Tropics
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A noontime scene from the Philippines on a day when the sun is directly overhead. |
The
tropics are the geographic region of the
Earth centered on the
equator and limited in
latitude by the
tropic of Cancer in the northern hemisphere, at approximately 23°30' (23.5°) N latitude, and the
Tropic of Capricorn in the southern hemisphere at 23°30' (23.5°) S latitude. This region is also referred to as the
tropical zone and the
torrid zone.
This area includes all the areas of the Earth where the sun reaches a point directly overhead at least once during the solar year. (In the
temperate zones, north of the Tropic of Cancer and south of the Tropic of Capricorn, the sun never reaches an
altitude of 90° or directly overhead.) The word "tropics" comes from
Greek tropos meaning "turn", because the apparent position of the Sun oscillates between the two tropics with a period that defines the average length of a
year.
Tropical plants and animals are those species native to the tropics.
Tropical is also sometimes used in a general sense for a
tropical climate, a
climate that is warm and moist year-round, often with the sense of lush vegetation. However, there are places in the tropics that are anything but "tropical" in this sense, with even
alpine tundra and snow-capped peaks, including
Mauna Kea,
Mt. Kilimanjaro, and the
Andes as far south as the northernmost parts of
Chile and
Argentina.
Tropical ecosystems may consist of
rainforests, dry deciduous forests, spiny forests,
desert and other habitat types. There are often significant areas of
biodiversity and species
endemicism present particularly in
rainforests and dry deciduous forests. Some examples of important biodiversity and/or high endicism ecosystems are:
Costa Rican rainforests,
Madagascar dry deciduous forests,
Waterberg Biosphere of
South Africa and eastern
Madagascar rainforests. Often the soils of tropical forests are low in
nutrient content making them quite vulnerable to
slash-and-burn techniques, which are sometimes an element of
shifting cultivation agricultural systems.
