rainforests have four layers:
These giant trees thrust above
the dense canopy layer and have huge mushroom-shaped crowns. These trees
enjoy the greatest amount of sunlight but also must endure high temperatures,
low humidity, and strong winds.
The broad, irregular crowns of
these trees form a tight, continuous canopy 60 to 90 feet above the ground.
The branches are often densely covered with other plants (epiphytes) and
tied together with vines (lianas). The canopy is home to 90% of the organisms
found in the rain forest; many seeking the brighter light in the treetops.
Receiving only 2-15% of the sunlight
that falls on the canopy, the understory is a dark place. It is relatively
open and contains young trees and leafy herbaceous plants that tolerate
low light. Many popular house plants come from this layer. Only along rivers
and roadways and in treefall and cut areas is sunlight sufficient to allow
growth to become thick and impenetrable
The forest floor receives less
than 2% of the sunlight and consequently, little grows here except plants
adapted to very low light. On the floor is a thin layer of fallen leaves,
seeds, fruits, and branches that very quickly decomposes. Only a thin layer
of decaying organic matter is found, unlike in temperate deciduous forests.
Soil and Nutrient Recycling
Most tropical rainforest soils
relatively poor in nutrients. Millions of years of weathering and torrential
rains have washed most of the nutrients out of the soil. More recent volcanic
soils, however, can be very fertile. Tropical rain forest soils contain
less organic matter than temperate forests and most of the available nutrients
are found in the living plant and animal material. Nutrients in the soil
are often in forms that are not accessible by plants.
Constant warmth and moisture promote
rapid decay of organic matter. When a tree dies in the rainforest, living
organisms quickly absorb the nutrients before they have a chance to be
washed away. When tropical forests are cut and burned, heavy rains can
quickly wash the released nutrients away, leaving the soil even more impoverished.
Comparison of Where Nutrients
Are Found in an Ecosystem Based on the Averaging of Major Nutrients.
||Temperate Deciduous Forest
|52% in Vegetation
||31% in Vegetation
|48% in Soil
||69% in Soil