Trees are the dominant organisms of forests. Climate and other factors determine which tree species grow in a forest. Forest ecologists have classified the forests of the world according to the species of trees that grow there. One classification scheme is described below.
Coniferous forests are characteristic of the boreal forests of cold regions of the northern hemisphere. The boreal forest is found in Canada, southern Alaska, northwestern America, northern Europe, and northern Russia. The dominant trees are conifers (cone-bearing plants) such as pines, spruces, firs, and larches. Many of these trees are important sources of wood used in construction, and of pulp for paper.
Broad-leaf forests are characteristic of temperate zones of central and eastern North America, central and southern Europe, and central Asia. Its dominant trees have broad leaves and are deciduous, in that they shed their leaves once a year. Oaks, hickories, maples, and sycamores are some of the trees commonly found in this forest type. Many broad-leaf trees are hardwoods, and are used for making some of our finest furniture.
Mediterranean forests are characteristic of regions with hot, dry summers and warm, humid winters. This forest type is found in southern California, northwestern Mexico, southern Europe, northern Africa, and southern Australia. The trees which grown in Mediterranean forests are adapted to minimizing water loss. Evergreen oaks and pines are well-known trees of this forest type. In Australia, about 600 different species of Eucalyptus grow in the Mediterranean forest type along the southern coast.
Savannas are characteristic of tropical regions with a very seasonal rainfall. The trees in a savanna are sparsely distributed and are specially adapted to minimize water loss. Savannas are found in northern Mexico, equatorial Asia, central Africa, and northern Australia. Acacias, Dracaenas, and the Baobab are well-known savanna trees.
Tropical rainforests are characteristic of regions with a relatively warm climate and a great deal of rainfall. This forest type is found in Central America, northern and central South America, central and western Africa, and the south Pacific region. Tropical rainforests have a great diversity of plant and animal species. The tropical rainforests of the world are currently threatened by people who are cutting down their trees at an increasing rate. At the same time, conservationists and tropical ecologists devote much effort to the preservation of tropical rainforests with their rich diversity of species.
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