Tropical rainforests are found
near the equator—between the latitudes of 23.5° N and 23.5° S. They have an
average rainfall of at least 200 centimeters per year. This large amount of precipitation
occurs in the area where the northern and southern hemisphere trade winds meet.
The intense Sun and warm ocean water cause this converging air to rise. As the
air rises, it cools, condensing into clouds and rain. This cycle happens over
and over, causing a period of thundershowers in the warmest part of the afternoon
almost every day. Because the tropical rainforests are near the equator, the
temperature varies little year round, averaging about 20 to 25 °C.
Rainforest life
Although tropical rainforests
cover less than 6 percent of Earth’s land, these biomes have extremely high
biodiversity. Half of all of the animal and plant species in the world are
found there. There can be as many as 100 different species of plants per
hectare (2.47 acres). The most abundant type of plants are tall trees that form
a dense canopy. Many foods we enjoy, including Brazil nuts, bananas, pineapple,
cocoa, coffee, vanilla and cinnamon flavorings, and coconut originate in
tropical rainforests
Trees and global climate
According to NASA data, an area
of tropical rainforest the size of North Carolina is destroyed every year. Land
is cleared for crops, grazing, lumber, or firewood. When clear-cutting occurs
in this type of biome, the thin topsoil soon washes away, exposing thick clay that
is almost useless for agriculture. This clay absorbs the Sun’s energy and then
emits infrared radiation, which is absorbed by greenhouse gases. This process
warms the atmosphere. Trees prevent some of this warming. Leaves appear green
because they reflect green visible light. Light at this wavelength is not as readily
absorbed by greenhouse gases as infrared radiation. In a forested area, more of
the Sun’s energy is reflected directly back to space without first being
absorbed by greenhouse gases. In this way, trees keep Earth cooler.
Temperate rainforests
Like temperate deciduous forests,
temperate rainforests are found in the middle-latitude regions. For example, temperate
rainforests are found in coastal areas of the Pacific Northwest. Because these
rainforests are in temperate areas, they may have temperate deciduous forest
plants like oak trees. Like a tropical rainforest though, temperate rainforests
experience a lot of rain (about 250 centimeters per year). Temperate
rainforests are cool and periodically covered in fog which provides more
moisture for the plants.