tropics

 

also called tropical zone or torrid zone, all the land and water of the earth situated between the Tropic of Cancer at lat. 23¹/₂°N and the Tropic of Capricorn at lat. 23¹/₂°S. Every point within the tropics receives the perpendicular rays of the sun at noon on at least one day of the year. The sun is directly overhead at lat. 23¹/₂°N on June 21 or 22, the summer solstice, and at lat. 23¹/₂°S on Dec. 21 or 22, the winter solstice. Since the entire tropical zone receives the rays of the sun more directly than areas in higher latitudes, the average annual temperature of the tropics is higher and the seasonal change of temperature is less than in other zones. The seasons in the tropics are not marked by temperature but by the combination of trade winds taking water from the oceans and creating seasonal rains called monsoons over the eastern coasts. Several different climatic types can be distinguished within the tropical belt, since latitude is only one of the many factors determining climate in the tropics. Distance from the ocean, prevailing wind conditions, and elevation are all contributing elements. The tropics contain the world's largest regions of tropical rain-forest climate (Amazon and Congo basins). These lush rain-forest regions, whose immense vegetation growth is attributed to monsoon rains, contain some of the most prolific and widely speciated regions on earth for a wide variety of flora and fauna. Toward the northern and southern limits are low-latitude savanna, steppe, and desert climates (with decreasing seasonal rainfall). Tropical highland climates, which have the characteristics of temperate climates, also occur where high mountain ranges lie in the zone. High temperatures and rainfall make rubber, tea, coffee, cocoa, spices, bananas, pineapples, oils and nuts, and lumber the leading agricultural exports of the countries in the tropical zone. Progress in tropical medicine, advancing technology, and the pressure of increasing populations have led in recent years to the cultivation and settlement of some rain-forest areas. Such population growth has led to deforestation of the tropical forest, which is thought to contribute to the greenhouse effect and global warming, and to the elimination of numerous unique species.

Bibliography

See P. Gourou, The Tropical World (4th ed. 1966); B. W. Hodder, Economic Development in the Tropics (1968); P. W. Richards, The Life of the Jungle (1970); F. Bourliere, Tropical Savannas (1983).

Seasons

Temperate Spring Summer Autumn Winter

Tropical Dry season Cool Hot Wet season

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.

(For the history of the term torrid zone, see geographical zone and page of discussion of this article)

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 angle 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 to hot 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. Places in the tropics which are drier with low humidity but extreme heat are such as the Sahara Desert and Central Africa and Northern Australian Outback.

Tropical ecosystems

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 endemism present particularly in rainforests and dry deciduous forests. Some examples of important biodiversity and/or high endicism ecosystems are: Costa Rican and Nicaraguan 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.

In biogeography, the tropics are divided into paleotropics (Africa, Asia and Australia) and neotropics (Central and South America). Together, they are sometimes referred to as the pantropics. The neotropic region should not be confused with the ecozone of the same name; in the Old World, this is unambiguous as the paleotropics correspond to the Afrotropical, Indomalayan, and partly the Australasian and Oceanic ecozones.

See also

• Tropic of Cancer
• Tropic of Capricorn
• Geographical zone
• Equator

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