating the climate, the canopy shields the understory from the harsh, intense sunlight, drying winds,
and heavy rainfall, and retains the moisture of the forest below. Thus the forest interior is a much less
volatile environment than the upper parts of the canopy ceiling. The interior region is protected from the
extremes of the canopy: temperature fluctuations, damaging solar radiation, and strong winds. Light
levels are diffuse and subdued, the humidity is higher and more constant, and there is very little direct
sunlight in the lower canopy.
The Forest Floor
The forest floor of primary tropical rainforest is rarely the thick, tangled jungle of movies and adventure
stories. It is actually quite the opposite: the floor is relatively clear of vegetation due to the deep darkness
created by perhaps 100 feet (30 m) of canopy vegetation above. The canopy not only blocks out sunlight,
but dampers wind and rain. A visitor to the rainforest during a rainstorm will usually not immediately feel
falling rain because so much is deflected and collected by various canopy plants. The blocking of wind by
the canopy makes the forest floor a calm place where only the slightest breeze blows during tropical
thunderstorms. When hiking in primary tropical rainforest a flashlight may be more useful than a machete
since the subdued lighting limits ground growth. Instead of choking vegetation, a visitor will find large tree
trunks, interspersed hanging vines and lianas, and countless seedlings and saplings and a relatively
small number of ground plants.
Despite its constant shade, the ground floor of the rainforest is the site for important interactions and
complex relationships. The forest floor is one of the principle sites of decomposition, a process paramount
for the continuance of the forest as a whole. It is also home to thousands of plants and animals, and
provides support for trees responsible for the formation of the canopy. The ground level is the region of
the forest which was first explored and has been the most intensively studied.