Forests can be classified according to a wide number of characteristics, with distinct forest types occuring within each broad category. However, by latitude, the three main types of forests are tropical, temperate, and boreal.
Most tropical forests receive large amounts of rain annually (up to 100 inches), which is spread evenly throughout the year. However, there are some tropical forests that receive seasonal rainfall and experience both a wet and dry season.
Tropical forests are particularly important since they are unusually rich in biological diversity, especially insects and flowering plants. This incredible amount of biodiversity—accounting for 50 to 80 percent of the world’s plant and animal species, with a potential for millions still undiscovered—is what defines these forests and makes them most unique. In just a few square kilometers, hundreds—even thousands—of tree and plant species can be found.
Deforestation is one of the greatest concerns in tropical areas, especially within rainforests which cover only a small area (approximately 7 percent) of the Earth’s surface. Aside from their vast biodiversity, tropical forests provide homes to a large number of indigenous people. And, in looking beyond the typical forest offerings, tropical forests supply both local and global markets with a variety of ingredients for medicines; nearly half of all medicines used today are linked to discoveries within these forests.
Temperate forests—common throughout North America, Eurasia, and Japan—are primarily deciduous, characterized by tall, broad-leafed, hardwood trees that shed brilliantly colored leaves each fall. These forests experience varied temperatures and 4 seasons, with winter often bringing below freezing temperatures and summer bringing higher heat and humidity. Rainfall also varies, averaging 30 to 60 inches annually, allowing for soils that are well developed and rich in organic matter. They also provide habitat for a wide variety of smaller mammal species, including squirrels, raccoons, deer, coyotes and black bear and many bird species, including warblers, woodpeckers, owls, and hawks.
Temperate forests are often most affected by human activity since they are located in or near the most inhabitable areas. The land in these areas has long been used for agriculture and grazing, although great expanses of forest regeneration and small areas of pristine forest exist. The hardwoods are valuable for making furniture and other commodities, and many remaining forests have been modified to accommodate recreation and tourism.
Boreal forests (also known as taiga) are located just south of the tundra and stretch across large areas of North America and Eurasia . They are one of the world’s largest biomes, encompassing about 11 percent of Earth’s land area, but have very short growing seasons with little precipitation and represent relatively few tree species. The forest is dominated by coniferous trees, which have needle-shaped leaves with minimal surface area to prevent excessive water loss. These forests provide habitat for a few large mammal species, such as moose, wolves, caribou, and bears, and numerous smaller species, including rodents, rabbits, lynx, and mink.
Despite the remote locations and often inhospitable environment, boreal forests have long been a source of valuable resources. Fur trading began in the 1600s and continued well into this century. Boreal forests are also rich in metal ores—including iron—and coal, oil, and natural gas. Most importantly, the forest serves as a major source of industrial wood and wood fiber, including softwood timber and pulpwood. However, the low productivity rate in these forests leads to a slow rate of forest regeneration.