About one-third of the earth's surface is covered by forests. Each climate or area of the world sustains different types of trees in its forests. There are three major types of forests with several subcategories under two of them. The types of forests are separated by their distance from the equator.
The first type is the tropical rainforest. These grow around the equator in South America, Africa, and Southeast Asia. The temperature remains around 60 degrees all year round. They contain over one- half of all the species of animals in the world. These forests receive at least eighty inches of rain per year. However, they do have two seasons, a rainy and a dry.
Because they are so close to the equator, these forests receive twelve hours of light each day. Up to one hundred different types of plants may grow within a one-half square mile. The trees grow very closely together, and their branches and leaves block the sun from reaching down to the understory. Although the soil can be several yards deep, it is not full of nutrients and cannot sustain plant life except in the thin top layer. Mosses, orchids, ferns and broad-leafed plants grow in this type of forest. Many species of animals which live in trees, such as monkeys, lizards, frogs, and snakes are found in this type of forest.
Six different subcategories of tropical rainforests exist. An evergreen type receives rain all year round. A seasonal has a short dry season with a long rainy one, but the trees stay green. The montane type of forest gets its water from mists which rise from the ground. The trees are mostly conifers or cone bearing. The dry type has a long dry season, and the trees lose their leaves. The tropical and sub-tropical coniferous has a warm, dry climate with coniferous trees suitable for varying kinds of weather. The sub-tropical rain forest exists north and south of the tropical rainforest. The trees must be able to withstand summer drought.
Secondly, temperate forests occur north and south of the tropical rainforests. They receive on the average sixty inches of rain per year. They experience four seasons each year. Most of the trees in these areas are deciduous, meaning they lose their leaves in the fall. Examples are maple, oak, elm, and hickory. Coniferous trees like pines and firs also grow in the temperate forest. The soil is very fertile due to a large amount of decaying leaves. Evergreen coniferous forests also exist in these regions, in northwest America, South Japan, New Zealand and northwest Europe. Because of the constant temperatures and large amounts of rain, large trees, such as cypress, redwood, and cedar, grow in these areas. Maple trees, mosses, and ferns also grow in these areas.
There are four sub-categories within temperate forests. The Mediterranean area exists south of the temperate region along coasts. Trees are evergreen. Palms grow in this type of forest. The dry conifer area exists at high elevations with small amounts of rain. Another type of temperate forest is the moist conifer and evergreen broad-leaf region. Summers are dry, and winters are mild and wet. A fourth sub-category, a temperate broad-leaved rain forest receives rain all year and mild winters. Trees remain green all year.
The third type of forest, the Boreal or Taiga exists in Canada, Scandinavia, Alaska, and Siberia. It is in the sub-Arctic zone. All the trees are evergreen and coniferous. The winters are long, cold and dry. The summers are somewhat warm and wet, but short. Most of the precipitation is snow. There is a very thin layer of good soil because the leaves do not allow much sun to penetrate the understory. Pine, fir and spruce trees do well here because they have needle leaves which can tolerate the cold. Animals living in this region must be able to withstand very cold temperatures and have good insulation.
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